Bio-Control Matters

This is long so I will cut it but think its important:To: Deke 

>From: JOEL GROSSMAN, 937 6th St. #5, Santa Monica, CA 90403; 310/394-1233

The Biological Pest Control Transition Experience at NaturFarm

authors = E.J. Dietrick, John Phillips, Joel Grossman

After a year of fallowing land farmed conventionally with pesticides by a 
previous owner, NaturFarm adopted a sustainable organic pest control 
approach relying on natural biological control organisms to keep pests from 
destroying crops. Some cultural measures, such as cultivating ant nests and 
growing pest break strips, were adopted to enhance the natural biological 
pest control. However, widely-used organic pesticide substitutes like 
soaps, oils, Bacillus thuringiensis [BT] and botanicals were not part of 
the NaturFarm pest control paradigm because natural biological control 
organisms are the most sustainable form of pest control.

This almost exclusive reliance on natural biological control organisms to 
provide sustainable organic pest control is rarely, if ever, attempted 
anymore. However, there have been times and places in California history 
where natural biological control organisms have provided all the pest 
control needed in major agroecosystems such as citrus, cotton and alfalfa. 

NaturFarm's pest control adviser on this biological control transition 
project, E.J. Dietrick, personally worked in these unsprayed agroecosystems 
teeming with natural biological control organisms while a researcher at the 
University of California and later in private practice with Rincon-Vitova 
Insectaries, Inc. Indeed, E.J. Dietrick's vision and practical knowledge of 
natural biological pest control, gained from several decades of firsthand 
experience and research, guided NaturFarm in this pioneering and innovative 
transition towards natural biological control of vegetable pests that are 
routinely sprayed with pesticides by most other farmers around the world. 

The pest break strips at the heart of the NaturFarm transition to natural 
biological control are a specialized form of strip cropping. Pest break 
strips are designed both to trap pests away from the vegetable crops and to 
act as insectary crops for growing beneficial insects providing biological 
control of pests in the market crop of vegetables. 

The pest break strips at NaturFarm go beyond traditional strip crop design 
in another important way. NaturFarm uses special management practices known 
as strip cutting or strip harvesting to maximize the numbers of pests 
trapped and the quantities of natural enemies grown in the pest break 

The strip cutting concept is rather simple. Only half the alfalfa or other 
cover crop is cut at any one time. At strip cutting time, half the alfalfa 
or other cover crop is flowering and ready to be cut, while the other half 
is young and lush. The young, lush uncut strips of alfalfa and other cover 
crops serve a dual role: first protecting the market crops by acting as 
trap crops catching pests moving out of the just-cut strips, but perhaps 
more importantly as insectary crops growing beneficial insects. 

Strip cutting for biological pest control was devised in 1956 by Evert I. 
Schlinger and Everett J. Dietrick as part of the University of California's 
statewide `war' against the spotted alfalfa aphid, a pest then causing $12 
million per year in damage to alfalfa. Tiny wasps imported from the aphid's 
foreign homeland provided excellent biological control until the entire 
alfalfa field was cut and harvested. After the entire alfalfa stand was 
cut, the beneficials starved to death or flew away. Then in the absence of 
their natural enemies, the few remaining aphids exploded in numbers with 
the regrowth of the hay. The strip cutting concept was devised to keep 
beneficial insects in the fields as a defensive army of sorts, preventing 
population explosions of aphids and other pests from occurring in the new 
crop growth. 

Another major benefit of strip cutting further developed by other 
University of California researchers [Stern, van den Bosch & Leigh, 1964] 
is that the uncut portion of alfalfa acts as a trap crop for pests like 
Lygus bugs, preventing damage to cotton, strawberries and other nearby 
crops. Continuously cutting the pest break strip before seed set also 
prevents the alfalfa or legume cover crop from becoming too favorable a 
habitat for seed feeders like Lygus bugs and certain leafhoppers. If the 
entire pest break strip is cut and there is not nearby uncut alfalfa [the 
preferred Lygus host crop], then Lygus and other pests typically migrate 
into nearby market crops. 

"Strip cutting works best and is started most easily on the first cutting.  
In the spring when days are short, alfalfa is slow to go into bloom," write 
Stern et al. (1967) in one of the definitive University of California 
how-to publications on the subject. "At this season, the correct time for 
cutting can be determined from the new buds at the base of the plant. The 
first set of strips should be cut when 25 percent of the new shoots are 1/2 
to 3/4 inches high. About 10 days later, the second or alternate set of 
strips should be cut. This will set up a harvesting differential for the 
second cutting." A 12- to 14-day cutting differential is important because 
adult Lygus, particularly females, begin moving out of maturing hay when 
alfalfa reaches three-fourths maturity. "If the alfalfa in the adjoining 
strips is 6 to 8 inches tall, these females will drift into these plots and 
remain there. Shorter hay is not as attractive to these drifting Lygus. At 
cutting time, when the alternate strips have about 10 inches or more 
regrowth, all of the Lygus are driven from the cut strips to this young 
succulent hay."

In essence, strip cutting subdivides the alfalfa or cover crops into at 
least two sets of crops always at different levels of maturity and on 
staggered cutting schedules. The staggered cutting schedule enhances 
agroecosystem biodiversity by providing plants of different ages or 
maturities, in much the same way that a forest is more diverse with 
different ages and species of trees. The diversity added to the 
agro-ecosystem by strip cutting alfalfa and cover crops provides stability, 
preventing wild insect population explosions and crashes. This freedom from 
pest outbreaks is a consequence of the pest break strips creating a more 
permanent habitat for the beneficial species providing biological pest 

[perhaps a place to insert diagrams of strip cutting schemes, like those 
from University of California publications]

Unfortunately, the necessity of providing permanent habitat for beneficial 
insects, spiders and mites is usually neglected in the design of both 
conventional and organic cropping systems. Besides a lack of appreciation 
of the benefits of ecosystem diversity, many farmers eschew strip cropping 
because of the extra work involved. Fueling up a spray rig is such a 
simpler solution, that even organic vegetable farmers usually succumb 
because it seems easier and is better known and understood than managing 
ecological complexity to achieve biological control. Also, prior to this 
CEC/NaturFarm/Rincon-Vitova Insectaries project, vegetable farmers had no 
prior case history documenting the energy and cost savings of the pest 
break strip approach and sustainable biological control.

The mental paradigm of most vegetable farmers, whether organic or 
conventional, is that managing noncrop vegetation strips is an extra chore 
in their already overworked and stressful lives. For instance, seed may 
need to be purchased and additional planting operations undertaken to 
establish special strips. Pest break strips must also be monitored just 
like any other crop. Strip cutting requires extra management inputs so that 
mowing gets done ahead of scheduled irrigations. Sometimes the irrigation 
needs of watering up the pest break strip regrowth conflict with the 
irrigation, equipment logistics or harvesting needs of neighboring 
vegetable crops. In short, adding on the pest break strip cropping system 
sometimes seems like a headache to those doing the farming, an unwanted 
burden superimposed onto an already hectic overly long day, despite 
knowledge of the cost savings and benefits.

In other words, managing pest break strips adds complexity to the farm 
operation, challenging the farmer's resources, as well as adding beneficial 
biodiversity and sustainable biological control to the agro-ecosystem. Even 
at NaturFarm, the demands of the pest break strip crops were a difficult 
burden to superimpose upon an already management-intensive cropping system 
of 30 different vegetable crops. Even though the increasing computerization 
of farms might ease scheduling tasks and smooth equipment utilization 
logistics, the humans running vegetable farms are still a key component in 
making the system work. The human component -- complete with the stresses, 
strains, perceptions, reactions and motivations  -- of integrating 
biological control and pest break strips into an energy-efficient 
sustainable agricultural system still needs more research attention if the 
NaturFarm transition model is to be more widely implemented.

In contrast, the extra energy-intensive spray rig runs required for pest 
control in the absence of the biological control benefits of pest break 
strips are so deeply ingrained that they are accepted as routine, a normal 
everyday part of modern farm life that often goes unquestioned. One result 
of this mindset in which spraying is the accepted and expected everday norm 
is that pest break vegetation strips are the rare exception, rather than 
the rule on vegetable farms. Lacking the permanent natural enemy habitat 
and agro-ecosystem stabilizing biological control benefits of pest break 
strips, both conventional and organic vegetable farms are heavily sprayed 
for pest control purposes with either conventional pesticides or organic 
substitutes like soaps, BT, pyrethrum and rotenone.

NaturFarm's goal with pest break strips is breaking this deeply ingrained, 
energy-intensive habit of constantly spraying both conventional and 
organically-grown vegetables to control insect pests. But the pest break 
strips at NaturFarm are more than just a paradigm shift away from spraying. 
The pest break strips are also about habitat creation. Just as it is 
essential to maintain wetland habitats for migratory birds, it is necessary 
to create on-farm habitats for beneficial arthropod wildlife in order to 
reap the benefits of biological control. Pest break strips are, in essence, 
island-like wildlife refuges for natural enemies of agricultural pests. 

Functionally, managed natural enemy habitats like strip-cut pest break 
strips are essential transition inputs, providing the sustainable 
biological control missing from most conventional and organic vegetable 
cropping systems. Thus, pest break strips are vital if vegetable farms are 
to be successful in transitioning towards an energy-efficient agriculture 
in which sustainable biological control of insect pests replaces the 
energy-intensive pesticide spray habit. 

Pest break strips are more than just theory on NaturFarm's diversified 
vegetable farm, where sustainable biological control is operative and even 
organic sprays are never used. Indeed, NaturFarm has documented substantial 
energy and dollar savings compared to conventional farms by substituting 
pest break strips and beneficial insects for pesticide sprays. Whereas 
conventional farms spend 26% of their dollar budget and 24% of their energy 
budget on non-weed pest control, NaturFarm spends only 1% of its energy 
budget and 4% of its dollar budget on non-weed pests. Thus, provision of 
natural enemy habitats like pest break strips to grow natural biological 
control organisms is the necessary next step in pest control if organic 
vegetable production is to become truly sustainable and energy efficient, 
rather than a mere carbon copy of the pesticide spray model substituting 
"organic" substances in the spray tank. 

[might be a good place for the energy & cost pie charts on pp. 12-13 of the 
1992 CEC NaturFarm Conversion report]

As a pest control paradigm shift, the strip cut alfalfa borders and rows of 
insectary cover crops among the 30 or so vegetable varieties grown on the 
70-acre NaturFarm are a bold leap beyond the less sustainable organic 
spray, pesticide substitution phase characterizing much of organic 
vegetable production today. Even NaturFarm's pest control adviser commented 
that on other organic farms he would have recommended sprays like soap and 
BT to combat high levels of pests that NaturFarm elected to tolerate. 
Instead, NaturFarm chose to risk and tolerate some short-term crop loss to 
further the longer-term objective of establishing sustainable biological 

In the face of a severe flea beetle infestation the first season, NaturFarm 
even elected to stop growing daikon radishes and switch to less susceptible 
crops for a season or two, until fall, so that long-lived Collops and 
Staphylinid beetle natural enemies would have more time to exert biological 
control on the soil life stages of flea beetles and worrisomely high 
populations of cucumber beetles [known as corn rootworms in the soil 
stage]. The beneficial beetles finally brought the flea beetles under 
biological control by the end of the first season, and daikons have been 
grown successfully ever since without any pest problems or sprays. 

Fortunately, NaturFarm was well-capitalized and had investors committed so 
strongly to sustainable biological control that they were willing to take 
short-term crop losses, if necessary, in the interests of the longer-term 
goal of establishing a reservoir of natural enemies for a more permanent 
and energy efficient form of natural biological pest control. Before 
embarking on this transition, NaturFarm's investors understood the risks 
and possible short-term losses that could result during the time needed for 
the pest break strips and natural enemies to establish a longer term 
presence. But the long-lasting and sustainable benefits of the pest break 
strips and biological control were perceived as being worth much more than 
any initial crop loss that might have to be tolerated in establishing an 
agro-ecosystem with sustainable biological control by natural enemies. 

There is no cheaper and more affordable army of pest-fighting beneficial 
arthropods than that found in strip-cut alfalfa, which is why NaturFarm 
made this the first choice for pest break strips. The millions of 
beneficials living in an acre of unsprayed strip-cut alfalfa are a ravenous 
army capable of destroying several million pests per day. Indeed, on a per 
acre basis, the number and diversity of natural enemies in strip cut 
alfalfa is so staggeringly high that it could not be purchased from 
commercial insectaries, though it can be grown for free! 

There are over a thousand species of insects interacting in complex 
ecological food webs in alfalfa. Describing and modeling the complexity of 
the alfalfa ecosystem, particularly when the insect diversity is further 
increased by intermixed crimson clover, ryegrass and various weeds, exceeds 
available taxonomic and entomological resources. But NaturFarm's pest 
control adviser, E.J. Dietrick, judged from his experience that the alfalfa 
pest break border strips at NaturFarm provided beneficial insect benefits 
similar to those that he and colleagues reported earlier from unsprayed 
strip-cut alfalfa fields in southern California [Schlinger & Dietrick, 

When strip cut, each acre of alfalfa has 400% more natural enemies than 
when the whole stand is cut or harvested at the same time. The young tender 
alfalfa is an excellent insectary for growing beneficial arthropods, 
providing biological control organisms an abundant food source of small 
soft-bodied insects that thrive in the strip-cut regrowth. Alfalfa plants 
also yield 15% more, an extra ton of hay per acre, when managed by strip 
cutting. When the cut alfalfa is sheet composted rather than removed from 
the field, an expanded food chain of decomposing organisms feeds an even 
more diverse and abundant fauna of beneficial arthropods. 

The strip-cut alfalfa food chain produces over 1 million predatory spiders 
per acre, which is 1,000% more than without strip cutting. Each acre of 
strip cut alfalfa also contains 287,000 of the parasitic wasps providing 
biological control of aphids, caterpillars and other pests; this is 400% 
more than without strip cutting. Big-eyed bugs, good general predators of 
small caterpillars, mites and other pests, number 401,000 per acre in strip 
cut alfalfa, double the number occurring without strip cutting. Lady beetle 
adults number over 200,000 per acre in the strip cut alfalfa habitat, 
versus under 50,000 without strip cutting. There are 232,000 lady beetle 
larvae per acre after strip cutting, 2,000% more than the 11,000 without 
strip cutting  [Schlinger & Dietrick, 1960]. 

Thus, strip cutting alfalfa pest break strips assures a more abundant 
supply of beneficial insects than could be produced under a more static 
management regimen. In contrast to strip cutting, when a whole field is 
harvested it is an ecological catastrophe for the beneficial insects, as 
they lose their food supply and are made homeless. The winged pests look 
for lush green nearby market crops to infest, while most of the beneficials 
either starve or disperse too far away to be available to combat new pest 
outbreaks. Strip-cut pest break strips remedy this situation by providing 
an alternative or trap crop for the pests, as well as simultaneously being 
a natural enemy refuge near the vegetable crops. As managed wildlife 
habitats for beneficial arthropods, pest break strips might be likened to 
military bases where beneficial arthropods are stationed and kept on alert 
to combat pest infestations as they arise. 

In other words, the reservoir of natural enemies in pest break strips 
stabilizes the vegetable agro-ecosystem by providing an army of beneficials 
lying in wait to ambush invading pests and prevent pest outbreaks. As a 
necessary component of an energy efficient agricultural system, pest break 
strips provide the habitat continuity that guarantees the presence of the 
natural enemies needed to provide biological pest control and idle the 
pesticide spray rigs. If conventional and organic agriculture are to kick 
the spray habit and become energy efficient with sustainable biological 
control, then strip cut alfalfa and other pest break strip crops will need 
to become integral components of the farm landscape.

Economics, as much as anything else in past decades, helped make unsprayed 
strip-cut alfalfa a regional reservoir of natural enemies protecting nearby 
crops, including cotton and lettuce, in southern California. This changed 
only when alfalfa hay became economical to spray with insecticides and 
herbicides, which reduced biodiversity by killing the grassy weeds and 
diverse arthropod fauna. When alfalfa and other crops producing beneficial 
arthropods for a regional agro-ecosystem are sprayed and natural enemies 
destroyed, there may be quite dramatic and costly consequences. 

For example, the decline of cotton growing from an over 100,000 acre 
industry to a few thousand acres in California's Imperial Valley in recent 
years coincided with the pesticide-induced loss of alfalfa's natural 
enemies and their replacement by massive migrations of secondary pests like 
whiteflies. Imperial Valley vegetables like lettuce, broccoli and cabbage 
similarly suffer now from the whitefly migrations that have replaced the 
natural enemy influx from alfalfa. 

NaturFarm is using pest break strips in an attempt to re-create on a one 
farm microcosm level the sustainable biological control benefits onced 
provided region-wide in southern California's desert valleys by unsprayed 
and strip-cut alfalfa. But turning the theory that worked area-wide in the 
inland desert valleys of California into a success at NaturFarms' coastal 
valley location has proven a tough challenge. 

First of all, establishing an alfalfa stand proved unexpectedly difficult, 
as gophers undermined the alfalfa. Since other alfalfa fields exist in the 
vicinity, this was not expected. In the inland desert valleys, where 
alfalfa is grown in whole fields and flood irrigated, an irrigator with a 
shovel or a dog can destroy many gophers as they emerge from their flooded 
tunnels. Indeed, many gophers were flushed out by a period of unusually 
heavy rains at NaturFarm. But the NaturFarm uses sprinkler irrigation, 
which does not routinely flood out gophers. In any event, flood irrigation 
is not compatible with the permanent raised bed planting system established 
for vegetable growing. 

What was learned here was that strips of alfalfa interplanted or grown as 
field borders are a different cropping system than alfalfa grown in whole 
fields. Natural gopher biological controls like raptors were not a factor 
in the first year of nature farming, a result predictable from ecological 
theory and classical predator-prey models. Namely, the gopher pests have to 
erupt to high levels before predators can be expected to move in and supply 
control. Though gopher tunnels were explosively destroyed, the alfalfa 
border strips never recovered enough to produce the strong stands 
associated with whole alfalfa fields. 

Needless to say, with the 20-20 vision of hindsight, NaturFarm would have 
benefitted by starting the alfalfa pest break strips a year ahead of 
planting the vegetables, as the problems of stand establishment could have 
been worked out in advance of the first year's plantings of market crops of 
vegetables. The failure to predict the gopher problem and get a year's 
headstart in establishing the pest break strips meant that the natural 
enemy habitat did not reach its full potential in time to provide maximum 
biological control of the first spring's planting of vegetables.

More research is needed into how to best integrate alfalfa and other pest 
break strips into vegetable agro-ecosystems for sustainable biological 
control. One option worth considering is interplanting small fields of 
furrow-irrigated alfalfa, which could be strip harvested for a commercial 
hay crop, around the vegetable farm. These pest break fields have the 
potential to ease gopher problems and management logistics, while still 
producing many of the same benefits as pest break strips. The right 
combination of pest break strips and/or small pest break fields of alfalfa 
needed to produce the desired benefits of trapping cropping and growing 
beneficial arthropods on vegetable farms has never been investigated.

A Sense of Place

Other human factors were also at work, such as the lack of sense of place 
that comes from years of working the land at one location. Being new to 
this farm location and unable to anticipate what the natural cycles of 
climate and the surrounding land would bring added an extra dimension of 
challenge to this transition farming experience, not that anyone could have 
predicted the weather and adequately prepared for its pest consequences on 
NaturFarm's first year. Specifically, the first year of cropping happened 
to be one of California's extreme drought years, which had enomorous pest 
consequences, especially when combined with the difficulty in establishing 
the pest break strips.

Drought years in California usually exacerbate a farmer's pest problems, as 
the surrounding wild vegetation dries up early, forcing insects to migrate. 
The lush green of irrigated farms acts almost like a magnet, attracting 
migrating insects from the the dying hillside vegetation in this part of 
California. In a more normal rainfall year, insects inhabiting the 
surrounding landscape would not have migrated in such large numbers to 
NaturFarm's first spring vegetable plantings. But being an extremely 
attractive [to hungry insects] island of lush green plants in a drying 
landscape, NaturFarm was like a beacon luring in insects migrating from dry 
hillsides and nearby drying lima bean fields early that first spring. Thus, 
the first spring transition vegetable crop at NaturFarm was challenged by 
unusually heavy numbers of cucumber beetles, Diabrotica species, and flea 
beetles coming off drying wild mustards, wild gourds, jimson weed, 
nightshade and other farms with drying crops. 

The combination of unusually heavy insect migrations and pest break strips 
weakened by gophers threatened to overwhelm NaturFarm's vegetable crops 
with flea beetles and cucumber beetles that first spring. Most organic and 
conventional farmers would have reached into their arsenal of sprays. But 
NaturFarm remained true to its paradigm of not spraying, even when its pest 
control adviser expressed some doubts about getting by without any pest 
damage in the face of heavy flea beetle attacks on daikons, cabbage aphids 
on cole crops like cabbage and broccoli, and cucumber beetle populations so 
heavy that they threatened to spill out of the pest break strips and 
overwhelm the farm. 

Basically, NaturFarm gambled that some initial crop loss to the daikons, 
cabbage and broccoli would prove an acceptable price for attainment of the 
longer-term goal of establishing sustainable biological control of pests. 
The underlying premise, based on E.J. Dietrick's decades of firsthand field 
experiences in similar situations, was that unusually high insect 
populations are a common phenomena at the beginning of abrupt transitions 
from conventional to organic farming. When freed from a pesticide 
population control regimen, pests initially enjoy a Malthusian geometric 
population growth spurt in the absence of natural enemies, which are scarce 
from having been sprayed into near oblivion. 

As might be predicted from ecological theory, natural enemies find these 
high concentrations of pests, but usually not until after there is some 
plant damage. Thus, without spraying or some type of pest control actions 
during the early phases of the transition, some crop damage like the flea 
beetle destruction of the daikons and cabbage aphid injury to the cabbage 
and broccoli, is to be expected. For a period of time early in transitions, 
Dietrick has also routinely observed that high populations of beneficial 
insects can co-exist with high pest populations, making for extraordinarily 
high total insect populations. 

Thus, even though biological control may be occurring when total insect 
population levels are high, the pest populations may still be so high that 
some damage and insect-contamination of crops is almost inevitable when 
there is no spraying or other pest control action early in the transition 
experience. Even high populations of beneficial insects like lady beetles 
remaining after destroying aphid infestations are an unacceptable 
contaminant on a harvested broccoli crop.

Eventually, usually towards the end of the first year, and almost always by 
the second or third year, a permanent lowering of total insect populations 
occurs. Also, the ratio of good bugs to bad bugs improves after the early 
stages of a transition, an outcome expected from ecological theory and 
empirical evidence of predator-prey ratios. At least this has been the 
general rule over several decades of Dietrick's experience implementing 
biological control for the University of California and private client 
farmers in California, Arizona, Mexico, Central America and elsewhere. 
NaturFarm's first year transition experience was no exception, only 
overlayed onto the expected high total insect populations was an 
unexpectedly heavy insect migration onto the farm due to the severe drought 
affecting the surrounding non-irrigated landscape. Indeed, total insect 
populations were 10-fold greater the first transition year than in the 
second year of the transition at NaturFarm.

Thus, NaturFarm was exposed to unusually heavy insect pressures when the 
abrupt transition from conventional to sustainable organic farming began. 
Though these high total insect populations early in the transition may be 
unavoidable, maybe even desirable for a sustainable long-term outcome, the 
20-20 vision of hindsight would have dictated preparing for unusually heavy 
drought-year insect migrations by establishing stronger pest break strips 
covering more acres. 

Ideally, at least 10% of the farmed area would be in pest break strips 
planted ahead of the main crop as trap crops to stop such a heavy pest 
onslaught. The type of experiment needed to determine the ideal size of 
pest break strips for heavy pest years is difficult, because it might have 
to be repeated for several years until another drought year of similar pest 
magnitude comes along. But 10% of the area to trap heavy pest populations 
is the figure experimentally determined in several other cropping systems. 
NaturFarm had planned to have 10% of its vegetable cropping area in pest 
break strips. But difficulties establishing the alfalfa pest break strips 
during the first year made the effective trap crop area less than optimum.

[perhaps a good place to insert a diagram of the layout of the pest break 
strips, showing a 35 ft pest break strip every 350 ft = 10% of area, and 
mentioning in caption]

In order to stop pests from moving out of the trap crop and into the market 
crop, trap crops are traditionally either destroyed along with the pests, 
sprayed or treated with some sort of cultural control like barriers to 
prevent pest migrations. Treating only the 10% trap crop area to destroy 
pests reduces pesticide sprays, energy inputs or other pest control actions 
by 90%, as compared to treating the entire cropping area. However, since 
the pest break strips at NaturFarm are designed to double as insectary 
crops and grow beneficial insects, the usual crop destruction and spray 
management options for trap crops were out.

Heavy cucumber beetle populations migrating into the pest break strips from 
the drying hillsides and threatening to spill over into the market crops 
were particularly worrisome that first spring of the transition. The 
question that might be asked here is why the pest break strips did so well 
at trapping cucumber beetles, but not cabbage aphids or flea beetles, which 
caused considerable crop damage. The simple answer is that the cabbage 
aphids attacking the cole crops and the flea beetle species attacking the 
daikons are what is known as specialist pests, attacking mainly members of 
the Cruciferae plant family, which includes daikon radishes, cabbages and 
broccoli. Unlike the adult cucumber beetles, which are attracted to a 
variety of blossoms, these cole crop specialist pests do not have much 
affinity for the alfalfa, strawberry clover or pasture grasses growing in 
the pest break strips, much less the squash, strawberry or lettuce crops.

A more complex pest break strip system could have brought the cabbage 
aphids under quicker biological control. Though, as a practical matter, 
what with the difficulties establishing the alfalfa pest break strips and 
other demands upon the farmer making an abrupt transition in a new setting, 
planting a special insectary blend to protect the first spring cole crops 
was not even attempted. Thus, the first spring planting of cole crops 
functioned like a pest break strip in what scientists would call the 
space-time continuum. In other words, NaturFarm's first spring planting of 
cole crops ended up functioning as a sacrificial trap crop for specialist 
pests like the cabbage aphid, as well as being an insectary crop producing 
cabbage aphid natural enemies for biological control of subsequent [in the 
time continuum] NaturFarm cole crops. 

Thus, cabbage aphids came under biological control when their natural 
enemies became more abundant after that first spring attack. Indeed, 
cabbage aphids remained under biological control for several subsequent 
cole crops, thanks to the descendants of the natural enemies of that first 
destructive spring of the transition. Only later did ant interference 
disrupt the biological control. The ants harvest honeydew from the aphids, 
and like good shepherds chase away the natural enemies attacking their 
aphid dairies. In order for biological control of aphids to function again, 
the ants require periodic management. A culture control, cultivating ant 
trails and nests, disrupts the ants enough to allow natural enemies to 
restore biological control to the cole crops. 

Of course, NaturFarm would have preferred that its first spring planting of 
cole crops be sold as a market crop, not become a de facto pest break 
strip. But this would have required advance planning, and added a layer of 
complexity for the already hard-pressed farmer, who would have had to plant 
a special cole crop pest break strip in addition to the alfalfa pest break 
strip. If the initial cole crop loss is to be avoided at the beginning of a 
transition to a no-spray sustainable organic vegetable agro-ecosystem, then 
special cole crop pest break strips are needed to compensate for the time 
lag between pest outbreaks and the onset of biological control. 

In classical predator-prey ecological theory, the time lag for onset of 
biological control exists because the prey [cabbage aphid] population peak 
reaches crop damaging levels before natural enemy [predators, parasites, 
pathogens] populations increase enough to dampen the infestation. In other 
words, pests are necessary to grow natural enemy populations; and if the 
pests are not to damage the initial cole crop plantings, then the pests 
needed to nourish natural enemies have to be grown in special cole crop 
pest break strips ahead of the market cole crop. Indeed, establishing cole 
crop pest break strips far enough in time in advance of the market crop 
would also help grow Collops beetle, Staphylinid beetle and other natural 
enemies for biological control of flea beetles, cucumber beetles and other 

[if available, might not be a bad place to insert diagrams or illustrations 
of the pests & natural enemies mentioned; e.g. cole crop roots attacked by 
larval flea beetle, which is attacked by Collops & Staphylinid beetle 
larvae, while adult flea beetle is munching shot-holes in leaves.]

Since cole crops are so heavily sprayed, with many pests resistant to 
pesticides, much more research is needed on integrating cole crop pest 
break strips into vegetable agro-ecosystems. Only one experimental 
paradigm, a strip farming experiment in Tennessee in the 1930s, even exists 
for using cole crop pest break strips to prevent cabbage aphid damage 
[Marcovitch, 1935]. In these early experiments, strips of turnips, a good 
cabbage aphid host, planted a month ahead of market crops acted as 
insectary plants, providing aphid natural enemies to nearby market crops. 
The turnips were partially destroyed by aphid infestations by late spring 
or early summer, but predators like lady beetles and parasites like 
Lysiphlebus testaceipes controlled aphids in the nearby later-planted 
market crops for most of the rest of the season. The NaturFarm experience 
was similar, only the planned market crops of cabbage and broccoli the 
first spring of the transition played the insectary crop role of turnips.

More research is needed to determine whether other Cruciferae family plants 
like the wild mustards [probably relatives of the mustard seed industry 
crop plants farmed nearby in bygone decades] and wild radishes growing in 
the vicinity of Naturfarm might also be harnessed as cole crop pest break 
strips in interplanted rows or around field perimeters. Integrating these 
locally adapted weedy crucifers [e.g. wild radish and wild mustards] into 
the agro-ecosystem might also help produce needed energy-savings in weed 
control, as these Brassica species are known for their allelopathic 
inhibition of other vegetation. Under a plastic tarp like those used for 
solarization, residues of Brassicas such as cabbage and mustards are as 
effective as soil fumigants against soil pathogens and plant-parasitic 
nematodes. Hence, the potential to rotate locally-adapted Brassicas into 
the strip cropping scheme for control of multiple types of pests and 
increased energy savings needs to be further investigated.

NaturFarm has so far only scratched the tip of the iceberg, as far as the 
potential of pest break strips to save energy and pest control costs. With 
such encouraging initial savings in energy and insect pest control costs 
compared to conventional farming, NaturFarm feels strongly that the concept 
of pest break strips needs to be further developed and extended to control 
a wider range of pests, save energy on other farm operations, and increase 
the overall sustainablity of farming. Many potential species, from legumes 
like peas to grasses and native plants like marigolds await testing in 
vegetable agro-ecosystems for insect, nematode, weed and pathogen control. 
Pest break strip cropping schemes can become even more varied to meet gaps 
in pest control. For example, strips of peas planted by Marcovitch [1935] 
in September grew pea aphids and their natural enemies, providing 
biological control of aphids on turnips and several other crops for several 
weeks into the fall. 

Future research should followup some of these many leads, and determine the 
best and easiest to use pest break strip cropping schemes for the long-term 
sustainability of vegetable agro-ecosystems. Research is also needed to 
fine-tune the planting times of pest break strips in relation to market 
crops for maximum biological control efficacy. The 1935 Tennessee 
experiments indicate that timing of plantings is critical -- the insectary 
crops had to be planted enough in advance, a month in spring, of the main 
crop for sufficient natural enemies to be available to nearby market crops. 
Perhaps by simply adjusting pest break strip species and planting times, 
transition farms like NaturFarm could get through the first season with no 
sprays, no crop loss and the same energy and pest control savings. Future 
research will have to address these and many other issues, including 
irrigation effects on pest management, if the transition to 
energy-efficient, sustainable no-spray organic vegetable farming is to be 
made easier to follow and more painless. 

In most cole crop production areas in California and worldwide, caterpillar 
pests like the imported cabbageworm, cabbage looper and diamondback moth 
are a problem, and sprayed with everything from microbials like Bacillus 
thuringiensis [BT] to synthetic pesticides. Pesticide resistance has turned 
diamondback moth into a major problem in the Asian Pacific Rim countries. 
Inexplicably, cole crop caterpillar pests like diamondback moth, imported 
cabbageworm and cabbage looper never became a problem at NaturFarm.

NaturFarm's diverse natural enemy complex, which contained many generalist 
predators, including large beetles capable of eating caterpillars, may have 
played a role in keeping caterpillar pests like cabbage looper, imported 
cabbageworm and diamondback moth from reaching pest status. However, 
another caterpillar pest, the corn earworm, did become a problem on sweet 
corn despite an abundance of its primary generalist predator, the minute 
pirate bug. Hence, there may have been factors other than direct biological 
control by natural enemies at work suppressing cole crop caterpillars but 
not corn earworms. For example, NaturFarm injected very low levels of the 
microbial inoculant EM in overhead irrigation waters sprinkled on crops. 

EM has never been directly tested or evaluated with respect to its 
potential direct or indirect control effects on pests. So, an EM role in 
suppressing insects like the caterpillars attacking cole crops cannot be 
entirely dismissed without further research. In fact, there is reason to 
suspect that the very low incidence of plant disease problems at NaturFarm 
might be related to EM. Microbes like those in EM are known to produce 
antibiotics, which can stop other microbes, including some plant pathogens. 
Also, microbes that do not harm plants have been known to occupy niches 
favorable to plant pathogens, thereby excluding colonization of the plant 
by the pathogen. In a phenomena roughly analagous to immunity, microbes can 
also be a factor in induced resistance of crop plants to pests. Microbes 
can also be antagonistic to pathogens in a manner analagous to the 
biological control of insects by predators and parasites. Indeed, recent 
scientific research indicates that the microbial products in compost teas 
sprayed on plants can stop plant diseases like downy mildew, powdery mildew 
and leaf blight [Weltzien, 1989].

Vegetable crops are known to be attacked by a wide range of plant diseases, 
and fungicide use is the rule on many conventional vegetable farms. Yet, 
surprisingly, NaturFarm's only plant pathogen problem of consequence was a 
blue mold on spinach believed to be downy mildew race 3. Like most 
California coastal areas, powdery and downy mildew occurred on cucurbits 
like squash, though were not severe enough to impact production. Whether 
this low level of disease incidience was coincidental, due to natural 
biological controls moving from the pest break strips with insects, or 
related to EM, cover crop, fertility or other practices associated with the 
NaturFarm farming system is unknown. It would take a complicated research 
design to determine what is happening at NaturFarm with respect to the 
extraordinarily low incidence of plant disease on the 30 vegetable crops.

Usually, overhead irrigation plays a role in plant disease and arthropod 
pest management. Sometimes, overhead sprinkler irrigation stimulates 
germination of the spores of plant pathogens like those causing downy 
mildew and powdery mildew. Other times, overhead irrigation timing is such 
that the plant pathogen spores do not germinate in greater than usual 
quantities. In fact, overhead irrigation sometimes reduces powdery mildew 
by washing off spores. Overhead irrigation also washes off arthropod pests 
as diverse as aphids, spider mites, thrips and caterpillars. Wingless pests 
washed off plants by rainfall or overhead irrigation have a more difficult 
time surviving and returning than do winged predators and parasites. 
Predatory mites survive because they float in water, whereas pestiferous 
spider mites drown. Irrigation, rain, fog, dew and other water sources can 
also create damp microclimates favorable to epidemics of entomogenous 
fungi, an occurrence observed when indigenous biocontrol fungi destroyed 
aphids living deep in the wet understroy of the pest break strips. 

In fact, there is also good reason to suspect that the irrigation process 
itself, in this case overhead sprinklers, could also be one of the reasons 
for the surprising absence of cole crop caterpillar pests. In fact,
in Hawaii, daily overhead irrigation was shown to control diamondback moth; 
however, the crop was watercress, an aquatic plant that could withstand 
moisture without fear of disease. But more recently in the Midwest, daily 
overhead irrigation of head cabbage growing in a well-drained soil was 
shown to reduce diamondback moths up to 90%, with no plant disease 
problems. The key to attaining such a high level of control is timing 
overhead irrigations for the evening hours, as this disrupts the calling, 
mating and dispersal of diamondback moth, a nocturnal pest [McHugh, 1993]. 

NaturFarm did not set up controlled test plots to investigate the effects 
of its overhead sprinkler irrigations on cole crop caterpillar pests like 
diamondback moth. So, there is no way to know what percent of the pest 
control effect can be ascribed to biological control and what percent 
ascribed to irrigation. There is also evidence that overhead irrigations 
timed for the hottest part of the day also reduce numbers of adult flea 
beetles, as these pests like it hot and dry. It might almost require a 
computer system to keep track of and schedule irrigations for pest control 
purposes so that fungal biocontrol agents are triggered against aphids, 
diamondback moths disrupted on cole crops by evening sprinklings and flea 
beetles deterred from daikons by overhead watering during the hottest part 
of the day. Factors like water conservation and energy use have never been 
determined for a system of this sort integrating irrigation and pest 

Future research into integrated pest management [IPM] systems might 
consider designing in and taking advantage of the potential pest control 
synergisms between irrigation and biological control by natural enemies. 
Thus, an overhead sprinkler irrigation system like NaturFarm's could 
potentially be fine-tuned to wash off pests, disrupt pest mating and 
optimize biological control in crops and pest break strips while delivering 
the optimum daily dose of water to crops. 

However, integrating irrigation into cropping systems as a form of pest 
control may not be simple, as evidenced by the irrigation scheduling 
difficulties encountered with the pest break strips. Vegetable farms might 
require a computer system with software combining the interactivity of 
expert systems with scheduling and forecasting [e.g. crop irrigation needs, 
expected pest problems] abilities; though this might be technically 
achievable, such a system has yet to be invented for vegetable farms. 
Designing a vegetable cropping system harmonizing the pest control 
advantages of irrigation and pest break strips with crop needs and farmer 
abilities and equipment limitations would be an innovative future research 

Another reason for learning how to better integrate the irrigation and 
maintenance of pest break strips into vegetable cropping systems is that 
the pest break strips may be the only year-round habitat available on 
vegetable farms for colonizing new natural enemies. Some pests became 
problems because when inadvertently imported from their foreign lands of 
origin, their natural enemies were left behind. In the absence of predation 
and parasitism by natural enemies from the native ecosystems of pest 
origin, pest populations can quickly explode to damaging levels. These 
damaging pest population explosions are also seen when natural enemies are 
missing for other reasons, such as pesticide spray mortality. 

Classical biological control remedies the absence of natural enemies from 
the pests native homeland, though the introduced natural enemies have to be 
protected from eco-catastrophes like pesticide spray drift. In classical 
biological control, natural enemies from the pest's homeland are collected, 
quarantined and evaluated, usually by the USDA, universities or state 
agencies. Natural enemies passing the test criteria and surviving the 
rigors of rearing are released in an attempt to establish a natural 
ecological balance similar to that keeping the pest rare in its native 

Not all classical biological control releases of natural enemies provide 
permanent pest control. Natural enemies imported for classical biological 
control programs are not always those best suited to the pest or climate of 
the new agro-ecosystem. Nevertheless, successful classical biological 
control programs more than pay for any R&D expenses and failures, often 
saving millions of dollars per year in pest control costs and reducing 
pesticide use dramatically. 

At NaturFarm, the year-round habitat provided by pest break strips afforded 
an opportunity for classical biological control not commonly found in 
vegetable agro-ecosystems. Most vegetable farms lack the year-round habitat 
provided by pest break strips, and are therefore inherently unsuitable for 
classical biological control. In contrast to less sustainable vegetable 
farms lacking pest break strips, NaturFarm was able to implement classical 
biological control, augmenting the indigenous natural enemy complex with 
exotic natural enemies capable of controlling tough potential pests like 
the diamondback moth and Lygus bug. 

A Braconid parasite, Peristenus digoneutis, imported from Europe by the 
USDA and impossible to raise in commercial quantities at the insectary, was 
released into the pest break strips to reproduce naturally and increase 
destruction of Lygus bug nymphs. The starter culture of two dozen mated 
female P. digoneutis were placed into an improvised field insectary, a 
tent-like nylon organdy cage slipped over a section of alfalfa in the pest 
break strip infested with Lygus. The idea behind this type of classical 
biological control is permanent establishment of the new natural enemy in 
equilibrium with populations of Lygus that become permanently lower than 
would otherwise be the case. 

Clasical biological control does not seek to eradicate the pest, as this 
would risk starvation of the natural enemy. Rather, the goal is reducing 
the pest to tolerably low levels. Besides release of P. digoneutis against 
Lygus bugs, an egg parasite was released to attack diamondback moth in cole 
crops. The diamondback moth egg parasite, Trichogrammatoidea bactrae, was 
collected as part of a University of California, Riverside, expedition to 
Australia for pink bollworm natural enemies. T. bactrae is a good candidate 
for establishment as a classical biological control because it attacks a 
wide array of moths in the family Gelechiidae, which includes many pest 
species. Also, T. bactrae can be produced commercially in the insectary.

NaturFarm also "seeded" the pest break strips and vegetable rows with 
well-known insectary-grown natural enemies like green lacewings, predators 
attacking soft-bodied insects ranging from aphids and tomato russett mites 
to corn earworms and cabbage loopers. The beneficial insect releases, 
designed to augment or supplement indigenous biological control organisms, 
also included Trichogramma egg parasites that stop moth and butterfly eggs 
from hatching into pests like damaging cabbage caterpillars and tomato 
fruitworms. These natural enemy releases can be thought of like vitamin 
supplements, helping ensure that the agro-ecosystem has the biological 
control "nutrients" needed to fight off pest infestations.

The supply of indigenous natural enemies found on NaturFarm included 
classical biological organisms introduced by the University of California 
many decades ago, a lasting reminder to knowledgable entomologists that the 
few thousand dollars spent on biological control many years ago are still 
working and paying millions of dollars in pest control dividends around the 
state every year. The most immediate source of the thousand or so species 
of natural enemies colonizing the pest break strips at NaturFarm was 
probably a nearby unsprayed alfalfa field. 

Had there not been quick natural colonization of the pest break strips by 
natural enemies from a nearby unsprayed alfalfa field, natural enemies 
could have been vacuumed harvested from a slightly more remote source in 
the same county and transported to NaturFarm for release. The same D-vac 
and Cycle Vac vacuum insect harvesting equipment used to sample fields as 
part of monitoring arthropod populations can be used to harvest "crops" of 
pests to study or beneficial insects to transport. With over one thousand 
arthropod species interacting in California alfalfa fields, practical 
population monitoring for everyday pest management requires using a rougher 
index, a ratio of good bugs to bad bugs, to monitor the progress of 
biological control on a more macro level. Since the D-vac and Cycle Vac 
collect huge numbers of insects, well-above the numbers needed for sampling 
and monitoring purposes, the excess not put into alcohol for preservation 
and possible future dissecting microscope identification to the species 
level can be utilized as a "crop." 

This huge excess D-vac or Cycle Vac harvested "crop" of living insects can 
be sorted via a series of screens of varying mesh size. For example, 
parasites tend to be very small, sometimes pin-head species like 
Trichogramma, and pass through the smaller screens. Larger insects like 
cucumber beetle adults remain behind. 

Indeed, this principle of insect separation after vacuum harvesting, which 
did not require energy expenditures beyond planned sampling needs, proved 
to be an excellent tool for managing the pest break strips as a cucumber 
beetle trap crop. Instead of spraying or plowing under the trap crop to 
destroy the cucumber beetle adults, the pests were vacuumed up and the 
beneficials returned unharmed to the pest break strip. 

The idea of vacuuming up pests and returning the beneficials to the field 
to improve the "good bug to bad bug ratio" is an innovation in vegetable 
farming. Since the invention of the D-Vac in the 1950s, E.J. Dietrick has 
sold over 1,500 D-Vac vacuuming units, mostly for scientific sampling 
purposes. Variations on the D-Vac concept, like Tractor Vacs, have been 
around for decades, mostly used by University of California researchers to 
harvest insects from alfalfa fields. Only recently have commercial 
quantities of tractor-drawn vacuum devices been sold to suck up everything 
from Colorado potato beetles on potatoes to Lygus bugs on strawberries and 
caterpillars on lettuce. 

However, there is a big underlying difference in the way that NaturFarm 
uses vacuuming to harvest insects. First of all, NaturFarm vacuums only the 
pest break strip area, when needed, or less than 10% of the acreage, not 
whole fields. Other vegetable farms tend to vacuum their whole acreage, 
which may have a different effect on the agro-ecosystem, much like the  big 
differences in numbers of natural enemies between strip-cut alfalfa and 
cutting the whole field all at once; but more research is needed, as these 
ecological changes have not been measured. Also, other vegetable farms do 
not screen their insect harvests and return the beneficials to the field -- 
so their paradigm is more like the pesticide era philosophy that "the only 
good bug is a dead bug." In contrast, NaturFarm integrates vacuuming as a 
selective [good bugs are returned to the pest break strips] cultural 
control tool that raises the good bug to bad bug ratio, and promotes the 
longer-term goal of sustainable biological control.

NaturFarm was fortunate that E.J. Dietrick's bag of biocontrol tricks 
included this innovative strategy of harvesting excess cucumber beetles 
from the pest break strips without disrupting development of biological 
controls. Since cucumber beetles also have a soil larval stage, much like 
flea beetles, and can damage crop roots, biological control of the soil 
stage of the pest could have better complemented the above-ground adult 
life stage vacuuming. Mulching around the susceptible crops would provide 
habitat for more natural enemies, as well as another food source from the 
food chain involved in mulch decomposition. As it was, the adult stage of 
the cucumber beetle was eventually lightly parasitized by a Tachinid fly, 
while the soil stages were attacked by larval Collops and Staphylinid 
beetles. The end result was as would be predicted from classical ecological 
predator-prey theory: namely, the Collops beetles, Staphylinid beetles and 
other natural enemies brought the flea beetles and cucumber beetle pests 
under sustainable biological control, and crops like daikon can now be 
grown without fear of crop destruction.

To be continued...