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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
strips.
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
control.
[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
control.
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,
1960].
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
pests.
[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
management.
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
direction.
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
homeland.
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...