Subject: Re: Bugs only bug unhealthy plants?
From: thodges@freenet.calgary.ab.ca (T Hodges)
Organization: Calgary Free-Net
Date: 6 Aug 1997 17:00:57 GMT
Message-ID: <MOD$970806.2012@rec.gardens.ecosystems>
References: <MOD$970804.12169@rec.gardens.ecosystems>


If a plant is growing rapidly and the herbivore (plant eating
thingies) pressure is not too great, then damage will not be
too noticeable. For example a plant is adding 10% new leaf area
each day and 5% is being eaten then the plant will appear to
grow almost as fast as if nothing was being eaten, also the
damaged leaves will be covered up by new foliage. Once the
plants are intercepting all the sunlight or accessing all the
soil resources then bigger plants will not contribute much to
bigger yield (except yield of leaves).

But if you get an insect that multiplies rapidly and you don't
have predators (for that insect) that also can breed very fast
then the grazing rate can quickly exceed the plant growth
rate and severe damage will result unless something is done to
control the population of the herbivore.

The most desireable approach is to control all the herbivores by
having active and diverse predator populations that respond to
increases in any herbivore with increased predation. But if
some hervivore gets out of bounds then either lose the crop or
find some way to control it. A broad spectrum insecticide will kill
many of your predators where it is applied so if you are trying for
biocontrol that will need to be followed by measures to restore
the predator populations.

Hope this helps, Tom

In article <MOD$970804.12169@rec.gardens.ecosystems>,
Dennis R. Moore wrote:
>
>It is a long held common garden wisdom that insects and diseases are
>problematic only on unthrifty or otherwise stressed plants. My own
>experience validates this supposition to some degree but, lately I've
>been wondering if there is any solid research supporting this thesis.
>Can anyone point me in the right direction? Thanks!
>
>Dennis
>Remove "nospam" from address if you wish to reply via e-mail
>
>moderator cookie: 970804.12169
>

--
Tom Hodges thodges@freenet.calgary.ab.ca
Professional Agronomist, member Baha'i Faith, Go player