Bugs only bug unhealthy plants? (fwd)

Allyn Weaks allyn at u.washington.edu
Sun Aug 10 01:10:38 EST 1997


In article <33eaa14b.6815047 at news.mindlink.net>,
dennis_goos... at mindlink.net wrote:
> Have you a theory for why insects would  be attracted to the least healthy,
> least nutritious plant material ? 
> 
> Our species and all animal species I have observed seem to select the
> healthiest, most nutritious plant material for food if that is what you
mean by
> "recycling".

The link is that a plant under stress doesn't have the resources to keep
it's own defences up to snuff.  Pesticide production is expensive, tough
tissues are expensive, and if an organism is on the edge, it won't be able
to afford enough of them.

>  In my greenhouse, the bugs seem to go for the youngest, most
> tender tips available. Active healthy growth seems  to pull them from miles
> around.

But for many plants, especially ornamentals, what we've been taught to view
as 'active healthy growth' is actually a sign of ill-health; often an
over-fertilization glut of too much nitrogen, but it can also be a last
ditch effort to set some seed in bad circumstances.  If the growth rate
outstrips the ability of the plant to produce its defences, it will indeed
be more attractive to herbivorous bugs, who like tender undefended tissues
just as we do.  Which is one of the reasons that many of our food plants
have pest problems--we've bred many of the bitter pesticides and tough
tissues out of them, leaving them nearly defenseless.  Pest control in the
veggie garden does require more than just healthy plants, though that still
doesn't necessarily mean applied pesticides.  A good predator population
and not planting in monocultures seems to be enough for a lot of people.
-- 
Allyn Weaks  allyn at u.washington.edu
PNW Native Wildlife Gardening:  http://chemwww.chem.washington.edu/natives/
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