Virus questions

Jane McGary
Sat, 13 Jul 2002 09:12:50 PDT
Mary Sue wrote, 
>I don't usually see aphids on my Brodiaeas, but am always fighting them on 
>my Alliums. I was interested in reading in Jane's article about her frames 
>that she uses a systemic as she pots to keep the aphids at bay. I know I 
>wouldn't want to do that. 

I don't routinely add systemic insecticide when repotting. Rather, I
sprinkle some on the surface and scratch or water it in when I notice
aphids on a particular plant, usually seedlings; they do not seem attracted
to mature plants of most species. Because my frames are open on both sides
and warm and dry, there are a lot of insect-eating insects in them, which
help to control aphids. I am not concerned with it harming birds and
animals, because the only birds and animals likely to come in contact with
this insecticide are there to eat my bulbs!

Using "chemicals" (in the common parlance; in fact, everything's made of
chemicals) in this way is a feature of "Integrated Pest Management," a
method of applying minimal intervention just when and where it is needed.
This assumes that the applicator's reverence for life does not extend to
aphids, Botrytis, malaria parasites, etc., at least in the immediate

There seems to be some confusion in this discussion between virus diseases
and diseases caused by bacteria (e.g., the iris rhizhome rot mentioned) and
fungi. The latter can be treated, though not usually eliminated, by
superficial means such as applying solutions that alter the chemical
environment on the surface of the plant, making it more acidic or alkaline,
or alter the physical environment by, e.g., gumming up the pores; milk
might do either of these things, resulting in a temporary improvement.

Diane Whitehead's observation about virus-tolerant lilies is very well
taken and probably applies to many other groups of plants: virus can be
present for many years without manifesting as disease symptoms, then appear
when the plant is stressed. In addition, there are many, many viruses that
exist in organisms without doing obvious harm, and presumably some of these
can mutate into injurious viruses from time to time, perhaps to "jump" from
one host that tolerates them to another that doesn't.

The best form of virus prevention is to grow all your plants from seed, but
I don't know of many gardeners to adhere to that strictly. For example,
Edward McRae is growing the stock for the Lily Species Foundation from
seed, isolated in a nursery on the east side of the Cascades.

Jane McGary
NW Oregon

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