I think there's a virus killing my winter and summer squash. The
leaves have yellow spots and they are curling, growth is stunted.
Does anyone know a source of non-gmo virus resistant seeds? Or variety
names I can search for that are resistant?
Thanks very much!
Infected plants should be removed immediately. Virus can be spread from
plant to plant during handling, so thorough cleanup after handling infected
plants is neccessary.
If it is Cucumber Mosaic Virus (CMV), all commercially available cultivars
are susceptible. There are no resistant varieties. Some varieties of
summer squash with the "precocious yellow" gene are described as
resistant, but the "resistance" is only in the sense that the fruit is less
likely to show the discoloration typical of the virus.
Winter weeds like chickweed can act as a reservoir for CMV and carry it
in their seeds. A number of perennial weeds can act as a reservoir for
Aphids are the main vector for the virus (early in the season). Aphids
are also the vectors for Watermelon Mosaic Virus (WMV), which, like
CMV, overwinters in weeds.
Perennial weeds suspected of acting as reservoirs for the viruses
mentioned include black nightshade, milkweeds, and some clovers
and other legumes.
Controlling aphids and eliminating problematic weeds is your primary
defense against these viruses.
Squash Mosaic Virus is seed-born in muskmelons and cucumber beetles
carry it (as well as bacterial wilt disease) to other curcurbits.
Good information Pat. Since you sound like an extension agent I have
another issue for your input.
I use 13-13-13 fertilizer for my vegetable garden and this year I ran
into a questionable issue. The bags content lists NPK as 13% each but
also sulfur 8% and chlorine 'up to 13%'. No one seemed to know why
they started adding these additional components to a 'standard'
fertilizer. I e-mailed the question to the manufacturer who forwarded
it to the plant manager. The plant manager's response was "Sulfur is
being added because of the reduction in it's emission in industrial
smokestacks due to lawsuits, and plants need sulfur. The chlorine is
the byproduct of preparing muriate of potash. It can be used in
vegetable planting but not with tobacco planting".
So my question was answered why it was added to their product but not
how it would affect vegetables. Chlorine is usually listed as a plant
micronutrient but 'up to 13%' is definitely not 'micro'. And if it is
absorbed by tobacco plants is it also absorbed by vegetables? I'm
wondering if extension service agents are aware of, or looking into,
Speculation - the chlorine was probably always in there, but a labeling
requirement let you know about it instead of keeping it hidden.
Think of it this way - you don't want pure potassium. Dangerously
reactive and probably unusable by your plants. So you get (one
possibility) potassium chloride or chlorate - likely hydrated. Or
potassium sulfide, or phosphate (perhaps laws against that too).
Some fertilizers have used mining slag with heavy metals. You have to be
careful what you're putting into your soil, especially if you're going to
be eating from it, or your kids might play in it.
I checked some previous years labels and some showed sulfur as .5-1%
and chlorine at .001% in the fine print. This year it was either
vastly increased or the truth was shown.
Slag is also a cheap lime source for cotton farmers. Might be why
cotton shirts weigh much more than silk ones. :o)
You were given a rather rosy view of the situation.
Each ingredient in chemical fertiliser is a salt. So muriate of potash
(potassium chloride) is a salt. Every salt has two (at least) parts, in this
case the potassium is the desirable part and the chloride is just along for
the ride. The chlorine is not a by-product it is an inescapable part of the
product as you cannot supply potassium as an element it must be as a salt.
If you didn't have potassium chloride as a source of potassium you would
probably have potassium sulphate, then you would be getting some more free
sulphur instead of chlorine. Most salts used in chemferts are like that,
where some of it is not particularly useful to the plant. There are some
exceptions such as ammonium phosphate which supplies both N and P but that
is rare. In the main the excess chloride or sulphate etc is not
specifically harmful. The matter of whether adding salts to the soil
overall is harmful is another issue altogether.
The maker did not start adding these things - they were already there. I
think you will find that the formulation didn't change but that the maker
started to declare all the extra elements that they have no choice but to
As for the story about sulphur being added from their smokestack I would be
very wary of accepting this at face value and interested to know what else
they might scrub out of their pollution that ends up in the fertiliser. Yes
plants do need sulphur but it is rare to find a deficiency as it can be
supplied in so many ways and it is not used up in huge quantities.
Apparently tobacco is very susceptible to fertiliser burn from muriate of
potash but I have never grown it so cannot say. Yes it is very likely that
your veges will absorb these chemicals but there is no choice about that.
The same applies to organic sources of nutrients. Just because a substance
comes out of a chicken's bum doesn't mean it is better than the same thing
from a steel vat. The good news is that most of these additions are not
harmful in themselves. There are problems with some true by-products, for
example gypsum (mainly calcium sulphate) is used as a soil conditioner and a
source of calcium. However some gypsum contains small amounts of cadmium (a
heavy metal) which is quite harmful and will accumulate in the soil if added
often. Read the fine print!
The moral of the story is whether you adhere to "organic" only soil
improvement or accept synthetics or a bit of both you need to watch what you
are putting into your soil and to evaluate as far as possible the whole
situation and what your soil needs rather than blindly add whatever is in
fashion or the makers want to sell you.
I had a few elective horticulture classes a long time ago, a lot of time
gardening, many books on hand and a fast internet connection.
Also, I have a particular interest in squash.
What he's saying is that cleaner smokestacks mean less deposition of
sulfur in rain and dust, so they have increased the amount they add to
their standard fertilizer mix to make up for it, but with an industrial
spin on the 'why' of it (lawsuits, due to the Clean Air Act). "It's an ill wind
that blows nobody any good." Nitrogen and sulfur deposition due to air
pollution is bad for natural systems, but agriculture is not a natural system.
Probably because they changed the source of potassium into potassium
chloride. Tobacco must particularly sensitive to it.
No. I've about gotten rid of mosaic virus in my squash by going on a
catnip eradication campaign, and spraying/dusting with insecticide at
the first sign of cucumber beetles. I think the catnip part was the
key, because I seldom get any cucumber beetles, and because the virus
usually infected the squash shortly after they started blooming if any
catnip was blooming nearby.
That probably explains my squash problem. I plant yellow and zucchini
squash and the yellow type dies before producing and the zucchini dies
after a couple of pickings. I also had been planting nearby wild
flowers (+catnip?) to attract bees for pollination and to draw insects
out of the garden, but I may well have been providing a storage source
for the MV. Our honey bees are gone and other type bees, except for
the darn carpenters, are few so I thought an attractant might be
beneficial but may be a hindrance.
Do you live where squash vine borers occur? Summer squash (or any
of the short-vined 'bush' type winter squash) are extremely vulnerable to
them, and will typically go into a rapid decline just when they begin to
flower or shortly after. They may show signs of other diseases as they
die, but the borers are ultimately responsible for the decline.
The squash vine borer usually leaves a very visible sign where it
bores and I saw none of that. The plant leafs yellowed and died
similar to tomato spotted wilt virus. There was some nematode
symptoms in some tomato roots but none in the squash roots. My tomato
selection this year is mostly VFFN.
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