Well the leaves continue to die at the crown although a couple very deformed ones have managed to survive. What I discovered this morning was the pot was crawling with tiny black flies. Must have been a hundred or more. So I hosed it with pyretherin spray and that killed them off quick. Could this damage be caused by a fly larvae?
Yes, fungus gnats. A thin layer of sand on the soil surface will discourage flying adults from laying more eggs. Use some kind of Bt next time you water (a dissolved mosquito dunk will work in a pinch) for longer term control.
Turns out it was ZYMV - zucchini yellow mosaic virus. Took one of the affected plants up to a good garden center with real gardeners running it (not teenage kids) and the guy said it was mosaic virus. He advised dumping the soil and scrubbing the container.
How serious is this? Is it totally contagious? Is it safe to reuse the soil with some other non-cucurbit plant?
Paul
Google is your friend (well, except when they are spying on you):
The disease may be introduced in infected seed, so sourcing clean seed can help prevent the disease. Control is largely dependent on using insecticides to control the aphid vectors. A form of "inoculation" or cross protection may also be used where seedlings are inoculated with a non-virulent strain of the virus (ZYMV-WK); this prevents infection with the severe strain. and so on.
Like all other aphid-transmitted viruses, ZYMV is extremely difficult to control with insecticides, reflective mulches, and mineral oils. Better results can be obtained with resistant cultivars.
Resistance has been found in lines of Cucumis sativus from China and in an accession of C. melo from India. However, this resistance proved to be strain-specific and is not effective against a second pathotype of the virus.
Resistance is available in a wild squash (Cucurbita ecuadorensis) and in a C. moschata line from Nigeria.
All commercial cultivars of Citrullus lanatus that have been tested are susceptible, but resistance is available in some accessions of C. colocynthis from Nigeria. A very high level of resistance was found in some races of C. lanatus from Zimbabwe, but it confers resistance to the Florida strain only.
In recent years, new squash lines possessing the coat protein gene of this virus have been developed and proved to be resistant under field conditions. The ZYMV coat protein gene has also been incorporated into melon and cucumber.
Almost entertaining.
I didn't see the original post, but the fungus gnats got in there mostly just because the soil was damp, which can come from either overwatering, or from sick plants that don't have the capacity to take the water up anymore (which sometimes comes from overwatering). Larvae can still munch on healthy young rootlets after their more favored decaying matter is spent. Not sure about this virus, but most can be killed by pasteurizing the soil. Whether you do this or replace it, clean the pot & sterilize it. Pretty much standard procedure for me anyway because it's just good hygiene, and whenever pulling a pot out of storage I don't have to worry what condition the last plant occupying it was in.
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