this post was submitted on 19 Dec 2023
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Sorry for the second post, but I started doing some research into the other viruses you mentioned. Maybe this is worth a separate post, but you seem knowledgeable so I'll ask here.
I don't see signs of mosaic virus with my other crops (including zucchini, other squashes, tomatoes, peppers and eggplants), just cucumbers; does that make it any more likely that my issue is one of the viruses in particular? From what I can tell, the name cucumber mosaic virus is historical, and doesn't necessarily mean cucumbers are particularly susceptible.
Or maybe there's another reason for my cucumber issues: infected seed (I purchase commercial seed), growing conditions that are stressing cucumber plants in particular, or another disease that I'm mistaking for a mosaic virus. Any recommendations other than plant and pray?
In order of likelihood.
The mottling pattern of Downy Mildew is the most commonly confused. It's a fungus that often attacks cucumbers first. The pathogen overcame the genetic resistance claimed on all the old OP's 20 years ago.
Angular leaf spot is the second one. It has a narrower host range. And often will infect the cucumbers and melons but leave others alone.
There are also whitefly transmitted viruses like CYSDV or CGMMV which are more common in the subtropics or greenhouses. CGMMV is seedborne but easily tested so most larger suppliers do it regularly. The symptoms for both start on the lower leaves.
Vector feeding preference: aphids transmit CMV, ZYMV, PRSV and WMV. They sometimes have are shown to have feeding preference based upon leaf colour or species.
Seedborne disease - the only serious virus that is significantly seedborne in cucumbers is CGMMV. ZYMV has been shown to be weekly seedborne low rates in Cucurbita pepo. SqMV is transmitted in cantaloupe seed.
The only one you are likely to run into in OP seed is ZYMV in C. pepo. This is because it is endemic to the seed growing regions but infects the seed at low levels. Hybrids for commercial available almost all have ZYMV resistance either from GMO or interspecific crosses with C. moschata "Nigerian" and are not routinely tested. OP seed is grown as cheaply as possible and is more likely to be infected with seedborne diseases.
So what do you do:
Plant your cucumbers in a different location and watch them closely. If signs of disease show up, post a pic and tag me. I can send you down the right path.
I personally have transitioned to more modern hybrids with stacked disease packages. I like the parthenocarpic gyneceous ones because they do not require pollination to set fruit. They also yield a lot more.
Thanks for the deep dive. I definitely didn't look closely enough to know whether I had downy mildew or mosaic virus - from pictures online it looks like a real possibility.
I had been trying to stick with heirlooms in the hope of saving seeds, but saving cucumber seeds is such a PITA anyway (need to bag male and female flowers and hand pollinate) that I'm OK going to hybrids. I'll look into those you mentioned.
Thanks again.
Planting some crops that are disease resistant is a must. The introduction of Roundup (glyphosate), has caused fungus and viruses to explode since the herbicide kills weeds that become disease factories. Wind carries the spores far and wide.
Tomatoes, cucumbers and squash seem to be particularly susceptible so look for disease resistant varieties. Keep in mind, resistant does not mean disease proof but healthy plants tend to withstand diseases and insect attacks better.
Yeah that's not how it works at all. I have no idea where that came from but it's all absolute bullshit.
How it actually works.
Any effective control that we use to keep pests or diseases at bay is an evolutionary selection pressure. Eventually with time and numbers the weeds/pests will overcome the controls. This is happening constantly across all sorts of species.
Pathogens and pests are constantly overcoming genetic and chemical controls.
A good example is Downy Mildew in cucumbers. For over 40 years (1960-2000+) Downy Mildew was completely controlled by a genetic resistance. Then the disease mutated and overcame the resistance. Now it is overcoming many fungicides as well and can not be easily controlled.
The fastest example I have seen was powdery mildew overcoming race 2 resistance in cantaloupes. After the introduction and adoption of a new resistant variety, the pathogen mutated and overcame it in a single year (race S).