In one of my raised beds, I have some squash plants – both summer yellow and zucchini – that are turning yellow. In the neighboring bed some of the late planted squash appears to be stunted. This is affecting the older leaves first. The edges turn yellow and the leaf surface is splotched with yellow areas. (This year I am growing some of my summer squash – both yellow and zucchini – in tomato cages to see if I can get a better control over the plants that would otherwise sprawl all over.)
The little squash plant to the front left of this caged plant appears to be stunted. The plant to the back, right of the center caged plant is OK. The problem plants are intermixed with plants that are just fine and looking good. This is a pointer to mosaic virus as opposed to a nutrient deficiency. I have a hard time thinking that a nutrient deficiency would only affect intermittent plants when the soil was turned over and mixed before planting.
And a closeup: The younger leaves are OK so far.
After spending hours searching for an answer, the 2 most promising answers are either a nutrient deficiency or a mosaic virus.
Below is a broader view. Some of the plants are affected while others aren’t. To add more confusion, I only made note of the varieties that I originally planted, not the subsequent 3 re-seedings that I had to do because of poor germination. (I don’t know why the seeds did not germinate well, the original planting was 2 year old professional seed that has been stored in the refrigerator.) The 2 original varieties were Superpik yellow and Obsidian zucchini, both on the Cucumber Mosaic Virus Resistant list at Cornell’s Squash resistance lists.
What is affecting my squash does not look exactly like any mosaic virus images I found, neither does it look exactly like Zinc deficiency, although it does look a wee bit more like the zinc deficient images. It could also be magnesium or manganese deficiency.
So what to do? I am not ready to pull the plants because I don’t know for sure if it is a mosaic virus. I am going to water the squash with a handful of Epsom salt in the water. Maybe I can crush a few zinc vitamin pills and add it to the magnesium sulfate mix.
Oh what to do? I have squished a few squash bugs and scraped numerous batches of eggs off of the leaves. My research has revealed that aphids and cucumber beetles are the culprits that transmit mosaic viruses, not squash bugs, although squash bugs are blamed for transmission of some plant diseases. No clear answer.