I visit the garden almost daily and one of the first things I do is check all of the plants for signs of problems. This is how you find you have a pest or disease problem before the damage becomes too severe. With experience we learn to recognize many problems, but there is always something new attacking our plants. The trick is to figure out what is causing the problem from the visual clues we get observing the plant.
I learned of a really great visual diagnostic tool from the High Mowing Seeds blog. The tool is the Landscape Problem Solver from the Home and Garden Information Center of the University of Maryland. The site works by starting with a description of the problem, then offers a list of possible causes. Select what you think might be the cause and you get a page with detailed descriptions and photographs with information on how to treat or prevent the problem. The advice includes information on organic and Integrated Pest Management (IPM) techniques.
This was a fortuitous find because I have just noticed a problem with my zucchini. I have my summer squash under floating row cover to hopefully ward off the squash bugs and borers. The downside is I have to check each day for female flowers and hand pollinate them. I have already harvested two zucchini and have two more successfully pollinated. But now I noticed a lot of leaf damage I am not familiar with. I took the photos below so I would have a reference to use when I go research the problem.
The leaves seem to have lots of small yellow/brown spots. Some of the leaves are starting to yellow and wilt. I looked under the leaves and around the raised bed for evidence of some kind of insect pest but found nothing. Using the HGIC website above, it seems like this type of damage is typical of squash bugs, which suck juices from the leaves. I suspect the bugs are capable of crawling under the row cover. I didn’t find bugs or nymphs or eggs under the leaves. Following the site’s advice, I will lay down some trap boards under the plants and check them each morning. Meanwhile. I sprayed the plant with insecticidal soap. And I decided to remove the row cover so I don’t have to hand pollinate. Hopefully it is late enough that the threat from squash pests is diminished.