What is causing damage to my summer squash and zucchini plants?

Question

I have a variety of problems with my summer squash and zucchini plants:

• The summer squash (and to a smaller degree the zucchini) has clear spots in the leaves:

• This morning one of the zucchini plants was dead and looked as follows with a white maggot inside:

My questions:

• Are these problems related?

• What is happening to my plants?

• What can I do?

EDIT: I live just outside Washington, DC on the MD side. I have a sprinkler like automatic irrigation system. The ugliest leaves are the ones that receive the highest amount of sprinkler water that goes on for 3 minutes at 9am and 9pm. Could this be the culprit? Am I over watering? Am I watering the leaves when I shouldn't? Do I have the wrong watering schedule, that is making the plant prone to this disease?

There is nothing alive in the dirt. The summer squash lives in a raised bed. There are one eggplant, one tomato, one green pepper and one basil in the same raised bed. All other plants are thriving.

The zucchini lives in a rectangular container. It is pretty big and there are other zucchinis in there. The zucchini plant, has a orange pulpish where the damage occurred (not sure it is visible in the second picture).

Answer 1

First picture: The picture appears to be powdery mildew, up close it would be a cottony fungal colony growing on the leaf. Your watering schedule is quite likely making the situation somewhat worse. Powdery mildew grows most aggressively under high-moisture and moderate temperature environments. Your 9 PM watering is ensuring the moisture part of the equation, and being in the DC area likely supplies the right amount of heat overnight.

Ideally, you would avoid wetting the leaves if possible. Failing that you should at least concentrate your watering in the morning, this will mean that any water that lands on the leaves evaporates quickly in the heat of the day so that the leaves aren't wet overnight when the temperatures are more favorable to mildew.

On a note unrelated to the disease problem, unless you are getting some amount of natural rain I doubt 6 minutes of sprinkler watering is adequate to the plants needs.

Second picture: Given your description of a 'white maggot' and the damage in the second picture I suspect the maggot in your zucchini plant was a squash vine borer. The orange-colored pulp looks to me like the droppings of a larvae feeding on the plant stem. The adults are moths described here they more closely resemble red-colored wasps with gray wings. They are active by day in late June and early July, they lay eggs against the base of plants that are suitable food for their larvae. These eggs hatch into white caterpillar/maggot-like larvae and immediately burrow into the stem of a squash, pumpkin or zucchini plant.

The best bet for preventing damage is unfortunately to either keep the adults away from the plant with floating row-covers or to find the eggs before they hatch and break them. To give yourself an idea of when the moths are in the area you can set out yellow 'trap pans' in the later end of June. The moths are attracted to the color yellow, so setting out a yellow bucket or bowl of water means that some will fly in to investigate and get trapped in the water. When you start finding the moths, you know you need to start looking for the eggs.

Answer 2

You have powdery mildew on your leaves, try spraying with neem oil or sponge with baking soda water mixture, it can be difficult to get rid of. The stem looks like it was damaged somehow, maybe a critter walked by it and broke it?