Problems with growing zucchini - part 3

Ever notice your beautiful zucchini plants suddenly wilt in what seems like overnight. If so, a squash vine borer is probably to blame. Unfortunately, the damage is already done by the time you notice the first signs of the plant beginning to wilt. The infested plants usually die very quickly (24-48 hours after I first notice the plants looking weak).

Squash vine borer larvae

The squash vine borer has a cream colored body with a brown head. It overwinters just below the soil surface and emerges in the spring as a moth. The moth looks more like a wasp with an orangish-red body and black wings. The moth lays individual small brown eggs on leaf stalks and vines of zucchini plants. Once hatched, the larva immediately bores into the stem where it feeds before exiting the stem to pupate in the soil. If the plant dies before the borer has completed its life cycle, the larva can migrate to a neighboring plant and resume feeding there.

Frass

The burrowing larvae destroy the internal tissue of the zucchini plant causing the whole plant to die. You will likely notice something that looks like wet sawdust around the base of the plant. This is excrement from the squash vine borer called frass and it is the telltale sign that a squash vine borer has been enjoying dinner at the expense of the zucchini plant. 

Squash vine borers are difficult to control, so the key to squash vine borer management is controlling the borers before they enter the stem. Promptly pull and destroy any plants killed by squash vine borers.

In my experience, the squash vine borer is the worst insect that can invade my garden as it does the most damage before it is even detected.

Problems with growing zucchini - part 2

They're baaack! Squash bugs. How do I know? I found their eggs on the backs of some of my zucchini leaves.

Typically, squash bugs begin arriving in the garden around mid June and attack all cucurbit crops (squash, cucumber, pumpkin, etc). However, in my garden, squash bugs show a strong preference for zucchini.

Squash bugs are often mistaken for stink bugs; however, squash bugs have a slightly longer and leaner body. (I find that squash bugs smell like bubble gum when squished, rather than skunk.) Both insects are equally annoying and difficult to get rid of from the garden.

As soon as they begin to feed, squash bugs start laying eggs, which are found

Squash bug eggs

primarily on the undersides of leaves, between veins of the squash plant. The eggs are brown, oval shaped, and often seen in groups of 10 or more.

The larvae hatch about 2 weeks after eggs are first laid. The larvae morph into nymphs that are light gray in color with black legs. The nymphs feed in groups until they mature into adults (5-6 weeks later).

Leaves and fruits become speckled with sunken puncture wounds from where the squash bugs (nymphs and adults) sucked the sap from the plants. Eventually the feeding will cause enough damage that the plant will wither and die. 

The adult squash bug spends most of their time hiding around the base plant and on the underside of leaves. This, and the fact that squash bugs disperse quickly when disturbed, make it difficult to control squash bugs. Thus, early detection of the squash bug eggs is the key to minimizing damage to the plant. Once I find the eggs, I squish them with the back of my fingernail. This helps to reduce the number of adult squash bugs I find later in my garden.

This year I planted zucchini late in the season (mid-July) to try to avoid a major infestation of squash bugs. This seemed to work, so I will do it again next year.

Problems with growing zucchini - part 1

I cannot grow zucchini for the life of me. I usually start off great with beautiful looking plants and just when they start to produce fruits, something causes its demise. Either a squash vine borer chews through the stem of the plant, squash bugs invade the plants and suck the juice out of the fruits, or powdery mildew strikes. Unfortunately, I have found all three in my garden this week!  It is not surprising since these problems often appear in July/August. But, did I really need to get all three problems at once. Well, it gives me something to b!tch write about.  

Over the next few posts, my plan is to cover each of the problems I have with growing zucchini. I will start with powdery mildew... 

Powdery mildew on zucchini leaves

Powdery mildew is a fungal disease that is favored by warm temperatures, high humidity, and poor airflow. It is often seen on zucchini, cucumber, and melon plants.

Shaded from the sun, powdery mildew first appears on the surface of leaves found in the crown or lower portion of the plant. It appears as white/gray, powdery spots on the top sides of leaves. If not controlled, powdery mildew can quickly spread to the stems and fruit of the same or closely related plant families (i.e. curbits: cucumbers, melons, etc).

Prevention ensures the greatest success. To minimize the risk of plants becoming infected with powdery mildew, it is best to grow zucchini (and other curbits) in full sun with proper spacing between plants. 

However, despite these preventative measure, it is still possible for the plants to get a powdery mildew infection. Thus, it is best to monitor the leaves on a weekly basis for signs of infection. 

At the first sign of infection, remove and destroy (do not compost) infected plant parts (leaves and stems). In addition, spray/dust sulfur on the leaves of the infected plants (preferably in the evening to avoid burning the leaves) to help control the spread of the disease. Continue to monitor and remove infected leaves and spray/dust sulfur on a weekly basis. 

Oh, and cross your fingers and hope for the best.