Borers and Other Questions
By Steve Reiners, Professor and Chair, Horticulture Section, Cornell University, Cornell AgriTech. This is part of a series of columns that he wrote about vegetable gardening during the pandemic that ran Spring-Summer 2020. Read more articles from 2020 | Read later articles in this series.
August 14, 2020
Every summer, I get a few zucchinis and then the plant dies. What’s wrong?
Although some may welcome the early death of zucchinis to spare everyone from the onslaught of fruit overload, this problem is often seen here in the Northeast. The likely cause is the squash vine borer.
The adult is a moth that resembles a wasp The adults lay small, oval, dull-red eggs near the base of the vine from mid-June into early July. The eggs hatch and the larvae quickly burrow into the stem, usually within 6 inches of the soil line.
The larvae grow for 4 to 6 weeks, eating the inside of the stem and girdling the plant. Often the first symptom is a slight wilting of the plant during midday. Eventually the plant wilts completely and dies.
You can check for borers by looking for the entry holes they make near the base of the plant. There will be lots of sawdust-like frass, pushed out of the hole, a combination of plant stem and insect poop. If you find the hole, very carefully slice the stem lengthwise until you find the inch-long borer, which will be white with a brown head.
Remove and destroy the larvae, then pile up some soil around the cut to encourage healing. To prevent the problem next year, wrap some old pantyhose or foil around the stem, up to 6 inches above the soil line to prevent egg-laying. All the eggs have been laid by now, so you won’t have any new attacks on later-planted squash.
If your plants are already dead, do not leave them in the garden. The larvae will overwinter as a pupae and emerge as an egg-laying moth next spring. Pull out the old plants and either burn or place in the garbage.
A lot of zucchini plants are looking a little ragged by now, whether you have borers or not. Try this trick to rejuvenate. Remove all the old, diseased leaves and leave just a couple of young, small ones. Add some compost or soluble fertilizer at the base of the plant and water heavily. In about 10 days you should see a flush of new, healthy growth. And zucchinis will follow.
The tops of my carrot roots are turning green. How can I prevent it and are they safe to eat? I know you are not supposed to eat green potatoes
These “green shoulders” come about when the top of the root is exposed to sun. As carrots grow, they have a tendency to push out of the soil exposing the top half-inch or so. Try putting some compost or mulch over the row to keep them shaded. The green in carrots is not harmful but will give that part of the root a bitter flavor. Just cut off the green part and use the rest.
Potatoes also turn green when exposed to light and green potatoes could make you sick if you ate a lot of them. Make sure you keep them covered with soil or mulch. This keeps the spuds buried until harvest and prevents greening. And once harvested, store them in a cool, dark location.
Are vegetables safe to eat if the plants are suffering from disease? There’s been lots in the news lately about onions causing illness.
The recent outbreak in California-grown onions has been caused by Salmonella, a human pathogen. This bacteria doesn’t cause any issues on the onions but can cause serious problems for you and me. But plant diseases, for the most part, will not harm humans and vice versa. There are a few exceptions but not likely any you need to worry about.
It’s difficult to grow any vegetable in this humid region without some plant disease creeping in. Plant diseases may reduce yield, quality and flavor. So technically the produce is still safe to eat but I’d compost anything that has started rotting.
This week in the garden
This is a good time to plant lettuce, spinach and Swiss chard for fall salads.
If you are harvesting carrots or beets or buying them from a farmers market, it’s best to remove the tops after you wash them. Although the tops look nice, they continue to transpire water, which dries out the roots. Beet tops are also very tasty and nutritious.