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Garden Help Desk: Protecting walnuts from invading larvae

By USU Extension - | Oct 16, 2021

Walnut husk fly eggs are laid under the skin of the husk where the larvae hatch and feed in the husk. Their feeding can damage the nutmeat or the husk.

What is wrong with our walnuts? Almost all the nuts from the tree at our new house are still stuck inside the husks and the husks are black and wrinkly.

This looks like your walnut husks were infested with Walnut husk fly larvae, a common problem with walnuts and sometimes ripening peaches and apricots. Beginning in July, female husk flies insert eggs into softening walnut husks. Larvae hatch and begin tunneling and feeding in the husks, causing the walnut husks to turn black. The feeding damage causes the husks to turn black and stick to the walnut shells instead of splitting open to release the nuts. Once the larvae are mature, they will drop out of the husks and pupate in the soil until the following summer.

The damage to the husks and nuts depends on how mature nut is when larvae hatch and start feeding. Feeding by Husk fly maggots that hatch during July and early August while the developing nuts are young can cause the kernels to mold and shrivel. The damaged walnuts will drop prematurely. Walnuts that are infested in early fall will still be edible, but the husk can be difficult to remove.

You can reduce husk fly damage in your walnuts by spraying an insecticide at the beginning of July to prevent infestation. Conventional insecticides with the active ingredient carbaryl, gamma-cyhalothrin, or malathion are effective choices. If you prefer organic options, look for the active ingredient Spinosad or pyrethrin, which also provide good protection. A second spray can be done in August, but by that time the husk fly damage will be limited to the husks, not the nutmeats, so you can also skip that application and do a little extra work when your walnuts are ready to harvest.

To salvage your walnut crop this year, you can gather up the nuts and put them in a damp burlap sack for two or three days to loosen the husks.

When walnuts are infested by walnut husk flies, the husks may blacken and might not separate from the nuts. Infested nuts shouldn't be left on the ground or on the tree.

You can reduce the husk fly population next year by completely cleaning up under the tree this fall. Don’t leave any walnuts on the ground or on the tree.

I want to overseed my lawn this fall I would like to when is the best time? When should I fertilize and how often should I water once I overseed? Should I aerate first? Fertilize? What is the best seed variety for our area?

I just had a sprinkling system installed in my lawn. Can I plant grass seed this late? If I plant now and it doesn’t germinate will it overwinter and germinate next spring?

Late summer to early fall is the ideal time to overseed. Temperatures are cooling off, but the days are still warm enough for good germination. It’s a bit late this fall to do overseeding. The seedlings need several weeks of growth before heavy frost, or they won’t survive the winter. It’s also too early in the fall to plant the seed and have it overwinter until spring because we’ll still have some days that are just warm enough for seeds to germinate.

If you’re anxious to get your seeds planted now because you know you’ll be busy in the spring, you can try the dormant seeding this winter. Once the weather is consistently too cold for the seeds to germinate, you can plant and let the seeds lie dormant until things warm up in the spring. Temperatures need to consistently be too cold for germination, though. The soil temperature should be below 50 degrees. December, January, and February are usually reliable months for dormant seeding.

When healthy strawberry crowns are transplanted early in the spring it doesn't take too many weeks before they look healthy and productive.

Aeration is fine and can be helpful. It can make it easier to get good soil contact for seeds when a lawn has a thicker thatch layer. Aeration is best when a lawn is actively growing, though.

Perennial ryegrass, tall or fine fescues, and Kentucky bluegrass all do fine here.

Can I transplant strawberry plants now? I have some plants that I want to move to a sunnier spot where I hope they’ll do better and make sweeter berries.

Your best chance for success is to wait until early spring to move the plants. If you move the plants now, they may not be rooted-in very well and could be heaved out of the soil during our winter freeze-thaw cycles.

You can get a head start by preparing a new location where your strawberry plants will get at least six hours of sunshine during the day and where the soil drains well. Then when the soil has thawed in the spring you’ll be ready to get the plants moved. Strawberry plants are frost tolerant, so you don’t need to wait until the danger of frost is passed next spring before you do the transplanting.

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