Question: The walnuts on our tree look terrible this year. Most of them have black hulls, and we can’t get the walnuts out. Will this kill our tree?
Answer: Your description sounds like you’ve had trouble with Walnut husk flies. They can make a mess of the walnuts, but they won’t affect the health of your tree.
Walnut husk flies lay their eggs in walnut husks once the husks have softened enough. After the eggs hatch, the larvae feed inside the walnuts.
If the nuts are very young when the eggs hatch the nuts may shrivel and drop to the ground. Feeding by larvae in more developed nuts causes the husk to turn black and soft but the nutmeats inside are often just fine. The blackened husks can be very difficult to remove but putting the walnuts into damp burlap bags for several days will make the job easier.
The time to prevent walnut husk fly damage with an insecticide begins during the last half of July. At that time, you can begin spraying your tree with an insecticide. You’ll repeat the sprays according to the label directions until the walnut husks begin split open.
Once the husks split, the walnuts aren’t at risk of being damaged anymore. A product with the active ingredient Spinosad, or pyrethrin will be effective and also less harmful to beneficial insects, but a conventional insecticide with the active ingredient malathion, carbaryl, gamma-cyhalothrin or acetamiprid is another effective option.
Each fall, make time to clean up thoroughly under the tree so that there aren’t any dropped walnuts left. Spreading tarps or weed barrier under your tree early in the season will make it easier to remove the dropped walnuts.
You want to get things as clean as possible after harvest, so fold up the tarps or weed barrier and collect and dispose of anything that’s dropped. You can also keep landscape fabric under the tree year-round to prevent the fly larvae from pupating in the soil when they drop out of the walnut fruits.
You already have pupating husk flies under your tree from this year’s infestation and installing landscape fabric now can prevent many of the adult flies from emerging next summer.
Question: Many of my peaches have a mottled looking portion on their skin. They taste fine but are harder to peel in those areas. Any ideas on what this may be and how to prevent it in the future?
Answer: This looks like Apple powdery mildew, which can also affect peaches. Apple powdery mildew is often called Rust spot when it shows up on peaches. The problem is usually just a cosmetic issue and the affected peaches are perfectly fine to eat but the damaged skin can be harder to peel off.
Apple powdery mildew overwinters on apple trees, and the fruit of nearby peach trees can become infected when the fungus becomes active in the spring. You may have noticed whitish-looking spots on your young peaches a few weeks after bloom.
Those spots were the early stages of the powdery mildew infections that caused the rusty streaking you noticed on the skins at harvest time.
The fungus only overwinters on apple trees, not peach trees, so good powdery mildew control on your apple trees is important for preventing damage to your peaches next year.
Spray a fungicide on your apple trees when the leaves first open. That’s called the “open cluster” stage, and you’ll find an example of that stage in today’s photos. You should spray again when the petals are dropping from the blossoms.
Sulfur, neem oil, and potassium bicarbonate are three organic spray options, or you can use a conventional fungicide product labeled for fruit trees that has the active ingredient myclobutanil. Read your product label carefully, as different products have different spray intervals.
In addition to spraying, do a thorough cleanup of the tree in late fall — remove the dropped leaves, any dropped fruit and any unharvested fruit that remains on the tree. Proper pruning will also help reduce powdery mildew problems by improving air circulation and removing infected twigs.
You can also try spraying your peach trees next spring with a fungicide that contains chlorothalonil or with sulfur — an organic option — at the shuck split stage.
Check today’s photos for an example of shuck split. After shuck split, you can continue to spray every 10-14 days if needed due to wet weather, but you should use a different, as chlorothalonil shouldn’t be sprayed after shuck split until the fruit has been harvested.