Killing skeletonizer larvae easier than adult moths

Q: I just sighted my first grape leaf skeletonizer moth. I’ve learned that Bt will control the worms. I’d like to try and minimize the larvae if I can by eradicating as many moths as possible. Can you recommend the best course of action, if any, to control the moth ?

A: Not a lot of people know what they look like. They are a dark, blue-black moth that resembles a wasp more than a moth. I will post a picture of the moth, eggs and damage on my blog . If you have grapes, you should start looking for these guys.

The adult only lives for about three days. Pretty much its sole purpose is to reproduce. The damage comes from the larvae eating the leaves, not the moth eating the leaves. The eggs are laid on the bottom of the leaf. The life cycle of the insect is about 60 days (two months). It takes about seven days for the larvae to hatch from the deposited eggs.

I know you want to control the adult in an attempt to control the young but it probably is not the best approach since the adult will be hard to kill. Soap and water or insecticidal soap will work if the soapy water comes in direct contact with the moth. But since the adult does not eat the leaves, you would have to actually spray the adults to kill them.

The larvae are fairly easy to kill since they eat grape leaves. You must spray it on the bottom of the leaves . The Bt (Dipel, Thuricide) has about a one-week residue on the leaves.

Spinosad also will work and has about the same staying power but is a little harder on bees.

Q: I have some well-established rose bushes (15 years) in our front yard. Five years ago we converted to desert landscape and the landscaper put about 3 inches of small rock in the area containing the roses. They seem to be healthy although the density and beauty of the blooms was weaker last year.

I’ve been using liquid Miracle-Gro. Is there a better liquid fertilizer, or should I consider pulling the rock away from the bases and fertilize through the soil .

A: Miracle-Gro products are fine but I also would add a separate iron fertilizer. Go to your local nursery and get a 1-pound canister of iron EDDHA. Follow the label directions, but I find it more effective to mix in a teaspoon of the product in a gallon of water and water it into the root zone of each plant.

Each rose should get maybe 1 teaspoon sometime in January through March, a once a year feeding. Although best applied early, an application will work now. They should be all right if you keep them on this fertilizer schedule. Select a product that has a big middle number .

Feed roses lightly about every two months starting in January through October. However the iron is needed just once a year. Do not neglect soil improvement as well by using composts and organic mulches that decompose into the soil. Roses will really appreciate wood mulch much more than rock mulch.

Q: I have a bit of a quandary. My male kiwi died and I did everything I could to keep it alive. I then contacted Parks Seed and they sent me a new male free of charge . But then something started eating the leaves of my female kiwi. I searched every leaf and found nothing. I thought whatever it is must be eating at night and hiding during the day. I was right. It was a beetle. I found and identified the culprit: a black vine weevil. Now here is my question. If they have laid eggs in the pots (still in their 1-gallon originals) of my new male or the original female, what do I do to stop the infestation if there are eggs or larvae feeding on the roots?

A: Kiwi is a bit cold sensitive for some parts of the valley, so be careful during the winter. However, we should be able to grow hardy kiwi here in most locations. You will have a hard time managing this plant in a 1-gallon container for any length of time. I would get it in the ground.

Yes, it could be a black vine weevil or possibly root weevils, which are more common here. It is possible the plant came to you with black vine weevil as a hitchhiker. Black vine weevil adults emerge in spring and cause plant injury by feeding upon blossoms, clusters and small fruits.

I would follow the same recommendations for growing it as our fruit trees; plant it in the ground with lots of compost at the time of planting, water it in thoroughly, stake the plant to keep it from moving and mulch the surface of the soil with organic mulch.

If you collect insects from the leaves at night and send them to the state entomologist through the state Agriculture Department we can get this resolved.

Control efforts are usually directed against the larvae living in the soil. Root weevils come out at night, as you have discovered, and chew on the edge of leaves leaving them raggedy looking. Control is difficult but they usually do not cause extensive damage that would kill the plant.

When they feed on ornamentals we usually just ignore root weevils. If it is black vine weevil, you would be looking at applying an insecticide to the soil in the container in an effort to control the larvae or immature forms. You would need to look for an insecticide that lists that it controls vine weevil, can be used as a soil drench and is labeled for fruit crops.

Q: Could you please give me some clue as to why my 10-year-old African sumac tree has started to get split limbs. They are splitting laterally along the length of the branch. I have had to cut off two branches in the last week because of this splitting.

A: This is the first I have heard of this problem with African sumac. Who is making the decision to remove the limbs and what is the reasoning behind it? I would be curious because there are unscrupulous or uneducated maintenance people who will point out something to a homeowner and recommend a job to make money .

Sometimes natural furrowing of the bark can be mistaken for cracking. I have had several homeowners get concerned and send pictures and that is all it is. I have had African sumacs split because of snow loads on the branches, but that is reasonable.

Most reasons for cracking would be excessive weight on the limbs. Are you sure there are no children doing pull-ups on some limbs?

This is a stretch but if the tree were growing rapidly and pruned incorrectly, I could possibly see that limb cracking might occur. Without a bit more information that is about all I can tell you .

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at


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