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IN THE GARDEN: Scale insect on plants can be treated with insecticide, or dormant oils in cooler weather

by Janet B. Carson | May 14, 2022 at 8:30 a.m.
Tiny white scale insects are sucking the sap of this dogwood tree. (Special to the Democrat-Gazette)

Q: This is a picture of our dogwood tree with white growths on it. Your help is appreciated.

A: Your dogwood tree has a healthy case of scale insects. Scale insects attach themselves to the host plant and suck out the plant juices or sap. This particular scale is commonly called Japanese maple scale, but it can attack other small ornamental trees, including dogwoods. You can use a systemic insecticide on the tree; or wait until fall and use a dormant oil, completely covering the tree after the leaves fall off. This oil can smother out the scale insects, but oil products will burn plants when the weather gets hot, so if you use dormant oil, do wait for fall.

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Q: I have a lot of phlox that have always done great in a flower bed around the pool. Full sun all day. This year, some of them have a white powdery substance on the leaves, both on top and underneath, and they have just recently broken ground. Is this some sort of mildew, and if so, is it easily treatable? [The reader sent a photo.] Thanks for your help.

A: Phlox is one of the plants that is particularly sensitive to powdery mildew. Some years, weather conditions are better for the disease than others. While some species are more resistant than others, under "perfect" conditions, they all can get it. Warm spring weather coupled with high humidity are perfect for this mildew. I have heard it said that the taller varieties are more susceptible than shorter varieties, but I have seen mildew on some plants every year, while others never had it. You have several options. One is keeping the plants as dry as possible after the sun sets — that means watering early in the day or using drip irrigation. Also, make sure the plants are not too crowded, as that can reduce air flow and make the disease worse. If the disease were only on a leaf or two, you could remove them, but that isn't the case here. You need to spray with a fungicide now and repeat about every 10-15 days for at least three applications. When the temperatures get really high, the disease tends to slow down. Products containing chlorothalonil, myclobutanil or propiconazole should all provide control. There are a lot of different products to choose from; common names include Daconil, Ortho Max Disease Control, Fertilome Liquid Systemic Fungicide, Spectracide Immunox and Banner Max. This fall, make sure you do a good clean up, removing all parts of the spent plant and the mulch around it, to start clean next season.


Q: On a guided nature hike around Pinnacle Mountain we were told that violet, as described in Saturday's column, was a bird's foot violet. The leaf looks like a splayed bird's foot. The flower has one dark purple petal with all the other petals much lighter. Do you know more about it?

A: There are several species of wild violets that are all in the genus Viola. The bird's foot violet is Viola pedata. It has very distinctive, thin-lobed leaves, as opposed to the almost heart-shaped or rounded leaves of the more common wood violet — Viola sororia, which is highly invasive in home landscapes. The flowers on the bird's food violet can be a solid purple or can have one petal much darker than the others.

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Q: I just found some weird orange growths on my cedar tree. It looks like orange jelly with tentacles. I have never seen anything like it before. Is this something I should worry about?

A: I have had several questions about this and a few pictures sent in. What you are seeing is the fruiting body of cedar apple rust. This disease needs two host plants to complete its life cycle — typically a cedar tree and an apple tree, but it could be a quince or hawthorn tree as well. On a cedar tree, particularly during spring rains, the galls on the cedar will produce gummy orange growths with tentacle-like protrusions. As soon as they dry out, they shrivel up to brown, knobby galls. They can rehydrate a couple of times in the spring, depending on the weather. When the spores leave the cedar tree and fall on an apple tree, the apple tree develops yellow spots ringed in orange. Once you see the disease, it is too late to control it. Unless it is a very small apple tree, rarely will the disease do any permanent damage, but the tree's fruits will sometimes have spots as well.

Retired after 38 years with the University of Arkansas Cooperative Extension Service, Janet Carson ranks among Arkansas' best known horticulture experts. Her blog is at arkansasonline.com/planitjanet. Write to her at P.O. Box 2221, Little Rock, AR 72203 or email jcarson@arkansasonline.com

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