Spider mites like it hot. Watch your roses

QUESTION: What could be stripping the leaves off the branches of my roses? I spray with a product that is supposed to protect roses from insects and diseases, but it hasn’t helped.

Keep an eye on roses when it’s hot and dry. Spider mites can turn a lovely rosebush into an ugly mess.

This time of year, with this kind of weather, suspect spider mites, which thrive when the weather is hot and dry, say rosarians at the Nashville Rose Society. The tiny creatures get on the undersides of leaves and feed on the plant’s juices. The damaged leaves look speckled, turn yellow and fall off.

Spider mites are not insects; they are more closely related to spiders, so insecticides won’t have any effect. You can use a miticide, but it can be expensive. The best and cheapest way to control them is with a blast of water directed at the undersides of the leaves, rosarians say. If you do this every three days for a week or so, you break the mites’ gestation cycle.

Here’s a little more information about the tiny arachnids: Adult mites are less than 1/50 inch long. They use their mouthparts to pierce individual plant cells and remove the liquid. They produce webs that can coat the foliage with a fine silk that collects dust, making the leaves look dirty.

You can’t see them, but you can certainly see the damage. Heavily infested plants will be discolored, and if they are not controlled, the rose can be stunted, or even killed.

Record heat is trouble for trees

Meteorologist Bobby Boyd sends me email from time to time about extreme weather conditions. The latest concerns the large dome of high pressure building eastward out of the plains and across the Tennessee Valley that has put Middle Tennessee, as he says, “in the pressure cooker.” We’re breaking records this weekend. No rain in sight, and gardens are suffering.

Young trees and shrubs are especially vulnerable. The Nashville Tree Foundation has sent an alert with watering guidelines and new tips that you can read here to help trees survive.

Keep these tips handy. It’s still only June, and we’ve got a long way to go.

Coming up in July

July 14:  Middle Tennessee Iris Society rhizome sale, 8 a.m. – 3 p.m. at Ellington Agricultural Center. All types of irises available in a variety of colors, priced from $1 – $6. A great chance to add to your collection! To learn more: For additional information see our web site www.middletnirisociety.org.

July 17: Middle Tennessee Orchid Society meets at 7 p.m at Cheekwood. On the agenda: an orchid auction and discussion on Cattleya Orchids. To learn more, visit www.tnorchid.com.

July 17: Perennial Plant Society meets at Cheekwood in Botanic Hall. Refreshments and plant swap at6:30; meeting and program at 7. Guest is Kelly Norris, horticulturist, plant breeder and manager of Rainbow Iris Farm inBedford,Iowa will present “The Modern Plant Explorer.” The meeting is open to the public.

July 26: Farmer Jason performs at Family Night Out at Cheekwood, 6:30 p.m. The event is free with regular Cheekwood admission. www.cheekwood.org.

July garden calendar

Does this heat make you wish for a shade garden? Find tips on plants that have it made in the shade, plus things to keep you busy in the garden in July, in Saturday’s Landscape & Garden calendar in The Tennessean.

No-fly zone

QUESTION: Some of the plants I brought in from outdoors seem to have tiny white flying bugs all around them, and are a nuisance. What are they? And what can I do about them?

 

Schefflera can play host to whiteflies.

These are likely whiteflies, and they often ride in on plants that spent summer outdoors. They’re more than a nuisance; they feed on the plant’s juices and can cause the leaves to turn yellow and die. The insects that are flying are the adults, and if you look at the undersides of the leaves you may be able to see the tiny yellow eggs and larvae.

Whiteflies feed on dozens of plant species and they reproduce quickly, so the problem could get out of hand quickly. To get rid of them, remove the badly infested leaves, then rinse the plant thoroughly and spray with an insecticidal soap. Be sure to treat the undersides of the leaves. Repeat the spraying every week or so.

Next fall, examine them closely to be sure there are no pests hitching a ride. Wash the leaves and treat the plants before you move them indoors. There are several other insect pests that you should watch for:

Aphids: they usually gather in clusters on tender young leaves. They also feed on a plant’s juices. Insecticidal soap, or washing with water or rubbing alcohol, is usually effective.

Mealybugs: You may see white, cottony clusters on stems or leaves, or where the leaf joins the stem. They also feed on the plants, so get rid of them by rubbing them off with water or alcohol.

Spider mites: They are barely visible, but you’ll certainly notice the damage – light-colored, speckled areas on top surfaces of leaves. You may see webbing stretching between leaves if there is a heavy infestation. Wash the plant with soapy water, and treat with insecticidal soap a day or two later. It may require diligence and several applications to control these insects.

UT Extension provides a booklet at its Web site that addresses these problems and more: Insects and Related Pests of House Plants (PB1157).