November 25, 2007

Gardener Annoyed By Spiders, Worm Found on Plants

Q . I believe I am having a spider mite invasion. Plants and trees affected have spider webs throughout them. Leaves are brown on the ends and dying fast. I have seen little tiny spiders on some. On my flowering dogwoods, planted this year, I found a small green worm. As an amateur gardener, I am becoming increasingly frustrated and disillusioned.

- Sharon, Chesapeake

A. Spider mites hate high humidity and rainfall, and we've had both this fall. Your letter was dated in late August so perhaps the pests are gone now. Entomologist Peter Schultz at the Hampton Roads Research Center says hosing off small trees works well. Later in the fall, spider webs often appear. Schultz says there should be no green worms now on dogwood. Inchworms (cankerworms) are common in springtime. If problems continue, spraying in September with Isotox or a product containing kelthane will help. Using a chemical spray, however, should be your last resort.

Q. Do you have any suggestions on how to get rid of alligator weed? We live on a lake that is slowly being taken over by the weed. It has spread every year for four years.

- Jana Sias, Virginia Beach

A. Virginia Tech weed scientist Jeff Derr says chemicals available for alligator weed control include aquatic formulations of glyphosate such as GlyphoMate 41 and Aquamaster as well as Renovate. Check with local and state water authorities to see if this is a public lake and whether permits are required. Check with a licensed pesticide applicator for aquatic sites on the Internet.

Q. I have two large bushes that had a tremendous amount of blooming. One is a lace-cap hydrangea and the other is a gardenia. They are near each other and have grown so huge that they compete for space. Do I prune them after they've just finished blooming, and how far back do I cut them? I don't want to hurt either one, but they need trimming badly. Do I cut back my rose of Sharon when it finishes blooming?

- S. Callahan, Virginia Beach.

A. The rule to follow is that the time to prune shrubs that bloom is immediately after they finish blooming. Also never prune off more than one-third of a plant at one time. So your work is cut out for you. There have been several questions in recent weeks regarding hydrangea pruning and they would provide the information you need. Briefly, prune off flower heads now. Stalks that have side stalks should be cut off at ground level, and you should be ready for next season.

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