
                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: SUNDAY, June 13, 1993                   TAG: 9306140583
SECTION: HOMES                    PAGE: C-1   EDITION: METRO 
SOURCE: John Arbogast
DATELINE:                                 LENGTH: Long

LEAF MINER A MINOR THREAT TO YELLOW LOCUST

Q: A couple of years ago you published an article in which you highly praised the qualities of our native yellow locust tree. I certainly agree with everything you said, but I wondered at the time why you did not address the fact that these trees are dying at a rapid rate, presumably as a result of attacks by the leaf miner. It appears to me that the die-off rate is increasing and that younger and younger trees are dying. I would like to know what the prognosis is. Will the yellow locust go the way of the American chestnut or are there biological controls which can save this valuable species? W.E.C., Stuart

A: I don't know who wrote that article; I didn't, so I don't know what it said.

The prognosis for the yellow locust tree is good, as far as I know. Of course, this species is not a long-lived tree anyway. The leaf miner only rarely causes locust trees to die because it begins to feed inside the leaves late in the growing season, after leaves have had a chance to make food for the tree. Readers who are concerned about trees but are unfamiliar with this pest may recall seeing scattered large trees that had brown leaves in July or August. Those trees were likely yellow locusts and the leaf damage was caused by the leaf miner. Because your letter asked about a future loss of the yellow locust similar to the loss of the American chestnut years ago, I shared your letter with Rob Trickle, forester in the Roanoke County office of the Virginia Department of Forestry, and Dr. Tim Tigner, state forest entomologist with that department. Tigner said the mortality rate of the yellow locust has increased only in localized areas. He said leaf miners do kill some of these trees but that their effect on the tree population is minor. Also, he pointed out that the leaf miner can weaken a tree and thus predispose it to other problems. These problems may especially affect the native locust because it often reproduces and grows on sites that are not conducive to long life. In summary, the native locust is not doomed and is a long way from the condition of the American chestnut.

Q: We have been growing rhododendrons for about 18 years. Every year they have been covered with blossoms. However, this year several of the plants that are about 15 years old have only a few blossoms. The foliage and blossoms are in superb condition. New growth, where blossoms would normally be, is vigorous and healthy looking. We are puzzled, since we have not changed our care program, which seemed to be successful over the years. Please explain why this situation occurred and tell us what we can do. H.E.H., Roanoke

A: Consider your situation and figure out the "cure" based on these four factors that may be responsible individually or in some combination for a lack of rhododendron blooms:

Past weather - rhododendron flower buds must form in late summer or fall. Adverse weather conditions at that time, particularly hot and dry conditions, will impede bud formation. Vegetative buds, which are smaller, may not be affected. If rhododendron flower buds formed but were unable to open in the spring, weather conditions any time after bud development the prior year could have killed the flower buds.

Nutrient level and soil pH - rhododendrons that grow in soil that is too rich, especially soil that receives a lot of nitrogen from nearby lawn fertilization, may be overstimulated and thus grow lush leaves and stems at the expense of flowers. Also, rhododendrons need an acidic soil and will be weakened in soil with a high pH.

A change in sun and shade - rhododendrons need shade, of course, but blooming can be reduced in dense shade. Maximum blooming is achieved if plants are exposed to morning sunlight or filtered shade that allows some sunlight but blocks strong midday or early afternoon sun.

Competition from nearby trees and shrubs for root room, nutrients, and moisture - this is definitely a factor as landscapes age.

Q: I received some tulip bulbs last week. They have begun to sprout about one inch. When should I plant these bulbs? Are they any good now? Mrs. R.L., Salem

A: If those bulbs were dug from outdoor beds or from pots after they completed a full cycle, which should have ended as the green foliage matured and turned yellow or brown, they should be stored in a single layer in a cool, dry place and planted this November. However, the sprouts you mentioned suggest that these are bulbs that should have been planted last fall but were not. If this is the case, they may not be good when the fall planting season arrives unless you can pot them now. Place the pot in a refrigerator and "force" them to grow and complete the cycle that keeps the bulb nourished.

Send short questions about your lawn, garden, plants, or insects to Dear John, c/o the Roanoke Times & World-News, P.O. Box 2491, Roanoke, Va. 24010-2491.

I cannot reply to all letters, but I will try to answer those of wide appeal each week; some Dear John mail will be saved for printing at times of year when reader mail is sparse.

John Arbogast is the agriculture extension agent for Roanoke

by CNB