Q. There is a deep round hole about the size of a 50-cent piece in the trunk of my dogwood tree. It is about 10 feet above the ground. Is this due to borers? If so, how can I get rid of them?

A. Almost certainly it is due to decay resulting from poor pruning. When a branch is removed from the tree and a stub of one or two inches is left, healing is very, very slow, and decay-causing organisms have time to become established. As decay progresses, the dead stub falls out, leaving the hole.

When a branch is removed, the cut should be made flush with the trunk or stem from which it originates. This type of wound, if no larger than a silver dollar, should heal quickly sometimes in a single growing season.

Q. My blueberry bush has grown to 71/2 feet tall and is quite leggy. The lower branches are nearly bare. It is bearing heavily this year but many of the berries (on one side particularly) are small and have poor flavor. The plant had no new shoots this year. Should it be pruned? If so, when and how much?

A. Prunning is generally not needed until the third year after planting. In early spring before growth begins, remove dead or injured branches, short or stubby branches near the ground, and old stems low in vogor. After the plant becomes 5 to 7 years old, it is important to remove all but 3 or 4 of the old branches close to the ground. This will allow vigorous roung branches to develop.

Pruning increases the size of the berry and promotes earlier ripening. If the plant has na unusually heavy load of fruit, the tips of the fruiting branches can be cut back to leave 4 to 6 fruit buds. Although this reduces yields slightly, the berries are appreciably larger.

The fruit buds are easily distinguished in the spring because they are large, round, plump buds. Leaf buds are smaller, thinner, and sharply pointed.

Under good growing conditions, vigorous shoots may rapidly develop and grow several feet tall. If these are cut back before August 1, they usually develop strong lateral branches that will bear fruit the following spring. Remove 3 to 4 inches when the shot is 4 to 5 feet high.

Q. How long does it usually take for tomatoes to ripen after they first form on the plant? Also, sweet peppers?

A. Tomatoes mature in 30 to 45 days, depending on variety and time of planting. Sweet peppers take the same time to mature to the green stage as tomatoes and another 15 days to turn red.

Q. Can Benlate be applied to most green shrubs?

A. Many people find that their spraying efforts for disease control of plants are unsuccessful. The effective use of fungicides, says Dr. Charles C. Powell Jr., Ohio University plant pathologist, depends upon following a few logical steps between first sighting or anticipating a problem and actually applying the sprays.

These steps are proper diagnosis, right material, correct method and good timing.

The most effective fungicides in use today have been developed for specific situations and specific diseases. Gone are the days when general materials provided control for almost any plant disease.

For instance, Benlate is highly effective for the control of septoria leafspots on shrubs or flowers. However, for alternaria leafspots, Benlate would provide absolutely no control.

The proper diagnosis leads to selection of the right material. There may be several materials that are effective against the disease. For example, Benlate, Dinocap, Sulfur and Cycloheximide will all control powdery mildews.

Before one of these is selected, read the label. Can you carry out the instructions given? Is the plant in question listed on the label? Is the pest listed specifically on that crop?

It is a violation of the federal pesticide law to use a chemical in any manner inconsistent with the label.

Fungicide sprays usually work because they act as a barrier on leaf, stem or flower surfaces. When the fungus pathogen arrives on the plant surface, it encounters this barrier and is unable to infect the plant. Therefore effective use of fungicides requires that this barrier be as complete as possible.

Q: Worms are eating my cabbage leaves. How can I get rid of them?

A: Three kinds of worms feed on cabbage: cabbage looper (greenish with a white stripe down each side), the diamondback (yellowish green) and cabbage worm (velvet green).

Bacillus thuringiensis, sold under the trade name of Dipel. Thurcide and Ciotrol, is a safe microbial insecticide (harmless to humans and animals) which takes care of all three species. Directions on the label should be followed closely.

Q: Large areas of grass are dying in my lawn. My neighbor says it probably is due to chinch bugs. Is there a way I can find out, and what is the required treatment?

A: Chinch bugs are black, about one-fifth of an ich long, with white patches on their wings. The young are tiny, red and wingless. Both old and young feed by sucking juice out of grass stems.

To find out if chinch bugs are present, remove the bottom from a coffee can and shove the cylinder into the soil where the grass is dying. Fill the can with water and check after five to 10 minutes to see if chinch bugs are floating in the water.

For control of chinch bugs, specialists recommend spraying with spectracide or sevin. Label directions should be followed closely.

Chinch bug injury is likely to occur in sunny rather than shady locations. Birds, especially starlings, pecking holes in the lawn are a strong indication of chinch bugs.