The main purpose of pruning most fruit trees is to thin out the top of the tree for better light penetration. Late winter is one of the best times. Color is one of the primary factors determining fruit quality, and exposure to light is essential to good color development.

If the apple tree is getting to be more than 18 to 20 feet tall, perhaps it should be lowered. It is difficult to spray and to pick the fruit at the top of the tree, and the top is likely to shade the lower part, reducing the quality of fruit that develops there.

The most flavorful and highest-colored fruit is produced on growth that receives 70 percent to 100 percent full sun. Apples receiving less than 50 percent full sun will be of inferior quality.

Height can be reduced by cutting off the upward growing trunk (leader). Makethe cut above a branch at the desired height. Treating wounds with a wound dressing is not considered desirable.

During a study of peach tree pruning, the method that produced the most high-quality fruit (2 1/2 inches in diameter or more) was thinning out. This involves the removal of weak wood and one-third to one-half of the new wood, with permanent branches cut back to outside growing branches at about nine feet in height.

The most desirable fruiting wood for peaches is new wood 12 to 18 inches long. Branches longer than this seldom have many fruit buds.

Once the tree has the desired height and spread, new limbs should be allowed to develop from the permanent branches which in a couple of years will replace the older limbs. In this manner young fruiting wood can be maintained.

Old trees, particularly apple trees, that have not been pruned for several years can often be revitalized and brought back into good productivity. This can be done by rather severe pruning and extra fertilizer. The pruning usually involves thinning out so that plenty of light can penetrate.

Pear trees are pruned about the same as apple trees, except that pears are pruned more lightly. Vigorous new growth is not desirable with pears because it increases the danger of the tree becoming infected with the fire blight disease. This is particularly serious with Bartlett and other high-quality varieties.

Fire blight attacks blossoms, young fruits, small twigs and water sprouts. Blossoms and leaves of infected twigs suddenly wilt, turn brown, shrivel and die, but usually remain attached. Pruning is the most important control measure. During late summer all infected twigs and branches should be removed and destroyed.

Q. Would it hurt my zoysia grass to burn it off in late winter? Two years ago I accidentally burned off a small patch and after a short time I could detect no ill effects.

A. According to specialists, burning it off is not recommended because of the fire hazard to trees, shrubs and buildings. Mechanical control is better even in areas where fire hazards are low, they say.

Q. I have several packets of seed left over from last spring and I am beginning to worry about them. Will they be okay to plant in the spring?

A. They should be good if given satisfactory storage. Humidity is an important factor; if it is too high in the refrigerator, put the seed in a jar that is airtight when the lid is on, and they should come through satisfactorily. But test them before planting in the spring.

Q. The roses I received on my birthday lasted only two days. Isn't that rather short for them?

A. When the rose starts to hang its head, fill the kitchen sink or bathtub with barely warm water. Hold the stem under water, cut about an inch off the end of the stem. Lay the rose flat on its side in the water and let it rest floating partly submerged for an hour or two. Then replace the rose in the arrangement. Usually the rose stands up straight as an arrow, just like new.

Q. I have trouble getting rid of mealybugs on my house plants. What can I use to control them?

A. Use wood alcohol (methanol) or rubbing alcohol (ethanol) to rub them off. It penetrates the insect's body; mealybugs are particularly susceptible to it. You may have to repeat once or twice a week for three or four weeks to get rid of new ones that hatch from eggs.

Q.Somehow an earthworm got into the pot of my philodendron. My friend tells me they do no harm. Is that true?

A. An earthworm in the ground can be beneficial but not in a pot with a potted plant. The slimy creature leaves a portion of its sticky coat wherever it goes and this tends to glue soil particles together into a mass impervious to water. Your best bet is to remove the plant from the pot and get rid of the worm.

Q. Will I get a better crop from my tomato plants if I stake them rather than let them spread out over the ground?

A. They will produce more harvestable fruit if you start the plants out on some type of trellis and keep them tied up as they grow and the fruit forms. There are a number of ways to keep them off the ground. The simplest method is staking. A five to six foot, 2-by-2-inch wood stake sharpened at one end then driven into the ground beside the plant works as well as anything.