Fire blight, a serious disease of pear trees and several other kinds of fruit and ornamental plants, was rather bad around here this past summer. It's a good idea for homeowners having susceptible plants to give them a close inspection now.

Pear varieties most susceptible to the disease are Bartlett, Clapps Favorite, Bosc, Flemish Beauty and Sheldon. Anjou, Comice and Dutchess are somewhat susceptible while Kieffer and Seckel have some resistance.

Apples most susceptible include Jonathan, Yellow Transparent, Wealthy, York, Rome Beauty and Transcendent crabapple. Flowering quince, hawthorne, mountain ash, pyracantha and cotoneaster also are susceptible. Some varieties of roses are, too, but most have considerable resistance.

Blossoms and leaves suddenly wilt, turn dark brown, shrivel and die, but usually remain attached.These give the tree a burned, blackened appearance, hence the name, fire blight.

If the attack is rather severe, the whole crown of the tree may appear black and dead. Sometimes the entire tree of a susceptible variety like Bartlett may be dead by the end of the growing season.

Sanitation is the first and perhaps most important control measure, according to specialists. During late summer and early fall, cut off and destroy all infected branches and twigs.

The cut should be made through healthy wood, six to eight inches below the point of visible infection, because the bacteria are usually found somewhat in advance of the obviously diseased tissue. Pruning tools should be sterilized frequently in alcohol during the operation to prevent carrying infection to new areas.

The bacteria usually enter a tree's vascular system through the young tender shoot tips or through flowers when the tree is in bloom. Depending on the tree's susceptibility, the blight may spread to leaves, branches, trunk and roots, killing all tissues it invades.

No satisfactory method of fire blight control has been found that permits a thriving commercial pear industry where warm temperatures and high humidity prevail. The only logical solution, specialists say, is the development of new varieties resistant to the disease. GARDENING Q&A

Q - I have just rooted the top of a pineapple plant. How do I take care of it?

A - Pot it in a six-inch clay pot. Give it full sunlight if possible, at least very good light, and relative humidity of 30 to 40 per cent. Water the plant whenever the soil starts to feel dry, good drainage is essential, and best temperatures for the plant in the home are 75 degrees to 80 degrees during the day, 70 degrees to 75 degrees at night.

Q - My Irish potatoes go to vine. How can I get them to bear potatoes?

A - Too much nitrogen fertilizer could cause a lot of vine growth and no potatoes. Also, too much shade.

Q - You suggested getting rid of leaves from our diseased tree to prevent over-wintering of the disease. Does this mean we shouldn't put them on the compost pile?

A - The fungi that cause many kinds of diseases over-winter on fallen leaves. In the spring new growth is infected by spores produced in the dead leaves.

Putting infected leaves on the compost pile may not be a good idea, but then again it may be all right. The temperature in a compost pike may reach 170 degrees, and at this temperature weed seeds and disease organisms will be destroyed.

But there is a possibility that the compost pile may not heat up sufficiently, or that the middle may heat up but the sides may not. That is the risk.