Enemies of trees and shrubs

Plant diseases and control

Among common diseases attacking shrubs are lilac mildew, rhododendron blight, juniper blight, hydrangea blight and dieback, privet blight, box leaf cast, and twig blight.
Winter injuries, injuries in transplanting, and poor growing conditions account for some of the blights of arborvitae, junipers, and other evergreen conifers; there is also a fungus disease of this type. The blight causes leaves to fall and kills twigs and larger branches. Bordeaux mixture may be used in the growing season, and wettable sulphur later, but it is especially important to improve growing conditions, providing plenty of air and sunlight. Periodic shearing also is necessary.

The dying back of hydrangea shoots at the tips is caused by late spring frosts, sudden growth check resulting from drought and heat following a period of fast growth, and injury to young shoots by aphids; a fungus dieback sometimes spreads from old flowers.

Remove wilted flowers and provide plenty of sunlight, for shady, damp locations tend to bring on the disease. Dead flowers frequently are the starting point of rhododendron dieback and must be removed immediately after blooming. Bordeaux mixture applications right after blooming time and later in the season help to control the disease.

The fungus of lilac mildew winters over in the fallen leaves. A common control method is to rake the leaves from around the bush at summer's end and burn them.
Lime-sulphur spraying, starting just before growth in the spring and continuing periodically until it ceases late in the summer, is the medication for box leaf cast and twig blight. Branches must be kept free of fallen leaves and protection should be provided against too much sunlight and cold, drying winter winds.

The branches of privet hedges, and sometimes the entire plant may be killed by a twig-blighting fungus. Control of this disease consists of fertilizing to maintain vigor, pruning away injured parts, and dormant lime-sulphur spraying.
Expert and accurate diagnosis of various tree diseases often necessitates investigation by specialists in this field. The same symptoms may be produced by poor growing conditions or by several specific organisms. Root diseases, causing various symptoms, such as death of branches, premature leaf fall, slow growth and thin foliage, often are difficult to identify and to cure.

Certain fungi may produce abnormal growth, cankers, discoloration, death of the bark and the wood below on twigs, trunks, and branches. Pruning well back of the infected areas can often eliminate diseases of twigs and branches, and even cankers may be cut out of trunks, but wounds made by such surgery should be treated with protective dressings and shellac.

Severe leaf diseases may be controlled by spraying with Bordeaux mixture or lime-sulphur, or dusting with sulphur. These are expensive measures when applied to trees and require knowledge as to the correct strength for the specific tree.

Information about diseased trees may be requested from the United States Department of Agriculture, Division of Forest Pathology, Washington, D. C. If it is feasible, send along with your inquiries a workable specimen of the diseased part and of the living parts adjoining it, and a description of the general conditions in which the tree grows.

Insect pests and control

Insects which attack trees and shrubs may be classed according to their mode of attack. There are leaf-eating insects, insects which bore into the bark or wood, leaf-mining insects, sucking insects and mites which extract vital juices from the plants, and gall-making insects.

Some of the sawfly larvae, beetle grubs, caterpillars, and fly maggots mine the leaves, eating into the inner tissue while leaving the surfaces intact. Protected as they are against sprays and dusts by the skin of the leaves, they are difficult to control. Picking off and burning the infested leaves is a sound attack. Nicotine sulphate sprays or tobacco dusts may also be used against several of the mining insects.

Beetles and their grubs comprise the principal borers, but they are supplemented by some of the caterpillars, ants, carpenter bees, and wood wasps. Borers usually attack ornamental trees and shrubs which have been weakened or injured. Naturally a primary means of combatting them is to keep the plants growing vigorously, treat injuries promptly, and keep wounds clean and shellacked until healed. If the borers have gotten into the wood, a few drops of carbon disulphide injected into their tunnels will usually kill them. Seal the openings they have made with putty or moist clay to keep the fumes in. Carbon disulphide can be bought at seed stores and drug stores. Be careful how you use it. It is poisonous and also inflammable and explosive when mixed with the air in certain proportions. Do not inhale the fumes.

Among the sucking insects are plant bugs, lacebugs, aphids, and mites, against which sprays of nicotine sulphate, pyrethrum, or derris, in strong solution, are effective. The suckers, however, include a group of scale insects, protected from sprays by their scale covering or by some waxy body secretion. There are numerous dependable sprays on the market for use against them, each with instructions for its correct use.

Galls, or abnormal swellings, are formed on plants by several types of insects, including aphids, moths, mites, flies, wasps, even beetles. Remove and burn fresh galls which contain larvae before they can complete their development.

Gardening Howto

Bulb planting
Boxes & tubes
Bulbs health
Bulbs spring
Bulbs summer & fall
Care & feeding
Cut flower bulbs
Every gardener
Flower arrangement
Indoor bulbs
Indoor permanent
Naturalizing bulbs
Rock gardens

Flower arrangement
Dried plants
Floral compositions
Flower arrangement ideas
Home made corsages
Japanese flower arranging
Mechanics flower arranging

Flower garden ideas
Crowded cities gardens
Fertilization garden
Garden propagation
Setting out plants
Soil flower-garden
Specific uses perennials

Alpine Greenhouse
Annuals & biennials
Bulbs half hardy
Bulbs hardy
Construction hints
Flowering shrubs
Foliage plants
Hard wooded plants
Hardy orchids
Hardy perennials spring
Perennials autumn
Potting shed
Routine work
Succulent plants
Suitable plants
Typical greenhouses

Indoor plants
Flowering indoor plants
Miscellaneous folliage plants
Specific home plants


Pests garden
Insects attacking plants
Insects enemies plants
Plant diseases

Planting vegetable
Planting asparagus
Planting beans
Planting beets
Planting blackeye peas
Planting Brussels sprouts
Planting cabbage
Planting carrots
Planting cauliflower
Planting celery
Planting Chinese cabbage
Planting chives
Planting cucumbers
Planting dandelion
Planting eggplant
Planting endive
Planting horseradish
Planting kale
Planting lettuce
Planting onions
Planting others
Planting parsnips
Planting peas
Planting popatoes
Planting radishes
Planting rhubarb
Planting spinach
Planting sweet corn
Planting sweet potatoes
Planting tomatoes

Roses in garden
American roses
Insect pests roses
Plant & Grow
Rose calendar
Rose diseases
Rose varieties
Special locations
Special purposes

Tree, shrub & lawn
Enemies shrubs & trees
Grafting & budding
Lawn care & maintenance
Planting shrubs & trees
Pruning shrubs & trees
Supervising growth

Pruning plants
Failure to bloom
Pleached allee
Pruning bonsai
Proper pruning
Pruning evergreens
Pruning fruit trees
Pruning grapes
Pruning hedges
Pruning herbs
Pruning house plants
Pruning perennials
Pruning roses
Pruning shrubs
Pruning tools
Pruning trees
Pruning understock
Topiary shapes