Orange rust does not kill affected plants but causes them to be stunted and weakened to such an extent that they produce little or no fruit. Badly diseased plants will often produce many spindly shoots instead of the few sturdy canes normally formed. The infected canes usually have few or no spines and the foliage is pale green and stunted or misshapen. After leaves pass the orange rust stage, they often dry up and fall to the ground. The remaining foliage may appear relatively normal, but the fungus occurs throughout most of the roots, stems, and other parts of diseased plants and remains active even though plants appear healthy.

From the orange spores (aeciospores) produced in early summer, small brown spots develop later on the lower side of leaves of black raspberry. The spots produce another type of fungus spore (teliospore), which infects cane tips that are in the process of rooting. Such tip layers show no evidence of infection until the following season, when the leaves become pale and malformed before production of the orange rust stage.

Of first importance in preventing the disease is the use of rust-free planting stock infected plants remain diseased until they die.

Rust-infected wild brambles near a planting site are a constant threat to nearby black raspberries. Therefore if such diseased plants cannot be removed it is best not to plant black raspberries. It is often possible to destroy wild brambles by burning or chemicals.

As soon as rust appears in a planting, the diseased plants should be removed by digging out the roots. If rust spores are present, however, the plant should first be burned or otherwise treated to prevent further spread of the fungus.

AMONG OTHER DISEASES of raspberry are some that generally are of minor importance but at times can cause serious losses.

Cane blight, a fungus trouble, often is associated with plants that have been weakened by winter injury or other causes. Fruiting canes may die before harvest or lateral stems may die or be so severely stunted as to produce only worthless fruit. This disease probably is important primarily because of other factors which weaken plants and predispose them to attack by the cane blight fungus.

Powdery mildew can at times cause severe foliage damage especially in warm regions and in dense, shaded plantings. Red raspberries are much more susceptible than blacks.

Crown gall has often caused damage to raspberries, but if disease-free stock is used there is usually little loss from it. During recent years its severity has decreased by strict nursery inspection.

Fruit rot can be a problem when wet weather prevails at harvesttime. Several fungi may be involved, but if a spray program, as outlined later, is followed until shortly before fruit ripens the disease should be largely prevented.

DISEASES OF BLACKBERRIES AND DEWBERRIES include anthracnose, which is caused by the same fungus that causes anthracnose of raspberries. Cane symptoms, similar to those on raspberry, consist of gray spots with a purplish-brown margin. The lesions may be so numerous as to affect large areas and may seriously weaken the canes.

Leucretia dewberries are very susceptible to anthracnose and in the Southern States all above-ground parts of the plant may be affected. Direct fruit infection often causes great loss. Green fruit may show rough, dry spots, which do not ripen and result in misshapen, worthless fruit. In some cases dewberries may be so seriously affected that they are shrunken, brown, and dry.

Of primary importance in the control of anthracnose is to cut and burn wild and escaped brambles near a planting. Removal and burning of fruiting canes and badly diseased new growth is important in obtaining adequate control of anthracnose. In southern areas where all growth is removed after harvest there is an excellent opportunity to help prevent this disease by carefully raking and burning all the canes and leaves. Spraying with a recommended fungicide is necessary in areas where anthracnose is severe and susceptible varieties are grown. Several applications of bordeaux mixture (4-4-50) have been recommended in Southern States. The spray schedule outlined for raspberries should give adequate control.

DOUBLE BLOSSOM, a disease of blackberries and dewberries, is caused by a fungus (Cercosporella rubi). Buds become infected and produce bunches of slender branches, which are known as witches'-brooms. Sometimes such abnormal branches may be a foot or more in length, but they often form a dense matted mass of compacted leaves which do not extend more than a few inches from the stem. Diseased flower buds are larger than healthy buds. Upon opening, the petals are twisted and misshapen and often are pink.

Infection by the double blossom fungus greatly lowers fruit production and results in weakened plants, which are very unsightly. The disease is more common in the South than in the North. Raspberries are not known to be affected by double blossom.

Control of double blossom is obtained by removing and burning infected canes and blossom clusters. In the South the disease on Leucretia dewberries is controlled by removal and burning of all growth as soon as harvest is completed. New growth formed during the rest of the growing season usually is free of infection.

Orange rust on the blackberry has symptoms similar to those on black raspberry notably the bright-orange, powdery spore masses on the under side of leaves.

Eldorado, Snyder, Evergreen (Black Diamond), and Lawton blackberries and Lucretia dewberries are resistant to orange rust.

Control measures given for this disease on black raspberry are adequate for blackberries and dewberries.

DISEASE CONTROL PROGRAM for raspberries and blackberries:

Use disease-free planting stock.

Plant in well-drained, fertile soil not recently grown to any bramble crop and preferably not to potatoes, tomatoes, peppers, or eggplant. Do not interplant with any of those crops.

Locate new plantings as far away as practical from other brambles.

Remove wild or escaped brambles surrounding the planting and continue to keep them as completely eradicated as is practical.

Space plants far enough apart so that the mature planting will not be crowded. Make provision for space for spray equipment to be moved through planting without damaging plants.

Use recommended varieties known to be resistant to disease.

Remove virus-diseased plants as soon as they are observed.

Follow recommended practices for control of aphids and other insect pests of raspberry.

Do not stimulate excessive new growth by too much fertilizer.

Keep weeds under control in and around the planting.

Follow a spray program recommended by your State authorities. A spray schedule that should give good control of most fungus diseases of raspberry and which is adapted to most eastern areas is as follows:

Delayed dormant. Apply at time buds begin to break and before leaves are one-eighth inch long. Use 2 gallons of concentrated liquid lime-sulfur or 1 Pint Elgetol or 1 quart Krenite in 25 gallons of water. Lime-sulfur at this dormant concentration (1 part to 12 parts of water) will readily injure actively growing foliage. Elgetol and Krenite can likewise kill foliage if improperly used.

New cane spray. Apply when new canes are 6 to 12 inches high. Use one-half pound ferbam in 25 gallons of water. (Ferbam is the common name of the chemical ingredient of such trade products as Fermate, Karbam Black, and Ferrodow.)

Preblossom. Apply when blossom buds begin to swell but before they open. Use one-half pound of ferbam in 25 gallons of water.

After blossom. Apply as soon as the blossom period is over. Use one-half pound ferbam in 25 gallons of water.

Fruit spray. Apply about 1 week before harvest begins. Use one-half pound ferbam in 25 gallons of water.

After harvest. Apply as soon as possible after harvest. Use one-half pound ferbam in 25 gallons of water. If possible all fruiting canes should be removed soon after harvest and new canes tied up. Then the after-harvest spray can be applied without much difficulty. Otherwise this spray is difficult to apply due to rank cane growth but should be applied even if fruiting canes are not removed until later.

Use only recommended materials and in the recommended concentrations. Raspberry foliage can be readily damaged by improper materials or excess dosages. Apply with a good sprayer, preferably a power-driven model that delivers at least 100 pounds pressure. Spray thoroughly, covering all surfaces of canes. Do not mix fungicides with insecticides unless it is known that the materials are compatible. Reliable spreader-sticker compounds will often greatly increase the effectiveness of fungicides.

W. F. JEFFERS is professor of plant pathology in the University of Maryland. He received the doctor's degree there in 1939 and since then has been active in research and extension work dealing with control of diseases of strawberries and raspberries.