Diseases of Berries in the West

Folke Johnson.

Raspberries and blackberries bring in about 10 million dollars a year to growers in the Pacific Coast States of California, Oregon, and Washington.

Diseases often are of great importance in so large an industry. They differ somewhat, according to locality and crop. California is concerned mostly with the trailing blackberries, Boysen, Logan, Nectar, and Young. Black and red raspberries are more important in Oregon. In Washington the leaders are red raspberries and the Cutleaf Evergreen blackberry.

The varieties of red raspberries produced commercially in Oregon and Washington are somewhat different. Production in Washington is almost limited to the Washington variety, but there are a few fields of Tahoma and Willamette. Oregon has a large acreage in Cuthbert in addition to Washington and Willamette raspberries.

A well-drained soil is needed for growing red raspberries. Silt loam or silty clay-loam soils even on moderate slopes are avoided because their water-holding capacity is often great enough to suffocate the roots. Sandy or porous soils with fairly heavy subsoil, where free water during the rainy season remains in the root zone for long periods, have the same effect. The choice soils are those of good texture, as loams or sandy loams, where excess water drains off or percolates away from the roots.

Root suffocation by water, one of the severest of problems in maintaining healthy plants, is referred to as wet feet. The symptoms are best described as a general decline in plant growth. On affected plants the lateral branches produced in the spring on the fruiting canes often are less than 12 inches long; normally they are at least 36 inches. The leaves are smaller, bronzed or yellow, and lack the bright green of healthy leaves. Usually all the canes in a hill are affected. The plants may die in dry hot weather or may linger on and produce a few weak canes, about 2 to 4 feet long, for the next season's crop. They remain unthrifty and finally succumb. A healthy plant annually produces 8 to 12 or more young, vigorous canes 8 to 10 feet or more high. Sometimes when the root system has been killed during the rainy season, only weak, short laterals an inch or two long are produced with small, undeveloped leaves, which soon wither and die. New canes fail to develop and the plant succumbs. The fruit from affected hills is greatly reduced in size, number, and quality. If the plants are dying when the fruit is ripening, it shrivels up, turns a dark red, and has little flavor. The fruit is crumbly and hard to pick.

Root suffocation is noticed mostly in late spring or early summer in the lowest places in the field. All plants in such locations are thus affected and a field may be spotted with dead or weakened plants, while in the higher levels the canes are normal. Symptoms of root suffocation do not generally appear until the second or third summer after planting, although older plants may also become affected, particularly after an unusually wet season.

The only known control is to provide better drainage. Replanting with new stock is not practical, because the new plants also will become affected. All commercially grown raspberries, such as Washington, Willamette, and Cuthbert, are susceptible. Newburgh tolerates the condition but is not grown extensively in the West. There is indication of tolerance or resistance among new hybrids, but they require further testing for other qualities before they can be recommended.

WHEN FIRST INTRODUCED in 1938, the Washington was resistant to western yellow rust, caused by Phragmidium rubi-idaei, which had plagued other varieties. In 1944, however, a new strain of the rust fungus infected the Washington variety. It has since become widespread in Washington and Oregon.

The most obvious symptom is the yellow flecks or pustules on the upper surface of the leaves in early spring. Light-orange pustules break out 2 or 3 weeks later on the under leaf surface, on the canes, or on leaf petioles. Sometimes they almost cover the leaves and cause them to die prematurely. The yellow or light-orange pustules contain numerous spores, which are carried about by wind currents or splashing raindrops. New infections arise all summer. In favorable weather all the plants in a field become infected. Severe infection means defoliation, and lesions produced on the canes weaken them so they break easily during subsequent cultural practices. The pustules and cane lesions turn dark and become black in late summer and early fall.

Another kind of spore remains over winter on the canes, fallen leaves, plant debris, fence posts, soil anything. Those spores do not germinate until early the next spring, when new infections arise on the young unfolding leaves in the form of inconspicuous, pin-point, orange blisters. Those are followed by the yellow stage on the Upper leaf surface and the life cycle has been completed.

Experiments by E. K. Vaughan, of Oregon State College, and me, demonstrated that a delayed dormant spray application to the canes when the buds have begun to unfold, usually in late March or early April, will check the disease. Several fungicides, such as bordeaux mixture, lime-sulfur, ferbam, Phygon-XL, Elgetol, and Cop-O-Zinc, have given effective control. They do not eradicate the disease but reduce it so that no great damage results before the crop is harvested. Of the newer varieties, Willamette and Tahoma are resistant. Prompt removal and burning of the old fruiting canes in the fall aids in reducing the spore load for infections the following year.

ANTHRACNOSE, caused by the fungus Elsinoe veneta, is present to some extent each season. It is worse on black raspberries than on the commercially grown red varieties. The disease is recognized in early spring on the lower parts of young canes by the appearance of round to elliptic sunken spots, one-eighth to one-fourth inch or more in diameter. Those lesions have light-gray centers with purple margins, are somewhat depressed in the centers, and may become so numerous as to impair the movement of water and nutrients through the canes. Similar spots, but smaller, may be present on the leaves and even on the fruit.

The spray schedule against yellow rust will usually suffice to hold in check anthracnose on red raspberries. Often an additional spray is required, especially in the black varieties. Several proprietary materials have given good results if applied when the current season's canes are 8 to 12 inches tall.

GREEN MOSAIC, a virus disease, is most prevalent on the Cuthbert raspberry. The effect on the plants is a gradual loss of vigor, reduced yields, and lower quality of fruit. Such plants are more easily winter-killed than are healthy ones. The outstanding symptom is a mottling of dark- and light-green areas on the foliage; the dark-green blisters are intermingled with the light-green areas near the veins. Such leaves are deformed and smaller than healthy foliage. Mottling is more evident on the young leaves near the cane tips. It is more pronounced in early summer than later in the season, when the symptoms become masked.

Mosaic may be introduced into a field by planting diseased nursery stock. Once established, it spreads rapidly by the feeding activities of aphids, Amphorophora rubi, which move about from diseased to healthy plants. Studies by L. K. Jones and Karl Baur, formerly of the State College of Washington, showed that in one field the number of infected plants increased from 9.5 percent to 51 percent in 2 years. They also showed that careful roguing was an important means of holding the disease in check.

The Washington, Tahoma, and Willamette varieties have shown symptoms of being infected with a virus disease called ring spot. The disease has closely followed the appearance in 1947 of aphids on those varieties. Ring spot was present throughout western Oregon and Washington in 1953. The main characteristic is the presence of circular, light-green rings bordering nearly normal green tissue. The rings are about one-fourth to one-half inch in diameter. It is not unusual to find ring spot and a mosaic mottle on the same canes, in which the former symptoms are present on the young leaves and mosaic on the older. Thus far no apparent stunting or loss of vigor has been associated with the disease.

Another symptom often observed on Cuthbert and other red varieties is a mild mottle, or flecking, of small, light-yellow areas scattered over the leaves. The flecks are more abundant on the older leaves of new growth. The symptoms disappear in hot weather and reappear when lower temperatures prevail. Experiments conducted by G. H. Huber, formerly of the Western Washington Experiment Station, demonstrated the virus nature of the symptoms. He refers to the disease as mild mosaic.

The virus may be transmitted by grafting tissue from diseased to healthy plants, and the large raspberry aphid, Amphorophora rubi, is the natural vector in the fields.

When the virus is transmitted from red raspberries to Cumberland and other varieties of black raspberry, by grafting or aphids, severe symptoms develop. The first effect is the appearance of water-soaked areas or streaks at the tips of the new canes. The streaks later become purple, and the tips bend downward and usually die. The lateral branches also show this discoloration, followed by tip die-back. Sometimes during high temperatures, when the cane tips have not been killed, growth is retarded and there is produced a rosette of branches and leaves, followed by near-normal growth. Leaf mottle, characterized by light- and dark-green areas scattered over the leaves, is associated with cane tip necrosis. As in red raspberries, the mottle becomes masked with high temperatures but reappears on the same plants during cool weather. Growth of affected plants is greatly retarded, and the fruiting laterals are shorter than on healthy canes.

The virus has been recovered from six red varieties, Antwerp, Cuthbert, Latham, Lloyd George, Marlboro, and Newburgh, but not from Washington or Tahoma. Of II black raspberry varieties (besides the wild species Rubus leucodermis) tested for susceptibility by using aphids as vectors, all were found susceptible by showing typical symptoms of cane tip, dieback, and mosaic.

THE TERM BLACKBERRIES includes the trailing forms that often are referred to as dewberries. In California dewberries are grown on about 6,000 acres. Most extensively grown are Boysen, Logan, Nectar, and Young, all believed to be derived at least in part from the wild Pacific coast dewberry, Rubus ursinus. Some of those varieties are grown in western Oregon but are of minor importance in Washington. In Oregon and Washington the Cut-leaf Evergreen blackberry, R. laciniatus, is important. Recently introduced varieties from Oregon are Cascade, Chehalem, and Pacific, which also are derivates of R. ursinus.