Diseases: Clovers

Part 2, Section 6: Forages Pest Management

Forages Pest Management

DISEASES

Clovers

The clover cyst nematode attacks red clover roots and crowns. It has been found only in central Pennsylvania, and its distribution throughout the state is not known. Rotating fields out of clover for two or more years should keep this pest under control.

Crown and root rot fungi, especially Fusarium spp., may severely attack red clover. This problem, coupled with injury caused by root-feeding insects, limits red clover stand longevity. Insects feeding on the leaves and stems also stress the plants and favor rapid root rot. The development of root rot is slower when good management practices are used to minimize plant stress. Management practices that help to slow down root rot include maintaining adequate potassium and phosphorus levels, maintaining optimal soil pH for vigorous plant growth, and following recommended harvesting schedules.

Bean yellow mosaic virus is the predominant virus in red clover, occurs generally throughout the state, and undoubtedly contributes to premature decline of red clover stands. Currently, no varieties are highly resistant to this disease.

Northern and southern anthracnose are diseases of red clover caused by different fungi, although their symptoms are quite similar. Leaf blotches, collapsed petioles, and wilted stems on the first harvest usually are the result of northern anthracnose. Similar symptoms later in the season usually are attributable to southern anthracnose. Current varieties have good resistance to one or both of these diseases and should be utilized.

Powdery mildew is distributed throughout the state and, although not considered a serious disease problem, does place an undesirable stress on the plants. Several of the newer varieties have good resistance to this disease.

Sclerotinia crown and stem blight is a problem on red clover during cool, wet springs and particularly following late snow cover. White to grayish growth of the fungus may be seen on the outside of stems, and black reproductive structures, sclerotia form on and in stems, crowns, and soil. Early spring growth can be delayed, and occasionally this disease kills plants in Pennsylvania. As soon as drier, warmer weather begins, the disease subsides. Rotation and deep plowing to bury sclerotia help reduce inoculum in the field.

Several fungi attack leaves and stems of red clover throughout the growing season. Although none of these is considered to be a major problem, they may become severe enough to stress the plant and reduce forage yield and quality. When leaf and stem problems are very severe, early harvest will be beneficial in retaining more leaves and in reducing inoculum in the field.

Depending on the species and variety, a number of fungal leaf diseases, including rusts and leaf spots, attack grasses. These generally are not of economic importance and can be minimized by using sound management practices and resistant varieties.

Brown stripe of orchardgrass is an endemic disease of Pennsylvania that can be found on orchardgrass from emergence throughout the stand’s life. Although this disease starts are small lesions on the leaf, the characteristic symptoms are seen as leaf tip dieback. This disease not only reduces the appearance of the hay, but has some impact on the nutrient value of the hay. This disease overwinters in both debris and older leaves near the ground. Disease evaluations on currently available varieties have been conducted at Rock Springs, PA and some resistance to this disease has been found. Further information can be found at http://cmeg.psu.edu/og/dis-eval.cfm

Fungicide Applications on Forages Quadris (azoxystrobin) has been labeled for use on alfalfa and clover in both pure and mixed-grass stands. Headline (pyraclostrobin) has been labeled for use on alfalfa for forage. Research is currently being done to determine the economic and yield benefits, if any, of using a fungicide on alfalfa.