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Production Perils 2

(The Tart Cherry Industry - continued)

Diseases

• Cherry Leaf Spot

  Cherry leaf spot overwinters on fallen leaves. In the spring, leaf spot spores are carried by the wind to new leaves, where they germinate and promote new infections. These infections then produce additional spores which spread the disease to adjacent leaves and trees. The infected leaves eventually turn brown and drop from the tree.

  In mild cases, cherry leaf spot may affect only a small number of leaves. During damp or rainy weather, however, the disease can “explode” in the orchard, infecting nearly all the leaves and defoliating the trees before the crop is harvested. Fruit on defoliated trees fail to mature normally, and are light-colored and low in soluble solids.

  Rotary mowing the orchard after leaf drop in the fall helps to control leaf spot by hastening the decay of fallen leaves and reducing chances for the fungus to overwinter. The main control, however, comes through the use of fungicides.

• Brown Rot

  Brown rot is common to all stonefruit and frequently causes heavy losses among cherries. This disease can destroy blossoms, fruit, and stems. The most significant losses result from blossom blight and destruction of the fruit. Fruit may be infected in the orchard, in transit, or while being held for processing. Brown rot can develop rapidly, and a few infected fruits can lead to the destruction of all surrounding fruit.

  Brown rot infection of blossoms appears as a sudden wilting and browning of the flower parts. If conditions are moist, the dead flowers are soon covered by grayish brown fungal spores that then infect the healthy fruit. Infections on the fruit begin as small, circular brown spots that rapidly increase in size and develop into a soft rot.

  Infected fruits that remain on the tree shrink and dry into firm “mummies,” which become a source of infection in future seasons. The brown rot fungus also infects twigs, causing oval-shaped cankers.

  The fungus lives over the winter in infected twigs, in fruiting spurs, and in mummified fruit on the tree or on the ground. Three methods are used to control brown rot. Cultivating around the trees to bury the infected mummies and pruning out infected twigs during the spring and early summer helps to eliminate sources of new infections. Providing open space around the trees to assure good air circulation helps eliminate excessively moist conditions that favor brown rot. As with leaf spot, however, the main control comes from the use of fungicides.

• Other Fungal Diseases Diseases including black knot, powdery mildew, leaf rust, scab, and verticillium wilt occur to some extent on tart cherries. These diseases are usually less serious than either leaf spot or brown rot. Most of them are held in check by the fungicides applied to control leaf spot and brown rot.

Viral Diseases

Prevention is the best control. The most effective preventative measures include the avoidance of potential sources of infection, such as planting diseased stock or selecting sites near orchards with infected trees. Promptly removing infected trees in a young orchard also helps reduce the chances of spreading the infection to healthy trees.