Better Yields Through Science
Cherries Diseases & Pests
|Disease||Symptoms, Life-cycle and pest management|
|Cherry Leaf Curl||Pathogen: Taphrina deformans or cerast
The fungus also affects peach and nectarine trees. The fungus spreads on water, sticking in the cracks of the tree’s bark and on newly developing buds. As the weather warms, the spores reproduce on the flowers and emerging leaves, but only if they are wet. Once a branch is infected, however, it will always produce infected leaves if preventative measures are not taken.
Leaves infected by the fungus will appear thickened and discolored. They may turn brown, yellow or even purplish and curl up or twist. Eventually, they dry up and fall off the tree. Spray the tree with a fungicide in the fall, after the leaves have dropped, and again in the spring just before the leaves begin to open.
|Cherry Leaf Spot||Pathogen: Blumeriella jaapii (previously called Coccomyces hiemalis)
The fungus overwinters in dead leaves on the ground. In early spring (about petal fall), fungal fruiting bodies called apothecia develop in these leaves. Spores (ascospores) are produced in the apothecia and are forcibly discharged during rainy periods for about six to eight weeks, starting at petal fall. The optimal temperatures for ascospore discharge are 61 degrees F (16 degrees C) and higher. Very few ascospores are discharged at temperatures below 46 degrees F (8 degrees C). These ascospores are spread by wind or splashing raindrops to the green, healthy leaves and serve as primary inoculum for disease. The ascospores stick to the leaf surface, germinate in a film of water, and within several hours at the proper temperature (Table 1), penetrate the leaf through stomata (natural openings) on the underside of the leaf. The small purple spots soon appear on the upper surface. Incubation time, from fungus penetration to the appearance of the spots, varies with temperature. Under damp conditions and with temperatures between 60 and 68 degrees F (15 and 20 degrees C), the period may be as short as five days. When rain and dews are absent and at lower temperatures, as long as 15 days may be required before symptoms appear.
Once lesions have developed, masses of secondary or summer spores (conidia) are formed from the slightly concave eruptions (acervuli) on the underside of the leaf. This mass of conidia provides the white appearance to the under-leaf lesions. Conidia are spread to other leaves by splashing raindrops and are capable of causing new infections (each producing thousands of additional conidia) under the temperature and wetness conditions. Serious leaf spot damage usually occurs in years with numerous rainy periods throughout late spring and summer, when repeated secondary infection cycles allow the disease to snowball into an epidemic. Preventive fungicides are recommended at petal fall, shuck fall and two weeks later.
|Coryneum Blight or Shot Hole Disease||Pathogen: Stigmina carpophila, syn. Coryneum carpophilum or Wilsonomyces carpophilus
Coryneum blight is also called shot hole disease, California blight, peach blight or pustular spot. Severe foliar shot holing may weaken a tree, while the most apparent damage is infection of the fruit.
Fruits are blemished and disfigured by spots and lesions from Coryneum blight. Outbreaks of this disease take place in spring and early summer and in cool, wet periods prior to harvest. Blight is difficult to eradicate because the fungus in infected buds and twigs may produce spores for two to three years, but the fungus does not overwinter in old infected leaves.
The fungus apparently overwinters in dormant infected leaf buds, blossom buds and small twig cankers. Spore production begins in early spring. The first symptoms of infection are observed on young leaves as small red spots that enlarge and become purple with a white center. These spots then drop out of the leaf blade leaving a “shot hole.” Numerous holes give a very tattered appearance to infected leaves.
Early season infections are characterized by the presence of a reddish-purple halo surrounding a light tan, scab-like center spot, which is the dead fruit skin killed by the fungus. Severe, early season infections also can have gummy ooze on the fruit surface.
Coryneum blight is serious in years when frequent light showers occur during the summer. Wind currents disperse the spores of this fungus from infected twigs and leaves to uninfected branches. These spores require four hours of contact with free water droplets on the fruit, leaf or twig surface in order to germinate and cause infection. Temperatures of 70 F to 80 F are optimum for Coryneum infections. Lesions can develop at 45 F but at a much slower rate. It takes from two to five days for a spore to initiate infection and cause a visible lesion. Because bud and twig lesions may continue to produce spores for two to three years, a conscientious program of chemical control and removal of dead wood is necessary to eradicate the disease.
|Peach Twig Borer||Scientific Name: Anarsia lineatella
The peach twig borer is widely distributed and is found on several hosts. The adult moth is about 0.3 to 0.5 inch long, with steel gray mottled forewings. Small larvae are almost white with black heads. Mature larvae are about 0.5 inch long and have black heads and brownish bodies with white portions between each body segment, giving the appearance of stripes. Peach twig borer overwinters as larvae in tiny cells, called hibernaculum, that are located in the crotches of 1- to 3-year-old wood and at pruning wounds. There may be three to four generations each year, but later generations occur after cherry harvest.
Dormant or delayed dormant applications will reduce populations of overwintering larvae. When control has not been achieved by delayed dormant treatment, additional applications should be made during the bloom to petal fall period or shortly thereafter. For summer sprays (May–July) on young trees, monitor for flagging or shoot strikes.
|San Jose Scale||Scientific Name: Quadraspidiotus perniciosus
The San Jose scale has no visible egg stage; scales emerge from under the edge of their mother’s covering as nymphs. There are three stages during the first instar: the crawler, which is mobile and locates a feeding site; the white cap, which feeds and becomes covered with a waxy secretion; and the black cap, which is a darker harder wax covering under which they may overwinter. The male scale will molt four times, and is elongate and black. The female molts twice, and is circular and gray. Males emerge as winged adults while the females remain wingless under the scale covering. There are three to four generations per season taking about 7 to 8 weeks per generation.
|Powdery Mildew||Pathogen: Podosphaera clandestine
Powdery mildew is marked by superficial, white, web-like growth on leaves, shoots, or fruit. The fungus overwinters in buds on twigs and as chasmothecia, which are spore-containing structures, on the bark of twigs and branches. Secondary spores produced in spring spread the fungus to new growth. Infections can be severe in commercial orchards during years of low rainfall, high humidity, and warm temperatures (70° to 80°F). The disease is particularly severe on new growth, such as shoots of inner scaffolds, and can infect fruit as well, causing direct crop loss.
To protect fruit, spray soon after petal fall and 2 to 3 weeks later if needed. Treat immediately if mildew is found on leaves or shoots of inner scaffolds or water sprouts.
|Cherry Scab||Pathogen: Venturia cerasi (Cladosporium cerasi or Fusicladium cerasi)
Scab can affect fruit, leaves and shoots. It first appears on fruits as small dark spots about six to eight weeks after petal fall. On mature fruits, the fungus forms small, circular, sooty-brown spots or freckles which become scabby. These can merge to form large, irregular dark brown lesions. When infection is severe, the fruit can crack, shrivel and fall prematurely. Scab lesions are pale green and remain flush with the fruit surface.
Leaf infections appear as sooty or olive blotches on the underside of leaves, and as dark lesions running along the mid-rib and petiole. Severe leaf infection can cause defoliation, but in some cases, little or no leaf infection can be found even when the fruit is badly affected. On the shoots, small brown lesions with slightly raised margins may appear. The margins of these lesions become olivaceous where the pathogen is sporulating.
|Brown Rot Blossom and Twig Blight||Pathogens: Monilinia fructicola, Monilinia laxa
Brown rot infection occurs through blossom parts and progresses into the twig, killing blossoms, spurs, and associated leaves. Small cankers on twigs form below infected spurs; gum may be present at the base of flowers and dead flowers remain on the tree. Beige-colored spore masses develop on diseased flowers under high humidity.
Infection is favored by rain or dew during bloom and moderate temperatures (about 58° to 77°F). One and sometimes two applications may be necessary and are most effective when made sufficiently in advance of rain so that the spray has time to dry. Start treatment at the popcorn stage of bloom, and spray every 10 to14 days until bloom is completed.