Common Diseases

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This article will instruct you how to prevent and treat disease and fungus on fruit trees.
by Brooks Wilson · All Zones · Diseases and Fungus · 0 Comments · June 14, 2010 · 22,335 views

Common Diseases on Apples and Remedies

During the early part of the growing season, apple scab, powdery mildew and fire blight are the principle disease problems. Apple scab affects both the fruit and foliage and infections can result in defoliation and malformed fruit. Powdery mildew primarily affects the foliage and is characterized by white fungal growth on the surface of affected leaves. Fire blight, a bacterial disease, can be particularly destructive during the bloom period causing blossom blight and shoot and branch dieback as the bacteria grow from the blossoms into the shoots. Cedar apple rust can be destructive on susceptible cultivars when they are grown in close proximity to the Eastern red cedar (the alternate host of the fungus on which cedar galls develop). Infections are characterized by yellow spots on the leaves and fruit. During the summer period, bitter rot, black rot and white rot, can all be destructive, particularly in poorly pruned trees with dead wood within them. The most common diseases during the summer period are sooty blotch and flyspeck. The pathogens which cause these diseases grow on the cuticle of the fruit, but do not cause any damage to the fruit themselves.

Apply a fruit tree combination spray when the first green tissue is visible and repeat at 7-day intervals until blossoms begin to open. Overall disease control will generally be better if captan is used instead of sulfur. However, acceptable apples can be produced with sulfur although sprays may need to be applied more frequently than suggested for the captan combination spray. DO NOT apply the combination spray during bloom because the insecticides can kill bees and other pollinating insects. However, spraying with streptomycin (AGRI-MYCIN) during bloom at the rate of 1 teaspoon per gallon of water (0.8 oz per 10 gallons) will aid in the control of fire blight. When flower petals begin to drop, make another application of the combination spray and repeat at 2 to 3 week intervals until 3 weeks before harvest. Use a 2-week interval if weather conditions are wet or there have been disease or insect problems in past years. Where cedar apple rust is a problem, include myclobutanil (IMMUNOX or KGRO 1.55%) at 1/2 fl oz per gallon of water (5.0 fl oz per 10 gallons) in the sprays beginning at tight cluster and continuing for one month after bloom.

Common Diseases on Pears and Remedies

Pears are affected with many of the same diseases as apples with the exception of pear scab, which has not been reported in many southern states, and cedar apple rust, which does not occur on pear. Fire blight tends to be more severe on pear than apple and can kill large limbs and even entire trees of susceptible cultivars. Pear leaf spot (fabraea leaf spot) can be important on some cultivars. Captan is not registered for use on pears. Use benomyl (Benlate) 1 teaspoon per gallon of water (3 tablespoons per 10 gallons).

Common Diseases on Peaches

The most common diseases encountered on peaches and nectarines are leaf curl, peach scab, and brown rot of fruit (the same fungus also causes blossom blight). Leaf curl can be controlled with a single application of Bordeaux mixture, fixed coppers or lime-sulfur (use rates recommended on product label). The spray for leaf curl must be applied during the dormant season before buds swell. Peach and nectarine foliage is very sensitive to copper and can be injured, thus copper should not be sprayed when leaves are present.

Use two dormant oil sprays at 2-week intervals before green tissue is present to control white peach scale. When flower petals begin to drop, apply the combination spray and repeat at 2 to 3-week intervals until 3 weeks before anticipated harvest. The two sprays beginning at petal-fall are critical and provide good control of the insects plum curculio and Oriental fruit moth and the fungal disease peach scab. Most insecticides should not be used within the 2 to 3 week period before harvest (check product label for specific instructions). However, a fungicide is needed for brown rot control because this is the time this fungal disease is most damaging. If weather conditions are wet and brown rot has been a problem previously, 2 to 3 applications of myclobutanil (Immunox or KGRO 1.55%) at 1/2 fl oz per gallon of water (5.0 fl oz per 10 gallons) should be used starting approximately 3 weeks prior to anticipated harvest. Use the formulation labeled for bearing fruit trees that does NOT contain insecticide. If sulfur is used for brown rot control, spray every 5 to 7 days starting 3 weeks before anticipated harvest when weather conditions are wet.

Common Diseases on Plums

The fungal disease, black knot, can occur on branches of cherries and especially plums. This is most common when these fruit trees are grown near wooded areas that contain wild cherry. Pruning out these knots as soon as observed and spraying a fungicide such as BENLTATE starting early bloom with 2 to 3 additional sprays 7 to 10 days apart can aid in reducing black knot. The disease most commonly encountered on cherries and plums is brown rot. Apply the first combination spray when the flower petals begin to drop and repeat at 2 to 3-week intervals until 3 weeks before anticipated harvest. If weather conditions are wet, apply 1 to 2 fungicide (myclobutanil) sprays as recommended for peaches during the 3-week preharvest period to reduce brown rot.

The peach tree borer can cause serious damage on the trunks of peach, nectarine, cherry, and plum trees. Damage caused by this insect can lead to tree death. To control peach tree borers, apply endosulfan 50W (Thiodan) at the rate of 2 tablespoons per gallon of water (7 oz per 10 gallons) to the lower limbs, trunk and base of the tree the first week in September.

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