Better Yields Through Science
Pear Diseases & Pests
|Disease||Symptoms, Life-cycle and Pest Management|
|Brown Mite||Scientific name: Bryobia rubrioculus
Brown mites overwinter in the egg stage. Eggs are red and spherical but do not have a stipe rising from the top. Newly hatched brown mites have six legs and are bright red. After they molt for the first time, they turn brown, develop eight legs, and resemble the adult, only smaller. Adult brown mites are dark reddish brown, and the first pair of legs is longer than the other three pairs.
Brown mites are usually the first mites to appear in spring. Brown mite is best controlled in the dormant season or early foliage season. In-season sprays are rarely justified.
|European Red Mite||Scientific Name: Panonychus ulmi
The female European red mite is about 0.02 inch long and has a brick red, globular body with long curved hairs that arise from white spots or tubercles on the back. Nymphs or unfed females may appear greenish. European red mite eggs are red, slightly flattened, and have a stipe protruding from the top. They overwinter in the egg stage on twigs and spurs. Eggs hatch in early spring just after the trees leaf out, and many generations (8–10) are produced before fall. Ordinarily European red mite populations build up slowly during spring and do not become apparent until large populations are present.
European red mites remove the contents of the leaf cells as they feed, causing leaves to take on a finely mottled appearance. During summer, look for stippling or bronzing on leaves. Generally treatments for this mite are applied in the dormant/delayed-dormant season.
|Pearleaf Blister Mite||Scientific Name: Eriophyes pyri (Pagenstecher)
Pearleaf blister mite (PLBM), also known as pear bud mite, and also by the synonym Phytoptus pyri Pagenstecher, is most often seen in unsprayed trees. This species is part of a complex of related species (E. pyri complex).
No reproduction or feeding occurs during winter in the buds. Mites begin to feed and oviposit as buds swell in the spring. Blisters begin to form at the cluster bud stage, on leaves 1/20 – 1/5 inch (1-5 mm) long. After 1-2 weeks, blisters begin to form small holes. Mites enter these holes and begin egg production. Usually only one female enters each blister. If present in fruit buds, feeding on floral parts will cause fruit blisters. Females produce 7-21 eggs each. In cooler weather, about 18 days are required for development; only 5-8 days are required in warmer weather. There are 2-3 generations per year. Activity ceases during June, July and August, resuming when cool evenings return. Mites return to buds from September to November.
This complex causes blisters on the undersides of pear and apple leaves, especially younger foliage, usually in a row along the mid-vein. The blisters are tiny green swellings at first, later expanding and turning red. These blisters eventually turn necrotic and brown (blisters that are not invaded by mites remain green). Leaf injury can result in small, sparse leaves.
Spray during the dormant or delayed dormant period. Lime sulfur may also be applied in the postharvest period.
|Pear Psylla||Scientific Name: Cacopsylla pyricola (Foerster)
Eggs are pale cream to yellow-orange. They are elliptical in shape, with a tiny peg inserted into plant tissue. Nymphs are pale yellow when young, but have brown sclerotized plates when older. They resemble flat aphids in shape.
Adults overwinter in or near pear orchards. Few adults are mated before overwintering. In early spring adults return to the trees, mate and begin ovipositing in crevices on fruit spurs and on young leaves as they unfold. There are three generations during the spring and summer.
Females lay an average of more than 300 eggs during their life. Most oviposition by summer adults occurs near leaf mid-veins; egg survival is also highest near mid-veins. As nymphs develop, they become engulfed in a droplet of accumulating honeydew. Such droplets may contain the shed skins of the preceding instars.
|Pear Rust Mite||Scientific Name: Epitrimerus pyri (Nalepa)
The pear rust mite (PRM) is found throughout the mid-Atlantic area where it occasionally causes injury to foliage and russetting of the fruit.
PRM is wider at the anterior end, however, giving this species a more “broad-shouldered” appearance. Adults are dull white to pale brown and have wedge-shaped bodies that are larger at the head than the tail end. The two nymphal stages look similar in shape but smaller. The round eggs are flattened, colorless when first laid, and extremely small.
The PRM overwinters solely as adult females beneath bud scales of leaf spurs and under loose bark of 1- to 2-year-old twigs. As the weather begins to warm, usually before buds break, mites move to developing clusters and begin feeding on the succulent parts of buds. Eggs are produced shortly after mites become active. As buds open, adults and immatures move to the expanding leaf tissue and eventually to fruit as the leaves mature and harden. Immature mites develop quickly through two instars, each followed by a resting stage.
|San Jose Scale||Scientific Name: Quadraspidiotus perniciosus (Comstock)
Most of the life cycle of this insect is spent under a secreted waxy covering that protects the soft, sessile insect from predators and to some extent even insecticides. Young scales have smaller, very light colored coverings that darken to a sooty black or ashy appearance as they grow larger and mature.
SJS overwinters as partially grown immatures on the trunks and scaffolds of the tree with the majority being in the first nymphal instar. The nymphal scales remain dormant under their waxy coverings until the sap begins to flow in the spring and then continue to feed until early May when they become mature. There are two to three generations a year with considerable overlap of the broods because of the long reproductive life of the females.
|Pear Scab||Pathogen: Venturia pirina
Scab first appears as velvety, dark olive-to-black spots on fruit, leaves, and stems. When infections occur early, fruit spots become scab like with age and the fruit may become misshapen. On leaves, infections cause leaf puckering and twisting and eventually tear with age. Secondary infections that occur later in the season appear as black, velvety pinpoint spots on fruit and leaves.
The fungus overwinters in dead leaves on the ground. Primary spores are discharged from flask-shaped fruiting bodies in infected dead leaves during spring rains and infect young leaves and fruit during periods of prolonged moisture. These infections produce secondary spores, which may cause further spread of disease during wet periods. Overwintering twig lesions from secondary infections may also be an important source of inoculum in spring.
Data has shown that applying high rates (6 gal/100 gal water with up to 24 gal/acre) of lime sulfur in the delayed dormant period can significantly reduce the viability of overwintering twig lesions, which are usually a significant source of disease inoculum during and in years following severe scab outbreaks. Applying a 5% solution of biuret urea spray at 50 pounds per 100 gallons dilute spray before leaf fall hastens leaf decomposition and may reduce spore production the following spring. Combining 10 to 12 gal/acre of lime sulfur with the urea before leaf fall may offer complementary control. Cultivating leaves into the soil, however, has not significantly reduced infection potential.
|Powdery Mildew||Pathogen: Podosphaera leucotricha
The white fungus grows on terminal shoots of pears. Pears are susceptible to fruit infection, which appears as black marks and russeting on young fruit.
The fungus overwinters primarily as mycelium (thread-like, multicellular structures) in infected terminal and fruit buds. It may also overwinter in sexual fruiting bodies on the surface of infected leaves and shoots (occasionally washing off into bark cracks and crevices). As the buds open in the spring, the mycelium grows out into the developing shoot and leaf tissues and soon begins to produce the asexual summer spores (conidia). These spores are wind-borne and germinate readily at mild temperatures and high humidity. The resulting new mycelium colonizes the exterior of the leaf, occasionally penetrating the surface cells to provide access to the food they contain and produce. The disease develops rapidly under cloudy, overcast conditions at temperatures of 70 – 90 F until late-June to early-July, when temperatures reach into the upper 90’s F and shoot growth stops.
Preferred spring application is at pre-pink and pink bud. Treat immediately if mildew is found on shoots or leaves on inner scaffolds. If powdery mildew continues to be a problem in the orchard, apply additional treatments as needed.