Integrated Pest Management for Apples

• Apple Leaf Curling Midge
• Apple Scab
• Anthracnose

• Leafrollers
• Syneta beetle
• White apple leafhopper
• Codling moth

Biology

Apple Leaf Curling Midge

Apple Leaf Curling Midge

The Apple Leaf Curling Midge (ALCM) adults emerge from the soil during bloom time.  Adults are small flies, approximately 1/16" long. They have dark bodies with clear wings. The antennae are long and beaded; they curve back like long horns.  Female adults lay eggs on leaves.  The hatched larvae are tiny pinkish orange and they begin feeding on the leaves.  The leaf margins become tightly curled.  Infested leaves roll into distorted tubes, turn red, then brown and brittle.  The larvae grow as they feed.  They pupate either in the leaf or after they drop to the ground.  Adults emerge approximately 13-18 days after pupation in the summer generations.  http://whatcom.wsu.edu/ipm/alcm/index.html

Apple Scab fruit and foliar lesions caused by primary infection in the spring.

Apple Scab

The apple scab fungus continues to release ascospores from overwintering fungal structures at this time of the year. Ascospore release and infection continues to be influenced by temperature and leaf wetness conditions in the orchard. These ascospores can infect both developing fruit and leaves under favorable conditions. The optimum temperature for ascospore germination is 70F. At this temperature, a wetness period of six hours is all that is required for infection. As the wetness period lengthens at a given temperature, the likelihood and degree of infection becomes more severe. As temperatures increase or decrease away from this optimum temperature, longer wetness periods are required for spore germination and the resulting infection. Foliar lesions caused by primary scab infection have been observed as early as mid-May in area orchards, indicating that this period is very important for disease control. Leaves infected with this disease will have velvety, olive-green spots on the leaf surface. These lesions will subsequently produce other spores called conidia, which infect other leaves and fruit. This is called secondary infection. Secondary infections allow the fungus to survive throughout the entire growing season and are very difficult to control. Every effort should be made to control this disease during the primary infection period, thus eliminating the need for season-long spraying and the resulting damage to fruit and leaves. This is a period of high risk for apple scab because terminal leaves are developing rapidly, fruit are highly susceptible, and secondary spores are becoming available during this period if primary scab was not well controlled.

Small circular or elliptical reddish lesions is the first sign of Anthracnose infection in the spring.

Anthracnose

This is a fungal disease which can directly invade and cause cankers on the main trunk and branches of apple trees. When uncontrolled, and after reaching epidemic levels, this disease can destroy an apple orchard. Similar to apple scab, there are two types of spores that are produced by this fungus; wind-borne ascospores and rain-splashed conidia, and it appears that they have overlapping infection periods. Both spore types are produced in anthracnose cankers which are allowed to survive on tree limbs within the orchard and in nearby non-commercial trees. The anthracnose canker first appears as small circular spots that are red or purple when moist. This is first seen, and most easily detected in April and May before trees are fully leafed out. Within the first summer, these lesions enlarge and lengthen, forming a sunken reddish area in the bark. A crack eventually develops between the diseased and healthy tissue. Later in the summer, the reddish area of dead bark takes on a grey color. It is this dead bark left within the canker that gives rise initially to conidia (rain-splashed spores) which are released in the late summer and fall of the first year of infection. Ascospores from these cankers are thought to be produced the following late winter or spring at the earliest. Long distance spread of the disease most likely occurs when cankers are allowed to overwinter within the orchard, living long enough to produce the ascospore (wind borne) stage. Taking out cankers during winter pruning will not prevent intensification of disease in a tree that is already infected, but will prevent spread of infection to other trees in the orchard. Although laborious, efforts to control this disease have focused on the identification and removal of cankers before they produce spores in the fall and early spring. New lesions can be cut out and mature cankers can be lifted out with a pocket knife.

Mature Obliquebanded leafroller larva

Obliquebanded Leafroller

Larvae of the overwintering generation feed on foliage and developing flowers and fruit. Damage to foliage is insignificant, but indiscriminate feeding within developing flower and fruit parts causes fruit deformity or scarring. Larvae are green in color with a brown to black head capsule and thoracic shield and about 1 inch long when mature. They usually mature and pupate in mid to late May, emerging as adult moths in early June. Adult moths mate, producing a first summer generation of caterpillars which usually begin to hatch in mid-July.

Adult Syneta Beetle

Syneta Beetle

This beetle overwinters as a larva in the soil. It pupates in late February or early March. Adult beetles begin emerging in April and can be active until mid-June. The adult beetle is slightly over ¼ inch long, pale yellowish -white to dull brown, often with darker stripes on the wing covers. They are attracted to the blossom and they damage apples by feeding directly on the developing fruit causing scars and fruit deformity. There is only one generation per year. They are not found in every orchard every season, but where present, they can cause significant damage after bloom.

Leaves damaged by White Apple Leafhoppers have white or yellowish-white stippling.

In fifth instar nymphs, wings can be distinguished in the wing pads.

White Apple Leafhoppers (WAL)

This insect overwinters as eggs that are inserted just beneath the bark surface. These eggs hatch into small "nymphs" which go through five stages (instars) of development preceding the winged adult form. There are two generations per season. Peak hatch usually occurs during bloom and the optimum timing to control this first summer generation is when about 10% of the nymphs are in the 4th to 5th instar. At this stage of development, wing pads are very noticeable. This timing is usually in late May (petal fall) and precedes the first "cover spray" for codling moth by a week or more. The codling moth degree-day model is a useful tool for timing scouting efforts, which will help determine the need for and timing of treatment. Both nymphs and adults damage leaves by feeding on individual mesophyll cells, which causes a white spotting or stippling of the leaves. They prefer older mature leaves. This feeding, if extensive and when accompanied by other stresses to foliage which reduce photosynthetic potential, may reduce tree vigor, fruit set and size, but actual indirect damage is not well understood or documented. Leafhopper excrement on fruit is seen as small black "tar spots" which are easily removed in normal washing and processing of fruit. Their biggest impact is probably as a nuisance pest, annoying pickers during the harvest season. If not controlled during the summer months, very high populations of second generation winged adults can be present during harvest, getting into the eyes, ears, nose, and mouth of anyone working close to the trees.

Mature Codling Moth larva over-winters below bark surface.

Codling Moth (CM)

This insect spends the winter as a mature larva inside a cocoon either within the orchard (under bark scales or in litter on the orchard floor) or nearby in wood piles, on farm buildings, on packaging bins and in numerous other protected sites. They change into pupae during pink stage and the first adult moths usually emerge after full bloom in early to mid-May. First generation adults will continue to emerge for 6 to 7 weeks. They mate and begin laying eggs primarily on leaves. These eggs usually begin to hatch into young larvae in late May to early June. These worms immediately search for and bore into the fruit, usually entering at the calyx end or through the side. As they feed, they push excrement (frass) out of the apple through the entry hole. They feed within the apple for 3 to 4 weeks and then emerge as a fully-grown larva. Most of these larvae will pupate in a protected place and emerge as second generation adult moths in mid-July which repeat the mating , egg laying, and fruit damaging cycle once again. Most second generation larvae exit the fruit prior to harvest and then search for a protected site to over-winter. The traditional approach to controlling this insect is the application of well-timed sprays that cover the leaves and kill the hatching larva before it is able to reach the fruit. The frequency and timing of sprays is based on pheromone trap catch results combined with site-specific temperature data that is used to predict the rate of development of the insect. This predictive codling moth modeling system is described in WSU Extension Bulletin 1072. This model was field-tested with Whatcom county apple growers during the 1996 and 1997 seasons and has proven to be a very useful system for managing this important pest. (See Pages 5-5 through 5-8 in the "Tables and Charts" section.)