Integrated Pest Management for Apples

• Apple Scab
• Anthracnose

• Codling moth
• Leafhoppers
• Spider Mites
• Rust Mites
• Dock Sawfly

Biology

Apple Scab lesions on fruit resulting from primary infection in the spring.

Apple Scab

Production and maturation of ascospores which are responsible for primary infection are typically completed in western Washington by mid to late June. Therefore, this approximate time marks the winding down of the primary infection period but calendar timing alone is not very precise. Once apples are about ½ inch in diameter, they are more tolerant of infection and this fruit stage is thought to coincide with the end of the primary scab infection period. Growers have recently expressed an interest in using an ascospore maturation model (developed by Gadoury and MacHardy in 1982) which relies on temperature and degree day accumulation to predict ascospore maturation. Ascospores which are mature are ready to discharge in the next rain. This model provides the basis for predicting when the supply of ascospores is exhausted. It also shows three different phases of ascospore maturation. It has potential to more accurately determine when the risk of primary infection is over (See details in the Monitoring section below). In the event that primary infection is not properly controlled, developing scab lesions produce spores (conidia) which are responsible for further secondary infection of fruit and foliage throughout the growing season. Although fruit can be infected with apple scab at any stage of development, it is less susceptible to infection as it matures. Fruit, which is infected late in development, can develop small black spots in storage, which is called pin-point scab.

Early Summer Anthracnose lesion on main stem of trunk. A crack is just beginning to form around this lesion

Anthracnose

Lesions on trunks and branches enlarge and lengthen during June, forming a sunken reddish area in the bark. Mature cankers are usually elongate, from 1 to 10 inches in length and up to a few inches wide. A crack forms around the canker as bark tissue around it continues to grow. The fungus residing within the dead canker bark begins to produce spores (conidia) in the late summer and fall. The conidia are spread by water down the trunk, causing new infections below the existing canker. the following spring and summer. If the dead bark is not removed from these cankers, the fungus can survive and produce infectious spores for several years. Control of this disease is largely dependent on timely removal of the spore-producing dead bark within the canker prior to late summer and fall production and release of spores.

The mature Codling Moth larva has a pink body and a brown or black head and thoracic sheild.

Brown frass or excrement extrudes from the codling moth entry hole, as the larva feeds within.

Codling Moth

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. Worms feed within the apple for 3 to 4 weeks and then emerge as fully grown larvae. Most of these larvae will pupate in a protected place and emerge as second generation adult moths beginning 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 overwinter. Sprays to control codling moth target the larval stage prior to entry into the fruit. Timing and need for sprays is based on pheromone trap catch and site - specific temperature data used to predict the insect's development.

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

White Apple Leafhopper

First summer generation adults usually begin to appear in late May and early June and can survive into the late summer. They feed on foliage causing a white spotting or stippling of the leaves where chlorophyll has been removed. The adult is about 1/8" long, elongate, and pale yellowish-white, with wings that are held roof-like over the body. Later stage nymphs, soon to become adults may still be present. Adults mate and the females deposit their eggs in apple leaf tissue during late June and early July. These eggs begin to hatch in late July giving rise to a second generation of nymphs and adults, which survive through September and October. This second generation is usually much larger than the first with all stages of the insect overlapping at the same time, which makes chemical control less effective. Second generation adult activity peaks in mid to late September just prior to and during harvest. Overwintering eggs are inserted just beneath the bark of the apple tree in 1- to 5-year old wood.

Adult female European Red Mites are red with little bristles.

Various stages of the European Red Mite including eggs, immature form, and adults.

Adult female Twospotted spide mite.

Mite-infested apple leaves may take on a brown discoloration; a condition called "Bronzing."

The predatory mite, T. occidentalis, are opaque white when they have not fed recently, but take on the color of the prey they feed on.

The stigmaeid predatory mite, Z. mali, has a yellowish-reddish color and is more pointed at the rear

Spider Mites

There are two dominant species of leaf-feeding spider mites which can be pests of apple in western Washington. They are the European red mite (ERM) and the twospotted spider mite (TSSM).

European red mite overwinters in the egg stage within the orchard on twigs and small limbs. The eggs are very small (1/160 (in diameter), red in color, with a short stalk, called a stipe attached. Eggs hatch during the tight cluster to pink stage, producing immature forms (larvae) which go through three stages before transforming into either male or female adult mites. The larvae are usually red but can also have a greenish cast. The larvae move to young leaves where they feed by inserting their mouthparts into leaf cells to suck out the contents, including chlorophyll. Adults feed in the same manner. The most commonly seen stage during the summer is the adult female, which is about 1/72 inch long, red in color, oval in shape and with strong white bristles on the back of the abdomen. The male is slightly smaller, yellowish red in color, and more slender than the female, with a tapered abdomen. Mobile stages of ERM as well as eggs can be found on both sides of the leaf surface during the summer months. Females live for 15 to 20 days and can lay 30 to 35 eggs. A single generation (egg to adult) can be completed within 10 days in warm weather but may take as long as 3 weeks in cooler weather. Populations can increase rapidly under optimum conditions, usually peaking in late July through mid-August.

Twospotted spider mite overwinters as an orange-colored adult female in the duff at the base of trees and in sheltered sites beneath bark scales. They become active at the half-inch green stage when they feed on leaves, change to a greenish color with two dorsal spots, and begin laying eggs. These eggs are about 1/150 inch diameter, translucent, and usually take several weeks to hatch. The earliest mobile larval stages initially look like eggs with legs. After feeding, they turn pale green to straw color and have two dorsal (back) spots, which give them their name. They molt through several immature stages before transforming into an adult. The female adult is about 1/60 inch long, oval in shape, and can vary in color from pale green to a more typical straw color. There are two distinct dark brown spots on the dorsal side towards the front half, just behind the eyes. The adult male is slightly smaller and has a more tapered abdomen. These summer female TSSM can live for about 30 days and produce 100 eggs during that period. As with ERM, a single generation can be completed within 10 days, which allows for potentially rapid population increase with all stages present at the same time. Unlike ERM, all stages of TSSM are predominantly found on the underside of leaves. Populations normally peak during August.

Although there are some differences in their life histories, the damage caused by both is very similar and researchers have not attempted to differentiate the effects of one species vs. another. Spider mites insert their mouthparts into leaves and suck out the contents, removing chlorophyll in the process. This damage is initially seen as white spotting or stippling of infested leaves. With continued injury, these leaves can then become dull brown in color which is referred to as bronzing. If uncontrolled and allowed to reach excessive density for prolonged periods of time, spider mites can cause damage by impacting one or more of several processes including photosynthesis, transpiration, shoot growth, trunk and limb growth, fruit color, soluble solids, firmness, return bloom, and return fruit set. The treatment threshold that has been used most often in apples is a population density of 30 mites per leaf.

Biological control: Scouting efforts conducted with cooperating growers in the Nooksack IPM Project have confirmed that there are two species of predatory mites which feed on and help to regulate spider mites. These are the western predatory mite, Typhlodromus occidentalis and a stigmaeid mite, Zetzellia mali. It is important to be able to differentiate these beneficial predatory mites from the damaging spider mites as they can be instrumental in containing spider mites below damaging levels. It has been our experience that young orchards which are less likely to support a complex of predatory mites are prone to spider mite flare-ups which require chemical treatment. In general, scouting has shown that older established orchards support a more diverse complex of predatory mites, which usually provide adequate regulation of spider mites, eliminating the need for chemical treatment.

In young orchards or in cases where non-selective use of pesticides has destroyed predator mite populations, it may be possible to establish them more quickly by seeding predators in the orchard. This tactic has not been tested in western Washington, but has been used successfully in other areas to hasten recolonization by predatory mites. Predators may be introduced by taking shoots from an orchard with rust mites and T. occidentalis and placing them in the affected orchard. At least one typh-infested shoot per tree should be used. Orchards with a history of anthracnose should probably be avoided when selecting a source orchard for this technique.

Rust mite feeding can cause bronzing and lengthwise curling of foliage.

Elongated, wedge-shaped Apple Rust Mites.

Apple Rust Mites

Although the apple rust mite can damage fruit and foliage, its major role is as an alternate food source for predatory mites. Rust mites are very small. The adult is medium tan in color and only five one-thousandths of an inch long. They spend the winter as adult females on twigs and under bud scales. As the buds begin to open in the spring, these females feed on the underside of new leaves, and lay eggs which give rise to multiple generations during the summer months. In cooler climates like western Washington, rust mite populations peak once in midsummer, usually in late July to mid-August. Initial feeding damage gives the leaves a silvery appearance, which tends to get browner later in the season. Infested leaves tend to roll lengthwise. If populations become excessive (> 300 mites leaf) fruit size can be reduced and a general disruption of photosynthesis and water imbalance can occur. Rust mite feeding can also cause premature terminal bud set, which may not always be a problem. On light colored cultivars, rust mite feeding can also cause a tan russeting on the calyx end of the fruit.

It is probably only necessary to control rust mites if populations are high in mid to late July (approaching 400/leaf), foliar discoloration is widespread, and there are no predatory mites to help suppess their populations.

The Dock Sawfly larva excavates a neat chamber in the flesh of the fruit.

Dock sawfly

This insect survives primarily on weeds in the buckwheat family within the orchard. These include dock, sorrel, knotweed, bindweed, and wild buckwheat. It completes up to four generations during the growing season. It is only the last generation larval stage which poses a threat to fruit. Fully mature sawfly larvae bore into mature fruit in late September in order to excavate an overwintering chamber. They will often bore several holes into one or more apples before constructing a final chamber. Damage is most commonly seen as a shallow hole about 1/12" in diameter drilled into the cheek of the fruit.