European Red Mite

European Red Mite (Panonychus ulmi) a major tree fruit pest attacking apples, stone fruits, and pears, is considered by many growers throughout Pennsylvania to be one of the most important apple pests. The mite was introduced into North America from Europe in the early 1900s and is now established in most fruitgrowing areas.

Eight-legged females are 1∕64 inch long, bright red, and have four rows of white hairs on their backs. Males are smaller, lighter in color, and have pointed abdomens. The adult female mites are brick red with white spots at the base of six to eight hairs on their back. The male mite is more slender and lighter in color than the female, with a more pointed abdomen.

Eggs are red, globular and somewhat flattened onion shaped with a slender stalk on the upper side. European red mites overwinter as eggs laid in roughened bark around the bases of buds and spurs on small branches. During the summer eggs are laid on the underside of leaves. Egg hatch in the spring is closely correlated with bud development and begins close to the tight cluster stage. During the summer, eggs require 7 to 14 days to hatch.

European red mites are rarely a problem on backyard apple trees. Predatory mites, ladybird beetles and the six-spotted thrips help to maintain these European red mite at nondamaging levels. This mite is considered a secondary pest, it typically only builds to damaging levels after its natural enemies have been depleted by insecticide applications used to control codling moth or other pests. Minimizing insecticide usage and selecting insecticides that are least toxic to beneficial organisms will help to minimize problems with this mite.

Life Cycle : The European red mite passes the winter in the egg stage. Eggs are usually laid on the lower sides of small branches and twigs. They are often found around the forks of two branches, in crevices and other rough areas. Egg hatch begins at about the tight cluster to pink stage of Red Delicious development and is largely complete within in 7 to 10 days.

The larvae move to young leaves to feed. Immature mites often rest and feed more extensively on the bottom side of the leaves, but adult mites inhabit both surfaces. Although mites feed on newly expanded leaves early in the season, they are more likely to be found on hardened-off foliage when it is available.

The sex of the mite can be determined at the deutonymphal stage when females are already larger and more oval than the males, but the difference does not become obvious until the adult stage. The first adults appear around petal fall on apple. Males emerge first. The male waits near a quiescent female until she emerges and mates with her immediately. After about two days, females begin to lay eggs. A female mite lives 15 to 20 days and lays 30 to 35 eggs on average. Eggs from unfertilized females produce only males, by arrhenotokous parthenogenesis, but eggs from fertilized females produce both males and females. Eggs are deposited on both sides of the leaf but are concentrated near veins and midribs. In hot weather, they can complete their life cycle in as little as 10 days, though it can take up to 25 days in cooler weather. There are 6 to 8 generations per year, which overlap more as the season progresses. Populations usually peak in late July or August, although the peak is probably modified by pesticide use patterns.

When mite populations reach high levels, they can disperse by a process known as “ballooning.” Mites, sometimes in great masses, crawl to a high point or a tip of a branch and raise the anterior part of the body. The mite spins a silken thread, which is caught by air currents, taking the mite along with it. This is one of the primary means of mite dispersal to nearby trees where canopies do not overlap.

Females start laying overwintering eggs in mid-August to September. An over-exploited food resource (i.e., badly bronzed foliage) can lead to earlier deposition of overwintering eggs. Females usually lay eggs on the bark, but when populations are high they sometimes deposit them in the calyx end of the fruit. Although European red mite does spin webbing, it does not do so to the same extent as do twospotted or McDaniel spider mite.

Damage : Although a pest of all tree fruits, apple and plum suffer most severely. Injury is caused by the feeding of all stages on the foliage. The lower leaf surface is preferred. Under high populations both surfaces are fed upon. The injury is caused by the piercing of the cell walls by the bristle-like mouthparts and the ingestion of their contents, including the chlorophyll. The injury results in off-color foliage which in severe cases becomes bronzed as compared to uninfested foliage.

The leaf efficiency and productivity is directly affected. Heavy mite feeding early in the season late June and early July not only can reduce tree growth and yield but also drastically affect fruit bud formation, and thereby reduce yields the following year. Additionally, mite injured leaves will not respond to growth regulators applied to delay harvest drop.

Monitoring: From the dormant period up to early pink, overwintering ERM eggs may be evaluated. Select at random 5-10 trees in an orchard block and inspect small branches using a magnifier. Close attention should be given to the bases of twigs and spurs.

Control:European red mites are rarely a problem on backyard apple trees. Predatory mites help to maintain the European red mite at nondamaging levels. This mite is considered a secondary pest, as it typically only builds to damaging levels after its natural enemies have been depleted by insecticide applications used to control codling moth or other pests. Minimizing insecticide usage and selecting insecticides that are least toxic to beneficial organisms will help to minimize problems with this mite.

Overwintering mite eggs should be controlled through the use of a delayed-dormant oil treatment, anytime between just before bud swell until 12 mm green. Control with dormant oil improves the closer to egg hatching.

Management of mites during the growing season is based on scouting and the use of miticides or summer oil treatments as needed. Often when heavy summer infestations exist, a second miticide treatment may be required 10 to 14 days later. Horticultural oils provide an alternative to traditional synthetic miticides, are able to kill all mite life stages, and are less toxic to the applicator. While effective control can be obtained with summer horticultural oil treatments, caution is advised as these may be incompatible with some other pesticides within seven to ten days of application, are phytotoxic at higher temperatures, and may affect fruit finish on some varieties.

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