Department of Entomology

Southeastern Apple Production ENTOMOLOGY

European Red Mite

Panonychus ulmi (Koch)

Description

Adult female European red mites (ERM) are bright to brownish red with an elliptical body, and are not much larger than a period. Females have four rows of curved spines on their backs, with each spine borne on a whitish tubercle (these spines can be seen with a hand lens). The overwintering eggs are bright red, spherically shaped and have a distinct white stalk (visible only under magnification) about as long as the diameter of the egg. Summer eggs are translucent.

Adults

Adult female detail

Eggs on twig

Egg

Life History

ERM is the most common and important mite found on apple foliage in the Southeast. ERM overwinter as eggs on twigs and begin hatching just before bloom. Mites then crawl onto leaves where they suck out the juices. Females lay approximately one egg per day. If the female has mated, the fertilized eggs develop into both male and female mites; if not, unfertilized eggs develop into males. Eggs hatch into six-legged larvae. The larvae then pass through eight-legged protonymph and deutonymph stages before becoming adults.

Ordinarily, ERM populations build up slowly during the spring, but under favorable summer conditions they can increase to unacceptably high populations. Hot, dry weather is favorable to population increases of this mite. Nine or more generations may develop per year.

Damage

ERM feed on leaves. Severe mite injury produces browning and loss of color in the leaves (commonly referred to as bronzing). Extensive foliage injury may reduce the quality and quantity of fruit and the following year's return bloom.

The extent of mite injury is influenced by numerous factors: (1) time of the growing season when injury occurs, (2) duration of feeding when injury occurs, (3) vigor and tree cultivar, (4) crop load, and (5) weather conditions.

Excessive foliage injury early in a growing season (May and June) is most detrimental to the trees. Injury at this time may result in excessive fruit drop, and it may reduce return bloom. Midseason (July) injury is less detrimental but with other stress may result in fruit drop, reduced fruit color, and reduced effectiveness of growth regulating sprays.

"Bronzed" trees (on left)

Monitoring and Control

Several beneficial arthropods can help keep ERM and twospotted spider mite populations below damaging levels. The most common in the Southeast are a phytoseiid mite (Neoseiulus fallacis) and the complex of generalist predators (e.g., black lady beetles (Stethorus punctum) and lacewings). However, recent research in North Carolina suggests that neither of these predators overwinters to any significant degree within orchards, so they must be reestablished in orchards in the spring. Hence, practices that delay the buildup of ERM and enable predators to increase before mites become a problem will favor biological control. The two most effective practices are applying a delayed dormant oil spray and avoiding insecticides toxic to these predators.

Monitoring Mite Populations: Use a regular monitoring program to follow the buildup of pest mite populations and to determine if and when supplemental applications of a miticide are necessary to avoid economic damage. Monitor each contiguous block of apples weekly beginning when adult mites first appear (which may vary from mid May to early July). Within each block, examine 5 leaves from each of 10 trees with a visor lens or hand lens. Rather than counting the total number of mites on each leaf, record the number of leaves infested with one or more mites, and estimate the mite density on a per-leaf basis from the table below.

Determining the Need for Miticides: When mite populations reach a density of 5 to 10 mites per leaf (80 to 90 percent infested leaves) decide whether to use biological control or a miticide to prevent mites from increasing to higher densities. Count the actual number of N. fallacis on sample leaves with a visor lens. If the ratio of N. fallacis to ERM is between 1 to 5 and 1 to 15, biological control is possible. For biological control with S. punctum to occur, the ratio should be 2.5 S. punctum to 1 ERM. S. punctum should be sampled by counting the number of adults and larvae observed during a timed 3-minute search around the periphery of mite-infested trees. S. punctum larvae must almost always be present if this predator is to control mites. If neither predator is present at sufficient levels for biological control to occur, and mite populations are between 5 to 10 mites per leaf, apply a miticide.

In areas where Alternaria blotch is a problem on Delicious apples, biological control is usually not an option. In the presence of Alternaria blotch, mite populations must be maintained at very low levels to avoid high levels of Alternaria and premature defoliation. If preventive control measures are not used, a modified threshold level of 1-2 mites per leaf should dictate the need for miticides.

Insect and Mite Management Overview
Insect and Mite Index

Updated March 22, 2007