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INSECT AND MITE PESTS
European red mite (ERM) was introduced into the United States, from Europe, sometime before 1911. Since that time, ERM has become one of the most common and important pests of fruit grown in the northern United States. ERM is reported on elm, apple, pear, peach, plum and prune, as well as other deciduous trees.
ERM is usually rusty in color, with newly emerging females being bright velvety red, changing with time to dark red-brown. Males are dull green to yellowish brown. Females are more globular shaped; males are narrower with a more pointed abdomen. Eggs are red-orange and have a hairlike projection on the upper side.
Overwintering occurs in the egg stage on twigs and branches of the host. Egg hatch usually occurs at or just before pink stages. The first mite stage (instar) has 6 legs and succeeding instars have 8 legs. Development from egg to adult may take from 1 to 3 weeks, and is very temperature dependent. There may be 6-8 overlapping generations per season. Summer eggs are laid on foliage. Winter eggs are laid on twigs and branches.
Damage due to ERM is caused by sap removal. ERM have a piercing-sucking mouth which they insert into the plant tissue. This feeding may result in bronzing and off-colored foliage. If intense infestations are present, defoliation and undersized, poorly colored fruits may result.
SCOUT: For ERM's by examining the undersides of leaves with a hand lens. Look first near the midrib for very small purple or red mites. Try to estimate the number you find on each leaf.
RECORD: The number mites per 100 leaf sample.
ACTION THRESHOLD: An average of 500 mites per 100 leaves in early season (until April 1), 1000 mites per 100 leaves during midseason (April 1 to June 1), and 1500 mites per 100 leaves late in season (After June 1). (See Appendix 3 if degrees days are available).
Twospotted Spider Mite
Twospotted spider mite (TSSM) is a pest of many crops worldwide. TSSM populations in apples are favored by hot dry weather and when predators have been destroyed by pesticides.
Twospotted spider mite
TSSM is light to dark green with two distinctive black spots on the abdomen. Eggs are spherical and clear when first layed. After hatching, the larva has three pairs of legs, but later stages will have four pairs. Male TSSM are smaller with more pointed abdomen than the females.
TSSM overwinter as full grown females under the bark or in leaf litter. In the spring and early summer, mites will feed on weeds and grasses, in mid summer they move into trees. Development from egg to adult may take no more than three weeks. There may be five to nine generations per season depending on the weather.
Damage due to TSSM is by sap removal and is similar to that of ERM.
SCOUT: Examine the undersides of the leaves with a hand lens. Look first near the midrib. Try to estimate the number found on each leaf.
RECORD: The number mites per 100 leaves.
ACTION THRESHOLD: An average of 500 mites per 100 leaves early in the season (until April 1), 1000 mites per 100 leaves in midseason (April 1 to June 1), and 1500 mites per 100 leaves late in the season (after June 1). If day degrees are available, see Appendix 3.
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