Managing mites in apples

John Wise, Michigan State University Extension, Department of Entomology; Nikki Rothwell<rothwel3@msu.edu> and Amy Irish-Brown<irisha@msu.edu>, Michigan State University Extension - July 01, 2014

European red mites are the predominant mite pest species of Michigan apples, and without biological control, miticides are often needed to prevent economic injury.

European red mites cause injury to the plant by piercing the top layer of the apple leaf and extracting the content out of the epidermal cells, resulting in leaf bronzing and necrosis. Excessive European red mite feeding can lead to leaf abscission, poor quality fruit and add overall stress on tree health. In addition to European red mites, two-spotted spider mites can occasionally be a problem in hot, dry years.

Monitoring

Scouting for mites should begin early enough to determine if European red mite populations are at a level that could cause economic injury. One method of monitoring motile populations of mites consists of sampling 25 intermediate-aged leaves at three to five sites within a block. Count the number of leaves that have one or more European red mites or two or more two-spotted spider mite motiles from each sample, and follow the binomial charts to estimate the number of mites per leaf. Treatment threshold for European red mites is five to seven mites per leaf through July, and then 10-15 mites per leaf in August.

Binomial sampling charts for two-spotted and European red mites

Number of leaves with two or more mites	Percent of leaves with two or more mites	Average number mites per leaf
Two-spotted spider mites
10	40	2.1
12	50	3.0
15	60	4.1
17	70	5.4
20	80	8.5
21	84	10.1
European red mites
10	40	0.7
12	50	1.1
15	60	1.6
17	70	2.6
20	80	4.7
22	90	11.4
24	95	15.3

Examine 25 leaves per site at each of three to five sites per block.
Charts are adapted from “Orchard Pest Management” published by “Good Fruit Grower,” 1993

Biological control

Conservation of predator mites in apple orchards is critical to control European red mites. The three most predominant predaceous mites found in Michigan are Neoseiulus fallacis (Phytoseiidae), Agistemus fleschneri (Stigmaeidae) and Zetzellia mali (Stigmaeidae). Predaceous mites are small, but can be detected with a hand lens. Predaceous mites also move very quickly across the leaf surface compared to European red mites. Carbamate and pyrethroid insecticides are highly toxic to mite predators, thus should be avoided if possible.

Chemical control

To control mites with miticides, good coverage of the tree canopy is critical. Some miticides, like Savey, Apollo and Zeal are active primarily on egg and larval stages, thus should be applied before mite numbers build beyond thresholds. Agri-mek is active on motile stages, but is also applied early because of its long in-plant residual. Other miticides, like Portal XLO, Nexter, Kanemite and Vendex, have primarily contact activity on motiles and should be applied after threshold populations have been reached. Envidor is active by contact to all life stages, but is not known to have as fast knock-down as some adulticidal materials. Because of resistance concerns, miticides of similar mode-of-action should not be applied consecutively or more than once per year. Please see table below for more information on miticides.

Miticides used for mite control

Compound trade name	Mode of action	Life-stage activity	Mite species controlled**	Residual activity
Savey (28), Zeal (14), Apollo (45)	Mite growth inhibitors	Egg/larvae	ERM, TSSM	8-10 weeks
Nexter (25), Portal (14)	Electron transport inhibitors (METI I)	Motiles*	ERM, TSSM, ARM	6-8 weeks
Acramite (7)	Unknown	Motiles*	ERM, TSSM	6-8 weeks
Kanemite (14)	Electron transport inhibitors (METI III)	Motiles*	ERM, TSSM	6-8 weeks
Agri-mek (28)	Chloride channel activator	Motiles*	ERM, TSSM	8-12 weeks
Envidor (7)	Lipid synthesis inhibitor	Eggs, motiles*	ERM, TSSM, ARM	8-10 weeks
Vendex (14)	ATP synthesis inhibitor	Motiles*	ERM, TSSM	4-8 weeks

* Motile forms include mite larvae, nymph and adult stages.
** TSSM - two spotted spider mite, ERM – European red mite, ARM – apple rust mite.
Pre-harvest interval listed following each trade name (xx days).

Drs. Wise and Rothwell’s work is funded in part by MSU’s AgBioResearch.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).