Mites already?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

Last season, we reported high levels of two-spotted spider mites (TSSM) and European red mites (ERM) in cherry and apple orchards around the state. Because of their late appearance, we predicted that these mites would not cause economic injury last season. However, our main concern was how these late-season mite populations would impact the 2009 production season.

ERM adults laid eggs on spur shoots and limb crotches last fall, and these eggs will serve as the starting point for this year’s spring mite population. Growers that did not apply a 2008 miticide in orchards with high ERM populations should have conducted apple pre-bloom monitoring for mites this season, and if ERM eggs numbers were high, a pre-bloom miticide application should have been made. If scouting reports indicate a high level of mite eggs and no miticides were applied earlier this spring, growers will likely battle ERM on apple fruitlets as nymphs can build to high numbers and can feed extensively.

Late season populations of two-spotted spider mite (TSSM) provided a slightly different situation. In cherries, post-harvest management of TSSM is common, particularly with the old miticides and their limited PHI’s. Control of TSSM is important in maintaining healthy foliage into the fall and is important for sustainable fruit production the following year. Overwintering adults and immatures move to rough areas of tree bark or in leaf litter on the ground in early to mid-September and once this overwintering migration begins, control actions are no longer warranted. Orchards with high TSSM populations in August should have been marked for scouting this May or June, which is much earlier than would be warranted under typical conditions. We have seen high populations of TSSM in both sweet and tart cherry this spring, and these orchards will likely require a pre-harvest miticide application. Most TSSM mites have been observed on cherry leaves on the inner canopy. As the tree grows and foliage expands, these mites will move out into the canopy. Growers should be sure to investigate many leaves on many trees as TSSM mite numbers look extremely high in spring when limited cherry foliage is present.

Additionally, we want to remind growers about rotating miticide compounds. Mites can develop resistance to commonly used miticides, and growers should choose their products based on rotation as well as price. Because of costs of miticides, the most economical option is appealing, but growers should keep in mind that overuse of a particular compound will likely lead to resistance issues. Also, miticide availability has been in question, so growers should call in advance if they know they will be applying a miticide in the coming weeks. We are fortunate to have a number of miticide products available for tree fruit, and a list is provided in Table 1 below.

We also recommend that scouts and growers document the levels of predacious mites in orchards this spring. If healthy populations of mite predators exist, they will continue to feed on ERM eggs and nymphs. To report on predacious mites, scouts and growers should collect a 100-leaf sample and count the numbers of each of the predator mite species. The three most important predaceous mites are Amblyseius fallacis (Phytoseiidae), Agistemus fleschneri (Stigmaeidae), and Zetzellia mali (Stigmaeidae) (see “A Pocket Guide for IPM Scouting in Michigan Apples” – E-2720 for pictures). Predaceous mites are smaller than adult ERM, but they can be seen with a hand lens and typically move very quickly across leaf surfaces.

Compound trade name***
Mode of action
Life-stage
activity
Mite species controlled**
Residual activity
Savey, Onager,
Apollo, Zeal
Mite growth inhibitors
egg/larvae
TSSM, ERM
8-10 weeks
Nexter, Portal
Electron transport Inhibitors
(METI I)
motiles*
TSSM, ERM, PNM
6-8 weeks
Acramite
 
unknown
motiles*
TSSM, ERM
6-8 weeks
Kanemite
Electron transport Inhibitors (METI III)
motiles*
TSSM, ERM
6-8 weeks
Agri-mek
Chloride channel activator
motiles*
TSSM, ERM
8-12 weeks
Envidor
Lipid synthesis inhibitor
eggs, motiles*
TSSM, ERM, PNM
8-10 weeks
Vendex
ATP synthesis inhibitor
motiles*
TSSM, ERM
4-8 weeks

* Motile forms include mite larvae, nymph and adult stages.
** TSSM - two spotted spider mite, ERM – European red mite, PNM – plum nursery mite.
*** Check the label to determine the specific fruit crops that each compound is labeled for use.

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