Noticed Some Sorry Looking Strawberry Plants?

By Mira Danilovich
District Horticultural Agent
Michigan State University Extension
West Central Michigan

Now that we are getting into the harvest season, all of a sudden people started calling about the "sorry looking" strawberry plants. They have not reached the normal size, look stunted...leaves are some what "off color" and crinkled... even the fruit is showing signs of deprivation and appear "seedy". Close examination of several fields in the northern part of West Central region singled out two tiny pests capable of causing very heavy damage. I am talking about two spotted mites ( Tetranychus urticae ) and cyclamen mites ( Phytonemus pallidus ). Two spotted mites invaded fully expended, older leaves while the cyclamen mites occupies the newly expending tissue.

Two spotted mites are usually found on the underside of the leaves; they are barely visible with the unaided eye. Mites are almost transparent to cream in color with two dark spots on a side. They are exceptionally active during the hot and dry weather. This pretty much describes the conditions we had prior to the latest storms. Population build up has been rapid; so rapid that we do not have typical "hot spots" but widely spread heavy mite infestation. The older leaves exhibit characteristic symptoms of the mite damage: curling, yellow stippling, some webbing on the underside of the leaves.

Cyclamen mites are serious pest of strawberries. Mature mites are soft-bodied, shiny and have pinkish-yellowish color. Eggs are big, almost translucent and grouped in large masses along the mid rib of the new, still unfolded leaves. As the leaf unfold, the female moves down to the next developing leaf. Cyclamen mites needs certain humidity level which they find in the folded leaves. I have found significant number of eggs, nymphs and adults on the plants. Though it might appear early I believe that they have reached their peak at this time. This is yet another fine mess El-Nino got us into!

The most recent cool weather has suppressed their activity to some extent. Still, in most cases miticide application is necessary. There are several good miticides labeled for use on strawberries. However, this late in the season with harvest underway, there is only one choice: Brigade. What makes it preferred choice is that there is no requirement for pre harvest interval. Use a lot of water (200 gallons) with high enough pressure (100 psi ) to insure good coverage and control.

June 3, 1998

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Last Revised: 3-5-99