Posted by: Mary Small, Jefferson County Extension
Eriophyid mites are one of the most curious creatures found on landscape plants. Their feeding causes a variety of (and often colorful) plant injury. Deformities, blisters, galls, pockets, velvety patches, silvering and russeting are common descriptors. Damaged tissue may remain green, but I’ve seen white, pink, bronze and/or red colors.
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| Erineum mite on viburnum |
Eriophyid mite injury does not usually affect plant health. Exceptions include mites that transmit viruses, such as rose rosette or situations where plants are heavily infested and/or already stressed from something else.
Plant damage may appear shortly after bud break, when the mites emerge from their overwintering sites on or near the host plant and begin feeding on new growth. Depending on the mite, more generations can appear throughout the growing season.
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| Russet mites on tomato leaf |
Most plant owners or managers find the damage from these miniature “walking carrots” a bit disconcerting because of the odd shapes, appearance and colors. It almost looks like some alien invasion has taken place. What I find disconcerting is the mites can be hard to find because of their size (1/100”) and well, yes, the age of my eyes.
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| Eriophyid mite damage to spruce |
On top of that, some of the injury looks pretty similar to that from herbicide or freezes. Telling the difference between mite damage and these environmental problems can be pretty tricky. Finally, I want to know where the heck the mites go when the plant tissues start to dry out. I save the damaged samples to show our volunteer clinicians. But if the infested plant has started to dry, the critters disappear into thin air (well, that’s how it seems!) I have always supposed they found greener pastures in the carpet or on someone’s desk.
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| Eriophyid mites on maple leaves |
When management is needed, (and it’s often too late for that), there are several options. Sometimes the plant obliges the homeowner and drops the offending part (like ash flower galls). If the tissue remains on the plant, it can be pruned out. Herbaceous plants with heavy infestations (such as a tomato) can be pulled. Soaps, oils, kaolin clay, neem oil and welirang are some of the “softer” chemical options. But they need to be applied while mites are still moving about. Once gall-makers have finished their creations, it’s too late to treat. Time for us to sit back and admire their handiwork!