One of the most damaging aspects of mites is that they arrive so early in the season. At a time when other pests are still latent, mites can bloom and engulf a lawn or turfgrass facility. If they are not countered early, they can devastate the grass.
Whitney Cranshaw, professor and extension specialist in entomology at Colorado State University, says that although damage from turfgrass mites can be severe, these pests can be managed successfully even after an outbreak. It requires vigilance early in the spring; once they are detected, quick action can save the grass.
There are two species of mites that are damaging to turfgrass in Colorado, Cranshaw says, and they both occur throughout much of the nation. They are pests, however, more on cool-season grasses in central and northern tiers of states. Mites are very small but still discernable with the naked eye; a magnifying lens should be used to properly identify them. Mites are arachnids more closely related to ticks than spiders.
The clover mite (Bryobia praetiosa) is smaller than the head of a pin and distinguished by its reddish to greenish color, and its two long front legs. One of the ways it is discovered is it leaves reddish streaks on clothing after someone has come in contact with infested grass. Another is by the damage it does to grass. Mites use piercing-sucking mouthparts to penetrate leaf cells and then feed on the cell contents. They basically destroy the grass leaf blade and desiccate the plant. Patches of grass that have a bleached appearance very early in the spring are likely caused by mites.
“Where they are usually an issue is where you have drying problems in the grass,” says Cranshaw. They favor grass that is on an exposed southern slope or other hot spot that dries out quickly. They also usually occur within 20 feet of a vertical surface, such as a house or tree, because that is where they go to lay eggs. The red, round eggs can be found in the cracks of building walls or tree bark, detectable with a 10X hand lens.
The Banks grass mite (Oligonychus pratensis) is a lighter color, usually a yellow or green, than the clover mite, and emerges later in the spring. It also is a significant pest in broadleaf plants, including weeds, and also chews up the leaf blades. Where the clover mite tends to leave bleached looking pockets of lawn, the Banks grass mite can leave an entire section of lawn skeletonized. This occurs especially on south-facing slopes, because it also is attracted to grass that dries out there first.
Cranshaw says the brown wheat mite (Petrobia lateens) occasionally damages turfgrass, but is not enough of a pest to warrant control measures. It is similar in appearance to the clover mite.
The first element in the prevention or treatment of turfgrass mites is early detection. Check first in the hottest, most-exposed parts of the lawn or facility where reflected sunlight can dry out adjacent grass and provide a vertical surface for clover mites. The two species can occur in the same area.
The next step is to get water to those sites that have dried out and attracted mite infestations. In areas where that have experienced outbreaks in previous years, it is wise to have irrigation systems prepped and ready as early as possible. Mites will proliferate and kill the dry grass quickly, but irrigation will revive the grass and create a less-favorable feeding ground for the pests.
Cranshaw notes that his primary chemical control measure for mites, chlorpyrifos (Dursban), is no longer registered for this purpose, though existing stocks can still be used. It was highly efficacious, and in his trials he has seen nothing as effective.
The most effective remaining miticides in his testing are the pyrethroids bifenthrin (Talstar) and lambda cyhalothrin (Scimitar), Cranshaw says. Both are liquid formulations that should be sprayed on in spot applications, only on affected areas and areas where grass is the driest. One application should be sufficient, he says, though a second application could be made within a couple of weeks if the first treatment isn’t effective. A fall outbreak is rare, and does not usually require treatment other than irrigation.
“I’ve tried every chemical I can think of,” Cranshaw says, and the pyrethroids are the best he can find that are registered for the use. He emphasizes that irrigating the grass early generally suffices to make it mite-resistant. Some Web sites on mite control indicate that organic compounds such as insecticidal soaps and horticultural oils may help, as can high-pressure water sprays directed at the infested sites.
Due to their need to shed skin and lay eggs in other areas, mites can invade homes and become quite a nuisance. It is known to send large populations into a house, so early control can avert not only lawn problems, but indoor invasions as well. Once they enter homes they can be deterred by powders such as diatomaceous earth and baking soda sprinkled across their path.
Don Dale resides in Altadena, Calif., and is a frequent contributor to Turf. He has covered the green industry for more than 10 years.