Turf-feeding critters that don’t mind the cold
Virtually all turfgrass managers have learned of the general agronomic emphasis to put your turf to “bed” for the season with the hopes that it will emerge the following spring in great shape. This emphasis has been primarily on fall reseeding, weed management and fertilizing to stimulate root growth.
Clover mites are mostly active in spring and fall and use their tiny mouthparts to rip open surface cells (note the white spots) when feeding on grasses between 50 and 70 degrees F.
PHOTOS COURTESY OF DAVID J. SHETLAR, PH.D.
Some managers also have to pay attention to the potential of winter disease management, especially the snow molds. What is often missed is education on the insects and mites that make their livings feeding on turf in late fall, during the winter (often under the cover of snow!) and in the early spring.
The primary culprits are clover mites, winter grain mites, bronze cutworms, crane flies (leatherjackets) and even some grub species.
Clover mites
Clover mites are actually relatives of spider mites, but this mite is most active in the fall and spring when temperatures are generally between 50 and 70 degrees Fahrenheit during the day and rarely drops below 25 to 28 degrees Fahrenheit at night. This is actually similar to the spruce spider mite.
Despite their name, clover mites prefer to feed on grasses. They can feed day and night on grass blades where they use their tiny mouthparts to rip open surface cells and extract the cell contents. This results in a blanching or whitening of the foliage of turf.
The most unusual habit of this mite is its need to move from the turfgrass to some nearby permanent structure (e.g., tree trunk, building surface, landscape timber, etc.) to molt or lay eggs. Because of this, most of the damage from this mite appears as blanching of the turf surrounding trees or along the edges of buildings, especially on the predominantly shady sides. Extensive damage is often mistaken for turfgrass mildews (also appears white from a distance) or winter desiccation.
Most homeowners or building managers miss the turf damage, but they notice the mites that often enter basements or lower floors looking for sheltered areas to molt and lay eggs. The mites can cluster by the thousands. In this case, we need to be aware that both turfgrass managers and pest management professionals (PMPs) can be called. Turf managers can treat these mites in turf, but may have issues if asked to treat the building, especially if they don’t have a license for this. PMPs can treat the building, inside and outside, and they can go a way into the turf with their treatments under the guise of a perimeter treatment.
Several types of pesticides can be effective. Pyrethroids like bifenthrin (Talstar), deltamethrin (DeltaGuard), lambda-cyhalothrin (Demand, Scimitar) and beta-cyfluthrin (Tempo Ultra) have clover mites on the label.
Of course, most of the regular miticides also work against this mite, but check the label to ensure that “perimeter pests” and/or “turfgrass” are included on the labels.
Winter grain mites
These are rather strange mites. They not only live and thrive in cold weather; they also have a rather strange body setup. They look like mites with a generally oval body that is dark green-black in color, almost fluorescent red-orange legs, and a strange yellowish spot on the upper side of the abdomen. This is their anus.
While this seems to be a pretty strange arrangement, the mites usually feed upside down on grass leaf blades, so this ensures that their excrement drops away from the body.
Most turf managers never see them, unless they are trained to look at the turfgrass at dusk and into the early night. The mite nymphs and adults hide in the thatch during the day and emerge at dusk to begin a long night of feeding. This mite is also so cold hardy that it often continues to feed under the cover of snow.
Extensive feeding damage results in turfgrass blades that are nearly white and lying over. When this happens under the cover of snow, most turf mangers assume the turf was hit by snow mold. Since these mites are not normal household invaders, they are generally missed until the damage has been done.
Winter grain mites often hatch in October and can remain active all winter when temperatures don’t drop well below freezing for an extended period. If there is an insulating cover of snow that keeps the soil-turf interface close to freezing, the mites can continue feeding and reproducing. In the spring, when temperatures regularly get into the 50 to 70 degree Fahrenheit range (at night), the mites lay special eggs that remain in the thatch through the summer months. Surviving eggs hatch the following fall to continue the cycle.
Treatments are difficult to find as most insecticides don’t list this mite. A few insecticides, like bifenthrin and lambda-cyhalothrin list “mites” on their labels and the winter grain mite qualifies, but other labels specifically state “spider mites,” which does not include the winter grain mite.
My normal recommendation is to ignore the mite damage and use a turf health management program that includes fall fertilization that maximizes early spring growth, which will quickly mask any winter grain mite damage.
Bronze cutworm
This strange cutworm actually engages in hedge betting. The adults fly in September into early October and lay eggs in turf or grassland habitats. In most cases, about half of the eggs hatch within a couple of weeks. The tiny green larvae begin feeding and molt a couple of times before turning a dark brown color with a bronzy sheen.
If it is a mild winter or there is a snow cover that keeps the soil surface temperature slightly above freezing, the larvae will continue to grow. By April, the larvae are about an inch long or longer. At this time, any eggs that survived the winter also hatch. These new larvae feed rapidly and also pass through the green, then brown larval instars.
Winter grain mites have dark green-black bodies and red-orange legs. They feed upside down on grass blades and leave facal matter below them.
The overwintered larvae often complete development by late May. They dig into the soil and remain as a pupa for the summer. The spring-hatching larvae continue feeding into mid- or late June before they pupate. The adults of both groups emerge at the same time in September and October to repeat the cycle.
Occasionally, this cutworm can create large populations that literally mow down the turf under the cover of snow. In the spring, when the snow melts back, inexperienced folks think the turf was hit by snow mold. However, upon closer inspection, one will quickly see that the turfgrass blades and stems are gone, not just lying over. A little digging into the thatch will often reveal the fecal pellets produced by the caterpillars and the caterpillars are also fairly abundant.
Most turf pros would be tempted to apply an insecticide upon discovering damage by bronze cutworms, but several factors should be considered. Is it late in the spring? Are the larvae still actively feeding? Most insecticides registered for turf caterpillar control will also control bronze cutworms, as long as the larvae are still feeding.
Another common question is, “Should I apply a preventive application next fall if I had damage this spring?” In general, the answer is “no”. Major damage from bronze cutworms is a rare event and even more rare to be repeated.
The common crain fly can have two generations per season with flights occurring in the spring and in the fall. Lawn care pros are seeing more of them in New York and Michigan.
Crane Flies (and their larvae, leatherjackets)
Cool-season turf managers occasionally experience overwintered turf that appears to have been severely damaged by crane fly larvae, leatherjackets. The normal routine would be for the turf manager to discover some patches of turf that didn’t green up in the spring. When digging around in this patch of dead turf, the elongated, gray-to-tan larvae would be found, often in large numbers.
There are several species of crane flies. The larvae of the European crain fly and the common crane fly do their damage in the spring.
In the past, these were native crane flies, and in spite of the turf managers’ proclamations, the turf was likely killed the previous season by disease or grub attack. The fall-flying crane fly adults detect this dead patch of turf, lay eggs and the larvae feed in the late fall and early spring on the dead and decaying plant material. This will likely happen this next spring across much of our cool-season, eastern and mid-central zones because of the extensive billbug damage that killed many lawns. We saw a pretty large flight of adult crane flies in October and they will have laid their eggs in the dead turf.
On the other hand, we continue to see the spread of the European crane fly species. The European crane fly and its close cousin, the common (or marsh) crane fly were discovered in Ontario Province of Canada some years ago and since that time they have crossed over into New York and into Michigan. Both populations are on the move and will soon be discovered in surrounding states.
Unlike our native species that have a pretty strict taste for decaying plant material, these invasive species dine on the living grass blades. Even worse, the two species are seasonal specialists. The European crane fly generally flies in the fall (September and October) and its larvae do most of their damage the next spring before remaining dormant for most of the summer.
The common crane fly can have two generations per season with flights occurring in the spring and in the fall (during the flight of the European crane fly). Damage to lawns and sport fields can appear in late fall, but is more common in the spring. The damage appears as a gradual thinning of the turf.
When the larvae are very numerous, a secondary annoyance can occur. Folks describe that walking across their lawns results in the sensation of walking over eyeballs: pop, pop, pop.
Where native crane flies appear, most turf entomologists recommend letting them finish their job of removing the dead turf matter. Where the invasive crane flies have become established, a curative treatment can be made first, but a preventive strategy is probably a better long-term approach.
If you discover lots of crane fly larvae and significant thinning of the turf, products containing clothianidin (Arena and Aloft) or dinotefuran (Zylam) have provided the best curative control. After that, it’s probably good to take a preventive approach by making applications in the fall, after the fall adult flight has finished. Products containing bifenthrin (Talstar), carbaryl (Sevin), chlorantraniliprole (Acelepryn), clothianidin (Arena, Aloft) or trichlorfon (Dylox) have provided the most consistent results with fall applications.
The Green June beetle quits feeding early in the fall and then burrows into the earth. They return to the surface in the spring and generally feed at night.
Changing white grub populations
Many of the traditional cool-season turf zones are experiencing some strange white grub activity, which seems to be caused by one of three of the white grub species. First, Japanese beetle populations have dropped off dramatically in the northeastern and Midwestern states where it has been well-established for years. On the other hand, the European chafer and Oriental beetle species continue to expand their ranges westward and southward. And, the native green June beetle is moving northward. On top of this, we are seeing regional outbreaks of our native May-June beetles.
The European chafer is a true cold-season grub. It is usually the last grub to go down in the fall and the first to surface, often in February. So, if you have skunk or raccoon digging that persists into November, be sure to check out the grubs and determine the species. Likewise, if grubs appear in February or March, suspect European chafers.
The best way to identify European chafer larvae is by its raster pattern. Each grub species has a different pattern.
The green June beetle can be a puzzle for folks who are not experienced with it. It stops feeding fairly early in the fall and digs a burrow into the soil. When the soil warms in the spring, the large larvae clean out this burrow, which can result in dozens of small molehill-like mounds on the surface. These cleanouts can occur in March or April, often the day after a spring rain shower.
Remember that green June beetle larvae come to the surface at night to feed on grass blades, so use caution when considering curative treatments. These large grubs generally die on the surface of the turf and having hundreds of big, smelly, rotting grubs on the surface of a lawn is not appreciated. You would be better served by waiting until August to control the new larvae as they appear.
The cool-season species of May-June beetles usually have two to three-year life spans. Because of this, you can find their larvae almost any time you dig into the turf profile. In some states, species of these beetles are beginning to reappear in sufficient numbers to damage the turf.
The larvae European chafer is the last species to burrow in the fall.
My thoughts are that we have changed the types of grub insecticides that we commonly use and, in general, we have reduced applications. May-June beetle larvae were highly sensitive to residues of no-longer-used organochlorine (especially Chlordane), organophosphate and carbamate insecticides. When it take two to three years to complete development, exposure is highly likely to take the populations out. In any case, be sure to check any damaging grub population to see which species is present. You might be surprised that they are no longer the traditional Japanese beetle or masked chafer grubs.
David J. Shetlar, Ph.D., (aka Bug Doc) is professor of urban landscape entomology, The Ohio State University, Ohio State Extension & Ohio Agricultural Research and Development Center.
