Insects and diseases that damage turfgrass can often be an issue on athletic fields. Some pest problems are relatively mild and can usually be tolerated without application of a pesticide. The management level on the athletic field in question will in many cases guide whether disease pressure is an issue. With insects, however, it can be more difficult to predict when and if they’ll be a problem.
Insect management on turfgrass can be a challenge in that many of the insecticides are more effective if applied prior to injury to the turfgrass (for example, a July application to control grubs feeding in August or September). But given the costs and the controversy with pesticide usage, it’s not practical in most cases to blanket apply preventative pesticides. There are some general guidelines for determining if insecticides are warranted. For example, if you’ve had a history of feeding damage, or if the turf is more than a few years old and has an extensive thatch layer. Here are some common insect pests found in turfgrass:
- Bluegrass billbug: The larvae have a white body and tan head, but are legless (as opposed to white grubs, which have three pairs of legs). These tend to be more of an issue on Kentucky bluegrass fields. Ryegrass and fescues contain endophytes, which provide some degree of protection against billbug. The female deposits eggs next to the crown of the plant and when these hatch, one of the first things eaten is the meristem of the plant (thus growth ceases). The appearance of the infestation from a distance mimics drought and usually occurs in June, about the time that temperatures are warming and the soil is drying out. So, oftentimes billbug damage isn’t detected immediately. Upon closer inspection, the impacted plants will have a frass material in and around the crown. Control of billbugs is best achieved with a May application of either chlorantriniliprole, clothianidin, imidacloprid or thiamethoxam.
- White grubs: These are the larvae of beetle species, most often Japanese beetle or northern masked chafer, though there are other species. The larvae reside in the soil and as they grow they feed on the organics around them, including the roots of turfgrass. If the number of grubs infesting an area becomes too large, the feeding damage to the roots can become quite severe; you’ll notice the grass beginning to wilt regardless of the moisture status of the soil. When this happens, you can usually lift the turf up as though it’s freshly laid sod, as the root system has been severed. Damage from grubs can be quite extensive. An ironic thing about grub control is that seeing large numbers of adults in early summer doesn’t necessarily predict that you’ll have a grub problem in late summer, since the female can deposit her eggs elsewhere.
- A better predictor of whether you may have a grub problem is the age of the turf and the amount of thatch. Also, beetles prefer healthier turf in which to lay their eggs, so the better you are at managing the field, the more susceptible it may be to grubs. To control white grubs and billbugs, apply either clothianidin or chlorantriniliprole in May. For white grubs, apply either of the products just mentioned, or halofenozide, imidacloprid or thiamethoxam in July.
- Earthworms: Though they’re considered beneficial, especially for soil structure, they may occasionally interfere with play by pushing a large number of castings onto the surface. With that being said, control isn’t generally recommended. When there’s severe disruption of the surface due to casts, either sand topdressing or the use of tea seed meal (Early Bird 3-0-1 natural organic fertilizer) can reduce the number of earthworms on the field.
- Ants: They don’t feed on the turf — the disruption is with the mounds they build. A large number of mounds can interfere with play in some cases. They can also be an issue on infield skins. In these cases, individual mounds may be treated.
One of the main reasons that a stand of turfgrass becomes diseased is that it’s stressed. One of the main reasons that turf becomes stressed is when it’s mowed short. Closer mowing results in more frequent mowing (if you’re doing it correctly), and more frequent mowing results in more frequent injury, thus more stress, thus more disease. This is why fungicides are very important in golf and nearly nonexistent in lawn care. Sports turf falls somewhere in the middle – you may have fields that are (relatively) high-cut tall fescue where disease might never be an issue. On the other hand, if you have perennial ryegrass or Kentucky bluegrass mowed short (such as for a college or pro stadium), then disease may be enough of an issue that you have or should consider the use of a preventative fungicide program.
Turfgrass disease diagnosis can be difficult. Diseases like red thread, dollar spot and brown patch are easily identified in the field because they have obvious or striking symptoms. But grey leaf spot and Pythium can be more difficult to diagnose.
Resistance to fungicides among pathogens is a serious issue, thus care should be taken when putting together a disease management program.
Some diseases are cosmetic and/or cause damage that the turf can recover from over time. Some cause more serious problems that will result in loss of cover (and the need to reseed or resod) and may compromise the safety of the playing surface. Below are three diseases in particular to be aware of:
- Gray leaf spot: This can be a particularly devastating disease and causes rapid blighting of the leaf tissue. Gray leaf spot is most often observed on perennial ryegrass, although tall fescue can also be affected. It occurs after prolonged periods of hot, rainy weather and tends to most frequently be observed in late summer. Stresses such as compacted soil or heavy traffic also favor this disease. When examining the leaf tissue, there may be gray lesions with a brown border. Affected leaf blades often twist as they die back from the leaf tip. Fungicide recommendations for gray leaf spot control are evolving – check your local university extension program for the latest recommendations. Unlike other diseases, effective control of gray leaf spot involves several applications of different classes of fungicides. The extent of disease pressure will greatly affect the performance of fungicides. But if the disease is in an advanced state by the time sprays are started, then control will likely not be very effective. Thus, application of fungicides should begin prior to the onset of gray leaf spot (usually the start of August) and continue every one to three weeks as needed until favorable weather conditions subside. Resistance to fungicides has been identified here, so rotation of products is critical. The use of tarps tends to exacerbate grey leaf spot issues.
- Pythium: Usually air temperatures need to be in the 90s during the day and in the 70s at night for three consecutive days before Pythium occurs. It causes circular spots of plants with a slimy appearance that mat together. Cottony mycelia may be visible in the morning. The spread of Pythium is rapid and tends to follow surface drainage or mowing patterns. There are many fungicides on the market for both preventative and curative control. If you see Pythium, the key is to act fast. It’s easily controlled with a fungicide, but left untreated can affect large areas of turf very rapidly (sometimes within 24 hours).
- Brown patch: This is a patch disease that produces a distinct “smoke ring” at the outer edge when it infects close-mowed creeping bentgrass. This classic symptom isn’t as distinct on high-cut turf. There also may be a frog-eye pattern to the affected turf. Hot temperatures (80 to 95 degrees) and high humidity also favor this disease. It’s most commonly seen on tall fescue and perennial ryegrass. There are several preventative and curative fungicides registered for its control.
- Red thread: This disease often manifests in foggy conditions with temperatures between 65 and 75 degrees after seven to 10 days of wet, overcast weather. It looks much more serious than the damage that’s actually caused. It doesn’t form a patch, rather it’s an intermix of living and dead leaves. Symptoms include a pinkish to red hyphae on the leaf. There may be 5- to 10-millimeter red masses that grow out of the leaf end and a pinkish to red cottony mass that grows on the leaf blades. The damage occurs on the leaf blades, not the crown, and thus in most cases the turf can quickly recover.
- Dollar spot: More money is spent on fungicides for the control of dollar spot than for any other disease. But most of this expenditure is for fairways and putting greens on golf courses. Keep in mind that high-cut turf is vulnerable to dollar spot (and the spots are a bit larger). Usually, high-cut turf isn’t treated with a fungicide and/or nitrogen is applied to help the grass grow out of the infestation. On high-maintenance fields, you may have an issue that requires use of a fungicide. On lower-maintenance fields, application of nitrogen will usually allow the turf to recover. A telltale sign is to look for dollar-spot size blighted areas; on individual leaves, look for hourglass- shaped lesions. There may be cobweb-like white hyphae over brown dew-moistened turf in the morning. Dollar spot is most frequently observed when temperatures are in the 60- to 80-degree range. Symptoms can appear when it’s as hot as 95 degrees. Excess thatch, poor air circulation, shade and low fertility also favor dollar spot.
- Rust: A ubiquitous disease of perennial ryegrass, it’s usually found in fall months (particularly if there’s any amount of shading of the turf). Conditions that seem to favor rust are four to eight hours of high humidity with temperatures in the 70s, followed by eight to 16 hours of high light, slow drying and temperatures in the 80s. Excess clippings and water stress also tend to favor rust. The orange pustules are noticeable and in severe infestations, shoes can become discolored orange while the leaves turn yellow. In these cases, damage is localized to the leaves and the grass is usually able to grow out of the infection without a fungicide.