Depending on your location, the species of grass you manage, and your other management practices, there are a variety of different weed, insect and disease pests that you may encounter this summer. This article will provide an overview of the pests that are most likely to be encountered on sports fields, along with some suggested management strategies or resources for additional information:

Broadleaf weeds

Dandelion and white clover are common perennial broadleaf weeds (Figure 1), and ideally they should be controlled in the fall. However, your use schedule or overseeding activities may conflict with this.

White Clover
(Trifolium repens) – P
Post in fall
PHOTOS COURTESY OF DAVID GARDNER.

For control during the summer, use a combination postemergence herbicide product that contains 2,4-D, MCPA or triclopyr to control dandelions and MCPP or ateuroxypyr to control white clover. In most cases you should use the amine formulation of these herbicides during warmer weather and apply in the early morning. The goal is to keep the herbicide in liquid form on the leaf surface for as long as possible. So spraying when it is too warm, especially if using an ester, will actually decrease control because the residues will dry too quickly.

Dandelion
(Taraxacum officinale) – P
Post in fall

Knotweed and spurge are examples of commonly observed annual broadleaf weeds. Annual broadleaf weeds can be controlled either postemergence (now) or perhaps with a preemergence herbicide next spring. To control these weeds now use a combination postemergence herbicide that contains 2,4-D, dicamba or triclopyr, and perhaps a protox inhibitor such as carfentrazone, sulfentrazone or pyraflufen ethyl.

Knotweed
(Polygonum aviculare) – A
Pre or post in spring

Control of summer annual broadleaf weeds can be quite difficult with post- emergence herbicides. In most cases, annual broadleaf weeds are favored in those areas where the stand of turf is thin and not as competitive. So, one long-term solution is to increase the vigor of the turfgrass with proper cultural management practices, including core aeration to alleviate compaction.

Spurge (Euphorbia supina) – SA
(Milky sap distinguishes from knotweed) –
Pre or post in summer

Since annual broadleaf weeds come from seed, you may be able to control them with a preemergence herbicide. While these products are most often used to control crabgrass and other annual grasses, they are also labeled for the control of certain annual broadleaf weeds. The issue with the use of preemergence herbicides is one of timing: usually knotweed germinates prior to when we recommend applying a preemergence herbicide to control crabgrass, and spurge may germinate after the preemergence herbicide has dissipated. Therefore, this should be viewed as a partial solution to the problem of annual broadleaf weeds. However, if you have problems with annual broadleaf weeds and you are using a crabgrass preemergence product, check the label to see if it also controls the annual broadleaf weeds that you have an issue with.

Crabgrass (Digitaria) – SA
(Germinates when soil temperatures reach 58_ F) –
Pre or post prior to tillering

Grassy weeds

Annual grassy weeds such as crabgrass and goosegrass are frequently found on sports fields. It’s important to know which you are dealing with, because the herbicide recommendations and timing of application differ somewhat. For either grass though, preemergence herbicides are most effective for control. If your budget does not allow for wall-to-wall application of a preemergence herbicide, an effective strategy is to map out the areas with weeds problems this year and apply preemergence herbicides to these areas next year.

Goosegrass (Eleusine indica) – SA
(Silvery crown and multiple florets per spikelet) –
Pre or post prior to tillering

When choosing a preemergence herbicide, make sure that its residual activity will not interfere with planned overseeding operations. For postemergence control now, consider the use of quinclorac for crabgrass and fenoxaprop-ethyl for goosegrass. Quinclorac is most effective if used prior to tillering or after the crabgrass has reached six tiller stage. Application between two and six tillers (or when the plants are flowering) is not as effective. Goosegrass should be controlled prior to tillering.

Yellow Nutsedge
(Cyperus esculentus) – SA
Post in late spring

Annual bluegrass can be annual or perennial, depending on your location. Chemical control of annual bluegrass is difficult. If you have a limited infestation, the best control may be physical removal. There are some preemergence herbicides that, if applied in fall, have been shown to reduce the annual bluegrass population, but this is not completely effective.

Annual Bluegrass
(Poa annua) – WA
Pre in fall or post

Creeping bentgrass is a perennial grass and may be selectively controlled using three sequential applications of mesotrione beginning in mid-August. If overseeding these areas, the seed should go down on the same day as the third and last application of mesotrione.

Creeping Bentgrass
(Agrostis stolonifera) – P
Post in fall

Yellow nutsedge is not a grass, but a sedge. Thus there are different herbicide recommendations for them. They are easy to identify because they have three-sided stems (triangle shaped in cross section). The best control of sedges is with sulfentrazone or halosulfuron. Additional information about weed control can be found at http://buckeyeturf.osu.edu.

Insects

Common insect problems on athletic fields include white grubs, which are the larvae of four different species of beetles, and bluegrass billbugs (Figure 2).

White grubs have three pairs of legs. The symptoms of infestation are similar: wilted turf that pulls up easily from severed roots. While there are many differences among the species, the most important consideration is the size of the grubs and, therefore, the level of infestation required for damage. In most cases, grubs are not present for a couple of years after a field is established until a thatch layer begins to build up.

One of the problems with grub control is that the most effective products are preventative in nature. The best control of grubs is with an application of halofenozide, a neonicotinoid such as imidacloprid or thiamethoxam, clothianidin or chlorantraniliprole. These should be applied in July prior to grub appearance. How can you predict if you need to make this application? If your field is more than a few years old and building up a thatch layer, and if you’ve had grubs before, these are good indicators that you may need this application. Ironically, the nicer the field, the more likely it is that you will have an infestation, because the insects consider that a more ideal breeding ground.

Gray Leaf Spot (Pyricularia grisea)

Conditions Favoring Development

Ryegrass or tall fescue. Prolonged periods of hot, rainy, humid weather. High nitrogen levels plus other stress, such as compaction or inappropriate herbicide use.

Symptoms/Signs of Damage
Blighting of leaf tissue. Leaf spots may be present on foliage. Gray lesions with brown border form along leaf margins. Leaf blades often twisted and dick-back from tips.

If you do not apply one of these products and you notice grubs in autumn, the best choice for control is trichlorfon. It is an old organophosphate insecticide, but it is one of the few choices available to control existing grubs; in other words it is a curative product.

Dollar Spot (Sclerotinia homoeocarpa)

Conditions Favoring Development
Air temperature 60 to 80 degrees, symptoms to 95 degrees. Excess moisture on leaf (10 hours per day). Excess thatch. Poor fertility. Shade or poor air circulation.

Symptoms/Signs of Damage
Light tan lesions with red-brown border becoming “hourglass” lesions on leaves. Spots on turf usually 2-inch diameter or less. Cobweb-like white hyphae over brown dew-moistened turf in the morning.

Billbugs, in contrast to grubs, do not have legs. They tend to be more of an issue on Kentucky bluegrass. Since ryegrasses and fescues are endophytic, this symbiosis affords a certain level of protection against billbug feeding. So a good way to control them is by using fescues and ryegrasses.

Pythium (Pythium spp.)

Conditions Favoring Development
Air temperatures 80 to 95 degrees during the day and above 70 degrees for three consecutive nights. Excessive fertilization. Excess moisture and high humidity.

Symptoms/Signs of Damage
Circular spots of slimy plants that mat together. Cotton-like hyphae visible in early morning on green leaves at margin of patch. Follows surface drainage and mowing patterns.

The best chemical control of billbugs is with the same imidacloprid, thiamethoxam, clothianidin and chlorantraniliprole products used for grub control. The issue here is one of application timing. These products need to be applied in May to be effective against billbugs. If you’re using imidacloprid or thiamethoxam, there may not be sufficient residues remaining if you also have grubs to contend with in late summer. On the other hand, a May application of clothianidin or chlorantraniliprole will control both grubs and billbugs.

Brown Patch (Rhizoctonia solani)

Conditions Favoring Development
80 to 95 dgrees and free water or high humidity. Moderate to high N fertility. Tall fescue and ryegrass. High thatch.

Symptoms/Signs of Damage
Patches 6″ to 1′, “Smoke ring” visible at outer edge in early a.m. Grass may not be completely killed. May have frogeye pattern. Wilted and thinning turf, may not see distinct browning.

Diseases

There are many diseases of varying severity on athletic turfgrass. Figure 3 highlights four of the diseases that occur most frequently on athletic fields during the summertime. There’s also information about conditions that favor the development of the disease, symptoms and signs of damage. Identification of the disease is important, so that the fungicide applied is effective. Diseases such as dollar spot and brown patch are fairly easy to diagnose because they have striking symptoms. Gray leaf spot and Pythium, on the other hand, are more difficult to positively identify. Control of dollar spot, brown patch and Pythium is fairly easy. However, if you have problems with gray leaf spot, the typical recommendation involves a program of multiple applications of different classes of fungicides.

Though not included in the figure, you may also notice symptoms of diseases such as spring dead spot on bermudagrass or summer patch. However, now is not the time to attempt to control either of those diseases. Disease diagnosis and control can be difficult, and resistance to fungicides is a serious problem, so care should be taken when putting together your disease management program. Tables with more details about disease identification, along with publications that detail management recommendations for each disease are available at http://turfdisease.osu.edu/home.