One of the key tools in an integrated pest management program is the turfgrass manager’s ability to predict turf problems. Turf problems are caused by biotic stresses, like pests, diseases and weeds, or by abiotic stresses, such as poor soils, adverse weather or man-made problems. Being able to predict turf problems as early as possible means the turf manager can be prepared to either prevent the problem from occurring in the first place, or have the best strategy in place for control once the problem occurs. There are several ways to predict turf problems: scouting, monitoring environmental data, phenology, lab testing and networking.
Prostrate knotweed germination March 22 in Columbus, Ohio. Prostrate knotweed is sometimes confused with crabgrass or a desirable grass, but it is in fact a broadleaf plant. It can quickly invade compacted areas like high-traffic areas on a football field, causing an inconsistent playing surface.
Everyone who cares for the athletic field, and even athletes and coaches, can be trained to look for problems. Having bright, colorful posters or pictures of common weeds, pests and diseases posted around the facility will show everyone what they’re scouting for. Ideally, fields should be checked at least once a day, preferably in the morning. The problem is then recorded, stating when and where it was seen. These recordings build up a field history, showing areas on the field that consistently have problems. For example, a low area that holds water, or a leaking irrigation head. Another method of scouting for problems is to set traps to catch insect pests. This is not a control method, but is used to get an idea of local insect populations so the turf manager can decide whether or not to make an insecticide application. Another way to check insect populations is to soak/flush the turf with a detergent, forcing insects to the surface.
Monitoring and recording environmental data is a vital part of turf management. Environmental data includes soil and air temperatures, relative humidity and duration of turf leaf wetness. If the sports field is located inside a stadium, the management of those environmental factors becomes critical. The environmental data collected can be used to forecast turf problems, such as diseases.
The soil temperature dictates whether warm or cool-season grasses can be grown, seed germination dates, heat stress of cool-season grasses, dormancy of warm-season grasses, and timing of chemical and fertilizer applications.
Relative humidity and duration of leaf wetness are two factors that have a great bearing on disease incidence, particularly in warm weather. Some weather stations and turf websites now include disease and insect forecasting models as part of their customer service. The models are based on environmental data and can be used to forecast the occurrence of a particular pest. For example, the GreenCast website (www.greencastonline.com) has pest outlook models for dollar spot, gray leaf spot, anthracnose and white grubs, among others. These models are indicators of favorable conditions for the disease, weed or insect to occur; they do not account for inoculum pressure, species resistance, fertility levels or future weather conditions. As such, the decision is left to turf managers on any control method needed.
Phenology is the study of the times of recurring natural phenomena. Examples in turf would include the date of emergence of weeds or seed heads. One way of working with phenology is to use growing degree days (GDD), based on daily temperatures. GDD models are temperature based. The models were originally developed to predict when annual bluegrass seed heads would emerge. The practical application for the annual bluegrass model was to time plant growth regulator applications for seed head control.
Microdochium patch, caused by Microdochium nivale, is probably the most common snow mold.
PHOTOS COURTESY OF PAM SHERRATT.
Lately, the GDD concept has been expanded and used for other turf problems, such as crabgrass germination. The GDD is then used to time herbicide or plant growth regulator applications to control Poa annua seed heads or weed seed germination. For example, using a 50-degree base, the plant growth regulator Embark is generally applied in the Midwest between GDD 50 and 75 to control Poa seed heads.
GDD can be calculated by any turf manager with access to local weather data. In addition, Michigan State University (MSU) has developed a GDD Tracker website (www.gddtracker.net) that can be used by any turf manager in Michigan, Illinois, Indiana or Ohio. Any state turf association that wants to be included in the website model should contact the turfgrass science team at MSU. Another useful way to use phenology is to use indicator plants to forecast problems in turf. One example of an indicator plant is forsythia. When the forsythia plant is in full bloom it’s time to apply preemergence herbicide for crabgrass control. Another plant used this way is bridal wreath spirea.
Calendar dates are an easy way to time pesticide applications. Keeping track of pests on a calendar is a sound agronomic strategy to make sure that target dates are not missed. For example, crabgrass germination in Central Ohio takes place from mid-March to mid-April, while in Florida the germination period might be mid-February to mid-March. It is best to apply the preemergence herbicide a little earlier than the emergence date to avoid missing the target date window. Remember, improper timing is considered one of the major reasons for preemergence herbicide failures.
Soil, water and leaf tissue tests can help build a more comprehensive picture of a sports field. Testing typically involves sending samples away to a turf testing lab or university extension service. The test results help pinpoint any problems, such as high levels of sodium in the water source or essential nutrients lacking in the soil. Testing can also determine the texture of a soil or the suitability of sand for topdressing.
Networking with peers and surfing the Internet is also a good way to garnish information and predict future regional turf problems. If one field is having a particular problem, chances are many others in the area are too. Sports turf managers that meet at regional seminars or get involved with message boards can find a plethora of information about local issues and helpful resources.
Common early-season pests
The following list of early-season problems will be dependent upon location and weather conditions during the fall and winter. Some of these issues could arise in February and March.
Winter injury – This term covers a multitude of problems that includes desiccation, freezing injury, ice cover, frost heaving, traffic and low-temperature pathogens. Looking more specifically at freeze injury, it can be an issue with bermudagrass, seashore paspalum, annual bluegrass and ryegrass along their northern range of adaptation.
It is important for the turf to cold acclimate during the fall and early winter, and there are a number of cultural practices that can prevent major injury from occurring, namely raising mowing heights to protect crowns, preventing standing water, reducing thatch, avoiding excessive growth in the late fall, minimizing shade and applying potassium fertilizer to warm-season turf.
Predicting field problems is easily done if the turf manager has a good grasp of phenology,problem diagnostics and environmental data collection, such as monitoring soil temperatures.
Recovering from winter injury involves a strong overseeding program and regular application of fertilizer to kick-start new seedlings. If at all possible, a growth blanket/cover should be used to protect new seedlings in case of frost. Some field managers might also use turf colorants to warm soil temperatures and stimulate growth.
Snow molds – Microdochium patch, caused by Microdochium nivale, is probably the most common snow mold. Known also by the common names of pink snow mold and fusarium patch. Pink snow mold is often connected with the disease when it occurs in association with snow, and fusarium patch when snow is absent. Typhula blight (Typhula incarnata), sometimes referred to as gray snow mold, is the second most common snow mold. In the case of Typhula blight snow cover is required for disease development. Perennial ryegrass is particularly susceptible to snow mold, so field managers with a lot of ryegrass might consider applying a preventative fungicide in the late fall. If symptoms appear at snow melt in the spring, rake all the dead plant material out and reseed.
Insect pests and varmints – There are a couple of insect pests that can cause problems under snow cover. Crane fly larvae and bronze cutworms are hardy pests that can feed on turf foliage under the cover of snow. When the snow melts, the symptoms may look like snow mold damage, but close inspection will reveal that the foliage has been eaten and the telltale fecal pellets, called frass, will be visible in the thatch zone. The European chafer white grub is also tolerant of colder temperatures and may become active as soon as snow melts.
If you encounter skunk or raccoon digging in February or early March, check for white grubs. This might also be a good time to look for signs of overwintering sod webworms. When these caterpillars first begin feeding, they can produce blanched patches of turf that look like dollar spot disease. Voles often cause turf injury under the snow, especially near flower beds or tree rows. These rodents chew their way through the turf, which creates unsightly pathways and trails. Once the snow melts they relocate to the safety of mulch layers and plant cover. The turf usually recovers with a little topdressing and seed.
Weeds – Early weeds, like prostrate knotweed (Polygonum aviculare) and annual bluegrass (Poa annua), are particularly problematic on athletic fields. Both of these weeds are indicator plants, meaning they can grow in areas of severe compaction and, therefore, are good indicators of poor growing conditions. These weeds can quickly invade damaged areas like sidelines, between hashes and goal areas.
Knotweed is the earliest germinator of all the annual weeds (see Table 1). As soon as soil temperatures are at 40 degrees it comes up and can sometimes be confused with desirable grass or early crabgrass, even though it is a broadleaf summer annual. Poa annua germinates soon after (soil at 45 degrees), and Poa annua plants that germinated the previous fall also green-up quickly. These weeds appear so early (as early as the first week of March in Ohio), that turf managers often haven’t had the chance to apply a preemergence herbicide.
What makes these two early weeds so difficult to control is that most effective preemergence and postemergence herbicides will also have a negative effect on seeding. Preemergence herbicides like prodiamine and dithiopyr are very effective (good to excellent) at preventing the germination of both weeds, but those areas cannot then be seeded for three to four months. Mesotrione can be used to suppress Poa annua germination without affecting the seeding program, but it is not labeled for prostrate knotweed.
From a postemergence standpoint, there are not too many selective options for Poa annua control in cool-season turf. Controlling knotweed postemergence with a selective broadleaf herbicide is an option but will also affect future seeding work. The key to both of these weeds it to have a plan in place for the previous fall that includes compaction relief and a strong seeding/sodding program to prevent weed invasion.
Pam Sherratt is a sports turf specialist at Ohio State University and serves on the STMA board of directors. Dr. John Street is an associate professor and turfgrass specialist at Ohio State University.
Contributing authors: Dr. Dave Shetlar and Dr. T. Karl Danneberger. Dr. David Shetlar is a professor in landscape entomology and Dr. Karl Danneberger is a professor in turfgrass science at Ohio State University.