Pest Prophecy

Cost effective insect management often begins with the cost of the insecticide selected to control the pest. However, many other factors can be equally important in determining the final outcome of insect control. Pest forecasting is a technology that continues to expand and is of interest to many turfgrass managers. Much of the current forecasting technology applies to turfgrass disease prediction, but some is available for insects. What many turfgrass managers don't realize is that they can make a lot of progress toward forecasting pest outbreaks simply by doing a good job of record keeping, mapping and monitoring the weather.

Forecasting pest outbreaks is important for many reasons. Providing a “head's up” on the potential for attack by certain pests can help avoid unnecessary pest damage. Forecasting can also insure you are treating at the optimal time. Furthermore, forecasting can help identify high-risk areas. As a result, pest forecasting can be a real money saver. It can save you money through time and product invested in pest control. If you learn how to focus on three different aspects of pest forecasting, you'll be able to use this knowledge to cut costs.

THE THREE THINGS

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Pest forecasting or predictions can cut costs by providing pest insight for three main areas. First, look at whether or not the pest will be present at damaging levels. Second, determine whether the pest will show up earlier or later than normal. Finally, forecasting may help us identify those locations that are at greatest risk of attack. Some pests are easier to forecast than others and for some pests more than one of these areas may be practical to forecast. As for other pests insight can only be gained into one area of the pest's biology.

DIVINING DAMAGE

We would all like to know if a pest will be present at damaging levels well in advance of the pest season. This, however, is very difficult to predict. For many insect pests the damaging stage is the larvae. This is true in the case of white grubs (the adult is a beetle) and armyworms/cutworms (the adult is a moth). The adult stage precedes the damaging larval stage. Research has typically shown that it is hard to forecast the number of larvae resulting from the adults laying eggs. A number of factors influence the subsequent larval population and that makes forecasting the abundance difficult based solely on adult abundance. While Japanese beetle traps, light traps and pheromone traps may provide insight into the timing of an infestation, they seldom shed much light on the intensity of the next generation outbreak.

Environmental factors may help us make better judgments on the abundance of a pest. Hot, dry conditions will certainly indicate a strong likelihood of high numbers of southern chinch bug. These same conditions may also encourage problems with fall armyworms as other vegetation may dry out, leaving irrigated turf more attractive. Wet, cool conditions may favor a number of predators, diseases and parasites that will reduce the number of armyworms. Dry conditions in early to mid summer may reduce the likelihood of white grubs, particularly in non-irrigated turfgrass. When the beetles lay eggs, it is critical that soil moisture remains at 10 percent or above over the next few days to ensure egg survival. Dry soil will deter egg laying and the eggs that have been laid will not hatch. Wet summers encourage white grub development in all areas.

Understanding what environmental factors encourage the pests you encounter in your location is helpful to give you an early warning. If you understand what conditions favor your most common pests and keep a close watch on weather trends, you are giving yourself some protection against being caught off guard by serious infestations. It can also help you prepare for certain pests that may be more common than normal.

TIMING IS EVERYTHING

The second area to forecast is the exact timing. This is a challenging area, yet can be of great benefit to turfgrass managers. Knowing when to look can help save time scouting and make sure you are using your time and your employees as efficiently as possible. It helps you avoid an early infestation that could catch you by surprise. Insects are cold-blooded creatures, which means their growth and development is regulated by the temperature. In general terms, that means the warmer it is, the faster insects develop. The translation: The warmer the spring and summer, the earlier the insects develop damaging populations. There are exceptions, but this is a rule that can help you each year. There are also interactions. A warm, wet spring may allow mole cricket egg-hatch to occur earlier, while a warm, dry spring may see a delay in egg hatch.

Some commercially available weather equipment and some Web sites contain forecast models for various pests including insects. These are typically based upon degree-day information. Degree days are a way to measure heat in heat units. Most insects have a minimum developmental temperature of around 50°F although many soil insects such as grubs develop at slightly lower temperatures. This means that at temperatures below 50°F, most insects do not grow or develop. The higher the temperature above 50°F, the faster they grow. A degree day is simply the average temperature for the day minus the threshold temperature. For example, if the average temperature for a day was 72°F, then subtract 50°F and the degree days for that one day equals 22.

There are a few degree-day models available for some insect pests of turfgrass. Some start on Jan. 1 and forecast when an insect will first appear. Others forecast the time to complete development once a generation has started. The latter are often difficult to use because it may be hard to determine exactly when a generation begins in the field. If you have interest in using degree-day models, contact your local university turf expert or consultant to obtain more information. Many of these models are pest and location specific.

Another way to forecast whether insect populations will be early or late is by observing plants that give a hint of a warm or cool spring from a biological perspective. Dogwoods, forsythia and spirea offer insight into the development of pests that are temperature dependent. Once again, local experts can offer additional advice on specific plants and pests.

LOCATION, LOCATION, LOCATION

The third area, and perhaps the most important, is that of forecasting which areas will be attacked by insect pests. This is the most important area of prediction because it allows you to focus your energies on scouting and treating only those areas that are highest risk. By treating only those locations that truly have a real risk of serious turf damage, much can be saved on insecticide expenditures. Understanding which areas are high risk can significantly reduce your scouting and monitoring time and give you a great deal of confidence. If you don't find the insects you are looking for in those areas, it means they probably aren't showing up anywhere.

Forecasting high-risk areas is based upon two pieces of information. First is a good knowledge of what makes an area more attractive or more susceptible to a certain pest. Maybe it is the lush green grass and good soil moisture that makes the site very attractive to Japanese beetles to lay their eggs that leads to subsequent white grub problems. A higher, dry, sunny area may be at greater risk to chinch bugs or billbugs. An area with a lot of thatch may be more attractive to green June beetle grubs. An area with lots of adult mole cricket activity in early spring is most likely where they will lay eggs later in the season. There are many scenarios that make an area more attractive to a certain pest and a working knowledge can help predict the likelihood of a pest problem and help you use your time and insecticides more effectively.

GOOD RECORDS EQUAL BETTER PROTECTION

Additionally, high-risk areas can often be defined simply through good record keeping. Some pests are creatures of habit and return to the same areas year after year.

This may be due to the fact that the area is highly suitable or may be related to surrounding vegetation and activities or other factors. The bottom line is that good record keeping through the years can help reveal trends for pest occurrence in certain location and provide guidance for your scouting efforts. It is also important that you record not only the specific locations, but also the timing for the pest occurrence. This can help you with the previously mentioned aspects of pest timing. By keeping good records of the timing of pest occurrence, you can compare cool and warm springs as well as the timing of pest outbreaks and become quite proficient at pest prediction.

A good question to ask is if forecasting increases your risk. For example, if your intuitive forecasting tells you that a pest won't be a problem or that it is going to be later in the season and you are wrong, what is the fallout from such a decision? If the answer is serious turfgrass injury and additional costs in trying to clean up a problem that got too much of a jump on you and a disgruntled customer, then you must proceed with caution. Obviously, any forecasting that indicates a problem will be later or less than normal must be carefully adopted. This does not mean sit back and relax, but rather it means you should stay alert and prepared. The safest way to use forecasting is to avoid getting caught off guard by problems that occur earlier than normal or the threat of more intense damage. In other words, it helps you stay one step ahead of problems, rather than slacking off.

NOT AN EXACT SCIENCE

Forecasting the location, timing and intensity of insect pest occurrence is often part science, part experience and part guesswork. However, by keeping good records and monitoring temperatures you can almost always improve your ability to know when and where to look. In doing so you can often improve insecticide effectiveness and avoid unnecessary applications, which all add up to more money in your pocket.

Rick Brandenburg, Ph. D., is professor of turfgrass entomology at North Carolina State University (Raleigh, N.C.) and co-director of the Center for Turfgrass Environmental Research and Education.

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