Look for the development of new injury symptoms to evaluate the effectiveness of fungicide applications made after full-blown infection is present.
Photo by John Fech, UNL.

Here’s a possible scenario: You get a callback from a customer with a lawn that you sprayed a week ago for sod webworms, and it looks horrible. If you can relate to this scenario, if getting maximum effectiveness out of pesticide applications is of interest to you, if saving money on pesticide purchases is important, and if making your customers happy is a goal for your company, then read on.

Measuring success

First things first. Endeavor to put into tangible terms what is meant by success. A green lawn? The presence of a few dead bugs? The presence of a few weeds? A good first step is to start counting actual pests, for example, with insects, looking for ones that are still moving and eating following an insecticide application. Compare the number of live ones found to the number of dead ones found. Be sure to inspect the turf in various areas. Begin by looking at the dead or dying parts of the lawn, and move out to the periphery or edges of the damaged areas. Do a little inspecting in the “good looking” parts of the turf as well.

Next, do the opposite. This is easily done with preemergent or postemergent herbicide applications. Look for the absence of troublesome weeds. This method is especially useful when counting large specimens, such as plantains or crabgrass. If the herbicide application has been successful, these weeds may have shriveled up and died and are no longer recognizable as a living organism.

When evaluating insecticide applications, notice the life stage of the insect. Certain insecticides are considered insect growth regulators (IGRs), which don’t actually kill the pest. Instead, they prevent it from changing from one life cycle stage to another, or from changing from instars within a life cycle stage. In some cases, the first instar of an insect is only a slight worry in terms of the potential amount of turf that can be consumed, while the latter ones are much more damaging. If the insecticide prevents the insect from developing into these more aggressive instars, then the product has been largely successful.

No matter whether the pest is a disease, weed or insect, the factors for measuring success must be put in the context of threshold. Once the number of damaging weeds or insects has been counted, sketch a map of the affected and unaffected parts of the lawn. Draw circles or ovals in badly affected areas and write in the average number of insects found. Make similar notations for the other lawn areas.

The concept of threshold is the level at which a plant specimen or group of plants can tolerate a low number of pests and still function well. A lawn may be able to look good and be relatively healthy with an average of three grubs per square foot. A large ground cover bed may contain six crabgrass plants along with the masses of sedum. Each pest species has a certain level of incidence where the damage that is produced by insects in greater numbers than the threshold level is unacceptable.

The location and function of the site both have an impact on the determination of threshold, as well as the feeding capacity of the pest. Low-maintenance sites, such as cemeteries, school grounds and parks can tolerate a much higher level of insect infestation than banks, insurance buildings and theme parks, in most cases.

Perception vs. reality

If you don’t know the significance of what you are looking at, then you may jump to false or irrelevant conclusions.

The first aspect of this factor to consider is one of misdiagnosis. Did the insecticide application fail, or did it actually reduce the number of pests to a level under the established threshold, and are there other forces in place causing the turf to be damaged?

There are many stressors that can adversely impact the health and appearance of a turf stand. Drought stress, extensive foot traffic and soil compaction are a few. If any of these are in place while insects are feeding on the turf, then the insects are not alone in causing the turf to be affected. In fact, in many cases, the other factors are more responsible for the health of the turf (or the lack thereof) than the number of bugs present.

The problem of multiple causes is difficult to deal with. Most clients tend to be one-dimensional in their understanding of turf problems, and may fail to take traffic stress, for example, into account.

Inspect turf at the periphery of the apparent damage to confirm the presence or absence of pests.
Photo by James Kalisch, UNL.

Many factors can be responsible

There are quite a few things that can go wrong with a pesticide application. If any of the preparatory or implementation steps are not carried out properly, it can lead to failure. The bottom line is to determine which one is responsible so that steps can be taken to prevent future problems.

Incorrect Identification of the Pest—This is commonly overlooked, because no one likes to admit that they made a mistake. Diseases are probably the most difficult pest problem to diagnose because of the size and vague nature of the indicators and the variability from one season to the next. Buy several turf and ornamental disease identification books and place one in each company vehicle.

Photodegredation—This occurs when the pesticide formulation is acted upon by changing it from one capable of killing pests into one that can’t. Photodegredation occurs primarily when surface-feeding insects (aphids, sod webworms) or broadleaf weeds are the target. Botanical insecticides such as Bacillus thuringensis or Steroniema nematodes are particularly likely to be affected by photodegradation.

Volatilization—This is the loss of pesticide from the grass or soil surface by actual evaporation upward into the atmosphere. This is a concern from the standpoint of reduced application effectiveness, as well as potential human exposure. High air temperatures and windy conditions increase the volatility of an application. Make applications on cool, cloudy and calm days to reduce volatilization.

Pest resistance—Resistance has the most potential to become a problem where repeated applications are necessary in a short period of time in order to control a pest, and the same fungicide or insecticide is used for each application.

Several practices can be utilized to reduce the likelihood of resistance:

  • Reducing treatment frequency by spot-treating rather than total cover sprays of the entire lawn.
  • Using short residual insecticides such as pyrethrins.
  • Alternating between classes of insecticides.
  • Using genetically resistant turfgrasses and other nonchemical methods of control.

Application Errors—The most common errors made are ones of equipment misuse. Clogged nozzles, gaps in coverage and so on are likely to be the culprit. Make sure your sprayers and spreaders are up to snuff by performing simple calibration procedures on them. It’s amazing how often nozzles do not deliver the proper amount of formulation or the tire tracks are hard to locate. Spray marker indicators can help to reduce coverage errors.

Wrong Pesticide Selection—Certain pesticides work better for certain pests. Check with local cooperative extension educators and specialists for the latest recommendations for specific pests in your state. Resist the temptation to select a certain pesticide because it is offered at a reduced price by your supplier. It may work quite well for insect A, but not for insect B.

Improper Timing—Each pest has a stage of vulnerability when it is most likely to be killed by an application. Insects in certain life stages can be virtually impossible to control. Similarly, certain weeds are much easier to control with a preemergent herbicide than a postemergent application.

Nonpest stressors, such as traffic damage, can create confusion in the mind of customers as to the effectiveness of pesticide applications.
Photo by John Fech, UNL.

Failure to Water the Application In—This is related to a “failure to penetrate the thatch” factor. Especially in the case of liquid applications for white grub control, the insecticide usually dries on the leaf blades or is bound by the thatch before it can be moved into the target area. Reduce this by selecting granular formulations for soil insects, inundating the customer about the importance of adequate irrigation before and after the application, and consider core aeration to assist with the downward movement of the formulation.

Using the Wrong Rate or Formulation—This is a matter of being sure to thoroughly read and follow label directions. Be sure you are using the effective rate and formulation for the target pest. Use liquids where residual herbicide or insecticide on the grass blades is necessary for control. The critical overriding factor to all of these considerations is to deliver the active ingredient to the target zone at the proper time.

Using High Water pH—The pesticide label will indicate the desired pH of the water in the spray tank. In many parts of the country, the pH of the water supply is alkaline, sometimes in the range of 9 to 10. If a pesticide that performs well at 5.5 is placed into alkaline water, it’s residual or duration of activity can be reduced from several days to several hours. A simple water test can be a big help for this problem.

In all situations, success in application is directly related to accurately identifying the pest, using information about its life cycle and habits to determine the best time to apply the product, and then placing the proper type and amount of formulation into the appropriate target zone of the insect that is causing damage. Strive to do this with each application.

John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln.