Insect pests present a unique set of challenges to sports turf managers, especially when it comes to chemical control. Frequent contact with the playing surface by athletes increases the risk of human exposure to pesticides. Often, management of sports turf falls under the jurisdiction of school districts that regulate pesticide use in accordance with local and state laws. Sports turf managers may face the dilemma of having to balance restrictions on pesticide use with the need to apply pesticides, based on presence of pests and/or damage. Thus, it is wise to know how insecticides can be used safely and effectively within restricted treatment windows. In this article, I discuss insecticides that are currently available for managing insect pests of sports turf within the context of using these tools safely and effectively.
Insecticide effectiveness depends on correct identification of the target pest and knowledge of its life cycle, required resources, and seasonal occurrence. Your county Extension office and state extension service are prime sources of information about the biology and management of pests, including non-chemical tactics that are part of an integrated pest management (IPM) program.
Annual training is essential (and legally required for commercial applicators) to retaining this information and staying current with important changes regarding pesticide registration, use, and safety. With respect to chemical control, the choice of insecticide will depend on several characteristics of the chemical including residual activity, mode of action (i.e., how it kills), and spectrum of activity. Other factors to consider include where and how the pest feeds, when susceptible life stages are present, and likelihood of insecticide resistance developing in the pest population.
With respect to resistance, the Insecticide Resistance Action Committee (IRAC) assigns insecticides and miticides to specific categories, designated as group numbers, according to mode of action. To delay or prevent the onset of insecticide resistance, it is best to frequently rotate among products belonging to different group numbers. More information about insecticide modes of action can be found at the IRAC website (https://www.irac-online.org/modes-of-action/).
There are two main categories of insecticides based on delivery method and target site. Contact insecticides must come into contact with the insect cuticle, or exoskeleton, in order to be effective. These products work best against pests that are exposed to the environment and feed externally on turfgrass. In contrast, systemic insecticides are absorbed by the plant and moved systemically to all plant tissues. Thus, systemic insecticides work best against insect life stages that live and feed within the plant.
Contact insecticides are widely available for turfgrass pests and often provide quick “knockdown”; therefore, the effect on pests is noticed immediately. Routes of exposure to the active ingredient involve ingestion or penetration through the insect cuticle. These insecticides are largely broad-spectrum compounds, so they kill a wide variety of pests. However, contact insecticides also kill beneficial insects, so they must be applied carefully to minimize risk of harming pollinators and natural enemies (i.e., predators and parasitoids). Contact insecticides labeled for turfgrass include active ingredients belonging to several chemical classes, mainly carbamates (Group 1A), organophosphates (Group 1B), and pyrethroids (Group 3A). Other contact insecticides labeled for use on turfgrass include spinosyns (Group 5) and oxadiazines (Group 22A). Most of these insecticides affect the nerves and muscles of insects. The nervous system of humans and other mammals is similar to that of insects and other arthropods, so these compounds can be toxic to people and pets if not applied properly.
Systemic insecticides are translocated (i.e., moved) throughout the plant after being absorbed through leaf or root tissues. Systemic products provide protection from insect feeding throughout the plant, and are effective against both chewing and sucking pests. These insecticides offer an additional advantage over contact insecticides in that they are effective against life stages that feed internally in plant stems, within crowns, or underground on roots. In other words, systemic products work where contact insecticides can’t reach.
Additionally, systemic insecticides have much longer residual activity than contact insecticides, and some products even provide season-long control of perennial pests such as white grubs. Systemic materials are generally broad spectrum but tend to be somewhat selective, exhibiting effectiveness on a narrower range of pests than contact insecticides. Several chemical classes contain systemic active ingredients, including organophosphates (Group 1B), neonicotinoids (Group 4A), and anthranilic diamides (Group 28).
Several insecticide products are labeled for turfgrass use that contain two or more active ingredients. Typically, these products are a combination of contact and systemic compounds. These products offer several advantages over those containing only one insecticide, including an increased range of target pests controlled, quick knockdown and long-term control, and time saved by not having to measure and tank mix multiple insecticides when warranted. However, the percentage of active ingredient contained within combination products is often much less than those products containing only one insecticide. Also, combination products are used prophylactically, targeting pests that may or may not be there. This increases the likelihood of a pest population developing resistance to more than one active ingredient. Therefore, decisions about when and how to treat should always be based on the presence of pests as determined through monitoring (i.e., scouting) and IPM.
Enhancing safety, protecting environment
Most insecticide labels prohibit re-entry into treated areas of turfgrass until after sprays have dried. While this requirement allows greater flexibility in timing applications, dried residues still pose a risk to athletes, especially children and others with sensitivity to chemicals. Dried residues can transfer to skin, while mist, dew, or sweat can rehydrate dried particles, increasing risk of absorption through the skin. To reduce exposure risk to athletes, especially those most sensitive to chemicals, it is best to wait 24 to 48 hours before allowing re-entry on a playing surface following a spray application. As noted above, this may present a challenge for scheduling applications on fields or pitches that are in high demand.
In addition to leaves, stems, and roots, systemic materials can move into flowers, creating a potential risk to pollinators. In particular, neonicotinoid insecticides can move into nectar and pollen and have been shown to harm honeybees, bumble bees, and other flower foragers. Many of these products have a warning on the label restricting their use to plants that are not in bloom at the time of application. This restriction also applies to flowering weeds, so turfgrass managers cannot use neonicotinoids in weedy areas. This shouldn’t be a problem for highly maintained playing surfaces that are free of weeds, but it will be of concern to managers of many practice fields, parks, and other recreational areas. Importantly, risk to pollinators can be reduced by making all pesticide applications when activity of beneficial insects is at a minimum—typically early morning, later in the evening, and on cloudy days.
Finally, IPM does not exclude the use of insecticides, especially when there are no other management options available for a particular pest. However, you don’t always have to choose the most toxic product when opting for chemical control. There are many reduced-risk insecticides that can be used just as effectively as their broad-spectrum counterparts. Examples of reduced-risk insecticides include botanicals like neem oil, which are plant derived, insect growth regulators (IGRs), and microbials. The latter include bacteria, fungi, and other microorganisms that cause disease in insect pests and do not harm non-target organisms. An example is the bacterium, Bacillus thuringiensis var. kurstaki (Btk), which produces an insecticidal protein that only works against caterpillar pests such as black cutworm and fall armyworm. Reduced-risk insecticides like Btk are safe for people and pose little risk to beneficial insects.
No matter which insecticide you use, be sure to use caution and follow all label directions. The label provides detailed information about proper mixing and application to maximize effectiveness, safety, and environmental protection.
Eric J. Rebek, PhD, is professor and state Extension specialist for horticultural insects, Department of Entomology and Plant Pathology, Oklahoma State University.