There's been a revolution in the types of insecticides registered for control of turfgrass insects over the past two decades. These new insecticides have extended residual action, different application timing strategies, and fewer non-target effects.
This is a Kentucky bluegrass lawn destroyed by the bluegrass billbug. Notice the green tufts of perennial ryegrass that have survived because they contain endophytes
PHOTOS COURTESY OF DR. DAVID SHETLAR.
In 1996, the U.S. Environmental Protection Agency (U.S. EPA) was directed through the Food Quality Protection Act (FQPA) to re-evaluate all registered pesticides with the goal of greatly decreasing real and potential exposures to people, especially children. But even prior to the FQPA, most of the organochlorine insecticides (e.g., DDT, dieldren, aldrin, etc.) had been banned or restricted because of their accumulation in the environment and non-target affects on animals.
Under FQPA standards, the EPA first evaluated the organophosphates (OPs) and carbamates because these chemistries have the same mode of action, cholinesterase inhibitors. It was soon determined that too many of these OPs and carbamates were being used in urban areas.
Manufacturers were given the choice: either keep these pesticides for use in agricultural production areas or spend a lot of money proving that they're not overly exposing people in urban settings. Virtually all the companies opted for the voluntary withdrawal of their OPs and carbamates from urban landscape use.
Faced with the loss of the major insecticide groups used to manage turf and ornamental plant pests, chemical companies got busy developing new chemistries and new modes of action that were lower-risk to humans and the environment. A group of insect growth regulators were developed, but this chemistry is difficult and expensive to make and use. Most IGRs also have very narrow spectra of pests controlled.
There was also a great deal of work on new bio-based pesticides derived from bacteria, fungi or plants and also biological controls, such as insect parasitic nematodes and fungi.
The first major breakthrough was the discovery of the neonicotinoids. This class of insecticides blocked the nicotinic receptors of nerves, and insects use more of these types of receptors than other animals. So, as Oftanol, Triumph, Turcam, Diazinon and Dursban disappeared, imidacloprid (Merit) burst onto the scene. This was considered to be a low-risk insecticide and it seemed to have pretty good efficacy and good residual action. It was also discovered that it had systemic action.
Merit was first developed for white grub control, but it was soon found that it did quite well against billbugs, chinch bugs and mole crickets. However, to be most effective against these other insects, it had to be used as a preventive rather than a curative treatment. Pyrethroids continued to be the chemistry of choice for curative control.
Within another decade, we had additional neonicotinoids insecticides, such as thiamethoxam (Meridian), clothianidin (Arena, and the combination product Aloft) and dinotefuran (Zylam). Unfortunately, since Merit was the first of this class to be used in turf, we have treated each of these neonics as if it's a Merit clone. In fact, each neonic has unique properties.
In general, insects exposed to neonics go into never-never land. They lose the ability to react to stimuli and they change their normal behavior. They don't avoid predators, they stop eating and lose interest in having sex and laying eggs. These are all things that will eventually result in the death of the insect. To get the greatest effect, the insect should be young when exposed.
Chemical arsenal grows
In the mid-2000s, a new category of insecticides was discovered, the anthranilic diamides, and chlorantraniliprole is the first molecule to be developed for turfgrass use, Acelepryn.
This group of insecticides exploits a unique difference in the way that insect muscle tissues use calcium to cause contractions. Simply, insects (and related arthropods) keep calcium in little packets, and these little packets release the calcium when the muscle cells are stimulated. Other animals don't use these little packets, so the muscles are not stimulated to contract if they're exposed to the chemical.
Basically, this chemistry gives insects major muscle cramps, but it has virtually no affect on humans, our pets, birds, fish, reptiles, amphibians or earthworms. If you think about it, you probably wouldn't die from a muscle cramp, you'd walk it off.
On the other hand, if you're a tiny insect that has just hatched out of an egg, you have to eat and drink to survive. If the first bite of food causes your mouthparts to stop working, you'll probably not survive. In short, anthranilic diamides have to be in or on the food of an insect when the first bite is taken.
In summary, both neonicotinoids and anthranilic diamides seem to have their maximum effect when very young insects are exposed. This generally means that they need to be used as preventive treatments, not curative treatments.
In this heavily infested turf, notice how the grubs have eaten the thatch visible on the turned-over flap of sod. This is where you want your grub insecticide to be present.
White grub control
Most turfgrass entomologists agree that we would prefer for turfgrass managers to use the principles of integrated pest management (IPM). Most everybody knows the IPM drill: sample, determine if control is needed, then use a control (cultural, biological and/or chemical) that's least disruptive to the turfgrass system.
This strategy worked very well when we had insecticides that could be used curatively. But now that the top-performing insecticides work best when used preventively, what should an IPM practitioner do?
My answer is to do some risk assessment and record-keeping. When white grubs are an issue, we know that turf that was damaged last year has, on average, about an 80 percent chance to suffer grub damage again. Likewise, turf that's less than four to six years old rarely has white grub damage. There's insufficient organic matter to support large white grub populations. Remember, white grubs eat organic matter, mainly thatch. They also eat the roots, stolons and crowns within the thatch. It takes several years for turf to build up thatch and the organic matter that's in the upper inch of soil.
*From studies published in Arthropod Management Tests (1976-2011), using Japanese beetle and masked chafer efficacy data where checks had four-plus grubs per square foot and significant results. (Studies from Shetlar, 1999-2010, were used that were not published in AMT.) Compiled by D. J. Shetlar, September 2011.
Another factor is turf quality and maintenance. High turf quality means that there's more organic matter present. White grubs rarely damage turf that's allowed to go dormant in July and August.
Egg and first instar larval survival are the major factors determining grub populations. White grub eggs need to absorb moisture from the surrounding soil in order to develop. If they don't absorb moisture within 24 to 36 hours after being laid, they'll die. The tiny first instar grubs are also very susceptible to desiccation. So, if turf is irrigated during the time that scarab beetles are laying eggs, the risk of having white grubs rises.
In our risk assessment, we need to: note if there was a damaging grub population in the previous season; determine the age of the turf and how much thatch is present; and determine if the turf is being kept green during July and August.
When all these factors are positive, the risk of having a major grub problem is high. In this turf, I would recommend preventive grub treatments. New neighborhood, no thatch and no irrigation, then the turf is probably at low risk and you can shy away from a preventive grub treatment.
The white grubs that would fit into the normal annual species are: Japanese beetle, masked chafers, European chafer and Oriental beetle. Virtually all of these emerge as adults in June through July, lay most of their eggs during this same time period, and have first instar larvae in the soil-thatch interface from late July into mid-August, second instar grubs from mid-August to mid-September, and third instar grubs from mid-September on.
Working back, if first instar grubs arrive at the soil-thatch interface from late July into mid-August, then that's the ideal time to have grub insecticide present. Since many of the neonicotinoids can have 60 to 90 days of effective residual in the soil-thatch interface (over 120 days for chlorantraniliprole), you can back your application up accordingly.
One reason you might consider doing this is the convenience of making the application over a longer period of time. Another reason is that you may be able to control other early-season pests at the same time. You can control several pests with one application.
Be aware that they're distinct differences among the neonics (Table 1). If we look at the efficacy of imidacloprid and thiamethoxam following June, July and early August applications, we achieve 90-plus percent control. However, applications in May drop in efficacy. Why? We suspect that these pesticide molecules are being broken down and aren't in the soil-thatch zone in sufficient amount when the first instar grubs arrive. On the other hand, clothianidin seems to last longer with 90-plus percent control even when applied in May. Chlorantraniliprole also does very well in May applications. In fact, we have had excellent control with this molecule when applied in April
Billbug adults are commonly seen wandering about. If you see them, be sure to check the nearby turf.
The bluegrass billbug is still our most damaging cool-season billbug, though we are seeing more lesser billbugs and hunting billbugs putting in appearances. It appears that in most cool-season turf, these three species have very similar life cycles. They overwinter as adults, become active in early May, lay eggs in grass stems into June, and the larvae can damage the turf by late June through July.
Our traditional method of dealing with billbugs was to apply an adult preventive treatment. Actually, this was a surface or contact insecticide applied to kill active adults, but the goal was to prevent these adults from laying eggs. We still can use this strategy by applying one of the pyrethroids that is active against the billbug adults, such as bifenthrin, deltamethrin, beta-cyfluthrin and lambda-cyhalothrin.
However, we know that the systemic action of the neonics will allow for uptake into the grass stems where the billbug larvae are feeding. There's also evidence that early neonics applications may also be killing the billbug adults, or at least, interfering with their egg laying behavior. In any case, an application of any of the registered neonicotinoids in May seems to be providing very good billbug control.
The problem arises with the use of imidacloprid or thiamethoxam. If you apply these in early to mid-May, you won't have sufficient residual action to kill the white grubs that will be arriving in July. If you can wait until the last week of May or first week of June and use the highest label rate, you will still be able to knock out the billbugs and get the white grubs.
We don't see this issue with clothianidin products. They can be applied anytime in May and get excellent billbug and white grub control. Chlorantraniliprole can also achieve double-duty, even with April applications, but our experience is that the higher rate (e.g., 0.2 pound AI/acre) is the most consistent.
This homeowner thought that his turf had "just gone dormant" due to high summer heat, but when the cool weather returned, it was discovered that grubs had killed the turf.
Finally, for a real long-term fix for billbug problems, use endophytic turfgrasses. The turf-type tall fescues and improved perennial ryegrasses generally have high endophyte levels and this fungal symbiont easily controls billbug populations when 35 to 40 percent of the stems within a turf stand have the endophyte.
This can often be achieved with a simple interseeding (use a slit seeder) of the fescue or rye into an existing stand of Kentucky bluegrass, especially if grubs, billbugs or chinch bugs have damaged the stand.
Chinch bug control
In cool-season turf, the hairy chinch bug has made a real resurgence, especially in pure stands of Kentucky bluegrass. In recent biology studies, we found that the second generation is often larger than the first generation, especially where turf is kept green, through watering and fertilizing, for the entire summer.
Fortunately, chinch bugs are relatively easy to control unless there's a turf thatch issue. Several pyrethroids will take out active infestations. Also, virtually all the neonics will control chinch bugs, but they may be slow to react. To counter this, apply a neonic in May when the chinch bugs are first getting started and you won't have the second generation. This is a prevention approach.
Again as with billbugs, interseeding or renovating with turf-type tall fescue or endophytic perennial ryegrass will help control chinch bug outbreaks.
Dr. David Shetlar (the BugDoc), is professor of urban landscape entomology at The Ohio State University, OARDC & OSU Extension, and is a frequent and entertaining presenter at turfgrass conferences.