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New insecticide options
1 Apr, 2002 By: Daniel Potter, PH.D. Landscape ManagementThese new target-selective insecticides give turf managers new hope in pest management
In the past 10 years there has been radical change in the kinds of insecticides available to turf and landscape managers. Organophosphates (OPs) and carbamates that had previously been mainstays were restricted, and old standbys like diazinon, Mocap (ethoprop), Oftanol (isofenphos) and Turcam (bendiocarb) were lost. Passage of the EPA's controversial Food Quality Protection Act in 1996 had many Green Industry professionals concerned that they would be left without any effective tools for managing insect pests.
 During the 1990s, management strategies for soil insects such as masked chafers (left), Japanese beetles (right), grubs and mole crickets shifted from curative to preventive control. |
The 1990s also saw the advent of new kinds of insecticides that can be applied at low use rates, with reduced hazard to humans and the environment, and products that work selectively against pest insects (Table 1). Many of them are more versatile and effective than past ones.
We no longer depend on just two classes of chemistry. In fact, from the standpoint of insecticides, a person could argue that we're in a stronger, more diverse and more defensible position today than just a decade ago. Let's take a look at current trends in turf insecticides and what may be on the horizon.
Grubs and billbugs
From 1969 to 1994, short-residual OPs and carbamates were the only option for grub control (Table 1). Turf professionals used these materials curatively, targeting young grubs. If the timing was too early, the residues would degrade before the eggs hatched. If it was too late, the large grubs would have already caused damage and be hard to control. The insecticides required immediate watering-in, and their broad toxicity to humans, birds and other non-targets made them less than ideal to use. In addition to the aforementioned products, Crusade (fonofos) and Triumph (isazafos), both OPs, were canceled for turf usage in the 1990s. Table 1. Insecticides then and now |
Registration of Merit (imidacloprid) and MACH2 (halofenozide) during the 1990s revolutionized grub control. These pesticides' residues persist in soil for several months, allowing flexibility in application timing. Both products, especially the granular formulations, are forgiving if not immediately watered in.
Merit, which belongs to a new class of insecticides called chloronicotinyls, selectively disrupts insects' nerves. MACH2 mimics the activity of the insect molting hormone, causing a premature, lethal molt. Both products are target-selective, which means they have low inherent toxicity, except to insects. Registration of Meridian (thiamethoxam), a new thianicotinyl with a control spectrum similar to Merit's, is expected within the next year.
 Most of the newer insecticides are target-selective, providing reduced hazards and low environmental risk. Here, grubs were induced to undergo an abnormal, lethal molt following ingestion of MACH2, a molt-accelerating compound. |
Applied before egg hatch, Merit and MACH2 usually provide excellent (>90%) control. Throughout most of the cool-season and transition turfgrass zones, the optimal treatment window for controlling annual grub species (e.g. Japanese beetles, masked chafers) with either product is June 10 to July 21. That timing ensures that fresh residues are in the soil at egg hatch.
Preventive grub insecticides do have limitations. Neither Merit nor MACH2 works well against large grubs. MACH2 will control small- to mid-sized grubs (up to the second instar) for several weeks after egg hatch, but as a "rescue" treatment it works too slowly to discourage skunks and other predators from digging. Both insecticides work well against masked chafers, Japanese beetles and black turf ataenius grubs. MACH2 is less effective than Merit against European chafers and Asiatic garden beetles, but it's more active than Merit against cutworms and other caterpillars.
The downside of preventive grub control is that the decision to treat must be made before the extent of infestation is known. Turf managers who practice IPM, reserving preventive treatments for high-risk areas, often find they must spot-treat some areas in late summer. Fast-acting soil insecticides provide the safety net in such situations.
With last year's cancellation of Turcam (bendiocarb), Dylox (trichlorfon) and Sevin (carbaryl) are the only fast-acting products left for curative grub control. Carbaryl has the drawback of being toxic to earthworms, bees and beneficial parasitic wasps. Losing these products would leave few options other than blanket preventive control.
Good products for controlling billbugs still exist. Merit and MACH2 both have systemic activity that will control young larvae within grass stems, as well as older ones that feed on roots in the soil. Either product applied at high label rate from mid-May to early June will preventively control billbugs, with residues persisting long enough to control white grubs later in summer. Alternatively, a pyrethroid can be applied in late April to mid-May to intercept female billbugs before they lay eggs in the stems. Consult entomologists at your state university for optimal timing in your area.
Surface-feeding pests
Cancellation or restriction of OPs and carbamates has had little impact on turf managers' ability to control surface-feeding pests. Some of the newer classes of insecticides work just as well, or better, than the old standbys.Pyrethroids, including Talstar (bifenthrin), Tempo (cyfluthrin), DeltaGard (deltamethrin), Scimitar (lambda-cyhalothrin) and Astro (permethrin) work great against cutworms, armyworms and sod webworms.
 Several newer classes of insecticides effectively control cutworms and other surface-feeders. |
Pyrethroids are synthetic versions of pyrethrum, a natural botanical insecticide, but with enhanced properties. They provide rapid knockdown of pests at low rates. Remember this when comparing costs because the price per gallon seems high until you factor in cost per application. Although they have low inherent toxicity to mammals and birds, most are labeled as "restricted use" because they're toxic to fish. They also work well against chinch bugs, greenbugs and other sucking pests, and for targeting adult females of billbugs or black turfgrass ataenius before they lay eggs in spring. They aren't effective against grubs because they bind in thatch and don't reach the root zone.
Conserve (spinosad), a novel insecticide derived from fermentation of a naturally occurring bacterium, is also highly effective against cutworms, sod webworms and armyworms. It has low-use rates and low toxicity to humans and wildlife. MACH2 (halofenozide), especially liquid applications, also works well for turf-feeding caterpillars. Applied for grub control, Merit has systemic activity against chinch bugs, greenbugs and other sucking pests.
Regarding older chemistry, Dursban (chlorpyrifos), Orthene (acephate) and Sevin (chlorpyrifos) are still labeled against cutworms and other surface-feeders on golf courses. Labeled rates for some products (e.g. Dursban) have been reduced. Orthene and Dursban are no longer labeled for home lawns. Turcam was canceled in 2001. Diazinon is no longer labeled for golf courses or sod farms; all other uses will be phased out by 2003.
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