Monday, July 28, 2008

Turf - Time for Grub Controls

It is time to apply grub control measures in turf. The following is information on grubs and products available to control them.

Just for a quick refresher on the white grub life cycle: All of the important species have only one generation per year (annual white grubs!) that only varies by a few weeks in timing among the different species. The eggs are laid in June and July among the roots of host plants like turfgrasses and ornamental plants and hatch in 2–3 weeks. The emerging larvae go through three larval stages feeding on roots and organic matter in the soil. The first and second larval stage will last about 3 weeks each so that by late August the first third stage larvae appear. By mid-September the majority of larvae will be in the third stage. The bigger the larvae, the more they feed (more damage potential) but the less they become susceptible to most control agents. The third stage continues to feed into mid- or late October, then spends the winter inactive deeper in the soil, to come back up clofor another 4–6 weeks between mid-April and mid-June. The larvae pupate deeper in the soil and emerge after about 2 weeks as the next adult beetle generation.

If you deem preventive applications necessary, here are your current choices by insecticide class. Among the neonicotinoid insecticides imidacloprid (Merit, Advanced Lawn Season-Long Grub Control, GrubEX) has more recently been joined by clothianidin (Arena) and thiamethoxam (Meridian). Imidacloprid and thiamethoxam are very similar in activity but clothianidin seems to have a slightly wider spectrum of activity. Among these neonicotinoids, only clothianidin seems to have decent activity against the Asiatic garden beetle but should be applied at the highest allowed rate for this species. All three of them are very active against the other important white grub species although at least imidacloprid should be applied at the highest allowed rate against northern masked chafer if later in the season (past late July).

The insect growth regulator halofenozide (Mach2) is a very safe insecticide and is very effective against masked chafers and Japanese beetle, however, provides only around 50% of oriental beetle and no control of Asiatic garden beetle. The anthranilic diamide (a new insecticide class) chlorantraniliprole (Acelepryn) just received registration. It is highly effective against all the important white grub species (and a variety of other important turfgrass insect pests), has extremely low toxicity to mammals, birds, fish, and honey bees, is applied at the lowest rate of all white grub insecticides (0.1–0.2 lbs/acre), and seems to be compatible with many predatory and parasitic insects.

Two more recent additions to the arsenal are combination products. Allectus combines imidacloprid with the pyrethroid bifenthrin, and Aloft combines clothianidin with bifenthrin. The idea of these combination products is that they simultaneously provide control of white grubs (through the neonicotinoid compound) and control of surface feeding insects (through bifenthrin). Thus, they are a matter of convenience. From an IPM (intelligent or integrated pest management) standpoint, these combinations are questionable as white grubs and surface feeders rarely cause problems in the same turfgrass area. Unless the latter is the case, combinations only encourage unnecessary insecticide use which increases (1) the chances of insecticide resistance or enhanced microbial degradation and (2) and unnecessarily kills beneficials (higher potential for secondary pest outbreaks). If a turfgrass area has the potential of problems with white grubs and surface feeders, make sure not to apply the combination more than 3–4 weeks before the surface feeders should be controlled to avoid the loss of bifenthrin activity.

Information taken from "To Treat or not to Treat: Update on Preventive White Grub Treatments" by Albrecht M. Koppenhöfer, Ph.D., Specialist in Turfgrass Entomology, Rutgers University in the June 26, 2008 edition of the Plant and Pest Advisory, Landscape, Nursery & Turf Edition, Rutgers Cooperative Extension.

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