Preventive ABW Programs Can Encourage Resistance

Better understanding of biology, natural suppression can mitigate blanket pyrethroid sprays

The annual bluegrass weevil (ABW), Listronotus maculicollis, is a serious and difficult-to-control pest of close-cut annual bluegrass (Poa annua) on greens, tees and fairways in the Northeast (Vittum et al. 1999). Over the last 20 years, the pest's area of impact has expanded from mostly around the New York metropolitan area to throughout the Northeast, west into Ontario, north into Quebec and south into Maryland (Vittum 2005, 2006, McGraw and Koppenhöfer 2007). Management practices, particularly lower mowing heights and reduced fertility, might be creating a better habitat for ABW and reduce the turf's tolerance for ABW feeding.

Photo 1: Adult annual bluegrass weevil.

ABW larvae can cause serious damage to annual bluegrass. ABW clearly prefers annual bluegrass over bentgrass, and the prior also appears to be more susceptible to ABW (Rothwell 2003). Young larvae tunnel the stems, causing the central leaf blades to yellow and die. The older larvae feed externally on the crowns, sometimes severing the stems from the roots. The most severe damage usually is caused by the first generation older larvae around late May/early June in the New York metropolitan area. Damage during this time starts from the fairway edges or the collars, where it also tends to be the most severe. Second-generation larvae in early- to mid-July typically occur in lower densities, but damage can still occur because of the greater environmental stress on the host plants during this time. There often is a third-generation in the metropolitan area, but other stresses on the turf mask the weevil damage on annual bluegrass.

Overwintering takes place in the adult stage in the rough or in the litter under trees (Diaz and Peck 2007). In April the adults migrate into annual bluegrass areas and, after a brief feeding period, the females start laying eggs under the annual bluegrass leaf sheaths. Development of the first generation in spring from eggs to adult takes about six weeks. The first-generation adults become active around mid to late June. Their offspring emerges as the second-generation adults in late July to August. Adults from the third generation migrate back to their overwintering sites from October into November.

Photo 2: Annual bluegrass weevil larvæ can cause serious damage along the edge of fairways.

Efficacy of synthetics

We have summarized data from insecticide-efficacy tests published between 1993 and 2005 conducted by university researchers in the Northeast (McGraw and Koppenhöfer 2007). The summary shows that pyrethroids were the most effective insecticides with no significant difference among the different compounds. The average control rates were 93 percent for bifenthrin (Talstar), 87 percent for cyfluthrin (Tempo), 84 percent for deltamethrin (DeltaGard) and 97 percent for lambda-cyhalothrin (Scimitar). It is presently recommended to apply pyrethroids against the overwintered adults between full bloom of forsythia and full bloom of flowering dogwood. However, our summary revealed no difference between pyrethroid applications in late April (89 percent) and early May (93 percent).

The organophosphate chlorpyrifos (Dursban) was more effective when applied in early May (83 percent) or late May (83 percent) than in late April (62 percent). While chlorpyrifos applications are now limited to 1 pound of active ingredient per acre (lb ai/acre), the data suggest that this rate was as effective as 2 to 4 lbs ai/acre. The organophosphate trichlorfon (Dylox) was ineffective when applied in late April and early May but provided 79 percent control in late May.

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