ABW Peak Activity
This week, GDD accumulations have reached the threshold of peak annual bluegrass weevil (ABW) adult activity (~100 GDD, base 50°F) in Western MA and the Hartford, CT area. Eastern MA and Cape Cod have accumulated only ~60 GDDs (about a week behind the inland sites).
GDD accumulations are very typical for the region this year. For the last 5 years average accumulations were ~100-110 GDDs by April 20th and ~130-140 by April 28th. 5 year average accumulations on the coast were ~60 and 70 GDDs by April 20th and 28th respectively. Plant phenology is in in alignment with GDD accumulations… Forsythia half green/half gold (HGHG) or approaching HGHG this week.
Though this season so far falls within typical observations, ABW adult emergence has been rather diffused and prolonged, mainly because of the short periods of warm temperatures that have alternated with cold spells. This means that we may not see a well-fined peak of adult activity. The pattern of emergence could make it hard to achieve good control with adulticides, meaning it may be better to focus on managing larvae this year
ABW adult numbers in the samples from fairways have been increasing steadily, even though we have not observed high numbers. All indicators suggest that this week (week of 4/28) and the following week is a peak of adult activity. If high ABW density is observed it is time to apply adulticides (if this application is planned) and/or prepare for larval monitoring in a couple of weeks. ABW abundance can be monitored by vacuum samples, soap flushes, or simply checking clippings collected in mower baskets (Fig 1). The weather forecast predicts warm temperatures, perfect for ABW adult activity and applications.
Pyrethroids (bifenthrin, lambda-cyhalothrin, cyfluthrin, deltamethrin, etc.) are the only available adulticides. This strategy was common in past years to deal with ABW adults and was relatively inexpensive and effective. Overuse of this chemical class, however, led to the development of ABW tolerance or resistance, thereby reducing the efficacy of pyrethroids and their broad-spectrum activity. Concerns have also been raised regarding non-target effects and risks for beneficial insects.
Another application that can be made at this time is novaluron, which is a chitin synthesis inhibitor (insect growth regulator (IGR) class). This active ingredient is mostly effective against eggs and young larvae but has demonstrated great efficacy if applied at the adulticide timing as well (because of possible effects on the reproductive system of adults).
The recent general recommendation for ABW management is to move away from adulticide application and focus on larvae management, considering the resistance issues and different active ingredients available for larvae control. In addition, we’ve observed relatively low ABW adult densities throughout the region in recent years. If a low number of weevils is observed, it is another reason to avoid pyrethroid application and target larvae instead, and to make the decision according to pest densities.
Other Insect Pests
Chinch bug adults are active, but there are no nymphs present yet. This year we haven’t observed high numbers of chinch bugs so far. This is due at least partially to the relatively wet spring, which creates favorable conditions for the naturally occurring entomopathogenic fungus Beauveria bassiana, which contributes to natural mortality of chinch bugs.
As soil temperatures rise above 60°F (within the top 2”), white grubs have moved up in the soil profile (we are finding grubs within the top 2” of soil, Fig 2) and have resumed their feeding. If densities are high, damage may become apparent. Usually, curative control of grubs in spring is not recommended unless the high grub densities occur in highly valuable areas where no damage can be tolerated. Arguments against application during this time are 1) the grubs will feed only for a limited time and soon they will be pupating, thus damaging feeding is limited; 2) during the spring there is enough moisture in the soil and damage is often masked by intense grass growth; 3) when grubs begin to pupate insecticides become ineffective, which translates to an incredibly narrow window for applications; and 4) very few insecticides can provide truly effective control at this stage. Our preliminary studies have demonstrated trichlorfon (DyloxTM) provides only ~80% control at best, clothianidin (ArenaTM) at the highest labeled rate provided up to 50-60 % of control when third instar grubs are targeted.
For areas where grub presence is observed it is a good time to conduct or schedule a preventive application against the next generation of grubs which will hatch in July. Chlorantraniliprole applications made at this time (from April 15 to June 15) will be not effective against the large “spring” grubs feeding now, however there will be excellent preventative effectiveness against the small “summer” grubs still to come. If you use other active ingredients for preventive grub application (for example, neonicotinoids) they should be applied during egg-laying (beginning of July).
Turfgrass Ants
Workers became active last week, however no mounds have been observed yet. According to last year’s preliminary data, mounds are expected to appear about 2 weeks after the first ants are found in the samples (this year probably 1st–2nd week of May), and peak closer to June. Mounds are the main issue caused by turfgrass ants (Fig 3), and therefore ants cause problems only on short cut grass (greens, trees, fairways) on golf courses. They are abundant in lawns however their activity is not problematic, moreover turfgrass ants are effective predators and should be managed only in high value short cut grass. Turfgrass ants do not sting, so they do not pose much risk for humans and pets.
Spring is the best time for ant management because populations are weak and less abundant after overwintering. Spring application of neonicotinoids (imidacloprid, clothianidin, thiamethoxam) at the first appearance of mounds is a common strategy to reduce mounding activity. Our preliminary lab study demonstrated high direct toxicity of neonicotinoids to ant workers. By killing workers especially in the beginning of the season, weakening of the colony might be achieved. Often, killing ant-workers only temporary reduced the occurrence of mounds, and multiple applications are necessary. Similarly, using pyrethroids can temporarily reduce worker numbers. However, to achieve long-lasting control, the queen must be killed.
The main colony with the queen is usually located outside of short cut turfgrass and relatively deep in the soil. The only way to reach the queen by insecticide is to use baits. Baits have two major components: a carrier/food matrix which is attractive to ant workers, and the slow-acting active ingredient. The ant worker picks up the bait particle and carries it to the colony as a food. The slow-acting AI allows enough time to bring it to feed the queen and brood with the bait, eventually killing them. Baits are available in granular form and can be broadcast via spreader to affected areas.
Submitted by: Dr. Olga Kostromytska