What impact will all this rain have on turf insects in southern New England?
Many areas in southern New England have experienced unusually heavy rainfall during July. In fact, areas near Amherst, MA received over 13 inches of rain in the first three weeks of the month. That is about what we would expect in four months. Many turf managers are wondering what the impact of that rain will be on insect populations.
Most species of white grubs that we see in New England (e.g., Japanese beetle, Oriental beetle, European chafer, Asiatic garden beetle) begin laying eggs in July. This year, beetle’ flights occurred as expected. The first Oriental beetles were found in traps on June 22, with densities peaking at the end of the month and the flight declining by the end of the second week of July. Asiatic garden beetles were slightly later and the adult presence has been more prolonged compared to Oriental beetles. Japanese beetles started flying at the end of June - beginning of July and peaked shortly after flight. Overall, we observed greater adult numbers of all three species in Western Massachusetts compared to previous years. In combination with the high soil moisture, which favors eggs and young larvae survival of some species, it might lead to greater population densities and more areas affected.
Where there is surface flooding and soils are saturated, many adults will delay egg-laying until soil moisture conditions improve… or choose an area with better drainage. So egg-laying may be a bit delayed this year. In addition, females will look for sites with "good" soil moisture conditions (not too wet). This year that might mean that they will seek out areas that are on higher ground or drain well, so look for grub populations in these areas when it comes time to scout in early to mid-August.
Normally we would expect heavy rains to at least slow down billbug activity but field reports suggest that billbugs are indeed quite active this summer. It is very likely that the recent relatively mild and wet weather allows grass to overgrow and that may mask billbug activity. However, our sampling reveals that billbug numbers are not any lower than previous years. According to last week’s sampling in Western Massachusetts, many larvae reached last instars and are at the peak of pupation. When pupating, billbugs do not feed and do not cause damage. After pupation, the adults are not expected to reproduce and they will not lay eggs or produce any more larvae. Newly emerged adults will probably feed and prepare for overwintering, and eventually move to overwintering sites. However, we are still finding smaller larvae in some samples, and the coastal Massachusetts areas especially are usually about a week behind Western Massachusetts in terms of insect activity. Scouting for billbug larvae will help you to diagnose the problem and make management decisions this year, as well as informing plans for the next season.
Of the two introduced species of crane flies that cause damage on turf in Massachusetts (European crane fly and "common" crane fly), so far we have only identified “common” craneflies (not to be confused with native species, which are usually not pests and not damaging to turf). Both species do better when soils are wet so more larvae may survive this summer than we normally see. We observed relatively large flights of adults in late April this year, in spite of dry conditions during the previous year. Because of the wet season, we expect even larger flights of adults in late August or early September and possibly greater larval densities. Watch for those flights and be prepared to treat areas that have experienced damage in previous years.
Annual bluegrass weevil
We had a relatively “normal” ABW season, with the life stages of the overwintered/spring generation occurring about one week earlier than observed previously. The peak of Adults peaked in late April and late June, and we expect the new adults to peak next week. We have started seeing adults at overwintering sites, so some of them have already started migrating.
The early stages of annual bluegrass weevils are stem borers, feeding inside of the stem, so they are therefore largely not affected by the rainfall. However, large larvae (fourth and fifth instars) of the annual bluegrass weevil often float to the surface when heavy rain occurs, and they will float down the fall line to puddles. If you experienced heavy rain at a time when many of the larvae were large enough to be outside the stem, you may see increased levels of damage in those low-lying, puddling areas. And some of the adults may have floated down to the puddle areas as well. The good news is that the presence of plenty of moisture often masks the damage the weevils may be causing as they feed.
Theoretically these insects suffer the most from the wet conditions. Hot and dry conditions favor nymph survival and fast development. Chinchbugs nymph are very small and wet conditions make it challenging for them to move around. In addition, the naturally occurring entomopathogenic fungus Beauveria bassiana is usually more virulent against chinchbugs in moist conditions. On the other hand, during hot and dry seasons grass is stressed and has low tolerance to insect feeding and damage is more noticeable.
We have, however, still received reports of chinchbugs causing damage this season. We observed young (red/orange colored) nymphs during the last week of June, more recent samples had mostly large nymphs and adults. Chinchbugs will continue feeding until they are ready to overwinter.