Like last year, we have reports of high numbers of spongy (= gypsy) moth larvae in cranberry beds near wooded areas. This is the same time that we observed them last year. Looking at the weather conditions, it is expected to rain and be windy and cold on Friday 06 May (tomorrow) and Saturday 07 May. At this moment, the larvae are small (early instars) and because it will be cold in the next few days, I don’t expect them to grow, or be active, that much. Thus, I think it is best to wait until early next week to spray to control them, if needed. The weather looks better next week.
Biology. Spongy moth has one generation a year. It overwinters as eggs. Eggs hatch at this time of the year (we should have already passed peak egg hatch). First instars “balloon” on silken threads from infested trees onto nearby cranberry beds. Thus, spongy moths tend to be one of the earliest caterpillars to show up in cranberry beds, usually during the first week of May. Observed larvae are mostly early instars and will feed on the terminal buds. Although less common, it is also possible that eggs overwintered on the bog floor and that older larvae will crawl later in the season onto beds from surrounding trees.
Scouting and Control – Spongy moth larvae are quite easy to detect by means of sweep net sampling and are easy to control with most of the insecticides at our disposal. The action threshold for spongy moth is an average of 4.5 larvae in sets of 25 sweeps. We recommend the use of Intrepid, Delegate, Altacor, Exirel, or Verdepryn if populations exceed action thresholds. These are reduced-risk insecticides that are very effective against lepidopteran pests.
