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Insect Pests To Keep In Mind: Black Cutworm, Alfalfa Weevil, And Cereal Leaf Beetle

Apr 28, 2016

By John Tooker

Significant numbers of Black Cutworm moths have been trapped in some locations in PA. Alfalfa weevil and cereal leaf beetles populations need to be monitored in the upcoming weeks.

As mentioned earlier in the month, again this year Penn State Extension and the Department of Entomology are monitoring black cutworm populations with pheromone traps. As moths arrive, if we capture eight or more moths over the course of two nights (a “significant flight”), there is an elevated risk in that particular area of cutting damage by caterpillars later in the spring. Over the past two weeks, black cutworm moths have begun arriving in the state, and we have detected two significant flights of moths, one in Franklin County (near Fayetteville) and the other in Lebanon County (near Cornwall). We continue to trap for others, but will now begin degree-day accumulations to predict the timing of cutting for those areas to inform folks when they should be scouting fields for damage. Rescue treatments are usually the most efficient and economical tactic for managing black cutworm.

For more information, see our fact sheet.

In your hay fields, alfalfa weevils have become active and according to the PA-PIPE system larvae should be active across the state (Fig 1). In the coming two weeks, it will be time to scout fields for feeding, looking for small holes on young leaves, particularly on south facing fields. Alfalfa weevil does not grow to damaging populations in every field, and in many fields small parasitoid wasps control weevil populations effectively. So get out there and scout to find where populations are and whether populations may need to be controlled later in spring. Our revised fact sheet accounts for recent higher prices for hay.

Figure 1:Predicted alfalfa weevil activity for 26 April 2016 across the state according to the PA-PIPE

The PA-PIPE system also indicates that cereal leaf beetles and larvae should be active, particularly in southern counties. In recent years, we have seen some fields with significant populations of cereal leaf beetle, but infestations are difficult to predict and can be very patchy. Natural enemies often control this pest species, but it can occasionally escape natural control and build into damaging populations. If eggs and young larvae are detected early, cereal leaf beetle is easily controlled with insecticides, but more difficult later in spring when larvae are older.

As is often the case, outbreaks tend to occur in fields that are not scouted regularly. The best defense against cereal leaf beetle is walking wheat, oats, barley and rye fields and looking for the pest. Insecticide treatments are warranted if populations exceed the economic threshold of one larva over 0.13 inches long per stem over a field or a portion of a field. A recently published fact sheet provides more details on their lifecycle and some images of adults, larvae, and their damage.

Source:psu.edu