Other Pests To Keep In Mind: Slugs, Alfalfa Weevil, Cereal Leaf Beetle

By John Tooker

At this point in the season only a few management tactics hold potential, and true relief will come in the form of warm, sunny weather that can dry out fields. If you have portions of fields that are heavily damaged, metaldehyde-base baits can be useful, but these baits can be ineffective at times, particularly when rain keeps coming.

Managing slugs takes an integrated approach that should be planned well before spring planting. The most diverse rotations tend to experience the fewest slugs, and cover crops can be part of the solution to increasing rotational diversity. Many farmers believe that cover crops tend to be part of the problem, but our research indicates that cover crops can be helpful in the fight against slugs. Other helpful tactics can include planting crops at appropriate soil temperatures and ensuring good furrow closure.

Our research is also showing that strong populations of ground beetles can help suppress slug populations. These beetles can be suppressed by insecticide use, including seeds treated with neonicotinoid insecticides, so consider avoiding treated seed if you have fields that are perennially damaged by slugs. Our fact sheet on slugs describes scouting and management options.

In your hay fields, alfalfa weevils should be starting to wrap up. According to the PA-PIPE system larvae should be actively feeding only in the northern part of the state; larvae in the rest of the state should have pupated by now, or nearly so (Figure 1). Our revised factsheet provide more detail on the life cycle of this pest species.

Fig. 1. Predicted alfalfa weevil activity for 24 May 2016 across the state according to the PA-PIPE

Cereal leaf beetle larvae are also active around the state, so it would be prudent to scout wheat and oat fields. This pest species is occasionally mistaken for slugs, but is easy to identify once you notice them (Figure 2). Larvae are most difficult to control when feeding on flag leaves, and are more easily controlled when infestations are detected early. As is often the case, outbreaks tend to occur in fields that are not scouted regularly. 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. For insecticide options, please consult Penn State’s Agronomy Guide.

Figure 2. Cereal leaf beetle larvae, shown from the side and the top, next to distinctive stripping damage that runs parallel to leave veins (white arrow). Larvae protect themselves from animals that may want to eat them by mixing their frass (excrement) with mucus and piling it on their back. Isn’t that cool?! (Photos by Chris Difonzo, MSU)

Source:psu.edu