As I write this on May 10, none of the insects highlighted here are active in New York – yet. But it won’t be long. I picked an insect from corn, alfalfa and soybeans that you need to watch for this time of year.

Corn: Black Cutworm (BCW)
Corn planting was off to a great start in April but cooler wet days in May delayed some plantings. These later planted fields will be vulnerable to attack by BCW in early June. BCW moths have been getting a slow start on their yearly travels north. In fact, the Midwest has been reporting catching more common armyworm (CAW) moths than cutworm moths. Let’s hope we don’t experience a CAW outbreak like in 2001!

To scout for BCW, walk the corn rows looking for cut, wilting or missing plants. If you find an injured plant, dig in the soil around the base. BCW are nocturnal and will hide under the soil during the day. If 5% or more of the plants in the cornfield are cut or injured, an insecticide spray is warranted.

Alfalfa: Potato Leafhopper (PLH)
Leafhoppers are more of a concern in second-cut alfalfa because the majority of them arrive after first-cutting haylage and dry hay harvest. I’ve found my first PLH as early as May 6 and as late as June 7.

All stages of PLH feed by sucking out plant juices. Severe feeding turns alfalfa leaves yellow and plants become stunted. Use a sweep net to sample the PLH population, taking five sets of 10 sweeps (50 sweeps) throughout the field. Calculate the number of PLH (adults and nymphs). See pages 96-99 in the 2008 Cornell Field Crop Guide for threshold numbers and insecticide recommendations for clear seeded alfalfa. For mixed alfalfa/grass stands, there are two insecticides labeled for New York – Mustang Max and Warrior.

PLH-resistant varieties have become more popular in recent years and are an economically feasible option. During the seeding year, PLH thresholds are the same for resistant varieties as nonresistant varieties. They still may have to be sprayed. Thresholds can be increased 2X in subsequent years.

Soybeans: Soybean Aphid (SBA)
Aphids overwinter in the egg stage on Buckthorn trees in New York. These local populations will begin to hatch and fly to young soybean plants during the first week in June. Like leafhoppers, aphids feed by sucking out plant juices. All of them are females and, therefore, reproduce very quickly. This requires a diligent scouting program.

Aphids will be found at the top of the plant on the underside of the newly emerged leaves. In most years these early populations have been controlled by natural enemies like the ladybird beetle. Current threshold for treatment is an average of 250 aphids per plant across the whole field. Be careful about spraying too early as this can cause rebound populations unchecked by natural enemies.

Happy hunting!

To learn more…
Mike Stanyard is the field crops and insect specialist with the Northwest New York Dairy, Livestock & Field Crops team. Contact him at 315-331-8415. Ext. 123. Email: mjs88@cornell.edu
See the 2008 Cornell Field Crop Guide for more information on insect thresholds and insecticide recommendations.
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