An ear of corn with healthy fresh silk. The grower will have to protect the silk with an insecticide as long as the silk is fresh and has not dried. Photo: Tom Ford
First, all corn is wind pollinated, so pollen grains need to come in contact with the "silk" sprouting from the ear. Corn silk is slightly sticky to the touch and fresh silk will start out green or pink and then dry to a dark brown color. Sweet corn is the most vulnerable to invasion by insect pests while the corn has fresh silk.
Growers historically sprayed at regular intervals in an effort to keep the various worm pests out of the ears. When you routinely apply insecticides without monitoring for pests you increase your operational costs while potentially compromising the population of beneficial insects that may be harbored in the sweet corn.
In an effort to reduce insecticide usage in sweet corn, many growers have adopted an Integrated Pest Management (IPM) approach which relies on the weekly trapping of adult pests (moths) in their sweet corn fields. These traps are not designed to capture the entire population of moths, but are used to tell the grower if a moth flight is occurring and what the level of pressure is in their field. Through the use of trapping, a grower can more effectively time the applications of insecticides to the sweet corn field and can select the most appropriate spray interval to maximize this protection effort.
In some years, growers have had the luxury to skip insecticide applications completely due to the lighter than normal capture of the adult forms of key sweet corn pests like Fall Armyworm, European Corn Borer, and Corn Earworm. But weekly monitoring is necessary as pest populations can increase dramatically which forces growers to spray.
A healthy sweet corn field in full tassel. The grower uses data from our trapping network to time his insecticide applications. His field is buzzing with honey bees as they collect pollen from the tassels. Photo: Tom Ford
Once the population of adult moths drops via the weekly trap counts, the growers will once again be able to stretch out their spray program and reduce the frequency of their insecticide applications. If you would like to see what the sweet corn pest pest pressure is in your area please go to our Pestwatch website.
One of four traps that Penn State has employed in a Blair County field. Data derived from this trap is posted to Pestwatch and is shared at our information station at the Morrisons Cove Produce Auction. Photo: Tom Ford