There is another beetle group - the flea beetles - on which this material is quite active. Several flea beetles (corn flea beetle, pale striped flea beetle, western black flea beetle, toothed flea beetle, sweetpotato flea beetle, the smartweed flea beetle) transmits the bacteria Erwinia stewartii, which caused bacterial wilt or Stewart's wilt in sweet corn. Choosing sweet corn cultivars with good host plant resistance is an important management tool for this disease. We may now have another tool.
Gustafasson is developing imidacloprid as a seed treatment in sweet corn. The seed treatment formulation is called Gaucho. Gaucho-treated seed will absorb the insecticide, which is systemic, and help control flea beetles during early growth stages, which helps with both insect and disease management.
Gaucho is not available for farmers to treat their own seed. The company is concerned about phytotoxicity by overdosing, and lack of efficacy due to an insufficient dose. Furthermore, absorption by the seed even during storage can affect vigor and germination. However, the seed producers are developing Gaucho as a seed treatment for certain cultivars.
As of this writing, a full federal EPA label to allow Gaucho treatment of sweet corn seed is pending. I cannot predict if it will be ready by the next field season. However, the major seed producers are expected to be able to treat seed under a temporary Section 24-C label in Idaho, Colorado, or Minnesota (where most of the seed treatment would occur) and then sell it in certain states. Alan MacNab and I worked to ensure that Pennsylvania is on the list of included states for last field season, where it was mostly relevant to processing cultivars. We hope the temporary label will be extending for the next field season, and the cultivar list be extended into fresh-market cultivars. Pennsylvania will again be included. Therefore, you can request to buy Gaucho-treated seed as part of a flea beetle and Stewart's wilt management program in sweet corn. However, you will need to request this from your seed supplier.
Any systemic will not work forever, and issues that effect uptake (temperature, soil moisture) might influence how well the material works. Be prepared to treat susceptible varieties with a foliar insecticide if there are 6 or more beetles per 100 plants. A banded application just over the plants should work. Keep scouting even after a spray, to make sure more beetles do not move in. The overwintering adults will feed on weeds and move into corn plants throughout May and June. Beetles tend to be more abundant on outer rows. Scouting on calm, sunny days works best - the beetles are most active then, and although they will jump away from you, it will be easier to spot them because of this activity.
Although you should not overly rely on a systemic, data from Illinois suggest that Gaucho-treated seed can be a highly valuable component of management, with greater value on the more susceptible cultivar. And remember, if you are interested in Gaucho-treated sweet corn seed, you will need to request this from your seed dealer.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Shelby Fleischer, Professor
Last updated January 2001