Sulfur for rootworm control

The use of unconventional products to protect corn roots from insect damage continues to attract the attention of a few Iowa farmers. Soybean meal, sugar, turpentine, dry molasses, and a mixture of kelp, fish meal, diatomaceous earth, and molasses have been suggested as effective products for corn rootworm control. The fascination behind the use of these unconventional products apparently is that they are less expensive and safer to use. Farmer testimonial has been used to promote the use of these products, however, I have yet to see any replicated field trials to substantiate claims that performance is equal or superior to that of conventional rootworm insecticides. All of these products have been tested by entomologists at Iowa State University, University of Minnesota, or University of Wisconsin. The results indicated that none of them protected corn roots from rootworm injury.

During the past couple of years, sulfur has been promoted by some as an effective corn rootworm control. Again, because there were no replicated data to validate the claims of performance, tests where conducted by ISU entomologists to answer farmer questions about the value of using sulfur to protect corn roots from insect damage.

Three tests were conducted in Iowa in 1992. The tests consisted of planting-time applications of Counter 15 and Lorsban 15G (both at 8 ounces per 1,000 row feet) feed-grade sulfur (99.5% at the rate of 18.4 ounces per 1,000 row feet), and an untreated check. Performance was evaluated by counting the percentage of lodged plants and rating roots for feeding injury. A rating of 3.5 or less suggests that the product performed adequately in protecting roots. A rating of 4 to 6 indicates that a product failed to protect corn roots and there was a high probability of yield loss.

The results are shown below and indicate that sulfur is not effective in protecting corn roots from rootworm damage; root ratings were very high and 48 to 55 percent of the plants lodged. In fact, using sulfur was similar to using nothing at all. A farmer that uses sulfur and doesn't have lodged corn may think that he has found a wonderful insecticide. In reality, his field probably has a very small rootworm population that wouldn't cause economic yield loss anyway. In a field with a large rootworm population, the use of sulfur could be devastating and result in yield loss. Based on this research, I would strongly recommend that sulfur not be used as an alternative for a soil insecticide.

                       Crawfordsville      Ames             Newell

Product  Root     %          Root     %       Root     %
                       Rating  Lodging     Rating Lodging   RatingLodging

Counter15G     1.3     2.5       0         2.8      0       2.5      0

Lorsban 15G    1.3     3.3       0         3.0      3       2.4      0

Sulfur 99.5%   20      5.5      55         4.6     48       5.4     48

 Check       --        5.0      67         4.6     62       4.4     25
Updated 03/04/1993 - 1:00pm