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Posted 9 March 2007. Crop Management. Managing Rootworms in Continuous Corn South Dakota State University. www.sdstate.edu Brookings, South Dakota (March 6, 2007)- The current high demand and market value of corn makes continuous corn attractive to producers, but it will also attract more rootworm pressure than usual, a South Dakota State University specialist warned.
SDSU Extension Entomologist Mike Catangui said in fields seeded to continuous corn, rootworms have a continuous food supply, resulting in the buildup of rootworm infestations of cornfields over several years. “Roots of corn are the exclusive food of rootworm larvae; they cannot normally survive on roots of soybean, wheat, sunflower, and alfalfa,” Catangui said. “It is this almost complete dependence on corn that makes rootworm larvae vulnerable to crop rotation. Remove corn from the field and rootworm larvae will starve to death due to lack of suitable food for survival.” Growing corn continuously on the same field is not yet very common in South Dakota. However, Catangui said that he knows of a few growers in the state who have been planting corn continuously for up to 40 years. Continuous corn planting also has been made easier to accomplish by the recent introductions of genetically engineered (Bt) corn hybrids that produce proteins in their roots that are toxic to rootworm larvae. Rootworm eggs are laid in the soil from late summer until the female rootworm beetle adults are killed off by the first killing frost in the fall. In South Dakota, rootworm eggs are still laid mainly in cornfields. Eggs of rootworms overwinter in the soil. Fields planted with corn the previous season will most likely already have rootworm eggs waiting for corn. Eggs hatch as soon as roots start growing from the planted corn seeds. Most injuries by rootworm larvae occur in June and July during the very active root growth phase of the corn plants. Larvae transform into pupae in mid July; adult rootworm beetles emerge from the soil starting from late July through August while the corn is silking and tasseling. Adult beetles feed on corn pollen, silk, and leaves. They also feed on the pollen, flower, and leaves of many other plants including soybeans, sunflowers, and garden flowers. South Dakota corn growers who wish to grow corn continuously will have to manage corn rootworms to improve yield and facilitate harvest, Catangui said. Root pruning by the rootworm larvae can result in reduced water and nutrient intake by the injured plants resulting in severe loss of yield. Partial and complete lodging of corn plants can also result because of reduced root support. Lodged corn is also very difficult to harvest and likely results in increased fuel cost at harvest. SDSU research in 2006 conducted by entomologists Billy Fuller and Brad McManus on 15th-year continuous corn near Garretson showed that corn protected from rootworms yielded between 19.3 to 46.9 bushels per acre more than unprotected conventional corn. The rootworm control tactics investigated were genetically engineered corn, granular soil insecticides, and seed treatments. In Bryant, on third-year continuous corn, the yield advantages were from 3.2 to 39.2 bushels per acre. Catangui and SDSU graduate student Jon Kieckhefer have also been conducting an inventory of all corn insects (from the roots to the ears) of conventional and genetically engineered corn hybrids since 1996. Results last season of their rootworm research indicated up to 39.7 bushels per acre yield advantage in fields where rootworm larvae were controlled using a liquid soil insecticide, genetically engineered corn, and seed treatments. That research is funded in part by the South Dakota Corn Utilization Council. In continuous corn, the main control tactics available to growers are genetically engineered corn hybrids, granular or liquid soil insecticides, and systemic insecticidal seed treatments. Genetically engineered corn hybrids containing the YieldGard Rootworm, YieldGard Plus, Herculex RW, Herculex XTRA, and Agrisure RW genes are resistant to feeding by rootworm larvae. Insecticidal proteins toxic to rootworm larvae are produced in the roots by these Bt-corn plants. Which Bt genes to utilize in the corn plant is decided upon by the seed brand or company. All corn hybrids containing the Bt genes effective against rootworm larvae are also automatically treated with a low rate of an insecticidal seed treatment. Insecticidal seed treatments available to corn growers are clothianidin (Poncho), imidacloprid (Gaucho, Prescribe) or thiamethoxam (Cruiser). These systemic insecticides are coated onto the seeds before the seeds are bagged and sold to growers. Granular or liquid rootworm insecticides are applied in-furrow or very close to the seed furrow during the planting process. Corn planting in South Dakota usually occurs from late April through early June. Soil insecticides labeled for rootworm larvae are bifenthrin (Capture LFR, Discipline), carbofuran (Furadan 4F), chlorethoxyfos (Fortress), Chlorpyrifos (Lorsban, Nufos), ethoprop (Mocap), fipronil (Regent), Phorate (Phorate, Thimet), tebupirimfos + cyfluthrin (Aztec), tefluthrin (Force), and terbufos (Counter). Always read and follow label directions. Contact: |
