March 30, 2007

Tips for No-tilling Corn on Corn

1. Rotate hybrids to take advantage of disease resistance packages. Be sure to select hybrids for continuous corn that are rated resistant or tolerant to diseases that overwinter in corn residue in your area, particularly if they’ve been a problem in the past. Examples would include grey leaf spot in eastern Nebraska and Goss’s bacterial wilt and blight that can occur statewide but was especially severe in western Nebraska in 2006. Changing hybrid numbers within the same family is not adequate because all members of that family will likely show the same susceptibility to the same diseases. If switching seed companies, check the rating scale being used to describe the hybrid disease resistance. Some companies use opposing rating scales. For example, a rating of 1 might equate to "excellent" for one company but "very poor" for another.

2. Manage corn rootworms. Knowledge of rootworm adult levels through scouting is an important tool to help manage rootworms in continuous corn. If threshold levels are exceeded, using a planting time rootworm insecticide or insect protection seed traits will likely increase profit to the grower. A seed treatment insecticide may provide adequate protection against low to moderate rootworm populations but is not recommended as a stand-alone treatment against high rootworm populations. Rotate control methods to reduce potential resistance problems and observe all refuge planting requirements when using seed traits (see Using the Right Bt Refuge for Your Seed in the March 9, 2007 issue of CropWatch).

3. Learn to recognize the insects and diseases that may be more severe in corn on corn than in a corn/soybean rotation. In addition, be aware of factors influencing disease development, such as environmental conditions and wounding. The higher risk environment of no-till corn on corn may make foliar fungicide applications for disease control more economical. Be sure to follow good IPM practices and don’t make pesticide applications automatically just because pests are present. Learn about economic thresholds and their effects on yield. Be aware that in continuous corn some problems may increase quickly because of the additional corn acres, the lack of rotation, and the accumulation of residue that serves as an overwintering site for some common pathogens and insects. This residue may support additional inoculum.

4. Scout for insects and diseases that can move in from other areas instead of overwintering in Nebraska. Some pathogens cannot survive in Nebraska, such as the fungus that causes southern rust. If there is a history of problems in your area or south of your area (from which pests would move in with summer winds), consider hybrid disease packages, seed traits, or preventive treatments. Proper scouting and timely treatments may be more economical and environmentally friendly when products are not applied unless thresholds are exceeded.

5. Use a cover crop after corn harvest to help decompose the residue and break some pest cycles. The humidity in the cover crop canopy increases biological activity to break down the residue, reducing some pests and diseases. A non-grass cover crop will affect carbon/nitrogen ratios, resulting in more soil biological activity and faster residue breakdown; however, some cover crops and especially grassy weeds may be alternate hosts for certain diseases and insects, so be careful with cover crop selection and weed control.

6. Be aware of the impact of planting date on late season insect and disease pressure. Planting outside the optimal window, either early or late, can increase the risk of damage, such as that caused by grey leaf spot. In particular, late planted corn is more prone to late season fungal foliar diseases, making disease resistance packages even more important.

Tamra Jackson
Extension Plant Pathologist
Bob Wright
Extension Field Crops Specialist - Entomology
Paul Jasa
Extension Engineer