NEWS for North Dakotans
Agriculture Communication, North Dakota
State University
7 Morrill Hall, Fargo, ND 58105-5665
July 30, 1998
Sunflower producers have few options for controlling weeds. A study at North Dakota State University's Carrington Research Extension Center is designed to help.
"We have very few herbicides labeled for use in sunflowersespecially post-emergence herbicides," explains Greg Endres, a cropping specialist with NDSU's Carrington Research Extension Center. "We're looking for ways to complement those options with some mechanical control." He's studying the use of a harrow and a rotary hoe for early season weed control.
After a preliminary study last year and after looking at early results from this year, Endres says the best results come from several tillage passes: once about five to seven days after planting and before the crop has emerged, and a second pass about a week later. A third is probably needed a week after that.
The tillage timing will vary based on weed and crop stage and environmental conditions. The best stage to control weeds with this strategy is just prior to or at early emergence. Endres says if grassy weeds have reached the one-leaf stage and broadleaf weeds have developed their first true leaves, the rotary hoe and harrow are generally ineffective because the root systems are too developed.
This tillage-only strategy controls weeds like foxtail, pigweed and nightshade, which emerge from shallow soil depths, but is not effective with weeds like cocklebur and wild oats, that both emerge from deeper in the soil. Endres says, "Those weeds are just anchored too firmly, and this approach is not effective against perennial weeds."
The key will be to suppress weeds long enough for the sunflower canopy to develop, Endres says. Once sunflowers begin to shade out weeds, they'll also compete effectively for moisture and nutrients.
That sounds easy, but it doesn't always work out so well in the field. "You must have Mother Nature on your side to allow timely tillage, or weed escapes are likely to occur," Endres says. That's especially true in solid-seeded sunflowers where producers can't use between-the-row cultivation.
Using a harrow or rotary hoe will reduce crop density, Endres says. For example, in this year's trial, three tillage passes reduced sunflower density 14 percent to 38 percent, so producers will need to increase their seeding rates and factor in the additional expense if they're planning to use this strategy next year.
Weed control likely will be reduced with a tillage-only program compared to one using herbicides, but the potential exists for lowering weed-control costs while maintaining sunflower yield.
"The outcome we expect from our research is to develop a system that uses a combination of reduced rates of herbicides and mechanical control that provides acceptable weed control at an economical cost," Endres concludes.
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Source: Greg Endres (701) 652-2951
Editor: Tom Jirik (701) 231-9629