Strategic weed control for the 90's.
Herbicides currently account for 85 percent of all pesticides used for producing the top 10 crops in the United States. Of the total herbicide used, more than 80 percent goes on corn and soybean fields.
Reducing this amount would please farmers--they'd save the money spent on chemicals and their application. It would also please people who want to reduce herbicide use to protect the environment.
"We need to find new weed control strategies that effectively balance the use of herbicides with environmental protection," says Edward E. Schweizer, Agricultural Research Service plant physiologist. "I think we can accomplish that by combining tillage implements with computer technology."
Key to this approach will be an expanded version of a model that selects an appropriate weed control strategy to minimize herbicides.
Schweizer originally developed the model in cooperation with Colorado State University. [See "Weed-Free Fields Not Key to Highest Profits," Agricultural Research, May 1989, p. 14-15.] Once the scientists include new data collected during a 3-year study near Fort Collins, Colorado, the updated computer model, WEEDCAM, will select several tillage practices--used with or without herbicides--to control weeds in irrigated cornfields.
The cultivation study evaluated three tillage implements, each used without herbicides. Weed populations, crop yields, and net income per acre on these plots were compared to similar plots treated with herbicides that the computer model recommended.
One implement studied was a standard rotary hoe that has 12-inch metal fingers rotating around a shaft when pulled across a field. The hoe breaks the soil surface, displacing many emerging weeds. And corn sustains little damage, because the hoe is used when seedlings either haven't emerged or when plants are large enough to withstand tillage.
Another device tested was a conventional row cultivator with small shovels that disturb soil between corn rows and uproot weeds. The third implement, an in-row cultivator designed about 30 years ago, has a series of tools that reach across the crop row and uproot weeds growing in-row between crop plants, as well as weeds growing between rows.
Correct timing of the tillage operation was found to be key to reducing weed populations and increasing crop yields. The rotary hoe worked best when weeds had germinated but not yet emerged from the soil. The row cultivator worked best when inter-row weeds were 6 inches or shorter. The in-row cultivator was most effective when weeds were shorter than 2 inches.
But by using the weed computer model to select appropriate herbicides to use with either cultivator, yields were 30 percent greater and generated about $65 more income per acre compared with in-row cultivation without herbicides.
Compared to standard cultivation without herbicides, the plots that the computer model was used on yielded about 70 percent more corn and generated about $120 more per acre.
"It looks like we'll need a combination of practices to achieve our goals. We cannot switch from using a herbicide-intensive system to one that involves only cultivation, if fields have many weed seeds. We might have to use herbicides for as many as 4 years to reduce heavy weed populations enough to make in-row cultivation feasible for keeping weeds in check," says Schweizer. He plans to incorporate the tillage data into WEEDCAM for further evaluation.
By Dennis Senft, ARS.
Edward E. Schweizer is in the USDA-ARS Water Management Research Unit, Agricultural Engineering Research Center Colorado State University, Fort Collins, CO 80523; phone (303) 491-8520. fax (303) 491-8247.