- Using the Economic Threshold Concept as a Determinant for Velvetleaf Control in Field Corn. E.L. Werner and W.S. Curran, 1995. Proc. NEWSS 49:23.
Using the Economic Threshold Concept as a Determinant for Velvetleaf Control in Field Corn. E.L. Werner and W.S. Curran, 1995. Proc. NEWSS 49:23.
Soil applied herbicides have been the emphasis of corn weed control programs throughout the region. The foundation of these preemergence herbicide programs have been products such as atrazine and alachlor, however, these herbicide programs are closely related to resistant weed populations and the water quality issues. An alternative to treating an entire field with a soil applied herbicide would be the "wait and see approach" treating only the infested areas postemergence. A planned postemergence herbicide program based on the economic threshold concept offers several advantages over more traditional programs. Postemergence herbicide performance is not affected by soil texture and organic matter, so the problem of matching herbicide rate to soil type is eliminated. Foliar applied herbicides do not require a timely rainfall to move them to the site of activity, and these products are less affected by tillage and residue which is especially important in reduced or no-till agricultural systems.
Field studies were conducted in central and southeastern Pennsylvania for the 1993 and 1994 growing seasons to examine the effect of increasing velvetleaf density on corn and velvetleaf growth and yield. Velvetleaf densities ranging from 0 to 96 plants per 20 ft row were established in field plots measuring 10 feet wide by 15 feet long with each plot containing 24 subplots measuring 30 by 30 inches. Parameters measured included corn and velvetleaf height, velvetleaf leaf area, velvetleaf aboveground biomass, corn silage and grain yield, and velvetleaf seed production.
At the southeastern site corn silage yield was reduced 20 to 36% as velvetleaf density increased from 8 to 96 plants in 1993, and a reduction of 12 to 29% in 1994. Grain yields in 1993 indicate a 9 to 25% loss as velvetleaf density increased from 8 to 96 plants and a 2 to 30% loss in 1994. There was no significant corn yield response from velvetleaf density at the central PA site.
An attempt was made at establishing an economic threshold by incorporating local corn grain prices and yield loss data from the two study seasons. Based on local corn grain prices an economic threshold of 3.4 plants per 20 ft of row was determined for 1993 and 6.9 plants for 1994. The difference in the number of plants tolerated for each study season is probably due to environmental factors. Corn was less competitive with the velvetleaf in the dry 1993 season, therefore was not able to tolerate as many velvetleaf plants compared to the 1994 season which had adequate moisture.
This study and others like it have shown variability from year to year of yield loss caused by velvetleaf and other weed species. Unless factors such as rainfall can be predicted for individual growing seasons on a local basis there is no definite way of knowing how an infestation will impact corn yield. However, information from this study and others like it combined with experience can be a useful tool in planning a control strategy.