Note: Program subject to change without notice

Monday, November 5, 2007

Impact of Broadcast Applications of Acetic Acid on Onion Injury and Weed Control.

Charles Webber, USDA-ARS, SCARL, PO Box 159, Lane, OK 74555 and J.W. Shrefler, Extension Service, Oklahoma State University, P.O. Box 128, Lane, OK 74555.

Interest in organic onion production is growing throughout the areas now producing onions with conventional methods, but weed control continues to be a primary obstacle.   Weed control is ranked as the number one research priority by organic vegetable producers. The few organic herbicides cleared for organic vegetable production are mainly non-selective, contact herbicides.  Research was conducted at Lane, OK to determine the impact of a broadcast application of acetic acid on onion injury and broadleaf weed control.  “Candy” and “Cimarron” onions were transplanted on March 13, 2007.  The experiment included 6 treatments (2 application volumes, 2 hand weeding levels, plus an untreated weedy-check and an untreated weed-free) with 4 replications.  Nutsedge and grass weeds were selectively removed to investigate the impact of the acetic acid on the broadleaf weeds. Vinegar (20% acetic acid) was applied as an over-the-top broadcast application at either 50 or 100 gpa on April 21, 2007 using four 8002 nozzles on 20 inch spacing. Within each application volume (50 and 100 gpa) plots were either handweeded or the uncontrolled weeds were allowed to grow. Crop injury and weed control ratings were collected throughout the growing season. The greatest onion injury was observed at 3 days after treatment (DAT), resulting in 38% onion injury for the 50 gpa rate and 56% for 100 gpa rate. There were no significant differences between onion varieties for injury. Weed control peaked at 7 DAT, averaging 95% and 99% total broadleaf weed control for the 50 and 100 gpa application volumes. The results indicate that the early season crop injury did not significantly impact onion yields.