"LIFE AFTER DACTHAL" - THE CONTINUING SEARCH FOR ALTERNATIVES -
HERBICIDE WEED CONTROL PROGRAMS FOR DRY BULB ONIONS
Presented at the 51st Annual conference of the California Weed Science Society in Anaheim, CA on January 12, 1999.
Umeda, K. 1999. "Life After Dacthal" - The Continuing Search for Alternatives - Herbicide Weed Control Programs for Dry Bulb Onions . University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension, Tucson, Arizona. URL: http://cals.arizona.edu/crops/vegetables/weeds/Dacthal.html
The projected loss of DacthalŽ (DCPA) herbicide will significantly impact many vegetable crop herbicide weed control programs. Dry bulb onion production will be affected with the loss of the effective broad spectrum at-planting time preemergence (PREE) herbicide. Onions emerge and grow extremely slowly after planting and the competitive weeds generally cannot be controlled with postemergence (POST) herbicides until the onions reach a more tolerant size. Hand-hoeing is often a very expensive alternative in place of the POST herbicides. Mechanical cultivation on raised beds is nearly impossible when there are as many as eight or nine seedlines on a forty-inch bed. The search for alternative weed control methods for onions intensified when the cost of Dacthal escalated after production ceased.
During the 1997-98 onion growing season in the low desert growing area of Central Arizona, several small plot field tests were conducted to evaluate potential PREE herbicides for use in onions when applied alone or in combinations and early timing of applications of POST herbicides. Herbicides applied PREE included pendimethalin (Prowl), bensulide (Prefar), propachlor (Ramrod), ethofumesate (Nortron), metolachlor (Dual), dimethenamid (Frontier), benefin (Balan), and thiazopyr (Visor), and lactofen (Cobra).
Treatments including Visor and Cobra severely reduced the onion crop stand when applied PREE. Some treatments that appeared to be relatively safe included Prowl, Prefar, Ramrod, Nortron, Dual, Frontier, and Balan. Prowl alone or combinations with Ramrod, Dual, or Nortron gave good weed control of London rocket, sowthistle, and yellow sweetclover. Prefar combined with Ramrod or Dual was more effective than either of the herbicides applied alone. Nortron combined with Dual or Frontier improved when compared to the herbicides applied alone.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.
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Information provided by:
Kai Umeda, email@example.com Area Extension Agent, Vegetable Crops
University of Arizona, Tucson, Arizona.
Material written January 1999.
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