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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED WEED MANAGEMENT SYSTEMS FOR ORGANIC AND CONVENTIONAL CROPS OF THE SOUTHEASTERN COASTAL PLAIN

Location: Crop Protection and Management Research

Title: Effect of sprayer output volume and adjuvants on efficacy of clove oil for weed control in organic Vidalia sweet onion

Authors
item Johnson, Wiley
item Davis, Jerry -

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2014
Publication Date: August 26, 2014
Citation: Johnson, W.C., Davis, J.W. 2014. Effect of sprayer output volume and adjuvants on efficacy of clove oil for weed control in organic Vidalia sweet onion. HortTechnology. 24:(4)428-432.

Interpretive Summary: Timely cultivation with a tine weeder is the primary tool for successful weed control in organic Vidalia® sweet onion, but conditions frequently arise that delay the initial cultivation. Weeds that emerge during the delay are not effectively controlled by cultivation and herbicides derived from natural products may have a role to control the emerged weeds. It has been reported that clove oil herbicide was more effective when sprayers were calibrated for higher output volume compared to sprayers calibrated at approximately 25 gal./A. However, when clove oil was applied at the recommended rate of 10% by vol., herbicide cost was doubled when sprayer output volume was doubled. It was theorized that herbicide adjuvants might improve clove oil efficacy and reduce weed control cost by not needing higher sprayer output. Trials were conducted from 2010 through 2012 to evaluate all possible combinations of two sprayer outputs and five herbicide adjuvants used with clove oil (10% by vol.) for cool-season weed control. Sprayer outputs evaluated were 25 gal./A and 50 gal./A, using spray tips of differing orifice size. Adjuvants evaluated were a material composed of saponins, citric acid plus garlic extract, an emulsified petroleum oil insecticide, a conventional petroleum oil adjuvant, no adjuvant used with clove oil, and a nontreated control. Weed control was not consistently improved by the sprayer calibrated at 50 gal./A compared to sprayer output at 25 gal./A. The inconsistent weed control improvements did not affect onion yield. Adjuvants provided minimal improvement in weed control from clove oil and did not consistently affect onion yield. Based on these results, clove oil does not provide suitable levels of weed control in organic Vidalia® sweet onion production to justify the expense.

Technical Abstract: Timely cultivation with a tine weeder is the primary tool for successful weed control in organic Vidalia® sweet onion, but conditions frequently arise that delay the initial cultivation. Weeds that emerge during the delay are not effectively controlled by cultivation and herbicides derived from natural products may have a role to control the emerged weeds. It has been reported that clove oil herbicide was more effective when sprayers were calibrated for higher output (>468 l/ha) compared to sprayers calibrated at approximately 234 l/ha. However, when clove oil was applied at the recommended rate of 10% by vol., herbicide cost was doubled when sprayer output was doubled. It was theorized that herbicide adjuvants might improve clove oil efficacy and reduce weed control cost by not needing higher sprayer output. Trials were conducted from 2010 through 2012 to evaluate all possible combinations of two sprayer outputs and five herbicide adjuvants used with clove oil (10% by vol.) for cool-season weed control. Sprayer outputs evaluated were 234 l/ha and 468 l/ha, using spray tips of differing orifice size. Adjuvants evaluated were a material composed of saponins, citric acid plus garlic extract, an emulsified petroleum oil insecticide, a conventional petroleum oil adjuvant, no adjuvant used with clove oil, and a nontreated control. Weed control was not consistently improved by the sprayer calibrated at 468 l/ha compared to sprayer output at 234 l/ha. The inconsistent weed control improvements did not affect onion yield. Adjuvants provided minimal improvement in weed control from clove oil and did not consistently affect onion yield. Based on these results, clove oil does not provide suitable levels of weed control in organic Vidalia® sweet onion production to justify the expense.

Last Modified: 9/23/2014
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