Weed control using ammonium nonanoate and cultivation in organic Vidalia sweet onion production

Authors: Johnson, Wiley - Carroll; LUO, XUELIN - University Of Georgia

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2017
Publication Date: 1/14/2018
Citation: Johnson, W.C., Luo, X. 2018. Weed control using ammonium nonanoate and cultivation in organic Vidalia sweet onion production. Weed Technology. 32:90-94.

Interpretive Summary: Weed control in organic Vidalia® sweet onion is costly, with reductions in handweeding cost needed to maximize profits. Cultivation with a tine weeder has been identified as a cost-effective means of weed control, but delays in cultivation cause some weeds to establish and escape. Herbicides derived from natural sources can be used in certified organic crop production and may provide weed control to supplement cultivation. Ammonium nonanoate is a salt of a fatty acid and registered for weed control in certified organic crop production. Ammonium nonanoate combined with cultivation with a tine weeder was evaluated for weed control in organic onion in Georgia. Three years of research indicated that ammonium nonanoate does not improve weed control over cultivation alone. Cultivation with a tine weeder consistently reduced weed densities compared to the non-cultivated control. Ammonium nonanoate at 4 and 6% did not adequate control weeds and onion yields were reduced. Ammonium nonanoate at 8 and 10% generally controlled cutleaf eveningprimrose and lesser swinecress equal to the standard of d-limonene (14%), but weed control did not consistently protect onion yields from losses due to weeds. These results are in agreement with previous studies using clove oil and pelargonic acid. The limitations of weed control using a tine weeder and unacceptable weed control using herbicides derived from natural sources indicate that other strategies are needed for overall improvement in cool-season weed management in organic Vidalia® sweet onion.

Technical Abstract: Ammonium nonanoate is registered for weed control in certified organic crop production and may be useful to control cool-season weeds in organic Vidalia® sweet onion. Cultivation with a tine weeder has been identified as a cost-effective means of weed control, but delays in cultivation cause some weeds to establish and escape. Ammonium nonanoate combined with cultivation with a tine weeder was evaluated for weed control in organic onion in Georgia. There were no statistical interactions between main effects of cultivation with a tine weeder and herbicides for cool-season weed control and onion yield, indicating that ammonium nonanoate does not improve weed control from cultivation. Cultivation with a tine weeder consistently reduced weed densities compared to the non-cultivated control. Ammonium nonanoate at 4 and 6% did not adequate control weeds and onion yields were reduced. Ammonium nonanoate at 8 and 10% generally controlled cutleaf eveningprimrose and lesser swinecress equal to the standard of d-limonene (14%), but weed control did not consistently protect onion yields from losses due to weeds. These results are in agreement with previous studies using clove oil and pelargonic acid. The limitations of weed control using a tine weeder and unacceptable weed control using ammonium nonanoate indicate that other strategies are needed for overall improvement in weed management in organic Vidalia® sweet onion.