Submitted to: Carrot Country
Publication Type: Popular publication
Publication Acceptance Date: 2/1/2004
Publication Date: 3/1/2004
Citation: BOYDSTON, R.A., WILLIAMS, M., PREST, G., SPELLMAN, D.E. CARROT WEED CONTROL - RESEARCH WITH CAPAROL AND NORTRON. Carrot Country. 2004. 12(1):6-8. Interpretive Summary: In regions with mild winters and where potatoes are grown in rotation with carrots, volunteer potato is often the most troublesome weed because of its vigorous growth and lack of effective herbicides registered in carrots. Carrots are small seeded, initially slow growing, and can suffer severe yield losses from weed competition. Volunteer potatoes reduce yields of carrots by direct competition for nutrients, water, and space and are a significant cost to carrot production. The weed reduces carrot yield and is a host to serious insect, disease, and nematode pests of potato, including early and late blight. This report summarizes recent research on the effect of volunteer potato density and time of removal on carrot yield, and efficacy of two potential herbicides for volunteer potato control in carrots; prometryn and ethofumesate. Potato did not reduce carrot yield when removed before the 4 leaf stage of carrot growth. Carrots grown with a low density of volunteer potato yielded only 78% as much as carrots grown without potato. Prometryn postemergence and ethofumesate applied preemergence or postemergence were safe on carrots and greatly reduced the number and weight of new potato tubers produced and prevented carrot yield loss from potato competition. These two herbicides, if labeled in carrots, could improve volunteer potato control in carrot production.
Technical Abstract: Volunteer potato is frequently a problem in regions with mild winters and where potatoes are grown in rotation with carrots. No herbicides are currently labeled for use in carrots that suppress volunteer potato. Hand weeding is usually required to remove potatoes at a cost of $150 to $250/acre. Volunteer potatoes at a density of 2,000 plants/acre in carrots reduced carrot yield by 22%, whereas a potato density of 32,000 plants/acre reduced carrot yield greater than 90%. When potato was removed at the 4 leaf stage of carrots or earlier carrot yield was not reduced. Prometryn and ethofumesate herbicicides were evaluated for volunteer potato control in carrots. Both herbicides visually injured potato and reduced potato growth and tuber production. Prometryn applied postemergence to potato reduced potato tuber yield 89 to 96%, while carrot yield was comparable to the hand weeded treatment. Ethofumesate applied preemergence delayed potato emergence. Ethofumesate applied postemergence stunted growth of potato shoots. Ethofumesate and prometryn treatments reduced potato tuber number from 28 to 91% and reduced tuber yield 46 to 99%.