CARROT WEED CONTROL - RESEARCH WITH CAPAROL AND NORTON

Authors: Boydston, Rick; Williams, Martin; PREST, G - WSU PROSSER; Spellman, Dallas

Submitted to: Pacific Northwest Vegetable Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/27/2003
Publication Date: 11/20/2003
Citation: BOYDSTON, R.A., WILLIAMS, M., PREST, G., SPELLMAN, D.E. CARROT WEED CONTROL - RESEARCH WITH CAPAROL AND NORTON. PROCEEDINGS OF THE PACIFIC NORTHWEST VEGETABLE ASSOCIATION, PASCO, WA. P 81-88. 2003.

Interpretive Summary: Carrot is a small seeded, initially slow growing crop that can suffer severe yield losses from weed competition. Weeds reduce yields of carrots by direct competition for nutrients, water, and space and are a significant cost to carrot production. In regions with mild winters and where potatoes are grown in rotation with carrots, volunteer potato is often the most troublesome weed because it is difficult to control. The weed reduces carrot yield and is a host to serious insect, disease, and nematode pests of potato, including early and late blight. No herbicides are currently labeled for use in carrots that suppresses volunteer potato. This report summarizes recent research on the effect of volunteer potato density and time of removal on carrot yield, and carrot yield and potato response to various treatments of 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: In regions with mild winters and where potatoes are grown in rotation with carrots, volunteer potato is often the most troublesome weed because it is difficult to control. No herbicides are currently labeled for use in carrots that suppresses volunteer potato. Hand weeding is costly and may remove carrots along with weeds. Carrots grown with volunteer a potato density of 2,000 plants/acre reduced carrot yield by 22%, whereas carrots grown with 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. Two herbicides, prometryn and ethofumesate, were evaluated for volunteer potato control in carrots. Both herbicides reduced volunteer potato tuber production and had phytotoxic effects on volunteer potato. Prometryn applied postemergence to potato and carrot reduced potato tuber yield 89 to 96%, and 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%.