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Weed Control in Sweet Potato ¹

William M. Stall²

Sweet potatoes are a long season crop. Control of weeds during the production can be difficult. Early season competition of weeds is extremely critical and a major emphasis on control should be made during this period. Growers must plan a total weed control program that integrates mechanical and cultural methods of weed control with the use of herbicides.

At the present time there are only three preemergence (to weeds) residual herbicides for sweet potatoes. Cultivation is also an effective way to manage weeds early in the season. Rolling cultivators either by themselves or behind hilling blades can uproot many annual weeds that have escaped the herbicide or have emerged since the last cultivation. Cultivation and hilling, while useful, will disrupt the efficacy of soil-applied herbicides. Fusilade may be applied at any time until 55 days of harvest and Poast or Select up to 30 days of harvest to control emerged grass weeds. These herbicides do not provide preemergence control.

Herbicide performance depends on weather, irrigations, soil type, proper selection for weed species to be controlled, and accurate application and timing (Table 1 ).

Before application of a herbicide: Carefully read and follow the label.

Tables

Table 1. Chemical weed controls: sweet potato, yam.

Herbicide	Labeled Crops	Time of Application to Crop	Rate (lbs. AI./Acre)
			Mineral	Muck
Carfentrazone (Aim)	Sweet Potatoes	Preplant Directed-hooded Row-middles	0.031	0.031
Remarks: Aim may be applied as a preplant burndown treatment and/or as a post-directed hooded application to row middles for the burndown of emerged broadleaf weeds. May be tank mixed with other registered herbicides. May be applied at up to 2 oz (0.031 lb ai). Use a quality spray adjuvant such as crop oil concentrate (coc) or non-ionic surfactant at recommended rates.
Clethodim (Select) (Arrow)	Sweet potatoes, yams (other tuberous corm vegetables)	Postemergence	0.1-0.25	0.1-0.25
Remarks: Control of emerged grasses. Always use a crop oil concentrate at 1% v/v in the finished spray volume unless tank mix instructions indicate otherwise. Do not apply within 30 days of harvest. Use 6 oz. to 16 oz. product to control actively growing grasses at recommended heights. For control of annual grasses, use 6 to 16 fl. oz/A, for perennial grasses, use 8 to 16 fl oz/A.
Clomozone (Command 3 ME)	Sweet potato	Pretransplant Posttransplant	0.48-0.56	----
Remarks: For control of annual grasses and broadleaf weeds, apply broadcast 1.3 pints/acre. Also, may be applied as a single application post transplant to the crop and prior to weed emergence at a maximum rate of 1.5 pints/acre.
Clomozone (Command 3 ME)	Tuberous and corm vegetables (arracacha, cassava, tanier, yams)		0.75-1.24	----
Remarks: For control of grasses and broadleaf weeds apply 2 to 3.3 pints/acre broadcast. Try on trial basis only on arracacha, cassava and tanier.
DCPA (Dacthal)	Sweet potato	Posttransplanting or layby	8-10.5	----
Remarks: Controls germinating annuals. Apply to moist soil or overhead-irrigate. Apply to weed-free field up to 6 weeks after transplanting.
Fluazifop (Fusilade)	Sweet potato, yams	Postemergence	0.188	0.188
Remarks: Controls actively growing grass weeds. A total of 48 oz. product may be applied per season. Do not harvest within 55 days of application. Apply a crop oil concentrate or non-ionic surfactant in the spray mixture. Consult the label for specific rates and growth stage for best control.
Glyphosate (Roundup, Durango Touchdown, Glyphomax)	Sweet potato	Chemical fallow Preplant, preemergence, Pre-transplant	03 - 1.0	----
Remarks: Roundup, Glyphomax and Touchdown have several formulations. Check the label of each for specific labeling directions.
Napropamide (Devrinol 50 DF)	Sweet potato	Postransplanting	1-2	----
Remarks: Apply to soil surface immediately after transplanting. Will not control emerged weeds.
Pelarganic Acid (Scythe)	Root and tuber vegetables, sweet potato, yam	Preplant Preemergence Post-Directed	3-10% v/v	3-10% v/v
Remarks: Product is a contact, nonselective, foliar herbicide. It has no residual activity. It may be tank mixed with soil residual herbicides. Consult the label for rates and timings.
Sethoxydim (Poast)	Sweet potato	Postemergence	0.188	0.188
Remarks: For control of emerged annual and perennial grass weeds. Always add 1 qt oil concentrate per acre. Do not apply to drought-stressed grass weeds. Minimum time from application to harvest - 30 days.

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Footnotes

1. This document is HS198, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised June 2005, October, 2006. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.

2. William M. Stall, professor, Horticultural Sciences Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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