|Foxtail amid sandbur|
|Row of foxtail|
Sandbur (burgrass) is a problem weed on sandy or coarse textured soil. Sandbur also grows on the fine textured soils, but seldom becomes a primary weed problem on such soils. Two common sandburs in potatoes are field (Cenchrus pauciflorus Benth.) and longspine [Cenchrus longispinus Benth.).
Sandbur is an annual plant which completes its life cycle through seed production in one year. Stems are 6 inches to 3 feet long, branched, flattened, and usually prostrate, forming a mat on the ground. Leaf blades are smooth, flat or rolling, and attached to a sheath with hairy margins. The roots are fibrous and relatively shallow. Seed spikes bear clusters of 10 to 30 burs. Spiny burs are 1/4 to 1/2 inch in diameter, with 1 to 3 seeds per bur. Each straw colored bur has many sturdy, backward hooked spines which cause discomfort to man and animals.
Sandbur seeds germinate throughout the summer months. Those that germinate in late July and early August still produce plants which have burs in the fall. It is difficult to totally eliminate sandbur seed production using herbicides and cultivation. Control of the early season flush of sandbur seedlings, however, should allow production of top yields.
The first flush of sandbur seedlings develop in May. Disking the soil twice with a time period between diskings can destroy germinating sandbur seed. Cultivation should usually supplement herbicides for effective sandbur control. Since sandbur is shallow rooted, cultivation can be very effective in removing escaped plants between rows.
Sandbur is best controlled by using a combination of good cultural practices, cultivation, and herbicides. Clean tillage implements and the combine after each field to avoid starting new infestations. Sandbur often spreads over the entire field from the border if good sanitation is not practiced. Some growers have found that, by using a more effective sandbur herbicide on the field borders, they can apply a less expensive herbicide treatment on the rest of the field.
Sandbur is a difficult weed to control. Many of the herbicides widely used do not specifically list sandbur as a controlled weed. Sandbur control will be in the 60 to 85 percent range with pre-emergence applications of metaloclor or pendimethelin. The relative ineffectiveness of commonly used pre-emergence herbicides on sandbur may contribute to the increase of this weed. Trifluralin can be used, but it may retard emergence and cause stem brittleness. Post-emergence grass herbicides labeled for potato, e.g., sethoxydim, may be used. Potatoes at all growth stages are tolerant to sethoxydim. A herbicide that provides good early season control of sandbur in potato and may be applied either pre- or post-emergence is EPTC.
The genus Setaria includes all the foxtails. There are three main species; all are native to Eurasia but are widespread in the U.S. Their most noticeable characteristic in the field is their fuzzy mature floral head, spike-like. They are summer annual grasses. They have shallow, fibrous roots that do not compete well with a healthy potato crop. Foxtails are controlled with grass herbicides.
Most problematic of the foxtails in potato is green foxtail (S. viridis). Although found throughout the U.S., it prefers cooler climates and is less frequently found in the south. The plant is usually less than two feet tall. Leaves are rough and without hairs.
Also, found in potato is yellow foxtail (S. glauca) which is found nearly throughout the U.S. It is slightly taller than green foxtail growing up to three feet. It has an erect, stiff and yellow floral head that distinguishes it from other foxtails.
The giant foxtail (S. faberi) does not occur throughout the U.S. but only from the mid-Atlantic coast to eastern Kansas and southeastern Nebraska, and south of the Great Lakes to the mid-south. As the name implies, plants grow to seven feet making them noticeable in the field with their fuzzy heads.
- Greider, R.S., D.R. MacKenzie, Z. Smilowitz, and J.D. Harrington. 1978. Potato Diseases, Insects, and Weeds: Northeastern United States. Publ. The Pennsylvania State Univ, University Park, PA.
- Nissen, S.J. and D.E. Kazarian. 2000. Common Weed Seedlings of the Central High Plains. Publ. Colorado State Univ, Ft. Collins, CO.
- Stubbendieck, J., G.Y. Friisoe, and M.R. Bolick. 1994. Weeds of Nebraska and the Great Plains. Publ. Univ Nebraska, Lincoln, NE.
- Whitson, T.D. (ed.) 1992. Weeds of the West. Publ. Weed Sci Soc Amer, Newark, CA.