There are two species of sandbur. Field sandbur (Cenchrus pavciflorus) ( picture) is the most common of the two. It is native to Arizona and is easily distinguished from southern sandbur. The leaf blade is thin like that of bermudagrass and the burs are yellowish. It grows in a prostrate manner although it is more upright than the other species. It can root at the lower nodes and form a mat. Southern sandbur (Cenchrus echinatus) ( picture) ( drawing) has a much broader leaf that is red. It grows more prostrate to the ground and also roots at the node and forms a mat. The burs are also reddish and broader than those of field sandbur. Field sandbur burs usually contain 2 seeds while southern usually contain 4 seeds. Southern sandbur is not native and was introduced from South America.
Both field and southern sandbur are appropriately named because they almost always are found in sandy, well drained soil. The reason for this is unclear. Both are described as summer annual weeds although there are almost always some plants that survive even very cold winters. This has an important impact on the ability to control this weed.
There are two preplant treatments available for alfalfa in Arizona. These are Balan 60DF and Eptam 7E and 20G. Balan is the most active and least selective of the three dinitroaniline herbicides (Triflualin, Prowl) which are commonly used here. It must be mechanically incorporated or unacceptable injury will occur. Injury in the form of crop stunting and stand thinning is not uncommon even when mechanically incorporated although this rarely results in reduced yields. Balan is effective on seedling field and southern sandbur.
Eptam is normally applied after planting in the germination water when the 7EC formulation is used. The 20G formulation can be applied after planting and prior to the first irrigation. Eptam is extremely volatile and should be incorporated with water within 24 hours of application. The 20G is a more efficient means of applying Eptam and no more than 2 lbs. active ingredient per acre whould be applied. Up to 3 lbs. ai/AC of the 7EC can be applied in the germination water although crop injury in the form of stunting and stand thinning is common. Like Balan, this rarely results in yield loss. Eptam is effective on seedling field and southern sandbur.
This test was conducted on the Yuma mesa and southern sandbur was the species that was present. The test contained four treatments that included 1 lb.ai/A of Trifluralin 10% granules, 2lb.ai/A of Trifluralin granules, 2 lb.ai/A of Eptam 10% granules, 3 lb.ai/A of Eptam 10% granules and an untreated check. The Trifluralin treatments were applied once on February 5. Four applications of both Eptam treatments were made, one on February 5, April 10, June 14 and July 15 for a total of 8 and 12 lbs.ai/A. The herbicides were applied with a valmar airflow ground driven applicator with 4 replications of each treatment.
1Plot size was 33’ X 600’, subplots were 1/10,000 of an acre or approximately 2 X 2 ft. Eight subplot counts were made per plot. There were 4 replications per treatment for a total of 36 subplot counts per treatment.
2Average of 4 replications.
Pendimethalin (Prowl, Pendimax) has also been evaluated and found to be highly effective in controlling both sandbur species that are coming from seed and not established crowns that have overwintered. Water-run applications at 1 to 2 pounds active ingredient per acre produce excellent sandbur control. Pendimethalin (Prowl, Pendimax) is not registered for use in alfalfa although efforts are underway to gain this registration.
Two grass herbicides are labeled for the postemergence control of sandbur in alfalfa. These are Poast and Select/Prism. Raptor, mainly a broadleaf herbicide with activity on some grasses, also has field sandbur on the label. I have had these and other grass herbicides in tests or sandbur control since the early 1980’s when the selective post emergence grass herbicides were first being developed and registered in alfalfa. Some of the other postemergence grass herbicides that have been tested are Fusilade which is registered for use on many crops including vegetables, cotton and soybeans but not alfalfa, and AssureII which is used on cotton, soybeans, sugar beets and other crops but also not registered on alfalfa. Table 2 summarizes the results of three tests conducted in 1994, 1995 and 1997 to evaluate Poast and Select/Prism for sandbur control in alfalfa. Both field and southern sandbur were present in these tests and the control levels reflect the activity on both. Sandbur was from two leaf to heading in these tests.
Sandbur control in alfalfa with Poast and Select.
The control levels in these tests are representative of those achieved in other tests and grower experience. Control was poor and far below what would be commercially acceptable. I have seen these herbicides kill seedling sandbur at the 1 to 2 leaf stage. Once these weeds reach the 3 leaf stage they become tolerant. In practice, it is difficult for growers to treat when all of the sandbur is at the 1 to 2 leaf stage because of the multiple emergences of this and other summer annual grasses and the difficulty in treating between frequent summer cuttings and irrigations. Cuttings occur every 28 to 35 days and lay in the field for 5 to 7 days. Irrigations occur every 10 to 14 days. It is difficult to fit herbicide applications into this schedule.
A more recent test was conducted last year to evaluate these older herbicides and some new experimentals. In addition to Poast, Select, Fusilade and AssureII, raptor, Pursuit and a Valent experimental, V-0139 were evaluated. The results are presented in Table 3. Although some differences between treatments were measured, it is clear that none of these herbicides and combinations were effective in controlling field sandbur. These treatments were applied on 8-19-03 when the sandbur was from 2 leaf to heading. The plots measured 20’ X 14’ and were replicated three times. All the treatments were applied with a CO2 backpack spray calibrated at 20 gallon per acre. A visual evaluation of control was made on 10-7-03.
Sencor is a broad spectrum herbicide with activity on many grass and broadleaf weeds. It is most effective as a postemergence treatment but causes moderate to severe crop injury if much foliage is present at the time of application. We have evaluated sencor pre and post emergence as a sprayable treatment, impregnated on fertilizer and as a granule. Control was partial and inconsistent.
The evaluation of 8 herbicides and herbicide combinations for field sandbur control in alfalfa.
Summary and Conclusions
Sandbur is one of the most dreaded and difficult to control weeds in
alfalfa. Fortunately, it is confined almost always to sandy soils. Complete
control with both pre and postemergent herbicides is difficult and this
weed has continued to be a serious problem for many years. Sandbur has
the ability to survive even cold winters and preemergent herbicides typically
produce 60 to 85% control. Postemergent herbicides are ineffective once
this weed reaches the two leaf stage. It is difficult to apply these herbicides
at that stage of growth due to multiple weed emergences and frequent irrigations
and cuttings. The best control option currently available is the use of
a preemergent herbicide in the spring followed by postemergent herbicide
applications as soon as possible after escapes emerge in the summer.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.
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Information provided by:
Barry Tickes, email@example.com Extension Agent, Yuma County
University of Arizona, Tucson, Arizona.
Material written June 2004.
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