Introduction
Liberty® (glufosinate-ammonium) has become a popular postemergence herbicide in Georgia due to its ability to control herbicide-resistant Palmer amaranth when applied in a timely manner. Numerous field crops grown in Georgia, particularly cotton, soybean and field corn, have been genetically engineered for resistance to Liberty®. In 2012, nearly 51 percent of the cotton acres in Georgia were planted using cultivars that could be treated with Liberty®. The popularity of these Liberty®-resistant cultivars (e.g., Liberty-Link® and WideStrike®) has led to an increased potential for off-target movement and sprayer contamination of Liberty® to sensitive crops such as peanut (Figures 1-2).
Liberty/Peanut Symptomology
When evaluating peanut fields for potential herbicide injury, it is important to first rule out other potential causes such as drought, low soil pH, nutrient deficiency, nematodes and plant diseases. These types of problems often mimic herbicide injury symptoms. Examples of Liberty® injury symptoms on peanut plants are presented in Figures 3-6.
Figure 1. Peanut production field in Pulaski County, Ga., accidentally treated with Liberty®.
Figure 2. Peanut research plot treated with Liberty®.
Figure 3. Peanut injury caused by Liberty®.
Figure 4. Peanut injury caused by Liberty®.
Figure 5. Peanut injury caused by Liberty®.
Figure 6. Peanut injury caused by Liberty®.
Liberty/Peanut Yield Loss
Research results on the effects of Liberty® on peanut yield loss in North Carolina and Georgia are presented in Tables 1 and 2.
| Table 1. Estimated yield loss of Virginia market-type peanut (cv. Gregory) caused by Liberty® applied at 21 days after peanut emergence in North Carolinaa. | |
| Liberty® Rate (oz/A)b | Peanut Yield Loss (%) |
| 0.8 | 2 |
| 1.6 | 0 |
| 3.3 | 3 |
| 6.6 | 15 |
| 13.1 | 50 |
| 26.3 | 70 |
| aAdapted from Jordan et al. 2011. bLiberty® 2.34SL herbicide available from Bayer CropScience, 2 T.W. Alexander Drive, P.O. Box 12014, Research Triangle Park, NC 27709. The typical use rate for Liberty® is 29-32 oz/A. |
|
| Table 2. Estimated yield loss of runner market-type peanut (cv. Georgia-06G) caused by Liberty® in Georgia. | |||
| Liberty® Rate (oz/A)a |
Peanut Yield Loss (%) | ||
| Time of Application | |||
| 30 DAPb | 60 DAP | 90 DAP | |
| 2 | 7 | 13 | 13 |
| 4 | 13 | 17 | 17 |
| 8 | 26 | 26 | 26 |
| 16 | 51 | 44 | 42 |
| 32 | 100 | 80 | 76 |
| aLiberty® 2.34SL. bDAP = days after planting. |
|||
Summary
Depending upon the rate and time of application, peanut plants can be very sensitive to Liberty®. Growers must be conscious of wind speed/direction and utilize drift reduction strategies when applying Liberty® near peanut fields. Additionally, Liberty® containers must be properly labeled and stored to minimize potential mixing errors that could result in sprayer contamination. Sprayers should be adequately cleaned of Liberty® residues, as recommended on the label, before utilization in peanut fields.
References
Jordan, D. L., Johnson, V. A., and Fisher, L. R. 2011. Peanut response to simulated drift rates of glufosinate. Crop Management doi:10.1094/CM-2011-0802-02-RS. Available online at http://www.plantmanagementnetwork. org/sub/cm/research/ 2011/drift/
Prostko, E.P. 2010. Peanut Response to Ignite. In 2010 Summary of Field Crop Weed Management Research. Department of Crop & Soil Sciences Publication CSS- 10-1115. Available online at http://gaweed.com/trials/prostko2010/PDF%20FILES/PE-01-10.pdf
Prostko, E.P. 2011. Peanut Response to Ignite ? Year 2. In 2011 Summary of Field Crop Weed Management Research. Department of Crop & Soil Sciences Publication CSS- 11-1115. Available online at http://gaweed.com/trials/prostko2011/PDF% 20Files/PE-07-11.pdf
