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Crop Tolerance to Soil Herbicide Residual

A farmer watching the sun rise in a bare, unplanted field.
Courtesy: U.S. Deparment of Agriculture

Some herbicides can persist in soil, especially dry soil. The past year was a dramatic shift in weather patterns for most of the state. This time a year ago, the state was recovering from one of the wettest years in history. According to the April 29, 2021 US Drought Monitor, most areas of the state are in various levels of drought, except for portions of the east central region. Herbicide carryover could be an issue in 2021 across the state depending upon last year’s moisture levels and field conditions. Besides low rainfall being a factor for soil herbicide residues, low organic matter can be an important factor as well. When these conditions are associated with erodible soils with extreme pH, the risk of herbicide carryover is significantly higher. Carryover can pose the highest risk in headlands, or areas where overlapping is common. Further, the fields that received late herbicide applications the previous year are also at risk. Producers should be careful in choosing rotational crops and herbicide programs in light of future plans. Thorough inventory of herbicide labels and rotation restrictions can be found on in the publication, Herbicide Rotation Restrictions. This chart can be a useful tool to select the best herbicide plan for your land. Also, a field bioassay may be necessary before planting a crop that could be sensitive to a potential residual herbicide applied the previous year.

Crop Tolerance to Herbicide Residue in the Soil*

 
Soil
 
Silt Loam
2–3% OM
pH less than 7.0
Sandy Loam
1–2% OM
pH greater than 7.0
Herbicide Active Ingredient Crop
Concentration (ppb)**
Atrazine 4L Atrazine Alfalfa
100
40
Oat
150
60
Soybean
250
100
Wheat
180
75
Classic chlorimuron Corn
3
1
Wheat
5
2
Command clomazone Corn
150
75
Wheat
75
15
Prowl H2O pendimethalin Corn
250
150
Wheat
300
200
Pursuit imazethapyr Corn
25
10
Sorghum
10
4
Scepter imazaquin Corn
10
5
Wheat
30
10
Treflan trifluralin Corn
150
100
Wheat
200
150

*University of Nebraska-Lincoln threshold guidelines.
**ppb = parts per billion of active ingredient

Any herbicide concentrations equal to or greater than those listed above may cause crop injury.

Soil Residual Herbicide Sampling and Analysis

Detecting herbicide carryover in plant tissues may be difficult due to the plant’s ability to breakdown or metabolize some or all the herbicide. Therefore, soil sampling may be a better option to accurately detect any residual herbicide that is present in the beginning of the season. The following laboratories provide soil residual herbicide analyses in South Dakota.

South Dakota Agricultural Laboratories
1006 32nd Ave., Suite 105
Brookings, South Dakota 57006
Phone: 605-692-7325
Email
Website

SGS North America
241 34th Ave.
Brookings, South Dakota 57006
Phone: 877-692-7611
Fax: 605-692-5908
Email
Website