As a result of the continued heavy rains and slow pace of corn planting in certain regions of Missouri, some producers now wish to plant soybeans into fields where pre-emergence corn herbicides have already been applied. Questions have arisen about the replant restrictions of these herbicides and what can be done in these situations. Table 1 provides a list of some of our most common pre-emergence corn herbicides and the replant restrictions of these herbicides for corn, grain sorghum, and soybeans. As you can see from this table, soybeans SHOULD NOT be planted into fields where applications of atrazine or an atrazine premix have already been made this season. The label clearly states that soybeans should not be planted until the following year due to the likelihood of soybean injury from residues of atrazine that may still be present in the soil. The average field half-life of atrazine will vary dramatically depending on the soil and environmental conditions experienced, but the Herbicide Handbook published by the Weed Science Society of America lists the average field half-life of atrazine as 60 days. High soil pH’s (>7.5) will also slow the degradation of atrazine, along with cool soil conditions. Fortunately, replanting corn or planting grain sorghum into these damaged areas will still be an option where atrazine or most of these atrazine premixes have been applied.
|Table 1. Replanting restrictions and intervals for some common pre-emergence corn herbicides.|
|Interval Between Application and Planting|
|Field Corn||Grain Sorghum||Soybean|
|Bicep II Magnum||0||0b||NYa|
|Dual II Magnum||0||0b||0|
|a NY=next year.|
b Replant interval only applies if safener-treated seed is used.
c Thoroughly rework soil before replanting.
d If 1/3 oz Basis applied, interval is 15 days. If >1/3 oz Basis applied, interval is 10 months.
e If 2.25 oz or less is used, sorghum can be planted 9 months after application.
f For the 3 oz rate, interval is 7 days for min. and no-till, and 30 days for conventional tillage.
g Interval will vary based on rate and soil type. Check label for specific restrictions.
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REVISED: May 30, 2013