Avoiding Carryover Issues
Monday, December 1, 2014
filed under: Weeds
Farmers understand first-hand the importance of proper crop rotation. Knowing which crop to plant in which field at which time can make all the difference in how well a crop grows, as well as in the health of the soil.
There are a number of things to consider when planning for next year’s crops, including chemical carryover issues. Herbicide persistence into the next growing season may restrict rotational crops, including sunflower. So what’s a producer to do?
Kansas State University research weed scientist Phil Stahlman has conducted extensive research on this topic. He points out that a number of products prohibit the planting of sunflower in the same season as the herbicide is applied. Most ALS/AHAS-inhibiting herbicides fall into this category, Stahlman reports. That includes products like Ally, Ally Extra, Amber, Finesse, Finesse Grass & Broadleaf, Glean, Maverick, Osprey, Olympus, Olympus Flex, Peak, PowerFlex HL and Rave. Other popular wheat herbicides, such as Starane Flex, Starane NXT, Starane Ultra and WideMatch, prohibit the planting of sunflower four or more months following application.
Conventional sunflower should not be planted following a Beyond application in Clearfield winter wheat, though Clearfield sunflower can be replanted or double cropped following Clearfield winter wheat that was sprayed with Beyond.
Keep stewardship issues in mind, however. The active ingredient of Beyond is imazamox, a member of the herbicide family of ALS/AHAS inhibitors. Limit the sole reliance on ALS herbicides to no more than two out of four years in the same field, and use alternate (non-ALS) mode-of-action herbicides to reduce selection pressure from continuous dependence on the ALS-inhibiting herbicide, and provide alternate mode-of-action to control volunteer Clearfield sunflower and other ALS-resistant weeds (e.g., ALS-resistant kochia) that may be present.
Products that do not prohibit sunflower in a crop loss or double-crop scenario, according to Stahlman, include bromoxynil and 2,4-D products. Also, sunflower can be planted 45 days after Express, Harmony GT or Harmony Extra application.
The Kansas State researcher points out that soil type is important for some, but not all, herbicides. Organic matter content also factors in. For example, ALS/AHAS-inhibiting herbicides with residual properties are more prone to carryover in coarse-textured soils having high pH and low organic matter content than in other soils. Again, herbicide labels usually include tables of recommended use rates for different soil textures and organic matter contents, and often DO NOT USE statements for certain conditions that are known to increase risk of carryover and crop injury. Some herbicides are more readily available for plant uptake at increasingly high soil pH, thus potentially increasing crop injury to susceptible crops.
Herbicide labels include information on crop rotation and recropping intervals, if any, under Use Precautions and Restrictions. Stahlman’s best advice: refer to the label. — Jody Kerzman