If drought hit your fields, no doubt you want to put this season in the rearview mirror fast and plan for a more normal crop in 2013. But before you begin to lock in whatever good seed numbers might be available during a coming year of short supply, take a detailed look at each field's 2012 herbicide and fertilizer applications.
If you remember Scepter herbicide damaging corn in 1989 following application to soybeans in the drought year of 1988, you know dry soil can cause some herbicides to linger into next season.
Risk of carryover to rotated crops varies widely field to field, and normally will appear in patches, not whole fields. Iowa State University Extension Weed Scientist Mike Owen reminds growers of factors to determine carryover risks: Understand chemical half-life, active ingredient rates applied; application date; soil characteristics (texture, organic matter, pH); amount of rain and when; sensitivity of rotational crops; and the growing conditions following planting next spring.
Owen reports that only a few of the herbicide active ingredients for corn and soybeans have characteristics that could lead to carryover in 2013. His high-risk category includes atrazine (numerous products), chlorimuron (Authority XL, Canopy, Envive, Valor XLT, others), imazaquin (Scepter) and simazine (Princep, others). In the moderate to slight risk category: fomesafen (Reflex, Flexstar, Prefix), clopyralid (Hornet), cloransulam (FirstRate, Hornet, Gauntlet, etc.) and imazethapyr (Pursuit). Also in that same moderate to slight risk category: the dinitroaniline family that includes pendimethalin (Prowl, others) and trifluralin (Treflan, others), along with the HPPD inhibitor family that includes isoxaflutole (Balance Flexx), mesotrione (Callisto, Lumax, Lexar), tembotrione (Laudis, Capreno) and topramezone (Impact).
Corn & Soybean Digestspoke with Jeff Carpenter, DuPont Crop Protection corn portfolio manager, who says their products containing sulfonylurea herbicides such as Envive and Enlite for soybeans and Breakfree, Cinch, Prequel and Realm Q for corn should not cause carryover issues. "As long as growers used labeled rates, used proper rates for their soils and pay attention to crop-rotation intervals, we should not see any problems. The good news is chemical hydrolysis does break down sulfonylurea even under drought conditions, so we don't anticipate problems going into 2013."
Best advice is to talk with a local agronomist or ag retailer to understand the amounts and timing of all herbicide active ingredients applied to your specific soils given your rainfall amounts.
Brent Wilson, DuPont Pioneer technical services manager, says that grain yield nutrient-removal calculations will be one good rule of thumb when determining how much N, P and K might remain in the soil for 2013 use. "In fields where corn yield dropped dramatically, calculating how much available nitrate-N is complicated. The potential exists to lose this N due to March through May rainfall. So our current advice in those low-yield fields is to hold off on fall N application to see what happens in early spring. If it's still dry, you can reduce N levels, then come back with needed sidedress N amounts," Wilson adds.
University of Illinois Extension crop scientist Fabian Fernandez reports that in fields under low N-loss potential (normal rain or drier conditions from fall through next spring), one should anticipate 50% of the total N remaining for the 2013 crop. Average N removal rate is 0.66 lb. N/bu. of harvested corn http://bit.ly/PFNgYb.