Climate, Weeds, and Crops

April 30, 1999
Cool, wet weather is ideal for preplant or preemergence herbicides to work on the crop as well as the weed. Delayed crop emergence plus cool, wet soils have maximized corn shoot and root exposure to soil-applied herbicides. A weakened immune system plus long exposure can lead to herbicide injury.

The acetamide herbicides alachlor, acetochlor, flufenacet, dimethenamid, and metolachlor differ in crop tolerance and water solubility. Acetochlor (Harness, Surpass, TopNotch) have a crop safener, and TopNotch is encapsulated. Metolachlor (Dual II Magnum) has a crop safener in the formulation (i.e., the "II"). Alachlor has no crop safener. Partner and Micro-Tech are encapsulated alachlor, but Lasso is not. Flufenacet mixed with metribuzin is sold as Axiom, and mixed with isoxaflutole (Balance) is sold as Epic. These have no crop safener, and metribuzin and cold, wet weather can lead to corn problems. Dimethenamid is sold as Frontier without a safener or encapsulation. It is quite soluble as it works at lower rainfall than most other acetamides except propachlor (Ramrod), which is still used in the Western Corn Belt because it can be used on corn or grain sorghum without a formulation or seed safener and works with low rainfall. Flumetsulam is the other corn herbicide that has had problems with cold, wet weather. It is sold alone as Python and in soil-applied premixes of Bicep Magnum TR, Broadstrike + Dual, and Hornet for corn.

The Clock Is Running on Early Preplant (EPP) Herbicides

EPP herbicides applied too early may need help. Split applications allow greater flexibility to maintain residual control, but even these may need "post" help. Be prepared.

Preemergence Knockdown (Pre-KD) Herbicides May Be on the Ropes

Yes, many soil-applied herbicides have foliar activity (especially when applied with crop oil or nitrogen fertilizer) for controlling existing weeds, but keep in mind that most have labeled weed size limitations of 2 to 3 inches, and often recommend adding a "real" knockdown herbicide if existing weeds are too big.

Postemergence/Preemergence Herbicides

Many preemergence corn herbicides allow delayed (postemergence) application with varying corn size limitations. Balance and Epic do not allow postemergence applications. So know when to say NO!--Marshal McGlamery, Aaron Hager

Author: Aaron Hager Marshall McGlamery