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Showing posts from May, 2015

Assessing frost injury to soybean: Is there an interaction with soil-applied PPO herbicides?

Jeff Gunsolus, Extension Weed Scientist
As people begin to assess soybean stands following the low temperature conditions of May 19th, questions are coming my way regarding the possible interaction of frost with soil-applied PPO herbicides. Is it possible? My answer is yes. Is it widely prevalent? As I receive more reports from around the state my current answer is, not likely.

An interaction of frost with soil-applied PPO herbicides is possible because cold temperatures slow the rate of emergence of the soybean through the herbicide-treated soil and the soybean is limited in its ability to metabolize the herbicide. However, the crook stage of the soybean plant that is expressing injury symptoms appears to be targeted to soybeans planted in early May (May 2 to 4 are frequently mentioned). Soybeans planted in early May were just cracking from the soil at the time of the low temperature conditions and were vulnerable to freeze damage.

Will soil-applied herbicides work in a dry year?

Tom Peters, Extension Sugarbeet Agronomist

Two questions are on farmers minds. First, how long will soil-applied herbicides ‘last’ in the soil if it doesn't rain and second, should a farmer consider using a rotary hoe or drag harrow to incorporate herbicides?

Volatility (evaporation), adsorption, and soil moisture effect soil-applied herbicides. Volatility is the change in herbicide physical state, from a liquid to a gas. Most soil-applied herbicides used by farmers have a medium or low vapor pressure meaning they generally will not volatilize during warm and dry conditions. However, understand that herbicides sprayed on soils will move with blowing soil and these effects may impact efficacy. Adsorption is the attachment of herbicides to soils. Herbicides must be bound to soils or they would easily leach away. Most herbicides are moderately or strongly bound to soils colloids and should not be impacted by our dry conditions.