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Showing posts from May, 2015

Seed Purity Standards

There have been some surprises this spring with rye showing up in fields when there was no rye planted previously, at least not intentionally. I figured it would be worthwhile to briefly discuss seed purity standards and control options.

First we have to make a distinction between PVP protected varieties and varieties that are, or are no longer, protected under PVP. If a variety is protected under Title V of the Plant Variety Protection Act, certification of the seed is required. Certification standards for the maximum number of seed of the other crops are 5, 10, and 30 seeds per 10 lbs. of seed for foundation, registered and certified classes of seed, respectively. That is roughly equivalent to 0.004%, 0.008% and 0.024% seed of other crop species in a seed lot of wheat, barley, or oats. The same standards apply to all varieties sold as certified seed - whether PVP protected or not.

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.

Frost injury to soybean

Bruce Potter, IPM Specialist, Phyllis Bongard, Extension Educational Content Development and Communications Specialist, and Seth Naeve, Extension Soybean Agronomist

Figure 1. Minimum and maximum temperatures recorded May 18–19 by NOAA.
Spring frost damage to soybean is relatively rare in Minnesota, as the last average frost dates usually occur before soybeans are normally planted. However, soybean planting and emergence is well ahead of the 5-year average, leaving the crop more vulnerable to early season frost events. Temperatures dropped into the low 30s and upper 20s (F) overnight in the west-central and northwestern parts of the state, likely resulting in some degree of frost injury to emerged soybeans in select areas.

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.