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Showing posts from 2015

Herbicide resistant giant ragweed control: Alternative herbicide options are limited

by Lisa Behnken, Extension Educator, Fritz Breitenbach, IPM Specialist SE Minnesota, Jeff Gunsolus, Extension Agronomist, Weed Science, and Phyllis Bongard, Content Development and Communications Specialist, University of Minnesota
With the increase in herbicide resistant weeds and no new herbicide chemistries on the horizon, what options remain for good weed control? Achieving acceptable weed control is particularly challenging in parts of Minnesota where giant ragweed is resistant to both SOA 2 (ALS inhibitors) and SOA 9 (glyphosate) herbicides.

Aphids in corn: The dilemma of post-pollination infestations

Bruce Potter, IPM Specialist, and Ken Ostlie, Extension Entomologist
As agriculturalists re-enter corn fields to scout corn rootworm beetle populations and begin to estimate yield potential, they often find some unwelcome aphid visitors. Heavy infestations on ears and adjacent leaves can grab your attention and trigger the “Should I spray question?” The crop protection urge may be strong with the corn crop we have this year; let’s review what’s known about aphids in corn before you make that spray or don’t spray decision.

What to consider when treating a soybean field more than once for soybean aphid

by Robert Koch (Extension Entomologist), Bruce Potter (IPM Specialist), Ian MacRae (Extension Entomologist), and Ken Ostlie (Extension Entomologist)

Soybean aphid populations in many areas of Minnesota are increasing. This year, there are a number of factors making population development and management less predictable than in the previous couple of years:
Late summer dispersal of soybean aphids is currently occurring, bringing high numbers of winged aphids to colonize fields; sometimes those that were previously treated. Forecasted weather conditions for the upcoming week look favorable for aphid population growth. A number of fields in southwestern Minnesota have reported unexplained failure (poor performance) of recent insecticide treatments and will require additional applications to control existing populations. All of these factors point to the importance of weekly scouting for soybean aphids and treating when populations reach the threshold of 250 aphids per plant wh…

Sugarbeet crop update

Mohamed Khan, Extension Sugarbeet Specialist
Planting
In North Dakota and Minnesota, ideal planting time is in mid- to late-April so that plants can close rows by June 21 to maximize photosynthetic activity during long daylight hours for highest yields. The lack of snow and rainfall preceding and during early April resulted in growers being able to plant over 90% of their sugarbeet crop during April. However, inadequate soil moisture in many areas resulted in delayed emergence, and in some fields, uneven seedling emergence. Fortunately, several rainfall events in May and June have resulted in adequate moisture for the sugarbeet crop as well as recharging of the soil moisture content. May was relatively cool but since June 1, average daily bare soil temperature was over 55°F resulting in rapid crop growth. As such, most fields in Minnesota had a full canopy by the 4th of July.

Pest alert - Two-spotted Spider Mites in Soybeans

Bruce Potter, Bob Koch and Ken Ostlie.

In spite of the abundant rainfall and the relatively mild temperatures, some Minnesota soybean fields have populations of two-spotted spider mites (TSSM) at or near economic damaging levels and mites can be found at lower levels in others.

The downside of insurance insecticide applications for soybean aphid

by Robert Koch, Extension Entomologist; Bruce Potter, IPM Specialist; and Jeff Gunsolus, Extension Weed Scientist

For soybean aphid management, we encourage you to rely on scouting (actually getting into the field and looking at plants) and the validated economic threshold (average of 250 aphids per plant, aphids on more than 80% of plants, and aphid populations increasing) to determine when to apply insecticides for soybean aphid (see "Scouting for soybean aphid"). The threshold number of aphids is below the number required to cause yield loss and allows time to apply an insecticide before economic loss is incurred. However, you might be tempted to apply insecticides for soybean aphids at low population levels or without regard to the size of the aphid population in field, just in case you might have a problem. These "insurance" applications of insecticides can have negative impacts.

Refresher on scouting for and managing defoliating insects in soybean

by Robert Koch (Extension Entomologist), Tavvs Alves (Grad. Student), Anh Tran (Grad. Student), and Wally Rich (Junior Scientist)

As you begin scouting soybean fields for soybean aphid, you should also be on the lookout for other insect pests and the injury they can cause on the plants. One such group of additional pests is referred to as “defoliators” or “defoliating insects.” Defoliators are insects that eat the leaves of plants. In soybean, we can find a diversity of defoliators, including various beetles, caterpillars and grasshoppers.

Armyworms in Small Grains

We are receiving calls regarding armyworms in small grains in NW MN.

At this time they are small larvae (1/2"-3/4" long) and feeding in the lower foliage.  Scout for armyworms at grassy margins of the fields, low, weedy areas in fields or in lodged grain; populations are more likely to develop in these areas first.  Armyworms prefer the edges of leaves first and are messy, wasteful eaters.  They generally retreat during the day under soil and plant residue on the ground and feed more often beginning at dusk, it’s easier to scout for armyworm damage than the armyworms themselves.  Look for leaves that have been notched/cut, partially eaten leaf material on the ground, and small round pellets (armyworm frass, i.e. poop) near the base of the plants.

Consider applying insecticide if: there are 4-5 armyworm larvae per sq. ft., caterpillars are ¾ - 1 ¼ in. long, leaf feeding or head clipping is found, and parasites are not evident.  By the time armyworms are more than 1 ½ in long,…

Postemergence Weed Control Strategies in Sugarbeet

Tom Peters, Extension Sugarbeet Agronomist, Univ of Minnesota / North Dakota State University

Sugarbeet are actively growing following ample precipitation the past three weeks and finally some sun and heat. Unfortunately for Farmers, so are the weeds. Farmers should be scouting their fields and preparing for postemergence weed control. With this in mind, I offer the following suggestions:

· Scout fields regularly. I suggest visiting fields at least every 7 days
· Properly identify weeds. Get help if you are unsure about weed identification
· Spray weeds when they are small, preferably less than 2 inches tall
· Use full rates of herbicides and the appropriate adjuvants depending on herbicide or herbicide mixtures
· Consider tank-mixes to provide multiple modes of action, especially on tough-to-control weeds
· Revisit fields for possible sequential herbicide applications

When is it too Windy to Spray?

by David Nicolai and Lizabeth Stahl, Extension educators - crops and Dr. Dean Herzfeld, Coordinator, Pesticide Safety and Environmental Education
The corn and soybean post-emergence crop protection application season is here. Corn and soybean growers will target post-emergence herbicide applications by the V4 growth stage in soybeans and the four leaf stage in corn to limit yield reductions due to weed competition. Targeting applications by these crop stages will also help ensure applications are made before weeds exceed three to four inches in height, which is the maximum height on many herbicide labels for most effective control.

As crops and weeds enter rapid growth stages, wet soil conditions due to recent rains have made it challenging to make timely herbicide applications. As growers rush to complete weed control operations, under very windy conditions, calls about injury resulting from herbicide drift are anticipated. Where fields of Roundup Ready crops are adjacent to non…

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.

Windbreak and crop yield study

Gary Wyatt, Extension educator - agroforestry
Recent land values, farm innovations and management such as adoption of no-till, minimum till, use of wide farm equipment, and windbreak plantings that are just getting old, have led to many windbreaks being removed. In time, windbreaks need to be renovated to restore the multiple benefits they offer rural landscapes. There are cost share programs available to plant new windbreaks and renovate mature plantings through the Natural Resources Conservation Service (NRCS). In most areas where windbreaks were planted, there have been documented crop yield increases.

Anhydrous Ammonia Applications

Fabian Fernandez, Nutrient management specialist
Anhydrous ammonia (AA) is one of the most widely used nitrogen (N) fertilizer source in Minnesota and the Midwest. Some of the reasons for its importance include the fact that this source is by far the most concentrated N fertilizer with 82% N (less weight of fertilizer per unit of N); it is readily available since AA is used in the manufacture of many commercial N fertilizers; it can be applied several weeks before planting with less N loss potential than other N sources; and most importantly AA normally represents a less expensive source of N. Some of the drawbacks of AA include the need for special facilities to store this gas as pressurized liquid, and special equipment to transport and applied this fertilizer; the application of AA can be slower than that of some other N sources; and because AA is released as a gas, it can pose a risk to human health if not handled properly. Every year as farmers start applying AA, invariably I ge…

Assessing Damage From In-Furrow or Pop-Up Starter Fertilizer for Corn

By Daniel Kaiser
Extension Nutrient Management Specialist

I have been fielding more questions on seed placed fertilizer in areas where rainfall has been sparse this spring and soils are dry. In my previous post I discussed the use of in-furrow starter fertilizer. Placing fertilizer on the seed can help speed up early plant growth but also can substantially reduce stand if a fertilizer is over-applied or soils are dry. How dry is too dry? That is a good question and the answer depends on the soil corn is being planted in. For medium and fine textured soils, the risk of damage typically is lessened when the soil moisture content is 25% or greater.

How Deep Dare I Drill Wheat, Barley and Oats Down to Find Moisture?

Ideally we like you to seed wheat, barley, and oats at 1.5 to 2 inches of depth.  The idea is that the seed should be placed deep enough to have access to adequate moisture yet shallow enough to emerge as quickly as possible. Seeds too close to the surface absorb moisture but are at risk of dying because roots cannot reach moisture quickly enough to sustain the germination and seedling growth.  Deeper seeding can reduce stand density and plant vigor because the inability of the coleoptile to reach the surface.