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Extension > Minnesota Crop News > June 2018

Friday, June 22, 2018

Continued Rainfall and Excessively Wet Field Conditions

Ryan Miller, Extension Educator - Crops, Liz Stahl, Extension Educator - Crops, Jeff Coulter, Extension Corn Agronomist, Seth Naeve, Extension Soybean Agronomist, Dean Malvick, Extension Plant Pathologist, and Fabian Fernandez, Extension Nutrient Management Specialist

It has been wet, for much of Southern Minnesota this has been one of the wettest growing seasons on record. Precipitation maps from June 12th show just how wet it has been.  In the week since these maps were published many areas have continued to see above average precipitation (see below).


The continued rainfall has made it difficult to implement postemergence weed control and has now created concerns about crop health due to saturated soils and flooded field conditions in some locations.

With the recent heavy rains, many corn and soybean fields have areas where crops are in flooded or saturated conditions. This article discusses agronomic and disease issues for corn and soybean exposed to prolonged periods of high soil moisture.

Agronomic considerations for corn

Growth and development

Although corn is at varying stages due to a wide range of planting dates this season, much corn is around the V8-V10 stage of growth.  Corn that is at less than the V6 stage of growth will be more susceptible to ponding and flooding since the growing point is still under the soil surface. 

Given the June 22nd calendar date, replanting corn is not an option.  We will have to wait and see how soil flooding affects corn mortality.   Completely submerged plants are at higher risk of mortality than partially submerged plants.  Survivability is impacted by how fast the water recedes and temperatures during the flooded conditions.  Cooler temperatures (mid-70’s or cooler) are generally better for crop survivability.  Generally corn should be able to survive a couple days of flooded conditions, but this is complicated by the fact that many spots have flooded multiple times this season.  Some root death is likely in flooded soils and new root growth will be hindered until the soil adequately dries.  Affected plants could be subject to drought stress if dry conditions follow.  

After the water recedes we will have to assess drown-out areas and determine how best to manage them.  Although accessibility to these spots may prove challenging, providing some sort of vegetative cover to aid in weed management and to help prevent fallow syndrome is recommended.  Read more on fallow syndrome and utilizing cover crops to prevent it at https://z.umn.edu/fallowsyndrome.

It may be prudent to consider more permanent vegetative cover in areas that persistently flood out.  Modern planting and spraying technology (i.e. section shut-offs) have made it easier to manage around vegetative cover.

Nitrogen management considerations

Wet soil conditions in the spring raise concerns that nitrogen (N) applied in early spring or prior might be lost. When soils become too wet, the potential for N loss is directly related to the amount of N present in the nitrate (NO3-) form. With the exception of urea-ammonium nitrate (UAN) solutions that contain 25% of the total N as nitrate, or ammonium nitrate that contains 50% of the total N as nitrate, most commercial fertilizers being used today are in the form of ammonium (NH4+) or forms that rapidly transform to ammonium (like anhydrous ammonia and urea). In the ammonium form, N is retained in the exchange sites of soil particles and organic matter.

The transformation of ammonium to nitrate, or nitrification, is done by soil bacteria that need oxygen. In fields where ammonium-based fertilizers were applied within a few days before soil conditions became excessively wet, the potential for N loss from the fertilizer is minimal as there was not enough time for the fertilizer to nitrify. Since urea is soluble in water, the only concern would be if substantial precipitation occurred soon after urea was applied in well-drained fields. In sandy soils or heavily tile-drained soils it is possible to move urea or nitrate as much as a foot for each inch of rain. On the other hand, movement is only approximately five to six inches for each inch of rain in a clay loam or silt loam soil. That said, between rain events nitrate will start to move back up as evaporation from the soil surface creates an upward suction force that moves water and nitrate closer to the surface. Similarly, evapotranspiration from actively growing crops will result in a similar suction force in addition to some nitrate uptake by the crop.

Nitrogen loss will occur in fields where N from fertilizer or organic N from the soil was present in the nitrate form before the soils became excessively wet. In fine-textured soils, water-saturated conditions cause N lost through denitrification. Denitrification rates increase after about a day under oxygen-depleted conditions that result when soil pore space is filled with water. Under these conditions, soil microbes utilize nitrate for respiration, and N is released as a bi-product in gaseous forms that are lost to the atmosphere. For each day the soil remains saturated with water under warm soil temperatures, it is possible to lose as much as 5% of the nitrate-N in the soil.
 
In coarse-textured soils or soils intensively tiled, N loss occurs mostly by leaching below the root zone or into tile lines.


Figure 1. Early N deficiency













Figure 2. Poorly developed canopy due to N deficiency














Nitrogen deficiency is characterized by yellowing along the leaf midribs, starting at the leaf tip and moving toward the stalk (Figure 1). Nitrogen deficiency will first be observed on the lowest leaves of the plant. The chlorotic areas will turn brown as the season progresses (Figure 2). Severe N deficiency will result in a poorly-developed crop canopy that will be unable to intercept all of the sunlight during grain fill. Nitrogen-deficient leaves also have a lower capacity for photosynthesis, further limiting the potential for grain fill.

Nitrogen uptake by corn from emergence through the V6 (six leaf collar) stage only represents about 5% of the total plant uptake. However, starting at about the V8 (eight leaf collar) stage, there is rapid accumulation of N by the plant, with about 60% of the total N uptake occurring between V8 and silking. Thus, it is important that N-deficient areas are detected early, and that supplemental N is sidedressed on these areas as soon as possible.

To determine whether supplemental N should be applied in corn, consider the U of M supplemental nitrogen worksheet for corn. For entire fields or portions of fields meeting the requirements for supplemental N, this worksheet recommends a rate of 40 to 70 lb N/ac, depending on the situation.  Additional information on N management during this difficult growing season can be found in a recent Minnesota Crop News, Sidedressing Nitrogen in this Challenging MN Growing Season.

Agronomic considerations for soybean

Although soybean is generally sensitive to excess water, soybeans can survive underwater for a week or more under ideal conditions. Typically soybeans tolerate 48 hours under water quite well, but flooding for 4 to 6 days can reduce stands, vigor, and eventually yield. Many factors determine how well a soybean crop will tolerate flooding. The most important factors that determine the fate of flooded soybean fields are: 1) duration of the flooding, 2) temperature during the flooding, 3) rate of drying after the flooding event, and 4) growth stage of the crop during the flooding.

Yield losses are seldom noted in fields flooded for 48 hours or less. Four days or more of flooding stresses the crop, delays the plants' growth, and causes the plants be shorter with fewer nodes. Flooding for 6 days or more can depress yields significantly, while flooding for a week or more may result in significant (or entire) losses of stand.

Temperature during the flooding event plays a large role in determining the fate of a submerged soybean field. Higher temperatures cause the soybean plant to more quickly deplete its stored energy. Additionally, soybean plants appear to be very sensitive to high carbon dioxide (CO2) levels in the soil. Higher temperatures cause plants and soil microbes to respire at high rates that quickly deplete the water of oxygen and increase CO2 levels. Cool, cloudy days and cool clear nights greatly increase the survivability of a submerged soybean crop.

The rate of field drying after a flooding event also plays a large role in soybean survival (Sullivan et al, 2001). Also, researchers have found yield reductions to be much greater on flooded clay soils than on silt loam soils when flooded for the same period of time (Scott et al, 1989). At the V4 stage, these researchers reported yield losses of 1.8 bu/ac per day of flooding on a clay soil and 0.8 bu/ac per day on a silt loam soil. The effects of flooding are even more detrimental during the reproductive phases of development. For example, flooding at the R1 stage caused yield losses of 2.3 and 1.5 bu/ac per day on clay and silt loam soils, respectively. Even larger yield losses would be expected in soybeans at the R3 to R5 stages.

Some of the main indirect effects of flooding on soybean yields are: 1) root diseases, 2) N deficiency, 3) and other plant nutrient imbalances. Caring for recuperating soybean stands should focus on reducing crop stresses where possible. For example, cultivation should be considered to increase soil aeration and herbicide stress should be minimized or postponed where possible.

Flooded and wet soil conditions increase risk of corn and soybean seedling diseases

Saturated soil conditions may lead to significant seedling diseases in soybean and corn.  Wet and flooded soils are especially favorable for the soilborne, moisture-loving pathogens Pythium and Phytophthora. Pythium appears to cause most damage to seedlings of soybean or corn, and Phytophthora can damage soybean seedlings or start infections in the early summer that may develop and kill soybean plants later in the summer. Cool, wet, soils can also favor sudden death syndrome, with is caused by the soilborne fungus Fusarium virgulifome (previously named Fusaium solani f.sp. glycines).  For more information on soybean and corn diseases, please visit the Minnesota Crop Diseases web site  (https://z.umn.edu/cropdiseases).

References


Ritchie, S.W., J.J. Hanway, and G.O. Benson. 1997. How a corn plant develops. Iowa State Univ. Coop Ext. Serv. Spec. Rep. 48. Iowa State Univ., Ames.

Scott, H.D., J. DeAngulo, M.B. Daniels, L.S. Wood. 1989. Flood duration effects on soybean growth and yield. Agron J. 81:631-636.

Sullivan, M., T VanTooai, N. Fausey, J. Beuerlein, J. Parkinson, A. Soboyejo. 2001. Evaluating on-farm flooding impacts on soybean. Crop Sci. 41:93-100.

Wednesday, June 20, 2018

Hay Auction June 7, 2018

by Randy Pepin, UMN Extension Educator, Stearns, Benton, and Morrison Counties
pepin019@umn.edu or (320) 333-1369

Keeping up with current hay prices is important for most livestock farmers. We calculate price averages, quality averages, and the corresponding ranges of the various hay lots from recent hay auctions in Sauk Centre, MN. We also keep an updated history of recent years of some selected hay lots and create graphs of four different quality types of medium square alfalfa bales. This is posted every month, about a week after the last auction of the month.

Managing Micronutrients

Seth Naeve, Austin Dobbels and Dan Kaiser cover micronutrients in this episode. Dive into BMPs and diagnosis, plus a special focus on iron deficiency chlorosis.

Tuesday, June 19, 2018

Evaluating responses of soybean to foliar fungicides in Minnesota

Bruce Potter, Extension IPM Specialist and Dean Malvick, Extension Plant Pathologist

Why worry about the disease control benefits of fungicides?

Soybean growers and their advisors are faced with a bewildering array of information, from many sources, about products and practices that might increase yield and profits. Management of soybean diseases is no exception. Foliar fungicides are valuable soybean disease management tools. However, when applied in the absence of controllable, yield-limiting plant disease, they are typically not a profitable input.

Monday, June 18, 2018

As June transitions into July what soybean weed management options are still available?

Jeffrey L. Gunsolus Extension Agronomist-Weed Science

waterhemp in soybean field
Waterhemp in soybeans. Photo: Liz Stahl
The combination of a long duration of wet weather and advanced growing degree days has created serious weed management challenges for many corn and soybean growers. Due to the impending June 20th cutoff date for approved dicamba formulations on Xtend soybean and weeds moving into their rapid growth phase, most of the questions I am receiving, and I hope to address, are focused on soybean.

Friday, June 15, 2018

Are Inversions Really That Common?

by Andrew Thostenson, Pesticide Program Specialist, North Dakota State University Extension Service; Jared Goplen, David Nicolai and Ryan Miller, University of Minnesota Extension Educators - Crops

Pesticide applicators have long been obliged and directed by pesticide labeling to understand, identify, and NOT apply during air temperature inversions. This has become acutely important because of the off-target movement of dicamba over the last couple of years. But a similar statement is also found on many other pesticide labels. 

EPA and pesticide manufacturers have made it abundantly clear they do not want pesticides applied during an inversion. But that is easier said than done. Until recently, very few people actually monitored inversions. That is fast changing. North Dakota and NW Minnesota via NDAWN now have 31 stations monitoring this in real time with alerts being posted to smart phones. Missouri has 11 stations. Pesticide manufacturers have also spent a fortune on predictive modeling and distribution of their estimates via mobile apps. Finally, hand held sensors developed by Innoquest are also widely available. Now that we can measure and monitor for inversions, an applicator has to assess this information and make a decision to spray or NOT spray. That is the hard part. 

Winter Camelina Field Day to be held June 27 in Waseca

The University of Minnesota Forever Green Initiative and the Agricultural Utilization Research Institute (AURI) invite processors, food entrepreneurs, culinary professionals, farmers, and the curious public to an open house event at the Southern Research and Outreach Center 35838 120th Street Waseca, MN. Throughout the event, scheduled for June 27, 2018, attendees will learn about winter camelina, an exciting new oilseed crop currently in the research and development phase, which has the potential to transform food, fuel and feed in Minnesota.

Register today for the July 2018 Field School for Ag Professionals

By Dave Nicolai, IAP Program Coordinator

The 2018 Field School for Ag Professionals will be held on July 25 - 26 at the University of Minnesota Agriculture Experiment Station on the St.Paul campus at the University of Minnesota. The Field School for Ag Professional is a summer training opportunity that combines hands-on training and real world field scenarios. The two-day program focuses on core principles in agronomy, entomology, weed and soil sciences on the first day to build a foundation for participants; and builds on this foundation with timely, cutting-edge topics on the second day.

Thursday, June 14, 2018

Small Grain Summer Plot Tours

by Jared Goplen, Extension educator and Jochum Wiersma, Extension small grains specialist
People in wheat field

University of Minnesota Extension is offering four Small Grain Summer Plot Tours across MN in June and July to address small grain production issues, variety performance, and insect and disease pests.

These programs are designed to provide farmers and crop consultants the tools needed to make small grains successful and profitable. This includes information on production agronomics, variety selection, disease identification, fungicide use, fertility, and economics. These programs are interactive and discussion based, featuring a tour of current research plots and discussion of on-farm experiences.

Wednesday, June 13, 2018

Corn and soybean weed management tour scheduled for July 3

Lisa Behnken and Ryan Miller, Extension educators
People on field tour

Weed management has changed dramatically in recent years with herbicide resistant weeds, new herbicide technologies and challenging weather conditions. How do we develop resilient strategies to deal with all of the different challenges? The 2018 Corn and Soybean Weed Management Tour will highlight ongoing research that addresses these challenges and introduces new ideas for crop producers and Ag Professionals on Tuesday, July 3.

Cutoffs for postemergence herbicide applications in corn and soybean

By Liz Stahl and Dave Nicolai, Extension Educators - Crops

A late start to the planting season, combined with warm temperatures and an abundance of moisture in areas of the state has led to quick crop emergence, and crops that are rapidly advancing through the growth stages. Crops may also be in a range of growth stages due to varying planting dates that resulted from working around a wet planting season. Almost all herbicide labels have a maximum growth stage and/or crop height after which applications should not be made. Application restrictions exist to help prevent potential crop injury, herbicide carryover, environmental or food safety concerns, or other potential issues.

Heavy seedcorn maggot infestations reported in some Minnesota soybean fields

by Robert Koch (Extension Entomologist) and Bruce Potter (Extension IPM Specialist)

Some fields in Minnesota have experienced significant stand loss caused by seed corn maggot. In a field in Dakota County (southeast Minnesota), research plots planted in the last week of May with untreated soybean seed incurred greater than 90% stand loss. This field had none of the typical risk factors for infestation by seedcorn maggot, except for likely planting during a period of fly activity. In addition, a report was received of a central Minnesota soybean field with seedcorn maggot injury. Portions of the neighboring fields had some seedcorn maggot injury as well. It turns out, that this field had been planted to sweetcorn in 2017, but the field was passed and not harvested. The resulting decaying sweet corn may have attracted egg-laying adults last fall and subsequently supported a very large population of overwintering pupae. Soybean planting into the still decaying sweet corn this spring was likely timed well with fly emergence and egg laying. As you perform early season scouting of your fields, keep seedcorn maggot in mind if you start to observe issues with plant emergence. Below, we provide an overview of the pest's identification, biology and management.
Injured cotyledons from an infested soybean field, and seedcorn maggot larvae and pupae collected from injured plants and soil near the injured plants.

Tuesday, June 12, 2018

No change in the June 20, 2018 dicamba application cutoff date for Xtend soybeans

Jeffrey L. Gunsolus, Extension Agronomist - Weed science

On June 8, 2018 the Minnesota Commissioner of Agriculture released a letter to stakeholders indicating that the MDA will be keeping the 24(c) restrictions for XtendiMax, Engenia and FeXapan in place for 2018. The Commissioner’s letter also explains the rational for holding to the 24(c) restrictions, despite the challenges presented by late planting dates for soybean in many parts of the state.

Sidedressing Nitrogen in this Challenging Minnesota Growing Season


Fabian G Fernandez, Nutrient Management Specialist

Most corn in Minnesota is between V3 and V8 and developing rapidly now with most fields around V5-V6. Up to this point corn has taken up around 20 to 25 lbs N/acre. That’s about 10 percent of the total N it will need by the time it reaches physiological maturity in the fall.

Herbicide drift symptomology

by Ryan Miller, Extension educator

dicamba damage in soybean
Dicamba damage in soybean
As we enter peak postemergence herbicide application season, there is an elevated risk for off target herbicide movement. Of particular concern is the movement of growth regulator herbicides onto soybeans. Growth regulator herbicides include products like 2,4-D and dicamba. These products cause leaf puckering, and epinasty or twisting of stems. Injury symptoms are most commonly observed on the newest most recent growth in soybeans.

Thursday, June 7, 2018

IPM Podcast: Update on Recent Corn Rootworm Activity and Bt Resistance Trends in Minnesota

Welcome to the 3rd IPM Podcast for Field Crops – this Podcast is sponsored by the UMN Extension Integrated Pest Management (IPM) Program.


Corn rootworm larvae feeding damage to corn roots. Photo: Dave Hansen
The purpose of the IPM podcasts is to alert Growers, Ag Professionals and Educators about emerging pest concerns on Minnesota Field Crops - including corn, soybean, small grains and alfalfa. We also review recent pest trends and research updates.

Wednesday, June 6, 2018

Nutrient Management Podcast: Mastering the Pre-sidedress Nitrate Test


The pre-sidedress nitrate test (PSNT) is a tool for making decisions on supplemental nitrogen application. Taken during June prior to side-dress N application around the V6 stage of corn growth, the PSNT offers a way to assess insufficient N in the soil. It offers guidance for efficient N management, but only if carried out correctly. Listen as guests Dan Kaiser, Fabian Fernandez, Brad Carlson and Jeff Vetsch talk through how to effectively use the PSNT to manage nutrients on your farm.

Monday, June 4, 2018

Refocusing attention on the most yield limiting pathogen of soybean

Angie Peltier, Phillip Glogoza, Jared Goplen and Seth Naeve (University of Minnesota Extension) and Sam Markell (North Dakota State University Extension)

Minnesota map of soybean cyst nematode spread
Figure 1. Soybean cyst nematode identification and spread in Minnesota
What causes an estimated 90,000,000 bushel yield loss of soybean in the North Central U.S. each year? What can cause an eye-popping 30% yield loss without above-ground symptoms? What can move any way that soil moves? What can invade a soybean plant and worsen brown stem rot and sudden death syndrome symptoms?

The answer to each question is the same: the soybean cyst nematode (SCN). SCN is a microscopic roundworm that was first found in the U.S. in North Carolina in 1954. SCN has since moved north and west, reaching southern Minnesota in 1978. Little by little SCN continues to spread, marching north in the state along with soybean production, cutting soybean yield-potential along the way (Figure 1).

Alfalfa Scissor Cuts May 31 & June 1, 2018

by Randy Pepin, UMN Extension Educator, Stearns, Benton, and Morrison Counties
pepin019@umn.edu or (320) 333-1369

Harvesting high quality alfalfa hay is a prime concern of most dairy farmers.  The ideal time to cut first crop alfalfa has many variables such as: spring weather, severity of the winter, the weather last fall, how the field was managed last fall, age of the alfalfa stand, alfalfa variety, fertility level, and each farmers criteria on desired hay quality.  Collecting a series of scissor cuts samples of an alfalfa stand beginning early in the growth stage will monitor the progress of the alfalfa maturity.  We harvest scissor cuts on a number of fields throughout central Minnesota to help dairy producers observe the maturing progress across several fields.

Friday, June 1, 2018

Tips and Tricks for the Pre-Sidedress Nitrate Test

Brad Carlson, Fabian Fernandez, Jeff Vetsch and Dan Kaiser are on this episode talking about the PSNT: pre-sidedress nitrate test. We cover when to take it, how to take it, why to take it and how to get it ready for the lab. Plus tips on what to do with banded fertilizer and how to translate results into management practices.

Here's What the Research Says About Managing Sulfur in Soybeans


Daniel Kaiser, Nutrient Management Specialist
Jeff Strock, Professor

Soybean plants need sulfur to complete their lifecycle. It’s a key component of amino acids and deficiency can affect soybean concentration and grain yield. While sulfur provides all these benefits to the soybean crop, research shows that the best way to manage sulfur in soybeans is not to apply fertilizer S directly to soybeans, but to corn in a corn-soybean rotation.

Off-target herbicide movement

by Ryan Miller, Extension educator

Tractor spraying in field
Photo: Liz Stahl
As we are all well aware, last year saw the addition of dicamba tolerant soybeans to weed management options in the U.S. The addition of this technology was not without the troubles of off target movement and subsequent plant injury.

This led to changes in the federal label for all brands of dicamba that can be applied to dicamba tolerant soybeans.

Alfalfa Scissor Cuts May 28-29, 2018

by Randy Pepin, UMN Extension Educator, Stearns, Benton, and Morrison Counties
pepin019@umn.edu or (320) 333-1369

Harvesting high quality alfalfa hay is a prime concern of most dairy farmers.  The ideal time to cut first crop alfalfa has many variables such as: spring weather, severity of the winter, the weather last fall, how the field was managed last fall, age of the alfalfa stand, alfalfa variety, fertility level, and each farmers criteria on desired hay quality.  Collecting a series of scissor cuts samples of an alfalfa stand beginning early in the growth stage will monitor the progress of the alfalfa maturity.  We harvest scissor cuts on a number of fields throughout central Minnesota to help dairy producers observe the maturing progress across several fields.
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