Crop Water Use, Weed Control  06/21/16 9:32:11 AM

Wiles Brothers Inc.
Calendar of Tour Dates Summer 2016
 
2016 Summer Field Tour Details
 
RAIN OR SHINE—If raining--we will gather in our seed building—If the sun is shining--at our plot on the West side of Mynard Nebraska—1 mile South of our plant—1/4 west on Mynard Road OR 1-1/4 mile West of HWY 75 on Mynard Road—South Side of the Road.   The tours would last no longer than 1.5 hours and address any current agronomic issues as well as allow the attendees to monitor developmental progress of Asgrow and DeKalb genetics throughout the growing season.  View the current genetic lineup as well as population trials, fungicide and insecticide seed treatment comparisons, biological seed treatments, the affects of starter fertilizers and more!   
 
Date                                                      Time                                      Location
Tuesday June 28th                                                 9:00 a.m.                                 Mynard
Tuesday July 12th                                9:00 a.m.                                 Mynard
Tuesday July 26st                                9:00 a.m.                                 Mynard                      
Tuesday August 9th                             9:00 a.m.                                 Mynard
Tuesday August 23rd                         9:00 a.m.                                 Mynard
 
Additional Topics Next Tuesday:
 
 
  1. Crop Water Use—Development Updates—Root Dig/Root Pits—View Root development in both Corn and Soybean.

  2. Janet Jurado and Brady Kappler with BASF will discuss current topics with corn plant health, new developments with corn fungicides, and the status of the corn crop vs. potential foliar infections
     

                        Dr. Tamera Jackson (Corn Plant Pathologist from UNL) has also been invited into the discussion

  1. 2017 Seed Programs—DeKalb Acre Plus

 
Bring your questions and a friend and we will see you next Tuesday Morning at 9:00 a.m!
 
Crop Development has shifted gears dramatically into a conservation mode this past week as signs of moisture stress are beginning to show in both the corn and the soybeans.  Although some areas received rainfall of widely varied amounts last Friday night (6/17) and last night (6/20), general rainfall had been scarce as both corn and soybeans demonstrated wrapped/rolled/cupped leaves in the heat of the afternoon. This is a normal plant phenomenon that cuts down on plant photosynthesis, and closes the plant stomata (respiration pores) to conserve plant moisture.   The dry surface soils will encourage deeper root growth where we currently have more moisture* (courtesy Hoeft, R., Nafzider, E., Johnson, R., Aldrich, S. 2000, Modern Corn and Soybean Production, p.264).   Certain fields are showing this more dramatically than others as a result of tillage practices, soil types, and pre-growing season soil moisture levels.  The plant will unfurl overnight once the temperature goes down, but this is an initial sign from the plant that moisture stress is occurring within the plant and available soil water left in the soil profile has begun to dwindle.  To test this observation, this past week I took a tile spade and dug down 2’ into the soil profile (approximately the current corn root depth) in a number of places across Southeastern Nebraska.  The profile was approaching 50% moisture capacity (wilting point) from about the 0-6” depth.  However, from the 6-24” depth, soil moisture is approximately in the 70-80% range of moisture capacity.  Corn is a bigger water user right now than soybeans.  Corn is trying to use up to 0.20 inches of water per day while soybeans are using about 0.15 inches of water per day.  Has the yield been hurt?  I don’t think soYes, rains definitely will help right now.  But, remember, that forty percent of water absorption in corn occurs within the top 12”, 30% in the second foot, 20% in the third foot, and 10% in the fourth foot of the soil profile. Water use in corn in Eastern Nebraska on average transpires between 25-28” of water through the plants during the growing season. Both corn and soybeans need the most water at the pollination and reproductive phases of development.  Earlier planted corn is approaching in the second of two critical reproductive stages (pollination) where fertilization of kernels and numbers of kernels per row on that ear will be determined. The final number of kernels will not be determined until after pollination and even then may change via kernel abortion through Dough (V4) stage if fertilized kernels do not complete development via drought, insect, or disease stress.
Soybeans react differently than corn.  They seemingly go to sleep in weather like this waiting for moisture and cooler weather to grow.  Although soybean roots can reach depths of 5 to 6 feet, the largest concentration of roots and the majority of soil water extraction occur in the top 2 to 3 feet of the soil profile. The total water use by a soybean crop is 21 to 24 inches per year. About 65 percent of this water is used during the reproductive stages. Yield potential reduction in soybeans is currently not a concern.  (courtesy Elmore, R.W., D.E. Eisenhauer, J.E. Specht, and J.H. Williams. 1988. Soybean yield and yield component response to limited irrigation capacity sprinkler irrigation systems. Jou. Prod. Ag., Vol. 1(3). p196-201.) 
 
 

CORN WATER USE PER DAY

 
Growth Stage                          Inches Water Use/Day
1-4 leaf                                                            .02 - .05
5-8 leaf                                                            .05 - .10
8-10 leaf                                                          .10 - .15
11-14 leaf                                                        .15 - .20
14-18 leaf                                                        .20 - .25
19 leaf - blister                                                .25 - .30
Milk - soft dough                                            .20 - .25
Hard dough - early dent                                 .15 - .20
Mid - full dent                                                .10 - .15
 
 

SOYBEAN WATER USE PER DAY

 
Growth Stage                          Inches Water Use/Day
Germination/Emergence                                 .1 - .15
Vegetative Growth                                         .15 - .20
Flowering                                                        .25 - .30
Pod Development                                           .20 - .25
Seed Fill                                                          .15 - .20
Maturation                                                      .05 - .10
 
 

Puckered/Discolored Soybeans—A number of producers have reported abnormal soybean growth in the past few days.  They have noticed soybean leaves that are not uniform in size, shape, or texture.  Many report crinkled, puckered, strapped, or cupped-shaped leaves on a few of the trifoliolates.  In some cases, these reports have occurred where pre emergence only herbicides have been applied.  Reports of this type are not uncommon, especially when temperatures and humidity’s have been high. 

 
Soybean plants that have experienced weather stress (we’ve had plenty of that) early in the growing season tend to grow rapidly once favorable conditions prevail.  Nitrogen metabolism increases dramatically in plants around the V3 growth stage and continues until stage R5.5.  At V3, plants tend to turn from pale green to dark green in color and new trifoliolate leaflets may appear every 3 days!  During this time of rapid growth, cell division and enlargement (fueled by abundant turgor pressure) often outpaces the ability of the plant to adequately supply photosynthates for uniform cell wall construction.  Unlike corn which has meristematic tissue near the ligule (junction of leaf blade and leaf sheath), soybean leaves have a broad U-shaped marginal meristem (generally ½-inch wide) located approximately one-third of the way in from the leaf edge.  Newly formed leaves (i.e. those just unfurling) tend to be lighter in color, have irregular leaf surfaces, and are comprised mostly of meristematic tissue.  Leaf maturation is governed by hormones.  They expand in all directions with the oldest part of the leaf located near the leaf edge and the youngest located in the center of the leaf (the marginal meristem).  Any aberration in hormonal control caused by stress (i.e. excessive temperature fluctuations, growth regular herbicide drift, plant viruses, SCN, mechanical injury, insect injury, frost, drought, etc.) will result in crinkled or puckered leaf tissue.  A mild case of leaf crinkling does not affect the photosynthetic capability and is cosmetic in nature, and does not negatively impact yields.  Crinkled or puckered leaves should be considered ‘healthy’ if they are dark green (except with prolonged drought stress) and the overall plant height is not affected. 
 

 
Controlling Marestail this year has again, been a struggle to say the least.   It has been most problematic now, when trying to develop an effective herbicide application in soybean fields   Marestail (also known as horseweed) is a winter annual weed that germinates usually in the fall.  It can however, also germinate and grow in the spring and summer.  This spring, it is prolific in number and given the weather patterns of late, thriving in growth with all of the early wet weather.  Marestail, Ragweed, and Waterhemp seem to grow by the foot overnight as both species can grow up to 6 feet in height.  Although small in size and many in number, marestail’s waxy leaves make it difficult for herbicide applications to be absorbed and translocated within in the plant.  This is especially true as the plant increases in size.
In Roundup Ready Crops, once it is more than 6” in height, higher rates of a Roundup are required and most times the Roundup needs a tank-mix partner to insure good control.    This does not mean it is resistant to Roundup.  It means that an appropriate rate increase along with a tank-mix partner provides the best control when the marestail is this big and “out of the range” of labeled control.  Below is a common sight, many times where the plant height was out of the range of control for the rate being used and the Roundup/Tank Mix partner—in this case Cobra.
 
Many of the tank-mix partner treatments can increase the chance of crop injury.  Although this injury is relatively minor, leaf speckling can occur and at this stage of development and usually means little to nothing in regard to yield potential.  

Our opinion is to try to kill marestail and most other weeds, before you are able to see them….An additional option in control is the timing of the herbicide applications that can be made.  As mentioned before, marestail is a winter annual by life cycle classification.  Fall applications of a number of pre-emergence soybean herbicides  such as Authority First, Canopy, Sharpen, Sonic and Valor all work well as a Fall Burn down of Marestail.    They are not in-fallible.  But, a fall herbicide application to fields with a historic population of marestail, will give you better control the following year.
 
WEED RESISTANCE--Stories about glyphosate (the active ingredient in Roundup,  Touchdown, and a host of other compounds) resistant weeds and concern about the use of Roundup Ready crops have circulated for years since the introduction occurred into row-crop use back in the mid-late 1990’s.  Most of these stories actually create fear of using beneficial technology and provide use recommendations not based not on scientific data but largely on emotions and assumptions.  This can create grower concern about using technology that has proven to provide many benefits including facilitation of conservation tillage systems, excellent weed control and excellent crop safety.  As the years of broad spread application have continued to develop, the incidence of more weeds (waterhemp, marestail, ragweed) escaping a treatment have also increased.
 
Does this mean that all escaped weeds populations are resistant??
            Monsanto introduced Roundup herbicide in 1974, providing growers with a new and effective tool for broad-spectrum weed control.  Roundup Ready crops were introduced beginning in 1996, providing growers with additional tools to obtain excellent weed control and crop safety along with greatly improved ease, flexibility, and potential cost savings.  Both of these novel technology introductions have revolutionized weed control practices in crops since then.  It is hard to argue that Roundup agricultural herbicides and Roundup Ready crops are excellent, economical solutions to weed control.  Over the past number of years, weed species such as pigweeds (waterhemp, palmer amaranth, redroot pigweed), giant ragweed, and marestail, have become routine candidates for weed control escapes from a Roundup treatment—primarily in soybeans.  This year is no different in having a glyphosate based treatments applied and subsequently having weeds escape the original treatment.
 
                        WHY?
 
 
  1.  Why does the treatment kill one weed completely and 3 feet away--NOT kill another weed of the same size?        
  2. Why is there seemingly more and more escapes every year?
  3. Why do certain fields that had tillage done earlier have more weeds/more escapes now?
 
There are number of confirmed weed species resistant to the active ingredient glyphosate in the U.S.  Glyphosate has no soil residual, and is tightly bound to soil organic matter and dust.  These two facts play important roles in why there continues to be weed escapes after application—even with high use rates. These facts also aid in the potential development of resistance.  
 
We have seen most escapes in the areas that are directly behind where the sprayer traveled in the field.  We have also seen many escapes along roads where excessive dust from the adjacent road has covered the leaves.  Dust/dirt on the weeds leaves will limit/tie up the glyphosate from being absorbed/translocated in the plant.  Areas that incurred tillage this year are seeing increased weed pressure.  This is likely due to the weed seed dormancy being broken via the tillage practice in the soil.  We won’t argue the justification for the tillage, we just notice that weed pressure is generally greater in areas that have had a tillage pass since that last cropping season.   This makes sense as tillage can “plant” weed seed to enable active growth.
 
We don’t think that every waterhemp, marestail, or any other escaped weeds from the glyphosate treatments are resistant to glyphosate.  The inconsistency of the weed control is LIKELY a matter of all of the following:
            --late application to BIG weeds (greater that 6” in height)
--application timing with no increased rate change for larger weeds
--the non-use of an additional tank-mix herbicide for control of these weeds in the     treatment
--hot, dry, dusty dirty conditions at application time—actively growing non “dirty” weeds are easier to kill.
--bigger weeds “shading” the smaller weeds.  This limits herbicide uptake on the small weeds.  The big weeds die off and a second flush emerges.
 
If you think back to pre-roundup ready crop days, we had the same problems with weed escapes with a multitude of non-roundup applications for these same reasons.
 
We encourage you to consider the use of full-rate, multi-mode of action tank mixes, and treating early in weed development if possible (I know the weather has been challenging), if you are having problems controlling weeds with your current applications.
 
 
 
 
John W. McNamara
Agronomist
Wiles Bros. Inc.
606 Wiles Road
Plattsmouth NE. 68048
(402) 298-8550--Office
(402) 499-3870--Cell
(402) 298-7174--Fax
 
 
 
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