Weed Mgt Changes  12/29/16 12:57:10 PM

Key Dates

 

Pre-Book Continues—Receive an additional 10% off of bulk herbicide prices when booked by

January 7th—See price sheet in lobby for complete listing

Yield Info.—2016 Yield Grids are complete! Visit the lobby for the complete genetics X environment version or our website for the summaries.

Key Dates—January 20th, 2017—12% Volume, 6% Cash Seed Discount Ends

January 24th, 2017--Customer Appreciation Dinner
Storm Date January 31st 2017

                                               

                                                March 8th—Spring Agronomic Mtg—Cass Co. Fairgrounds

 

Winter is good time to review herbicide programs success and failure rates based on the types and density of weed species present in your fields.  AS ALWAYS, timing of the application can/will determine treatment success rates and with large amounts of No-tilled acres, and/or acres that were treated with a non-residual application this past growing season, many producers are experiencing the increase of winter annual/biennial weeds prior to planted the following growing season.    This is far more of an issue for acres going into corn than soybeans but it is a universal problem as all weeds compete for soil water, nutrient use, and eventually yield reduction.  Many times contact/burn down/non-residual treatments are made when the targeted weeds are too large in size for the treatment to effectively work.  Last year’s example was again marked by marestail escapes. 

 

The time of weed emergence influences which species will be the most serious weeds in a given crop production practice and allows you to predict what application is priority given the weed species present. It also determines which weeds will be most susceptible to certain control measures. The wide range of species present in corn and soybean complicates prediction of weed emergence patterns. Many factors, such as tillage system, crop rotation, weed control history and weather patterns regulate the weed population of a given field. However, general emergence trends among species are predictable. See the table below, which details the emergence sequence of problem weed species of crop production in our geography.

 

Marestail, for example, is currently alive and well in a number of fields.  Many of these plants are now in the rosette stage of development.  Likely hidden under crop residue, un-noticed unless you are specifically looking for them.

So, if you have a winter annual weed problem normally a burn-down treatment of some sort, along with your residual treatment, can be a tried and true application for early spring  (March)  Shoot absorbed, fall applied treatment will not work on weeds at this stage of development.  Now, can they still work on the un-emerged winter annual weeds?  Sure, but the application needs to be applied before the weeds emerge from the soil. 

 

If Winter annual weeds aren’t that much of a problem for your fields, then the “weed and feed” applications at or near planting time would be a consideration in making the applications closer to the time of weed germination.

 

Lambsquarters, velvetleaf, cocklebur, and foxtail species are relatively early spring emergers, while tall waterhemp, and palmer amaranth generally emerge later in the growing season.  Late germinating weeds such as these pose the biggest problem/threat as many of the pre-emergence residual compounds are likely starting to run out of strength when they begin their life cycle and IF a non-residual post emergence treatment had been used, weed escapes can be an issue.  As the crop canopies, germination of new weeds normally slows down. BUT, if above average precipitation patterns exist and the crop has yet to canopy, additional flushes of weeds can occur.  Once canopy occurs, this will usually reduce weed competition.

 

Relative Emergence of Common Weeds of Summer Annual Crops

 

Relative emergence of common weeds

     

Prior to Crop Planting

 

Winter Annuals

Early

 

Biennials

Spring

 

Group 0

Group 1

Group 2

Horseweed/Marestial

Kochia

Quackgrass

Downy Brome

Prostrate Knotweed

Giant Raqweed

Field Pennycress

Wild Mustard

P. smartweed

Sheperd's Purse

Dandelion

C. Lambsquarter

Biennial Thistles

Russian Thistle

Wild Oats

Wild Carrot

   

Dandelion

   
     

At Crop Planting

   
     

Group 3

Group 4

Group 5

Smooth Brome

Canada Thistle

Green Foxtail

C. Ragweed

Giant Foxtail

Milkweed

Wholly Cupgrass

Cocklebur

Barnyardgrass

Velvetleaf

Yellow Nutsdege

Yellow Foxtail

Wild Buckwheat

Redroot Pigweed

Field Sandbur

     

After Crop Planting

 

Group 6

Group 7

 

Nightshade

Fall Panicum

Palmer Amaranth

Shattercane

Crabgrass

 

Venice Mallow

Morninglories

 

Waterhemp

Jimsonweed

 

S. Groundcherry

Witchgrass

 

 

Table adapted from Iowa State University Extension Publication SA-11

 

This may seem a bit “preachy”, however, we bring all of this redundancy up as we think there is a need more vigilance in knowing our weed life cycles and when to expect their presence.  It has been 21 years since Roundup Ready Soybeans entered into the row crop market.  That was soon followed by Roundup Ready corn.  A quick transformation was made in our entire approach to weed control and everyone ran to glyphosate based post emergence treatments only—especially in soybean production.  For the first few years it worked fairly well.  But then new weeds such as marestail and waterhemp emerged.   (they weren’t new—just recognized as they begin to become present more in soybean fields with a lack of pre emergence treatments in use.  Many of the pre-1996 herbicides worked fairly well in achieving their control.)    

 

We were then challenged with this issue--

 

How many of your fields have EVERY weed at the same plant height at the time you want to make your post emergence application?

    

 In 1995, we tried to kill weeds before you saw them with  multi-mode, pre-emergence treatments.  POST Treatments were considered as a last ditch effort for weed control.    The fact is this:  many current weed control/escape problems are a result of leaning on post emergence programs too long as the only form of weed control—especially in soybean production.   Additionally, I have yet to find any one field with just one weed species present, that germinates at one specific time of year.  There must be a combination of pre-emergence and post emergence treatments in order to achieve better weed control.  The number of weed species present, when they germinate, and how they compete with your crops, make its almost impossible to achieve season long control with only one application of anything.

      

So, this really isn’t about whether you think you may or may not have resistant weeds species in your fields.  This is about revamping our management necessary for general weed control success.  What was old is now new again and honestly needed when considering the current weed populations present in many fields and the need of both pre and post emergence treatment combinations.     Post emergence herbicides can and will still be a viable part of many programs---It should not be the ONLY part.     Consider these thoughts when thinking about weed control programs for 2017.

 

 

 

Weed Competition

Corn competes differently than soybeans, sorghum or wheat can against different species of weeds. The following is some work done from 1996 to present through the University of Nebraska Weed Science Department that addresses just this issue.  Note the number of broadleaves compared to the number of grasses it takes to cause the same percentage of potential yield reduction. Table A. represents the number of weeds per 100 ft2 that will cause a given yield reduction in corn.  This assumes that weeds emerged with corn and no herbicide has been applied.  These numbers only consider the effect of the weed in the current year and do not take into account future weed problems due to weed seed production. This should be considered if these numbers are used to make long-term decisions.

 

Number of weeds per 100 ft2 causing a 1.0, 2.5, 5.0, and 10.0% yield loss in corn.                                                    
                                                                
    % Yield Loss                         

Weed                                       1.0                   2.5                   5.0                   10.0

Foxtail                                       7                    19                    39                      85

Lambsquarters                           5                    12                    26                      57

Common ragweed                     5                    12                    26                      57

PA Smartweed                          5                    12                    26                      57

Kochia                                       3                      7                    16                      34

Pigweed                                     3                      7                    16                      34

Waterhemp                                3                      7                    16                      34

Velvetleaf                                  2                      4                      9                      20                 

Cocklebur                                  1                      3                      7                      16

Sunflower                               <1                       2                     4                        9

            (University of Nebraska-Lincoln Weed Science Department.  1996) 

 

So, at a 10% yield loss level, 9 sunflowers per square foot has the same yield loss potential as 85 foxtail plants.

 

HIGH P LEVELS PROVE TO BE IMPORTANT—Dated now but still revelent , University of Minnesota research conducted in 2009 at Waseca showed that soils with a very high P test (Bray P=22 ppm)—with no extra fertilizer P added—produced higher and more profitable corn yields compared to low P-testing soils where recommended rates of P were applied.   The research—two studies at Waseca- MN- clearly points out the economic penalty (up to $100/acre/year) associated with low P-testing soils, even when P fertilizer is applied. So it’s even more important for farmers to know the soil test P status of their fields, especially those rented or recently acquired.

Effect of Bray P Soil Test on corn and soybean yield response to fertilization (Gyles Randall, University of Minnesota)

         

Three-year average corn yield

   

Application Method

P Rate*

 

Low P Soil

High P Soil

 

High-P Advantage

     

lb P2O5/Acre

bu./acre

bu./acre

 

bu/acre

%

None

   

0

 

148

192.8

 

44.8

30

Pop-up

   

25/20

 

158.1

191.6

 

33.5

21

Deep Band

 

25/20

 

157.7

196.4

 

38.7

25

Broadcast

 

25/20

 

166.4

196.2

 

29.8

18

Deep band + pop-up

25/20 + 25/20

 

171.5

189

 

17.5

10

Pop-up

   

50/40

 

165.7

194.5

 

28.8

17

Deep Band

 

50/40

 

166

186.4

 

20.4

12

Broadcast

 

50/40

 

167

190.2

 

23.2

14

       

Average

162.6

192.1

 

29.6

18

     

Bray P1 Soil Test

6-9 ppm

20-27 ppm

     

*Rates for low-test/high test sites

           
                   
         

Three-year average soybean yield

 

Application Method

P Rate**

 

Low P Soil

High P Soil

 

High-P Advantage

     

lb P2O5/Acre

bu./acre

bu./acre

 

bu/acre

%

None

   

0

 

34.5

49.1

 

14.6

42

Pop-up

   

25/20

 

36.4

49.1

 

12.7

35

Deep Band

 

25/20

 

34.7

48.8

 

14.1

41

Broadcast

 

25/20

 

36.7

50.3

 

13.6

37

Deep band + pop-up

25/20 + 25/20

 

40.8

49.3

 

8.5

21

Pop-up

   

50/40

 

38.2

48.9

 

10.7

28

Deep Band

 

50/40

 

38.5

49.1

 

10.6

28

Broadcast

 

50/40

 

37.1

48.4

 

11.3

30

       

Average

37.1

49.1

 

12

32

     

Bray P1 Soil Test

6-9 ppm

20-27 ppm

     

**Residual Rates are for previous corn crop low-test/high test sites

     

 

 

 

 

 

 
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