UGA Weed Science Web-Page Updates (Culpepper and Prostko)

Numerous circulars and slide presentations have been added over the past few weeks for agent use on the UGA Weed Science Web-Page (www.gaweed.com).

Circulars (found on home page):

1.  Methyl bromide alternatives

2.  Weed control in broccoli, cabbage and cauliflower

3.  Weed control in watermelon

4.  Controlling Palmer amaranth in cotton

Slide Presentations (click weed management toolbar on homepage; then click slide presentations):

1. 2016 Cotton Weed Control
2. 2016 Fumigant Systems
3. 2016 Vegetable Pesticide Update: Weeds
4. 2016 Vegetable Weed Control
5. 2016 Watermelon Weed Update
6. 2016 Wheat Weed Control

7. Influence of Nozzle Type of Peanut Weed Control Systems

8. 2,4-D and Dicamba Resistant Soybeans in the Southeast

9. Influence of Tractor Speed and Boom Height on Spray Coverage

Weed Science Update Follow-Up (Prostko)

1) Slides sets (field corn, soybean, peanut, grain sorghum/canola/sesame/tractor speed, UGA Herbicide Recommendations) from the December 9, 2015 Weed Science Update are now available at the following web-address:  http://gaweed.com/slides.html

2) There was much interest in the field corn herbicide tolerance charts.  Here is what is available as of today:

2015 Pioneer Corn Hybride Herbicide Management Guide
https://www.pioneer.com/CMRoot/Pioneer/US/products/stewardship/2015_corn_herbicide_guide_ProdList.pdf

Dekalb Corn Hybrid Information (Herbicide Safety Column)
https://www.dekalb.ca/eastern/en/corn

Grain Sorghum Dessication (Prostko)

Seems like I am getting more questions this year about the dessication of grain sorghum.  The change in the weather has everyone getting ants in their pants.  Growers need to know that the use of harvest-aids in grain sorghum has shown little effect in reducing grain moisture content.  A summary of 2 older papers is as follows:

1) Hurst, Harold.  1991.  The Use of Dessicants For Field Drying Grain Sorghum With and Without Weeds.  Mississippi Agricultural and Forestry Experiment Station Bulletin #974.

"Overall, these studies did not result in any distinct advantage for application of dessicants to reduce grain sorghum moisture."

2) Olson, B.L.S, T. Baughman, and J.W. Sij.  2001. Grain Sorghum Dessication with Sodium Chlorate and Paraquat in the Texas Rolling Plains.   Texas Journal of Agriculture and Natural Resources 14:80-83.

"Results from our 2-year study indicate that dessicant applications were generally ineffective (and most likely uneconomical) in reducing grain moisture in late-planted grain sorghum."

In my opinion, the major (only?) benefit of using a harvest-aid in grain sorghum would be to reduce the amount of green plant material that goes through the combine and might end up in the grain.  I know of only 3 things that will dry down grain sorghum seed: time, a hard freeze, and/or a grain dryer.

Wheat Weed Control 2015-2016 (Culpepper)

The circular for controlling annual ryegrass and wild radish has been finalized. You can access the circular on the UGA Weed Science Web-page.  The link is listed below   This publication is also included in this blog (if you click on the picture, it can be viewed in a larger format).  If you want laminated handouts for your growers send me an e-mail including 1) the number of copies that you want and 2) the address that you want them sent to.  I will have laminated copies for this circular and other circulars during our December 9^th training but I realize this will be too late for growers wanting to experiment with Zidua or Fierce.  I would encourage everyone to try a few acres of these new herbicides if ryegrass is a problem.

http://www.gaweed.com/HomepageFiles/2016%20wheat%20-%20Final%20-%20Oct%205.pdf

 PAGE 1

PAGE 2

New Section 24(c) Label for Fierce in Wheat (Culpepper, 2015) - For UGA Extension Agents Only

Fierce, active ingredient pyroxasulfone and flumioxazin, just obtained a new approval for postemergence applications in Georgia wheat as a Section 24(c) Special Local Need Label.  We did have a label for Fierce last year but we improved its use pattern for this 2015/2016 season.   

Our goal is to help growers struggling with ryegrass that is resistant to postemergence herbicides; although our research would also suggest that Fierce provides good to excellent wild radish control.  Our intentions for the 2015/2016 crop are to have a controlled use of Fierce allowing growers the chance to determine if the herbicide can be used to effectively manage problem weeds while having acceptable crop injury.  

Application of Fierce:

1.  Follow the label exactly (Figure 1).

2.  Wheat must be planted 1 to 1.5 inches deep and cannot be broadcast spread.

3.  Apply Fierce at 1.5 oz/A in ONLY CLEAN water when wheat is between the spike and 2-leaf stage; ryegrass needs to be ½ inch or hopefully much smaller.

4.  Apply Fierce only in water.  Notice I just mentioned twice that you cannot have anything in the tank other than clean water and the herbicide; no exception!

5.  Must use 10-15 GPA; prefer 15 GPA if weeds are emerged.

6.  Do not apply with airplane.

7.  Only for wheat!!  Again, only wheat.

8.  DO NOT USE ON SANDS!

Crop Injury:

1. Greatest potential for injury occurs when 1) label recommendations are not followed and 2) when open/cracked seed furrow allows herbicides to directly contact the seed, when seed are planted to shallow, or when seed are planted in a deep furrow that allows herbicide concentration after a rain/irrigation event while wheat is growing. 

2.  Even when following the label, injury will occur in some environments.  This is why we are taking such a conservative approach.  With that said, our research suggests the benefits in weed control far outweigh injury concerns when following the label; you guys need to tell us if the research is accurate or not.

3.  Strongly suggest growers try only few field acres; do not treat the whole farm!!!! 

Also, just a reminder about Zidua which is the other new ryegrass herbicide we have available.  See the 2015-2016 UGA Wheat Production Guide for the lastest weed control information.

Figure 1.  24(C) Special Local Need Label for Fierce use on wheat in Georgia.  

What's that Weed? (Prostko)

In the last few weeks, I have received a few samples of  the weed known as old world diamond flower or flat-top mille graines (Hedyotis corymbosa) (Figures 1 and 2).  Its not very common, at least in my world.  In fact, I only touched it for the first time last year in a corn field in Decatur County. This summer annual plant is a member of the Rubiaceae (Madder) family and is closely related to more common plants such as poorjoe and Virginia buttonweed.   

Can't find any control data for row crops but a bunch exists for turf.

Figure 1.  Old world diamond flower (Photo Source: C. Tyson - Tattnall County)

Figure 2.  Old world diamond flower

Screening Palmer Amaranth Samples for Liberty Resistance (Culpepper and Prostko)

Without question, the amount of Liberty (glufosinate) applied during 2015 was much greater than in previous years.  Unfortunately, overuse and abuse of the herbicide was also more prevalent.  If Liberty is lost to resistance, it is questionable if our agronomic growers will remain viable in the long-term.  We must work hard to help growers make better decisions with Liberty and we must also determine where resistance develops rapidly.

Therefore, we are committed to screening some pigweed samples taken by county agents this winter.  Fields treated numerous times with Liberty, fields treated with Liberty multiple years in a row, or fields in which you felt timely Liberty applications were made but control was inadequate are ideal situations. 

The screening process is only as effective as the sampling technique.  Some suggested guidelines for seed collection are as follows:

1.  Harvest at least 25 FEMALE seedheads when MATURE.

2.  Female seedheads are usually the prickly ones and, of course, have the seeds.

3.  At least 75% of the seeds must be completely dark black; if they are burgundy or lighter in color they are likely not viable.  To check seed color/maturity, shake seedhead over hand allowing seed and seed cover to fall in hand; rub aggressively and seed should dislodge from cover. 

4.  Place seedheads in a paper bag (suggest cutting seedheads in sections so the will lay down in bag). Do not use a plastic bag!

5.  Write GPS coordinates, county, and your name and/or grower name on bag.

6.  Carry samples back to office, open bag, and place them in dry area for a few days.

7.  Bring to Tifton when visiting or send with someone going to Tifton.

8.  Drop off at Dena Watson's office in Horticulture Building.

 Note: Palmer amaranth plants are currently mature in fields that were planted during late April or very early May and the pigweed emerged with the crop.  Pigweed emerging later in the season are probably still a few weeks from being mature.

Figure 1.  A large Palmer amaranth plant survives an untimely application of Liberty. Not good for long-term resistance management!!!!!!!