Programs for Controlling Ryegrass and Radish Circular for 2021-2022! (Culpepper and Vance)

Agents, our wheat weed control circular is finalized. For the most part, it remains similar to last year with a few minor adjustments including:

1. Added liquid Zidua formulation (both liquid and dry formulation are labeled)

2. Added comment regarding Fierce and the expectation of the liquid formulation obtaining a label during 2022 (dry formulation labeled now).  

3. Removed Axial from circular; Axial Bold has replaced Axial.

4. Hopefully made tables even more simple to understand. 

If you would like a copy, email Jenna Vance at jcsmith3@uga.edu and ask for one of the following options:

Option 1: Request laminated circulars to be mailed to you. Provide the number of circulars that you would like and provide and address to send them.

Option 2: Request laminated circulars to be brought to you at our Dec. 1 weed training.

Option 3: Request a pdf version. An email response will provide the PDF as an attachment. 

Plans are to bring laminated vegetable circulars to you at our Dec. 1 weed training. In regards to the cotton circular, we are waiting on decisions from the U.S. EPA regarding auxin herbicide labeling requirements/restrictions for 2022 before making edits.

 

 

 

 

Soybean Green Stem (Prostko)

Last week, I received a few phone calls about soybean green stem (SGS) (Figure 1).  The causes of SGS are not well understood but are likely attributed to various stresses that can effect soybean pod development.  Stresses include problems such as stinkbugs, aphids, thrips, disease, viruses, and environmental.   The use of foliar fungicides, especially the strobilurins, have also been associated with SGS.  Cultivar may also be important as well.  

Herbicides such as paraquat, although very useful for soybean leaf defoliation, have been inconsistent in their effect on SGS.  At this time of year (i.e. harvest), the only management tactics for SGS are making sure combine teeth are sharp, reducing combine speeds, and possibly delaying harvest until when/if/maybe a hard freeze occurs.

For more information, check out this recent (September 2021) publication about Green Stem Syndrome in Soybean from Oklahoma State University. https://extension.okstate.edu/fact-sheets/print-publications/pss/green-stem-syndrome-in-soybean-pss-3003.pdf

Figure 1.  Soybean green stem.

Post-Harvest Weed Control (Prostko)

As you have heard many times before, Culpepper and I have been encouraging growers to consider the use of post-harvest (field corn) tactics (tillage, mowing, herbicides) to help manage the soil seedbank for weeds such as Palmer amaranth and tropical spiderwort.  The pictures below are from one of my corn fields that I recently treated with a combo of Gramoxone (paraquat) + Tricor (metribuzin) + NIS.  The green, untreated strips are there by design (checks).  This is one of my preferred post-harvest herbicide treatments especially for Palmer amaranth.  In many fields though, it might be too late if weeds have already produced seeds and/or if younger plants are likely to get terminated (before producing seed) with the first frost (about a month away in many locations). 

FYI, current Tricor label would allow field corn or soybean planting next spring but cotton and peanut rotations are 18 months.  We are trying to get the label changed to allow for a shorter rotation interval for these important Georgia row crops.  

Custer's Last Stand or Using Wipers or Mowers For Late-Season Weed Control in Peanut Fields (Prostko)

At some point, peanut growers must realize that it is futile to continue spraying herbicides over the top of their crop.  Either the weeds are too big and/or pre-harvest intervals cannot be followed.  In that case, there are 2 last resort weed control options for troublesome fields.  These include the use of either a non-selective applicator (i.e. wiper/wick bar) or a flail mower.  Flail mowers (vertical blades) are preferred over rotary mowers (horizontal blades) because they uniformly distribute debris rather than dump it on one side of the mower (which can cause major digging problems).  The main goal with these weed control methods is to increase fungicide deposition and/or improve harvestability.  At this time of year, it is really way too late to recover any weed competition related yield losses.  Here are a few things to consider for both options.

1) A 33% or 50% solution of paraquat (depending upon formulation) is legal to apply in a non-selective applicator for the control of Palmer amaranth.  Check out page 223 in the 2021 UGA Pest Control Handbook for more specifics (tractor speed and weed heights are very important).  This treatment will also work well on Florida beggarweed and sicklepod.  No other herbicides are labeled for this type of application so don't bother asking me about Liberty or dicamba (FYI, they don't work well in these applicators either!!!).  I have tested several types of applicators over the years and prefer any of the ones pictured below. You can also check out the following slide set for more information about the research I have conducted on non-selective applicators (http://www.gaweed.com/slides/prostko-swss-2011/index.html).

2) I have used a flail mower to clean up my weedy test plots for many years.  I usually set the mower to remove about 2"-3" of the peanut crop in addition to topping any weeds that are there.  Generally, 1 pass with the flail mower is OK but 2 passes are better (opposite directions). Check out these pictures from earlier today.

 

Rain Delays and Weed Control (Prostko)

Recent rains over the last few days at the UGA Ponder Farm (1.75"+) have kept me out of the field for today so I thought it would be a good time to squeeze in a quick blog. The frequent rain showers we have had over the last month or so have caused many problems with growers who have not been able to get in the field to make pesticide applications.  Since its now July 20 and getting late for just about everything, here are a few things to think about in regards to weed control in various crops:

1) The application cut-off date for all dicamba applications in tolerant soybean was June 30 and is July 30 for tolerant cotton. 

2) If at all possible, growers need to avoid making applications of Cobra or Ultra Blazer to peanuts during the 60-80 DAP time frame.  There have been yield losses (5-10%) associated with the application of these herbicides during this period (usually R5-R6 or beginning to full seed stage).  Cobra can legally be applied up until ~100-105 DAP since it has a 45 day PHI.  The PHI for Ultra Blazer is 75 days.

3) Yes, it is my opinion that it always a better idea to apply a POST grass herbicide at least 3 days before a peanut fungicide application rather than tank-mixing them together.  However, growers in a tight bind who just have no other choice but to co-apply (fungicide + POST grass herbicide) should consider increasing the rate of the grass herbicide (5-10%) to help overcome potential antagonism.  They must also realize that they still might not get optimum control especially since grasses are likely larger than desired.  Growers will be wasting money on the grass herbicide if applied to large plants.  Generally, flowering grasses are way too big to control with these herbicides.  The POST grass herbicides (Select, Fusilade, Poast) have a 40 day PHI.  Check out page 234 of the 2021 UGA Pest Control Handbook for more information about grass control in peanut:

4) 2,4-DB has a 60 day PHI so legally it can be applied up until ~80-90 DAP (for most peanut cultivars). There are at least 8 different formulations of 2,4-DB out there and these labels can vary slightly.  Late applications of 2,4-DB can be tank-mixed with most fungicides.  Don't expect any home-runs here since 2,4-DB is not very effective on most weeds that are growing above the peanut canopy (except common cocklebur).  

5) Since field corn harvest is rapidly approaching, I have gotten a few questions about the pre-harvest control of annual morningglories.  My usual recommendation is to apply a combination of Roundup + Aim within 3 days of harvest.  This treatment will not miraculously remove the running morningglory plants, but it will desiccate them enough to facilitate harvesting (i.e. makes the vines more brittle and less likely to wrap).  See below for more specifics (from 2021 UGA Pest Control Handbook, page 73).

Tank-Mixing Cobra or Ultra Blazer with Cadre in Peanuts (Prostko)

Over the last few days, I have had a few questions about tank-mixing Cobra or Ultra Blazer with Cadre + Dual Magnum + 2,4-DB.  Most are concerned about potential crop injury but this tank-mix has not been overly caustic in my research (Figures 1 and 2).  But, keep in mind that crop injury with tank-mixes can vary greatly depending upon many factors including time of application, GPA, air temperature, leaf wetness, and humidity.  Thus, I can provide no guarantees when 4-6 products are dumped in 1 spray tank.  

Peanut growers who suspect (or are not sure) that they have ALS-resistant Palmer amaranth and/or other weeds that Cadre is less effective on (i.e. tropic croton) would greatly benefit from this tank-mix.  In this scenario, Dual Magnum could be replaced by Outlook, Warrant, or Zidua (grower preference not mine).  Also, I would probably avoid Anthem Flex in this particular situation because of the Aim (carfentrazone) in the Anthem Flex.  When using Warrant or Zidua, a NIS should be included (0.25% v/v or 1 qt/100 gals).

Figure 1.  Cadre + Dual Magnum + 2,4-DB + Cobra.

Figure 2.  Cadre + Dual Magnum + 2,4-DB + Ultra Blazer.

Weed Control Update - June 16, 2021

Just a few things I thought you might be interested in seeing from my research plots over the last few days (a la Dr. Bob K., the E-Mail King of Georgia): 

1) The most effective weed control program (in any crop) happens by starting clean, using a strong residual program that gets activated by rainfall/moisture, and making timely POST applications.

2) Lots of folks interested in using Anthem Flex (pyroxasulfone + carfentrazone) on their peanut crop.  Anthem Flex is a very good herbicide but it will cause more peanut injury than the other WSSA Group 15's. Growers need not forget the other WSSA Group 15's that work equally as well in the UGA recommended peanut weed control programs including Dual Magnum (s-metolachlor), Outlook (dimethenamid-P), Warrant (acetochlor), and Zidua (pyroxasulfone). 

3) Preliminary herbicide/fungicide/peanut response tank-mix research with Provysol looks promising.  I have observed similar results positive results with Cobra and Ultra Blazer.

4) Check out this soybean injury from 2,4-DB (2 oz/A) applied in combo with Reflex (24 oz/A) + Classic (0.5 oz/A).  The use of 2 oz/A of 2,4-DB in just about every POST herbicide application in soybean was very common in the late 1980's/early 1990's before all of the technology explosions.  Looks worse than I remember.  Good weed control though!

Irrigating Peanut Fields Treated with Valor (Flumioxazin) During a Hot/Dry Period (Prostko)

The weather forecast for Tifton and many other areas of south Georgia over the next 10 days is not great (> 85 F and < 35% chance of rain).  Consequently, growers are wondering if it is a good or bad idea to irrigate cracking peanuts that received a PRE application of Valor.  Growers are very conscious of the fact that the potential for Valor injury significantly increases with moisture especially around the time of peanut emergence.  

I am of the opinion (based upon 20+ years of research/field experience with Valor) that if a grower needs to irrigate a Valor treated peanut field in order to get a good stand, he/she should do so.  What is worse?  A crappy peanut stand or Valor injury?  The impacts from a poor stand are more detrimental than Valor injury.  Production/history/research over the last 20 years has confirmed this.  Also, an irrigation event of 0.3"-0.5" over several hours is not the same as a 2" rain in 20 minutes!

I recently completed a 3 year study where the main goal was to try and injure the peanut crop by subjecting the field to as much irrigation/rainfall as possible,  In these studies, the peanuts received anywhere from 7.8 to 11.2 inches of rainfall/irrigation in the first 30 days after planting (Table 1).  Yes, the peanuts did suffer from Valor injury (as expected) but they recovered without yield loss even at a 2X rate (Table 2). UGA does not recommend the use of 6 oz/A of Valor (also not labeled) but this high rate was used to demonstrate peanut tolerance and simulate worse case scenarios.

I have addressed the Valor/peanut injury issue in numerous other blogs so check those out for more information/injury pictures/etc. (May 20, 2014; May 4 and 27, 2017; May 6, 2019; May 21, 2020).

Table 1. Rainfall/irrigation data (in) for first 30 days after planting for Valor/Dual Magnum high moisture peanut tests in Georgia (2017-2019).

Time (DAPa)	2017			2018			2019
	Rain	Irrigation	Total	Rain	Irrigation	Total	Rain	Irrigation	Total
0-7	0.5	3.7	4.2	0.0	5.3	5.3	0.2	3.0	3.2
8-14	0.4	0.0	0.4	1.1	0.0	1.1	1.2	2.3	3.5
15-21	1.2	0.5	1.7	1.5	0.0	1.5	0.6	0.5	1.1
22-30	0.5	1.0	1.5	3.3	0.0	3.3	0.0	0.5	0.5
Total	2.6	5.2	7.8	5.9	5.3	11.2	2.0	6.3	8.3

^aDAP = days after planting.

Table 2. The influence of Valor on peanut injury, J-rooting, and yield under high moisture conditions in Georgia (2017-2019)^a.

Valor Rate	Peanut  Injury (%)		Peanut J-Rooting	Yield
oz/A	10 DATb	50 DAT	%c	lbs/A
0	14 cd	8 b	46 a	5842 a
3	31 b	9 b	48 a	5870 a
6	51 a	16 a	50 a	5823 a

^aAveraged over three years (2017, 2018, and 2019) and four Dual Magnum rates (0, 16, 21, and 42 oz/A).

^bDAT = days after treatment.

^cData collected 21 days after planting.

^dMeans in the same column with the same letter are not significantly different according to Tukey-Kramer method (P<0.10).

 

Heat or Herbicides? (Culpepper)

Next week is shaping up to be a challenging week for cotton planting, similar to late May of 2019. Remember that soil temperatures greatly influence cotton emergence, Figure 1 includes a graph from a USDA manuscript sharing the relationship of lateral cotton root development as influenced by soil temperature (McMichael and Burke, Environmental and Experimental Botany, Vol 34, I added the F temperatures to their graph). Take special note the highest soil temperature that they studied was 104 F; next week we could easily exceed 115 F if predicted air temperature and lack of cloud predictions are accurate. Back in 2019, most blamed herbicides for the lack in cotton stand when in fact most issues were a result of high soil temperatures. Thus, Figure 1 also shares different levels of visual symptoms of cotton damage from hot soils (pictures from no-herbicide control plots). Any factor cooling soils may have a positive influence. For example, one of Dr. Camp Hand's graduate projects conducted during late May of 2019 noted 35% better stands with a rye cover crop compared to tilled systems; although stand was reduced in both systems. 

Herbicides and Dusting in Cotton Can Be a Mighty Challenge! (Culpepper)

The most effective approach to minimize cotton injury from preemergence (PRE) herbicides is to place the cotton seed in moist soil where it can imbibe (absorb) clean water free of herbicides (Figure 1). Next, we need our cotton roots to “out run” the herbicide as the herbicide is moving down into the soil with rainfall or irrigation. When placing cotton seed in dry soil and then applying a PRE herbicide, it is likely impossible for water to get to the seed without being contaminated with the herbicide causing much greater potential for injury.

Thus, dusting cotton in and applying PRE herbicides is far from ideal in regards to avoiding cotton injury. The next thought from every grower, is to hold off on the herbicides until the cotton emerges. This thought is extremely dangerous when considering the monumental challenges our family farms face with herbicide resistance in Palmer amaranth. However, it may be the only option in some environments. If one does follow the path of not using PRE herbicides and planting cotton into dry soils, there are several key points to consider.

First, there needs to be no weeds emerged (especially Palmer) when the cotton seed is placed in dry soil. If there is, get the backhoe out to dig the Palmer up later in the year. In theory, if the field is weed-free when dusting cotton in the soil then no additional weeds should emerge until it rains.

Second, the first postemergence herbicide application should occur as soon as the cotton is fully emerged; the treatment must kill emerged weeds and must include residual herbicides. The level of selection pressure placed on the postemergence herbicide in this situation is very high and not sustainable over time.

Third, a second postemergence herbicide application should be made 12 to 15 days later and again include a residual product, this timing assumes you were timely with the first postemergence application. If you were not timely, the interval needs to be tightened down following label recommendations.

And finally, the value of a layby application in fields without a PRE increases astronomically in regards to herbicide sustainability. Although it is very time consuming, it is still better than hand-pulling pigweed!

Why Does UGA Only Recommend Dual Magnum in Cantaloupe and Watermelon Row Middles? (Culpepper)

Agents, many of you have asked “What will happen to my melons if Dual Magnum is applied broadcast prior to transplanting or broadcast overtop after transplanting”?  Figures 1 and 2 will help you understand why we need to avoid these application methods and focus on using Dual Magnum only in our row middles!

Mixing Order of Pesticides is Important (Prostko)

This is a friendly reminder to all young and old extension agents that the tank-mixing order/sequence of pesticides is very important.  I discussed this topic in a previous UGA Weed Science Blog (Tank-Mixing - April 4, 2018) so check that one out so I do not have to reinvent the wheel.   

Got a call from a industry tech rep today about some mixing problems with Roundup PowerMax3 and Zidua SC.  You can see in the slide below that when the Roundup was put in the plastic bottle first followed by the Zidua, that some problems (i.e. the formation of precipitates that could gum up a sprayer) occurred immediately but did not do so when the Zidua was mixed in the bottle first.  This simple demonstration was conducted using 1500 mls of water (0.396 gallons) so just imagine the potential mess in an 800 gallon sprayer.  This problem could have been easily avoided by reading page 13 of the Zidua SC label (https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/ZiduaR_SC1t_herbicide_Label.pdf).

Strongarm Carryover from Peanuts to Field Corn (Prostko)

The 2021 field corn production season has not been great.  Cold, cloudy, wet weather has many farmers scratching their heads about the way some of their fields look.  There are many possible causes of these problems (i.e. fertility, disease, insects, nematodes, weather, herbicide carryover, etc.).  My colleagues and I have tried to address these issues as needed.  With that in mind, I would like to give you my thoughts on the potential for Strongarm (diclosulam), applied to peanuts in 2020, to have carried over to field corn in 2021.

1) In general, I am of the opinion that the potential for herbicide carryover (assuming 1X rates were applied) for many herbicides in Georgia is low.  Why?  We have warm temperatures, lighter/low OM soils, abundant rainfall, and soils that never freeze (maybe in extreme North Georgia).  These are conditions that are very favorable for the microbial degradation of herbicides (the major breakdown method for most herbicides). 

2) The labeled rotation restriction for field corn following an application of Strongarm is 18 months.  Consequently, any grower/consultant/county agent who actually reads the label might automatically assume that this could be the cause of many field corn problems.  But, there is more to this story.

3) What does Strongarm injury to field corn look like?  See the pictures below.  These are from research trials that I conducted in 2013/2014 where I applied various rates of Strongarm to irrigated field corn immediately after planting (i.e. PRE). Remember that the labeled rate of Strongarm is 0.45 oz/A.  

4) The NOEL (no effect level) for Strongarm's influence on field corn yield (based upon 3 years of irrigated field trials in south Georgia) is 0.029 oz/A (1/16X rate).  

5) The greatest/longest reported half-life for Strongarm is 43 days (range of 13-43 days).  Thus, based upon our data, it would take 172 days or 5.7 months for the 0.45 oz/a rate to breakdown to this 0.029 oz/A rate. So, field corn planted after that time period would be unlikely to be affected by Strongarm carryover (in irrigated fields and normal weather patterns).

6) A few other random thoughts:

    a) Sweet corn is way more sensitive to Strongarm than field corn.

   b)  PRE applications of Strongarm would be more likely to carryover than POST applications (i.e. more herbicide reaches the soil).

   c) Much of the Strongarm used in Georgia peanuts is applied at reduced rates.  Many growers who use Strongarm PRE only apply 0.225 oz/A.  Many growers who apply Strongarm POST only use 0.30 oz/A.

    d) The potential for Strongarm carryover would be greater in dryland fields vs. irrigated fields.

7) I will never say never but it is my opinion that Strongarm applied at 0.45 oz/A or less to irrigated peanuts is unlikely to cause carryover problems in irrigated field corn planted more than 6 months (7+ months even safer) after application.  But, it is never a good idea to use Strongarm in dryland peanut fields that will be rotated to dryland field corn and never a good idea to use Strongarm in any peanut field (dryland/irrigated) rotated to sweet corn.

8) The label is the law so growers who choose to plant field corn earlier than 18 months after an application of Strongarm do so at their own risk.  It is not very likely that Corteva would ever change the current Strongarm field corn rotation restrictions based upon previous UGA test results. 

9) Soil/tissue tests for pH/fertility problems and a nematode test are always very helpful when diagnosing field problems since these types of problems can look very similar to herbicide injury. 

10) The refereed journal article for this research is as follows:  Prostko, E.P. and T.M. Webster.  2015.  Field corn response to diclosulam.  Crop, Forage, & Turfgrass Management 1:1-5.