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.   

Glyphosate Residual Activity Impacts Vegetable Transplants (Culpepper)

Over the past several years, we have been discussing how glyphosate applied pre-transplant to vegetables can be problematic depending on rate applied, time interval between application and transplanting, and rainfall amount between application and transplanting. A current graduate student's project further stresses the importance of understanding this challenge (photos below) and the importance of following our new label (below) when transplanting into bare-ground or mulch production systems.  

For a better copy of this new label:

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Roundup_PowerMAX_II2t_Herbicide_2EE.pdf