Category Archives: Weed Science

2017 Using Pesticides Wisely Trainings

Cotton and soybean varieties with tolerance to auxin herbicides (2,4-D or dicamba) are being commercialized. Prior to making applications of dicamba to dicamba-tolerant cotton/soybean or 2,4-D to 2,4-D-tolerant cotton/soybeans in Georgia, growers will be required to attend the training “Using Pesticides Wisely”. The training will focus on helping applicators/growers make wise decisions when applying not only 2,4-D and dicamba but all pesticides. Growers are strongly encouraged to bring their applicators with them. Attendance is suggested for all on farm applicators to confirm that they have been provided the best management practices when applying all pesticides. 

Growers who attended 2015 or 2016 trainings, as long as they registered, are not required to attend the meeting again. However, they are welcome to attend as many times as they like. The trainings have resulted in 1499 Georgia growers completing the required training. A survey conducted of these trainings noted 99% of growers felt the training was worth their time and 98% of them believed the training would help them increase on-target pesticide applications. If you have questions concerning your registration, please contact your local county extension office.

For growers who have not previously attended this training, options for 2017 are provided below. Select a time/location and RSVP, at least 2 days in advance, to the specific location for attendance. The required trainings will cover a 2 to 2.5 hr time period and will provide pesticide re-certification credits.  Snacks and drinks will be provided (no meal).

2017-usingpestwisely

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Zest Approved For Use In Inzen Grain Sorghum

Zest™ 75WDG (nicosulfuron) has received Georgia approval for use on Inzen™ herbicide-tolerant grain sorghum varieties. Grain sorghum growers who use this technology will now be able to get better POST control of Texas panicum and other grasses. Nicosulfuron is the same active ingredient in Accent, which is registered for use on field corn.

A couple of reminders from UGA Extension Weed Scientist Dr. Eric Prostko:

1) Zest can only be used on Inzen herbicide-tolerant grain sorghum varieties. The use of Zest on conventional sorghum varieties will result in crop death! Inzen grain sorghum varieties are not GMO’s.

2) The current formulation of Zest is a WDG.  I have been testing a liquid formulation so rates would be different in any slides you have previously seen from me.

3) UGA has limited variety performance data (i.e. none).  As far as I know, the only company with Inzen varieties is Advanta/Alta (http://altaseeds.advantaus.com).  Pioneer will likely have some varieties in 2018 or 2019?  Thus, I would suggest Georgia sorghum growers proceed with caution until an adapted variety is identified.  I have not been overly impressed with the varieties that I have been testing up until now.

4) I would still recommend the use of Concep treated seed + a PRE application of Dual or Warrant in this system.  Atrazine should be tank-mixed with Zest to improve the control of broadleaf weeds.

5) A copy of the complete Zest label can be accessed from the following location:
http://www.cdms.net/ldat/ldDEH000.pdf

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Intermediate Paspalum

paspalumintermedium

Here is a grass that looks very similar to cogongrass but is not. We originally looked at this exact spot in 2012 and thought it was cogongrass. One of our cogongrass experts is Mr. Mark McClure with the Georgia Forestry Commission. He quickly knew this was not cogongrass since the midrib IS centered, and it is a bunch-type grass WITHOUT rhizomes to spread.

This is intermediate paspalum. My leaf picture is not focused, but the difference is where the midrib sets. This perennial, bunch-type grass is now moving from the planted pines across the road and causing problems for our county road maintenance. In forestry situations, the only hope is to use a 4% glyphosate, and possibly mow before seeds head. Once nighttime temperatures drop to the mid-40s, not much herbicide is translocated within the plant. We can spot spray through the growing season, and also through fall is better.

Intermediate paspalum

Intermediate paspalum – centered midrib

Off-center midrib

Cogongrass – off-center midrib

 

Intermediate paspalum - seedhead

Intermediate paspalum – seedhead

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Cotton Defoliation

cottondefoliated

We have defoliated some cotton in the county already. UGA Extension Cotton Agronomist Dr. Jared Whitaker discussed some points on defoliation at our field day a few weeks ago. Here is a summary of what we need to think about as we start defoliating.

Timing

Cotton defoliation is a sensitive process. For a successful harvest, defoliation must be carefully timed and carried out. Poor defoliation can lower fiber quality, while defoliating too early lowers yield and micronaire. Late defoliation increases the likelihood of boll rot and lint damage or loss due to weathering.

Late defoliating also increases the possibility that defoliant activity will be inhibited by lower temperatures.

Three ways to determine crop maturity and defoliation timing:

  1. 60 to 75% open bolls (only 60 for uniform crop)
  2. Sharp Knife – cotton strings when boll is cut – Seed are fully developed (brown coat & cotyledons)
  3. NACB – 4 or less (around 3 days per node)

There is often a relationship between percent open bolls in the canopy and the number of nodes between the uppermost first position cracked boll and uppermost first position harvestable boll (NACB).

Water Volume

Most harvest aid materials do not translocate or move very far within the plant. Therefore, application coverage is important. To ensure adequate foliar coverage use the proper spray pressure, ground speed and nozzle size in order to apply the desired spray volume in accordance of label instructions.

WATER VOLUME CAN SIGNIFICANTLY IMPACT OVERALL PERFORMANCE, THE MORE WATER THE BETTER (SHOOT FOR 15 GPA).  The wind damage from tropical system last week may make defoliation with ground sprayers a challenge for area cotton growers.

Rainfall occurring after applications can affect defoliant activity. Be sure to consider weather forecasts when making applications and pay attention to rain-free periods of particular products.

Thidiazuron is of particular concern, since it requires a 24 hour rain-free period.  Below is a chart of rainfast periods of cotton defoliants.

rainfast of cotton defoliatants

Three way mixtures:

Below is a chart to help with defoliation rates for the “Three Way” program:

uga3-way-rates

Additional Weed Control

If weeds are present at harvest, some defoliants have herbicidal activity on plants. The table below is from the UGA Pest Management Handbook as a guide to weed control.

harvestaidweedmanagement-cotton

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Morningglory Identification

I posted this last year from UGA Weed Scientist Dr. Erick Prostko. There are many species of morninglory weeds to learn in the field. We have to make sure we have proper ID for control.

Why is this important? Not all morningglories are controlled equally by certain herbicides. Here are a few examples:

  • Gramoxone (paraquat) is generally good on most morningglory species but not smallflower. 
  • Basagran (bentazon) is generally not effective on most morningglory species but will control smallflower.
  • Staple (pyrithiobac) is generally considered to be an excellent morningglory herbicide but not on tall.
  • 2,4-DB is less effective on pitted morninglory than other species.
  • Aim (carfentrazone) is considered a good morningglory herbicide but not on smallflower.

Here are some photos of morninglory UGA Extension Weed Scientist Dr. Eric Prostko shared from LSU and Virginia Tech.

Cypressvine-MG Tall-MG Red-MG SmallFlower-MG PurpleMoonflower-MG Pitted-MG Palmleaf-MG Ivyleaf-MG Entireleaf-MG

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Weed Control Following Forage Establishment

PastureSprig (6)

We have been looking at recently sprigged pastures this past month to determine weed control needs. We can use Diuron immediately after sprigging, but for most everything else, the pasture needs to be established. So, when is it established?

Sprigging Bermuda

There are a few ways to look at this. One way to look at it is, if you can pull on the plant and it snaps off – rather than pulling up roots and all – then it is “established.” There are other definitions of establishment based on runner length. Many of our herbicide labels answer this question. The label may say it is considered established when runners reach 8 – 10 inches. Sometimes labels describe establishment with days after sprigging and say, “use only on bermudagrass established for 60 days.”

The pasture pictured above has 8-10 inch runners in 40% of the pasture and the rest was 3 – 4 inch runners. In terms of safest postemergent application, UGA Extension Weed Scientist Dr. Patrick McCullough says, the 2,4-D and Weedmaster products will be the safest to use on immature bermudagrass during establishment. However, we are too risky to apply these products now, so mowing will be our only option here until we can buy some time on establishment.

PastureSprig (5)

Seeding Bahia

Here is some TifQuik Bahia that was drilled in mid April. It’s only at 3/10 of an inch of rain since then, but coming up good. We have a more variety of weeds here, and automatically lose any option with mesulfuron since it’s Bahia. Some seedlings are still emerging, but most of it is 3 -4 inches. The rule of thumb here is when grass is 8 – 10 inches tall, it is considered established and safer to apply herbicides. In this situation, we would mow throughout the growing season, then come in the fall with a phenoxy herbicide to start control.

TifQuikBahia 010 TifQuikBahia 012

 

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Peanut Herbicide Tips

We’ve been talking more about peanut weed control this week with different field situations. One especially on making our own Storm out of Ultra Blazer & Basagran. UGA Extension Weed Scientist Dr. Eric Prostko answers this and more with an update on peanut herbicide tips:

  1. Can we mix orthene with our cracking treatments? Generally, there should be no major problems mixing Orthene (acephate) with paraquat cracking treatments (Peanut Science 2014 41:58-64).
  2. What rates of Basagran + Ultra Blazer are used to make Storm? UPI is in a sold out position for Storm 4SL herbicide. However, Storm is in UPI’s production schedule for next year. No worries though since growers can make their own Storm if need be. 1.5 pt/A of Storm would be equivalent to 1 pt/A of Ultra Blazer 2SL + 1 pt/A of Basagran 4SL. FYI, when making your own Storm cocktail for mixing with paraquat, I prefer 1 pt/A of Ultra Blazer + 0.5 pt/A of Basagran. 0.5 pt/A of Basagran still helps “safen” the peanuts but this new ratio will be slightly more active on the weeds.
  3. What issues will we see with Valor injury on peanuts? Guess what? When it rains on peanuts that were treated with Valor, especially at cracking, you get crop injury. It happens all the time, regardless if they were irrigated immediately after application or not. Unless something funky has happened (i.e. sprayer problems, excessive rates, misapplication, etc.), research results and on-farm experiences since 2001 would suggest that is very likely that the peanut plants will recover from Valor injury with no yield loss.

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Herbicide Considerations When Replanting Cotton

Here is some good information on replanting cotton and herbicides from Dooly County Ag Agent Ronnie Barentine I wanted to share from their Dooly County Extension blog:

Replant considerations where Warrant WAS used at planting:

If replanting cotton is necessary, one needs to consider the herbicides used in the original planting.  Cotton is tolerant to the herbicides we use pre-emerge in cotton, with the exception of Warrant and Warrant Extra. Over time the active ingredient (acetochlor) in Warrant is released from the capsules that make it safe at planting. Once released, it can be very injurious to cotton.

Based upon research by Dr. Stanley Culpepper, use the following recommendations when replanting cotton on land that was treated with Warrant at planting:

  1. Cotton can be replanted 2 weeks after the original application if the land is strip tilled with ripper shank, before replanting. This will dilute the acetochlor.
  2. If no tillage is performed, wait 3 weeks before planting.

Replant considerations where Warrant was NOT used at planting:

Should replanting be necessary where soil-applied herbicides are used other than Warrant, it is best to run the planter back in the original drill without any soil preparation if soil conditions permit. If reworking the seedbed is necessary then the following procedures are suggested:

 Strip tillage: Rerun the strip till rig which should include ripper shanks followed by planting. After replanting, apply a PRE herbicide mixture that includes both a non-selective herbicide to control emerged weeds/cotton and a residual herbicide. The residual herbicide should be different chemistry than that used with the original planting. It is likely the residual herbicide used with replanting may offer limited residual Palmer control; thus, the first early POST application must be made quickly after replanting in a Roundup Ready system (likely 10 d or less).

Conventional Tillage: For growers who do not have strip tillage implements, use shallow tillage such as light disking. Do not re-bed without first disking. Re-bedding without disking can lead to severe injury. The amount of time that has passed and the amount of rainfall that has occurred between herbicide applications and replanting will determine the need for additional herbicides.In general, additional herbicides will be needed when replanting but one should switch residual herbicide chemistry from that used during the first planting.

Glyphosate, paraquat, or Liberty must be included to control emerged weeds and cotton when replanting. Paraquat (Gramoxone, others) or Aim will control small emerged cotton. Liberty is also effective controlling cotton as long as it is not a cotton cultivar tolerant to Liberty.

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Spiderwort In Pastures & Hay Fields

Spiderwort (3)

We are seeing spiderwort in pastures now. I was asked if I knew what this weed was last week. It was actually growing along the roadside where we first looked. It is in both pastures and hay fields. Spiderwort emerges in early spring, flowers in March-April, and then produces seed through mid-summer. It is an issue in grazing forage because cows avoid it. In the situations we looked at, the large, fleshy stem makes spiderwort an issue in hay production. When cut with a grass forage, spiderwort does not dry at the same rate as the grass and can cause spoilage when the hay is baled.

Spiderwort

Spiderwort

Control

Here are some control options from Dr. Jay Ferrell, University of Florida Weed Scientist found in their blog post: Spiderwort: A Troublesome Weed Invading North Florida Hays & Pasture Fields.

Experiments were conducted in High Springs, Florida to compare the activity of commonly used pasture herbicides on fully emerged and flowering spiderwort.  All herbicides were applied with crop oil concentrate (COC) at 1% v/v.

Spiderwort response to all herbicides was similar at 1 week after treatment (WAT) and control was less than 50% (Table 1). Triclopyr resulted in 86% control while very little change was noted from all other herbicides at 4 WAT.  Triclopyr exhibited excellent control (95%) at 8 WAT, while the other treatments remained at 50% or less.  Control of spiderwort by triclopyr began to decline shortly after 8 WAT (data not shown), and spiderwort re-established in all plots.

SpiderwortControl-UF

Conclusion

No single herbicide application was found to fully control spiderwort.  The greatest control was found when triclopyr was applied at 32 fl oz/acre. Canopy growth did not recommence in the triclopyr plots for another 4 to 6 weeks after the initial burn-down.  However, the majority of the spiderwort plants did eventually regrow in the triclopyr plots. Therefore, it is important to keep in mind that the results from triclopyr may be temporary. With this timeline in mind, producers should treat infested fields at least a month prior to cutting hay.  Fortunately, producers should have at least a month after burn-down to cut and bale their hay without experiencing any issues associated with spiderwort. It will take multiple cycles of regrowth and burn down to reduce the population in a field.  When feasible, hand removal is still the most effective control method.

 

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Prowl vs. Sonalan In Peanuts

Here is an update from UGA Extension Peanut Weed Scientist Dr. Eric Prostko on Prowl and Sonalan.

Recent price increases in Sonalan 3EC (ethalfluralin) have many growers taking a closer look at the cheaper priced pendimethalin formulations (Generic Prowl 3.3EC and Prowl H2O 3.8ASC) for use in peanuts.  With the exception of use in reduced tillage systems (i.e. Prowl is preferred there), there have been no consistent differences in peanut tolerance and weed efficacy between Sonalan and Prowl in peanut (Table 1). It has always been my position that I have no preference between these two herbicides and that every peanut acre in Georgia should be treated with one of them.  If a grower is trying to save a few bucks on input costs, there is no reason not to use a cheaper formulation.

Prowlvs.Sonalan

A couple of other comments about this issue:

1) The Weed Science Group at UGA has not been able to detect any major differences in the performance between Prowl 3.3EC and Prowl H20 3.8ASC.
2) 2016 estimated costs for 1 qt/A are as follows:  Sonalan 3EC = $10.50; Generic Prowl 3.3EC = $6.75; and Prowl H2O 3.8ASC = $8.75.
3) The lb ai/A for each formulation are slightly different at the 1 qt/A typical use rate as follows:  Sonalan 3EC = 0.75 lb ai/A; Generic Prowl 3.3EC = 0.83 lb ai/A; and Prowl H2O 3.8ASC = 0.95 lb ai/A.  This might need to be considered when figuring the true cost differences per acre.  

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