Weed Science Information (Row Crops/Vegetables) for County Extension Agents
In a previous blog (March 9, 2022), I discussed the negative interaction that can occur when Counter (terbufos) or other OP insecticides are used in-furrow and followed by applications of certain herbicides in field corn. Here is the newest information about the use of Counter and herbicides in field corn from AMVAC® (click on pictures for better clarity).
Many growers are now in the process of spraying pre-plant burndown herbicides. Low temperatures over most of Georgia are expected to drop below 40 F over the next three days. These temperatures are not very favorable for optimum weed control with herbicides such as Roundup (glyphosate) or Gramoxone (paraquat). Thus, you might want to advise your growers to hold off for a few days until temperatures warm up again (above 40 F but I would prefer warmer). Here is some data to chew on:
1) From some older air temperature research (47 F, 56 F, 65 F, 75 F, and 87 F) conducted by my colleague at Michigan State University, Dr. Christy Sprague:
a) Air temperatures had very little effect on the control of common chickweed with Roundup. However, common chickweed control at lower temperatures was compromised with Gramoxone (only 70% control at 47 F).
b) Air temperature had a significant effect on the control of henbit with both Roundup and Gramoxone. When applied at 47 F, henbit control was < 30% with both herbicides.
2) From Harre et al. (2021) in Weed Technology 35:279-288:
a) Shoot biomass reduction of horseweed and purple deadnettle was 34% and 28% greater, respectively, when paraquat was applied at day/night temperatures of 81/61 F than when applied at 64/55 F.
I just received the news earlier today that Brake (fluridone) has received EPA approval for use in the 2023 peanut crop. After final label approval from the GA Dept. of Agriculture, it should be a done deal. I have been working with this herbicide for 10+ years and am very glad that peanut growers will have another tool in their toolbox. Here are a few questions/answers that you might find helpful when talking about Brake with your growers:
1) Who is the manufacturer of Brake herbicide?
Brake was developed by SePRO Ag (https://ag.sepro.com)
2) What is the active ingredient in Brake?
The active ingredient in Brake is fluridone. Fluridone is also sold in the aquatic weed control market under the trade name of Sonar. Fluridone was first registered for aquatic use in 1986.
3) What is the mode of action (MOA) of Brake?
Brake is a WSSA/HRAC Group 12 herbicide. Group 12 herbicides block carotenoid biosynthesis in susceptible plants by inhibiting the phytoene desaturase enzyme. This ultimately leads to the destruction of chlorophyll and membrane lipids. Brake has the same MOA as Solicam/Zorial (norflurazon) which has been labeled in peanut since 1993 but has not been used that much (at least in my 26 year peanut career).
4) How long has UGA been testing Brake for use in peanut?
Initial research on the use of fluridone in peanuts began in 2013.
5) What rate of Brake should be applied in peanut?
Brake 1.2LC can be applied preplant (14 days) or preemergence at 12 oz/A (0.113 lb ai/A) but no later than 36 hours after planting. We are collecting additional data with the goal of increasing this timeline after planting (but before cracking/emergence). Brake needs at least 0.5" of rainfall or irrigation to be properly activated. Peanut seed must be planted at least 1.5" deep.
6) Is Brake a stand alone product?
NO! Brake should always be applied in combination with a grass herbicide (i.e. Dual Magnum, Outlook, Prowl, Sonalan, or Warrant) and Strongarm (when rotations permit). It can also be tank-mixed with Valor.
Figure 1. Comparison of a Valor-based peanut weed control program and a Brake-based peanut weed control program, Ty Ty, GA (2022)
7) What peanut cultivars has Brake been tested on?
Brake has been tested on the following peanut cultivars in Georgia: GA-06G; GA-16HO; GA-18RU; GA-20VHO; GA-12Y; AUNPL-17; TifNV High O/L; and FloRun 331. In some tests, GA-16HO has exhibited more leaf injury (bleaching) but yields were not reduced. Injury from Brake is more likely to occur when excessive rates are used and when environmental conditions are unfavorable (i.e. cold and wet).
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| Figure 2. Brake (fluridone) injury on peanut. |
8) How much will Brake cost?
Estimated cost for 12 oz/A will be somewhere around $16.
9) What are the crop rotation restrictions for Brake?
Current crop rotation restrictions for Brake are as follows: cotton = 0 months; soybean = 2 months; wheat/barley/rye = 8 months (5 months if grown as cover and not harvested); corn/sorghum = 10 months; and tobacco/sunflower = 18 months.
10) Why would a grower consider using Brake in a peanut weed control program?
a) Brake adds an additional herbicide MOA to the peanut weed control toolbox which is extremely beneficial for resistance management.
b) Brake is very effective on Palmer amaranth.
11) A copy of the following Supplemental Label must be in the possession of the user at the time of application (after GA Dept. of AG approval):
As Dr. Culpepper and I have begun our annual winter weed tour around most of Georgia, one of the many things you will here us discuss is starting weed-free (clean) at planting using a combination of practices such as tillage, cover crops, and/or herbicides. The use of cover crops and tillage will vary by grower. There are risks/rewards to both of these practices.
The question you might often get asked by growers is "Why/how does tillage influence weed control?" The simple answer is that when soils are not disturbed with tillage every once in awhile, weed seeds accumulate at or near the soil surface. Generally, most annual weeds will readily germinate and emerge from the 0"-2" soil depth. When those seeds are buried deeper in the soil profile with inversion tillage (i.e. moldboard plow), it is more difficult for plants that develop from those seeds to emerge. Of course seed size matters and plants that have larger seeds have greater potential to emerge from deeper burial depths than plants with smaller seeds (more energy in bigger seeds). If you are interested in some data about the effects of weed seed burial depth on emergence, check out the following graphs. The general trend in these graphs is that more weed emergence occurs at shallow burial depths and less emergence occurs at greater burial depths (note that a couple of these graphs have burial depths in cm and remember that 2.5 cm = 1 inch).
A few things you might find interesting:
1) Here's why Valor (flumioxazin) ain't labeled for weed control in sunflowers!
2) Lots of questions lately about windmillgrass aka fingergrass (Chloris spp.). Could be an annual or perennial plant depending upon the species. Supposed to be very sensitive to Roundup (glyphosate), Poast (sethoxydim), Select (clethodim), and Assure II (quizalofop) when applied from seedling to tillering stage of growth but less sensitive to these herbicides when applied at heading [Hennigh et al. 2005. Weed Science 53(3):315-322].
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| Windmillgrass photo courtesy of H. McLean (Syngenta). |
Dr. Culpepper recently gave you his 2 cents worth about the control of goosegrass in the most recent UGA Cotton Newsletter - July 2022 (http://www.ugacotton.com/vault/file/July-2022-Cotton-Team-Newsletter.pdf). Thought I would add my 3 cents worth as well since my ears are also bleeding from all the phone calls.
1) The #1 enemies of POST herbicide applications are big weeds and dry weather. If POST graminicides (i.e. Select, Poast, Fusilade, or generics) are applied applied to large plants, they will not work. A flowering goosegrass plant is way too big!!!
2) Check out this greenhouse data from a few years ago. Keep in mind that herbicides are much more active in the greenhouse than in the field. The take home message here is that rate and timing are very important.
