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Questions of the Week… April 23, 2021

Topics this week includes infurrow treatments for cotton and peanut. Nitrogen applications and weed control in corn.

Thoughts on cotton weed control…

BURNDOWN: Palmer amaranth must not be emerged when planting, regardless of cotton cultivar planted.   

Standard programs using Valor (before Palmer emergence), Direx, and Gramoxone + Direx are advised. Dicamba or 2,4-D would be beneficial for primrose, horseweed, and radish (2,4-D is much more effective on radish). All weeds and cover crops with the exception of cereal grains should be killed at least 14 days before planting.  No plant back interval exists for XtendiMax or Engenia in XtendFlex cotton; other cultivars may be planted 30 d after 1” of rainfall. No plant back interval exists for Enlist Duo or Enlist One in Enlist cotton; other cultivars may be planted 30 d after application.   

Preemergence (PRE) applications: Include 2 active ingredients for better control, less crop injury, and less herbicide resistance development.  Below are some choices of preemergence treatments. 

1) Brake + Reflex   2) Brake + Warrant   3) Direx + Warrant   4) Reflex + Direx    5) Reflex + Warrant

HERBICIDE RATES ASSUME TIMELY SEQUENTIAL POST APPLICATIONS AND DIRECTED LAYBY

 1) Brake contains fluridone; 1 pt/A is an effective rate in mix with other herbicides. Fluridone requires significant rain/irrigation to become fully active.

2) Warrant:  For most soils, 32-40 oz/A is in order. Effective on most grasses, pigweeds and is essential for spiderwort.

3)  Direx:  For most soils the ideal rate is 10-16 oz/A; lower rates on sands or under intense irrigation. Avoid diuron PRE if it was applied within 14 d of planting as a burndown. 

4) Reflex: For most soils, ideal rate is 10-12 oz/A when in these tank mixtures. Reflex mixtures are the most effective option for Palmer.  

 NOTE:  Add paraquat if pigweed is emerged; a jar test is strongly advised if mixing with Brake.

More comments from Bob on the topic of seedling diseases in cotton

SEEDLING DISEASES IN COTTON are typically more severe during cooler and wetter weather, Why?  Primarily the cool, wet soils slow germination and slow growth and development of the seed and seedling.  Slow germination and emergence coupled with low vigor early on gives our most important seedling disease pathogen of cotton, fungus Rhizoctonia solani, the chance to attack and cause significant stand loss.  Rhizoctonia can (and does) certainly cause losses even in warmer soils, but the impact is greatest in cooler and wetter soils.

NOTE:  the key here about increasing risk to seedling diseases is less about “cooler and wetter” and more about ANYTHING that slows germination and development.  Other factors include 1) poor seed quality, and 2) some considerations with herbicides and possibly other things put directly in the furrow.

NOTE 2:  Rhizoctonia almost always causes post-emergent damping-off seedling disease.  Plants come up, kind look ok, and then buckle at the knees and die, or they just stay small and fail to thrive.  Dig the plants up and you should see a beautifully diagnostic lesion just below the soil line.  If the plants NEVER come up, you may have Pythium (possibly especially in cooler soils) or other seed-rot issues.

SO, what to do?  To minimize risk to seedling diseases, 1) make sure soil temps at 4 in. are AT LEAST 65F, 2)avoid planting in cooler and wetter conditions are imminent, 3) make sure you have the best quality seed (ask conditions); smaller seed is sometimes prone to greater stand problems than is larger seed, 4) insure a good fungicide seed treatment package (most commercial seed is already treated with a combination of excellent fungicides, and 5) if you are worried about higher risk to seedling diseases, consider additional treatments.

Additional treatments for cotton include 1) additional, higher-end seed treatments, and 2) liquid in-furrow fungicide.  Neither additional treatment is a “general recommendation” for me as our standard cotton seed treatments are adequate to protect stand much of the time.  However, when in doubt, additional treatments are good “insurance” against seedling disease, especially use of azoxystrobin (6 fl oz/A) in-furrow against Rhizoctonia.

Bob Kemerait answers a few questions about PEANUT Early-Season Treatments

Question 1:  “Bob, do I have to use a fungicide seed treatment on my peanut seed?”

Answer 1:  “Only if you want to pick peanuts at the end of the season.”

Question 2:  “Bob, which peanut fungicide seed treatment should I use?”

Answer 2:  “Most peanut seed will be treated with Rancona this year because it was more effective in 2020 against pathogens such as Aspergillus flavus and Aspergillus niger than was Dynasty PD.  If, for some reason, your seed is treated with Dynasty PD in 2021, this does not mean you will have a stand problem, it is still a good treatment, but there will be higher risk to stand issues.”

Question 3:  “Bob, does every peanut farmer in Georgia need to use an in-furrow fungicide to compliment the fungicide seed-treatment?”

Answer 3:  “Great question, and the answer is “NO”.  Many growers, especially those with high-quality seed, good rotation, careful planting dates and conditions, do NOT need an in-furrow fungicide.  In-furrow fungicides provide additional stand insurance, that may or may not be needed.  Growers MOST likely to consider use of an in-furrow fungicide product at planting are those who 1) have questions on quality of their seed, 2) are planting saved seed (but not always), 3) growers planting into cool and wet or hot and dry soils, 4) growers who are planting in a field where getting a good stand has been a historical problem, and 5) growers who will just sleep better at night knowing they put one out.

Question 4:  “Bob, what about putting Azoxystrobin out in-furrow?”

Answer 4:  “Azoxystrobin is inexpensive and effective against some important fungal pathogens, especially Rhizoctonia.  It is less effective against Aspergillus crown rot.  As an inexpensive “good but not great” fungicide, I like it.  But, it may not be needed and it does have limitations.”

Question 5, “Bob, in addition to azoxystrobin, what else is there and when would we use them in-furrow?”

Answer 5:  “Glad you asked, see below.”

Peanut nematodes (single row, in-furrow only) Velum 6.5-6.9 fl oz/A  (Remember “VELUM” is NOT “VELUM TOTAL” and does not include a thrips material.  To control thrips would require coupling Velum with Thimet or imidicloprid, etc.  Also provides additional control of Aspergillus crown rot and some early-season control of leaf spot.

Peanut nematodes (single row, in-furrow only):  AgLogic, 7 lb/A also controls thrips

Peanut nematodes (single row, in-furrow only) Propulse 13.6 fl oz/A + Velum 1.5 fl oz/A.  Note, this option also covers Aspergillus crown rot, CBR, early season leaf spot and some suppression of early -season white mold.  MUST ADD something for thrips control

CBR and other diseases but not nematodes (single row, in-furrow only) Proline, 5.7 fl oz/A OR Propulse 13.6 fl oz/A.  Propulse is also good on Aspergillus crown rot.

Note:  If you are using Velum or Propulse, there is no need to also include Azoxystrobin, unless there is some reason to be concerned about Rhizoctonia seedling blight.

FOR TWIN ROW Peanuts:  All above rates are cut in half for EACH twin row.  Yes, if effects efficacy, but that is the way it is.

Nitrogen Management in Corn…  To increase the efficiency of nitrogen recovery during the season, split applications of nitrogen are recommended. Apply 25 to 30 percent of the projected nitrogen needs before or at planting. The remaining nitrogen can be applied sidedress and/or injected through the center pivot systems (fertigation). If all the nitrogen is applied with ground equipment, apply 50 to 75 pounds per acre at or before planting under irrigated conditions and 20 to 50 pounds per acre in dryland environments and the rest when the corn is 12 to 16 inches tall. If nitrogen is to be injected through the irrigation system, apply 40 to 60 pounds at or before planting and begin ground or injected applications of 30 to 60 pounds of nitrogen per acre when the corn is 8 to 12 inches tall. Continue on a bi-weekly basis until the total required nitrogen is applied. Three to five applications of nitrogen will be needed during the growing season. Nitrogen applications after pollination are NOT recommended unless a severe nitrogen deficiency is detected. 

Can I Use Prowl Postemerge on Corn? I had a couple of questions about using Prowl POST on corn… Below are a few words from Dr. Eric Prostko, UGA Weed Scientist, on this subject. 

I have heard that a few field corn growers have been reluctant to apply Prowl POST in field corn due to potential injury concerns, especially root pruning.  POST applications of Prowl can cause root injury but this usually only occurs when the corn seed has been planted < 1.5″ deep and seed-furrow closure is not adequate.  With 21 years of data under my belt in Georgia, I am not overly worried about POST applications of Prowl causing unacceptable field corn injury (assuming correct application rate, timing, seed depth, etc.).  Figure 1 presents some recent research data from UGA which indicated that the addition of Prowl to Roundup + Atrazine did not reduce corn yields (note the very high yields).  In fact, the combination of Roundup + Atrazine + Prowl has been the standard POST program that I have compared all other newer herbicide programs to for many years (Figure 2).   

If you have questions please contact the Colquitt County Extension office. UGA Cooperative Extension does not endorse any products mentioned in this post.

Jeremy M. Kichler

Colquitt County Extension Coordinator

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