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Please read below for the April row crop disease updates from Dr. Glen Harris and Dr. Bob Kemerait:

Per Dr. Glen Harris, UGA Extension Agronomist for Soils and Fertilizer:

Glen Harris here with some requested comments on how getting a “pile” of rain can affect fertilizer plans for 2021 Georgia cotton…

The good news… I don’t think there is reason to panic…for a number of reasons:

  1. Even if you already put out your preplant N-P-K (which is probably most growers)…phosphorous is basically immobile and even though K is mobile it is not as mobile as N.
  2. We have time to correct this issue without suffering significant yield reductions.
  3. So the concern is nitrogen…but not all of the N was in the leachable “nitrate form”…(ammonium and urea N is not susceptible to leaching)
  4. And what we got was not what I would call a “leaching rain” i.e.  lots of rain over a long period with a chance to soak in and move down through the soil profile .  We got what one of my old colleagues would call a “frog strangler” or what I call a “runoff” rain, i.e. where a lot left the field going sideways instead of down.
  5. And the official recommendation is to only put out ¼ to 1/3 of your total N at planting – this is designed to get you to side dressing time and one of the reasons we don’t like to put a larger portion of N out at planting (too much vegetative growth early is another). I already got a call where a grower already put out 2/3 of his total N. News flash – some of that will need to be replaced at some point.
  6. But what about potassium? Like I said, it’s not as mobile as N and may have gotten pushed down into the soil profile. But once the cotton tap root gets down deeper (and that probably happens a lot faster than you think) it should still be there. So…what should you do?

Let’s agree we can take phosphorous off the table and potassium to some extent. I am actually more worried that the “packing rain” we got this weekend will do more to compact soil and limit root growth — and therefore potassium uptake –than I am worried about what K we lost.  I wouldn’t look to replace potassium now, but if you already planned to put some more K out I would do it no later than sidedress time (first square to first bloom). Don’t forget we can also foliar feed K once we start blooming if need be.

I also would not be in a huge hurry to replace any nitrogen you think you may have lost,  but would simply evaluate what the cotton looks like at first square and be prepared to go with an early N sidedress. Tissue sampling would be amazingly helpful in this regard also. Take a tissue sample sometime right before squaring or at squaring (should be around 35-45 days after planting) to check on N levels. The beauty of this is that we can also check on P and K and everything else – including sulfur !

Sulfur is also highly mobile in soil, like N. so I would recommend including sulfur with your N sidedress. This is pretty easy to do with liquids (like 28-0-0-5(S) and 18-0-0-3(S) and by adding to ammonium sulfate to urea or ammonium sulfate solids. There is also Amidas, urea and ammonium sulfate homogenized into a 40-0-0-5.5(S) granular.

Back to N, if you haven’t planted yet and have the capabilities of putting starter fertilizer in a “2 x 2” (2 inches to the side and 2 inches below the seed), you might consider putting 10 gallons of 10-34-0 in a 2 x 2. Or likely a more economical treatment would be 3-5 gallons of 28-0-0-5(S) in a 2 x 2.

Bottom line…it may not be economical to replace 30 lb N/a right now, especially on large acreage, so be prepared to sidedress N at on the early side of the window (first square rather than first bloom) and maybe bump up the rate 10-25 % then.

Lastly, take a tissue sample right before side dressing if possible.

Per Dr. Bob Kemerait, UGA Extension Plant Pathologist :

There are spots, and then there are spots on corn.  It is getting to be time to prepare your growers for the spots they will find and what they need to do about them.

Spot 1: Most, if not all, corn farmers in Georgia will at one time or another this season find circular bleached spots on their corn leaves.  Sometimes there will be more of the distinctive bleached circles, sometimes there will be fewer spots.  You will likely get call that go something like this.  “I got some spots in my corn.  You say that the best way to control disease is to catch it early.  I caught it early.  What do I do? It will most likely be herbicide drift. However, even if it is Holcus leaf spot, caused by a bacterial pathogen, there is nothing to spray and the disease is cosmetic and won’t hurt you at all.  But it is EXCELLENT that you are scouting your fields! 

Circular leaf spots on corn caused by herbicide drift

Spot 2Northern corn leaf SPOT (not blight… that is next).  This disease is caused by a fungus and is VERY common in the lower leaves of corn prior to tassel.  Northern corn leaf SPOT is characterized by small, orangish-brown elliptical lesions that almost always have semblance of concentric rings.  Norther corn leaf SPOT can look impressive early on, but it rarely progresses into the season and I have never recommended a fungicide spray to protect the crop from this disease.

Spot 3Northern corn leaf BLIGHT:  this disease is characterized by larger, more robust, elliptical lesions (usually tan or gray) about the size of a Swisher Sweet.  Beautiful lesions. Northern corn leaf BLIGHT is typically incidental, meaning only a few scattered plants in a field with very low severity.  A few scattered symptomatic plants is something to watch but not to pull the fungicide trigger over.  However, northern corn leaf BLIGHT can be a serious problem, especially when a susceptible variety is planted and/or when corn is planted on short rotation.  The fungal pathogen will survive in the old corn debris from previous season.  IF a grower finds this disease developing in their crop (again, often because of variety that is planted) a fungicide application is recommended. 

WHY MORE SPOTS MAYBE SOON?  All of that rain from this past weekend likely bounced spores from the debris in the soil up on to the your plants.  Look to see if beaucoup spots occur in about 7 -14 days. 

Lastly, Growers are likely asking now if it is ok to “dribble” liquid nematicides and fungicides in-furrow through and orifice, or if the liquids need to be sprayed into the furrow, as with a flat fan tip turned “cock-eyed” to 45 degrees?

My answer is that both dribbling the fungicides or nematicides through an orifice or spraying into the furrow can be effective.  Here are some points to consider.

  1.  Dribbling the product through an orifice directly onto the seed increases the amount of product that is DIRECTLY in contact with the seed.  Care should be taken to check the label and perhaps contact the chemical rep to make sure there is no increased risk to damaging the seed or young seedling with the product concentrated in such a way.  (Usually there is not a problem.)
  2. If the product is sprayed into the open furrow, there is better coverage of the seed AND the soil surrounding the seed which may lead to better protection of the germinating seed the young seedling.
  3. If growers are trying to apply both a liquid product (for example Velum) and a granular product (for example Thimet) at the same time, there can be problems if the liquid spray boogers up the granular product, possibly plugging the liquid and/or the flow of the granule.  Such rarely occurs when liquid product is dribbled through an orifice but can easily occur when sprayed.  Care should be taken to consider the position of the spray tip in relation to the granular application tube.

In short, applying products in-furrow to protect against diseases and nematodes is a critical strategy to protect yield.  Growers should always consult the product label and seek additional help if needed to determine what application strategy is best for them.

As always, if you have any questions, please give me a call at 478-472-7588, 478-957-6700 or contact your local County Agent.

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