Peanut Pegging and Pod Set Considerations From Jay Chapin

Here is another round of production tips from Clemson Peanut Specialist Jay Chapin.

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An application of Cobra + crop oil went out on killable pigweed and it didn’t even slow them down.  What went wrong?

The Cobra was applied late in the afternoon, almost at dusk.  Mike Marshall reminds us that the cell membrane disruptor herbicides like Cobra and Blazer need sunlight.  Photosynthesis forms oxygen which allows the production of the hydrogen peroxide that damages weed cell membranes.

I would have guessed that the herbicide would still be fairly effective the next morning, but not so in this case – one more reason to spray in the morning when weeds are more susceptible during dry weather.

Yellow Spots and Streaks

Other than temporary “Cadre flash”, yellow areas at this time of year are almost always either inoculation issues or Manganese deficiency.  It’s pretty easy to tell the difference.

Mn deficiency  has the characteristic green veins on the yellow leaflets (picture on pg. 74 of 2015 Guide).   Mn deficiency is most apparent where there was an old lime pile, in streaks where lime overlapped, or on clay knolls.  Apply 0.5 lb actual Mn twice with fungicides and avoid 2,4-DB tank mixes.

Manganese deficiency

Manganese deficiency

Inoculation problems usually occur in row patterns and the taproot lacks large (1/8”) nodules.  When a total inoculation failure is confirmed, an immediate application of at least 120 units of N is required (pg. 12-13 inoculation failure diagnosis and treatment).

Lack of Nodulation on Rotated Peanut Land

Once a field is successfully inoculated we usually have an effective “safety net” if the inoculant accidentally gets turned off the next time peanuts are planted 3 years later.  That is, our soils are generally inoculant friendly.

But not always; we do see cases of slow nodulation of rotated land where the inoculant got turned off.  This is more prevalent in reduced tillage systems.

Two weeks ago I saw an even more unusual case where the field had two previous peanut crops and had inoculant applied this year, but the crop still turned yellow with almost no nodules at 50 DAP.   It turns out that a “root enhancer” was tank mixed with the inoculant.  My advice is to never ever mix anything with an inoculant other than imidacloprid products (e.g. Admire Pro) needed for thrips control.

Dead Spots

As usual, the 45 – 60 day interval is when some badly stunted, or dead spots are often first noticed in peanut fields.  Nine times out of ten it is Zn toxicity which can easily be confirmed by the characteristic pattern of damage around old house spots, the split stems on some plants, and/or a soil test.

Usually Zn toxicity is localized and of minor economic consequence, but large areas can be affected when there is a history of manuring or an old peach / pecan orchard combined with low pH.  Liming is the answer to avoiding or greatly reducing future damage in these fields.   See pg. 17 of Production Guide for liming guidelines.

My fungicide was on for 1½ – 2 hrs before it rained what should I do?

Count your blessings if you included a soil disease product.  You get the full benefit of early season white mold prevention and a significant amount of leaf spot control.  In tests where we irrigated off leaf spot fungicides after 2 hrs we still got a good bit of leaf spot control even with a non-systemic like Bravo.  As a general guideline, if you get rained out of the field or the fungicide doesn’t have time to dry on the plant, come back with a full 1.5 pt rate of Bravo as soon as the weather clears.  If it dries on the plant but is on less than two hours, maybe shorten the interval to 10 days.  If it’s on over two hours, maintain the 14 – 15 day interval.

What is Equation fungicide?

Equation is generic Abound.  We are testing Equation for the first time this year.

If I use Fontelis, can I “skip a spray”?

You can do a lot of things and get away with it sometimes, depending on leaf spot pressure.  Any of our recommended dual purpose leaf spot and white mold applications can be used at longer spray internals than 14-15 days and provide acceptable leaf spot control – sometimes.  Fontelis is an excellent white mold material and a very good leaf spot fungicide, but based on our head-to-head efficacy comparisons against late leaf spot, I wouldn’t stretch it a day further than I would Abound, Provost, Priaxor, or tebuconazole + 1.5 pt Bravo under the same circumstances.

Our fungicide programs are designed to be conservative in having some margin of safety.  This is because we are making decisions in June and July for potential weather conditions in October.  Maintain spray intervals; don’t let late leaf spot get started.

Leaf spot spray intervals can be stretched during dry spells by keeping track of rain events (see alternative to calendar sprays, pg. 41 of Production Guide), but under S. C. conditions there are practical limitations because we need white control applied before it rains.  Pop-up showers are hard to predict.

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