Peanut Herbicide, Fungicide, and Nutrient Tips From Jay Chapin

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

The big picture right now of course is the extended high temperatures and lack of rain in many areas.  Peanuts are very resilient in yield potential, but fighting weeds on dryland runner varieties is more challenging and expensive.  The crop is very slow to close the row middle, so the weeds just keep coming.  That potentially causes repeated 2,4-DB and grass herbicide applications with our fungicides.

Drought stress and high temperatures also greatly increase the risk of lesser cornstalk borers and spider mites getting started.  A little timely rain or a pivot is the solution to all our major peanut insect threats.

Should I even be spending money spraying herbicides and fungicides in this weather?

It usually doesn’t work out to apply a pre-emergence residual herbicide like Dual with only a 10% five-day forecast, but we can’t just let pigweeds or high populations of sicklepod, morningglory, or grass take over the crop either.  We have to do the best we can with early morning post-emergence sprays and good coverage.

As mentioned in the previous bulletin, prolonged dry weather absolutely does slow down leaf spot.  So extending leaf spot spray intervals a few days is OK using the guidelines on page 41 of the 2015 production guide.

The big BUT that goes along with the above statement is that hot, dry weather does not reduce white mold; it just drives it under ground.  Generic Folicur (tebuconazole) is about $3/ac.  When we get close to 60 DAP, there’s no way I won’t have something applied for white mold when I see some chance of catching a shower to wash it in the soil.  In fact, even at 45 DAP with a reasonable chance at a shower, I’ll add tebuconazole to Bravo on anything but Bailey or Sugg varieties.

Some growers have runners for the first time this year after growing all Baileys.  Our current runner varieties have great yield potential, but none of them are anything special on leaf spot or white mold.  Many growers used to Bailey are not aware of what a nasty surprise white mold can be at digging time – especially with a soybean history.

The 2,4-DB guidelines say “do not apply if peanuts are under drought stress.”

Frankly, the same statement could be applied to most of the post-emergence herbicides we use.  We have measured yield reductions with paraquat, Blazer, or Cobra applications to dryland peanut, and not always under a great deal of drought stress.  Valor can also severely stunt, even kill a few plants even when timed correctly.

I don’t know of any herbicides that directly do a peanut plant any good; it’s always a risk / benefit trade off.  Our experience in measuring yield impact has been that 2,4-DB poses less yield risk than any of the contact materials like paraquat, Cobra, or Blazer; whether stressed or unstressed.

2,4-DB is a cost-effective option for control / suppression of escaped sicklepod, morningglory and pigweed.  If we need it now, the weeds won’t wait.  Apply as early in the day as possible when at least we get the most upside out of the stress put on the crop.

Will Provost plus 2,4-DB cause peanut injury?

That seems to be a repeated question right now.

Not usually, and we have done it a lot just because a 2,4-DB follow-up treatment around 60 DAP is often needed when dual purpose fungicides like Provost go out.

Provost tank mixes are erratic in causing some phytotoxicity symptoms on peanuts.  When it happens it is usually relatively minor leaf spotting compared to all the surfactants, crop oils, and herbicides we abuse peanuts with.  But on Ga 09B in particular we can get some ugly yellow leaflets and even some leaflet shedding.  When we try to duplicate these symptoms with the same tank mixes and water source, we can’t make it happen.  In fairness, we can get some of the same symptoms on 09B with other fungicides.

We have alternatives to Provost on Ga. 09B if growers have had phytotoxicity problems (Bravo tank mixes with tebuconazole or Convoy; or Abound, Evito, Fontelis).  But I would not hesitate to use Provost and 2,4-DB on other varieties where 2,4-DB is needed.    One way to reduce phytotoxicity risk is to avoid unnecessary surfactants.   We absolutely need non-ionic or crop oil for most herbicides to perform, but not with just fungicides or with 2,4-DB + fungicide mixes.

I have a lot of Horsenettle, what controls it?

You’re not going to kill it, but Cadre + 2,4-DB and then a 2,4-DB follow-up has consistently kept it uncompetitive and a non-factor at digging time.

I have a lot of sicklepod and some morningglory and don’t want to use 2,4-DB with Cadre because I use the sprayer for cotton.  Is Cobra a good choice?

Not for sicklepod, and neither is Blazer.  Either rely on Cadre, or find a way to add the 2,4-DB by cleaning out good or borrowing equipment.  Cobra / Blazer are great options to have when killable sized pigweeds are present and we have passed paraquat timing, but we risk burning the peanuts for next to nothing if it’s just sicklepod and a few morningglories.

What’s the best time to add Mn to fungicide?

In general no earlier than 75 DAP, for three reasons.  First, we often need 2,4-DB follow-up around 60 DAP before the canopy closes, and we don’t want to mix  2,4-DB and Mn.  Some formulations get away with it, but unless you know for sure from a clabber test, the mess is not worth the risk.

Second, peanuts usually don’t show Mn deficiency before 75 DAP anyway, and finally any Mn that misses the leaves is wasted, so you want a big enough peanut plant to do some good.

My crew messed up and put out almost a double rate of Cadre.  How bad am I hurt?

The wallet is $8/ac lighter and it didn’t do the peanuts any good, but it’s happened before and we still made good peanuts.  The bigger issue is cotton rotation where corn is not an option next year.  As much as we hate to do it, it may be more advisable to break the peanut rotation by doubling up next year, than to risk the double rate of Cadre on cotton.

Can I skip land plaster on dryland virginia peanuts with a 1,000 lb soil test Ca level?

I’d still put out a half ton on Virginia types.  If we get marginal soil moisture during pod fill, having a more soluble form of Ca can make the difference in reducing pops.  On runners you are OK with a 1,000 soil test.

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2 Responses to Peanut Herbicide, Fungicide, and Nutrient Tips From Jay Chapin

  1. Chad Lehner says:

    Is there a time when it is not beneficial or a time that is harmful for the development of peanut to apply post emergence quizalofop and fomesafen? I am being told not to apply before 40 days. My weeds are growing considerably. But it has only been 23 days since planting. I want to apply now, but worry I may hurt the peanut somehow.

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    • Fusilade(quizalofop) can be applied safely at anytime throughout the growing season. There is a 40 day PHI, so be mindful of that. Fomesafen is not labeled for use in peanuts. Instead, for broadleaf weeds, Clemson Weed Specialist Mike Marshall recommends Storm (1.5 pt/a) plus Gramoxone (12 oz/a) plus a surfactant applied separately from Fusilade.

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