Peanut Insect, Diesase, and Heat Update

Clemson Peanut Specialist Jay Chapin put together the following information for peanut growers.

Extreme temperatures and drought stress are never good for peanuts in late July.  The majority of our crop is in the 60 – 80 DAP interval, a critical period for setting and beginning to fill pods.  We have time to make a peanut crop, but life is much easier at harvest when it matures uniformly and on-time.

Soil moisture is very spotty with some areas remaining very stressed and others getting showers to keep the crop moving and out of stress.  A weather front across the state would go a long way right now.

Hopperburn

We sprayed a few fields this week for leaf hopper injury.   Pay particular attention to Bailey variety and areas next to drying corn fields.  Runners are not immune – we got a nasty surprise in a field of lush, irrigated Ga 09B; the worst hopper injury I have seen in awhile.

Pyrethroids are cheap, should I put some in my next fungicide to prevent hoppers?

Don’t do it unless you absolutely see hopperburn starting to spread across a field from the border rows.  Our spider mite risk is already high in this weather and we don’t need to do anything to make it worse.

Another reason to avoid blanket pyrethroid treatment is that our earworm populations are just starting to pick up.  Not a good idea to kill predators unnecessarily right before a moth flight.

One convenient strategy that sometimes prevents hopper spread is to ring the border with a pyrethroid one time when cotton is being sprayed.   Even this limited approach can backfire on dryland peanuts if we trigger spider mites on the border rows.  It doesn’t take long for mites to move across a field once they get stated.  We seldom have to worry about mites under irrigation.

Leaf Spots

There are leaf spots in every peanut field at this point in the season.  Some of it is chemical injury from previous herbicide, fungicide, surfactant treatments; some of it is residual Thimet phytotoxicity;  some of it is physiological leaf spot from stress and other environmental conditions (pictures pgs. 73-75, 2015 Production Guide).

Physiological spot.

Physiological spot.

Virtually none of the leaf spot that is currently visible will respond to fungicide treatment.  Even in our test plots which have not gotten any fungicide all year, you can’t find any late leaf spot yet.  But by harvest, there won’t be a leaf left.

Stay the course with proven fungicide programs to prevent germination of the late leaf spot spores that you can’t see yet.  If you are finding ANY sure enough late leaf spot (picture pg. 75) lesions down in the bottom of the canopy this early in the year, even only one leaflet out of a thousand, we have a tough fight on our hands to make it to harvest maturity.  If we prevent germination of the spores we can’t see, everything else will take care of itself.

My peanuts are not growing, should I add some foliar N?

If they have good color and nodules you’re wasting time and money.  They just need water.  We have a lot of peanuts that are slow to close the row due to stress. There’s plenty of N there, but the plant can’t use it.

If they are yellow but have nodules, it’s probably Mn deficiency (picture pg. 74).   Clay knolls often show Mn deficiency.

Most of the inoculation issues we are seeing are not significant enough to justify supplemental N.   It is mostly skips or partial inoculation in a limited percentage of the field.  But we have had to apply N in some cases of total or near total inoculation failure on rotated land.

IMG_20150723_124804_915

Poor inoculation on the taproot on the left, excellent inoculation on the right.   Both taken from same field.

We have more inoculation issues showing up on rotated land this year than I have ever seen in fields with a peanut history.  As usual, it is more prevalent in reduced tillage.  On land with a peanut history residual inoculation carryover usually covers up our inoculant application sins, but not so much this year.  That’s why we keep applying it every year – we want to load the tap root with nodules rather than rely on adequate residual nodulation of lateral roots.

Even though most of the inoculation patterns showing up late don’t justify N application, it’s an opportunity to check how consistent the planter innoculant application set-up is and whether it needs improvement.

2015 Clemson Peanut Production Guide

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