Dry Weather Peanut Decisions and PPO Resistance Update

Here is another field update from Clemson Peanut Specialist Jay Chapin.

Most areas struck out on meaningful rain last week.  I got a pretty good snapshot of the crop going across the state last week and in dryland peanuts we have it all.   The size of the bush doesn’t necessarily indicate what the pods are doing.

Wilted vines.

Wilted vines.

There are fields that are severely stressed with what taproot crop there is backing away from the hull.  These fields will essentially have to make a crop starting from whenever it rains.  A quarter mile down the road you can find another wilted dryland field that has a good, firm taproot crop and plenty of healthy pegs and small pods coming on.  The next field might be in between, having essentially a split crop.  Overall, dryland runners look remarkably good for the rain they have had in many areas.  Some of the stressed fields that have not nearly lapped the middle still have very good potential.

The dryland virgina type fields I have looked at generally don’t have near the pod set as runners do.The one thing in common is that they all need rain and the sooner the better.

Worm populations are still very light (1-2 per ft or less) in most fields.  Not a lot of hopperburn, but increasing in Bailey, Sugg; especially along corn edges.

Should I stop spraying drought stressed fields?

If the field has been severely stressed and has no significant pod crop to protect, at this point in the season it is legitimate to take the approach of waiting for a rain before making another fungicide application.  In other words, under severe drought, make the crop show you some potential first.

Even where yield potential is better we can get away with extending the spray interval a few days when there has been no rain since the last spray.  I never recommend doing either of these earlier in the season.  As a general rule, if you are ever going to stretch or eliminate fungicide applications, do it later in the season, not early.

Of course the other point to keep in mind is that we have $9 fungicide treatments and we have $25 fungicide treatments.  The reality is that many fields only justify $9 treatments from here on out.

Don’t let those pigweed escapes go to seed.

In previous bulletins I mentioned the recent confirmation of PPO herbicide resistance (Valor, Blazer, Cobra) in pigweed and the fact that weed wipers are under used for killing pigweed escapes.

Don't let these escapes go to seed.

Don’t let these escapes go to seed.

The following information about the threat of PPO resistance comes from Dr. David Jordan (NC Peanut Specialist). 

“We are going to experience an explosion in PPO resistance in the next couple of years. My suggestion and I think this is a consensus among weed scientist is that growers should do everything in their power to keep escaped Palmer amaranth from seeding out. This is not a new recommendation but I think if folks don’t try hard on this in the next couple of years but most especially this year, we will be in trouble in peanuts and soybean. I am going to start recommending higher rates of paraquat in the peanut crop and maybe 2 applications based on the label. We have few alternatives that are effective. Residuals in addition to PPOs need to be emphasized (DNA and chloroacetamides) although we are already using those. Regardless, trying to get the escapes pulled that may be early populations of PPO resistant biotypes will be beyond critical and can’t be overemphasized. Don’t let anything seed out. It will pay in the long run.

1) Lessons learned from glyphosate resistance include a field going from a few Palmer amaranth plants to the entire field in 3 years unless changes in management occur.

2) With peanut we are rotating with cotton, corn, and milo so alternative chemistry can be used but soybean is in at least 25% of peanut rotations in NC. But we are using a large number of PPOs in peanut and they are fundamental for Palmer amaranth – flumioxazin (Valor SX and generics); acifluorfen (Ultra Blazer, Storm); and lactofen (Cobra). Carfentrazone (Aim), sulfentrazone (Spartan Charge), and pyraflufen ethyl (ET) are PPOs but these 3 are of no value in Palmer amaranth management (In fact because these burn Palmer amaranth some but do not control it and therefore may be increasing selection pressure for PPO resistance in a manner similar to spraying an effective herbicide like Cobra or Ultra Blazer to large weeds which results in poor control. There is evidence that this phenomenon hastens development of resistance.) Selection pressure is very high now in both peanut and soybean for PPO resistance.

3) It is harder (and thus easier to ignore) to pull up escapes in soybean compared with peanut because of narrow rows, higher acreage in soybean for each farmer compared”

Calendar reminders:

Sept. 3rd 9 AM, Peanut Field Day Edisto REC

Jan. 28, 2016 State Peanut Meeting Santee Conference Center

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