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prostko-spiderwort-2.jpg Dr. Eric Prostko
Benghal dayflower/tropical spiderwort research in Grady County, Ga., peanut field in 2004.

An old weed foe returns — and it’s not pigweed

Benghal dayflower/tropical spiderwort was PUBLIC ENEMY No. 1 prior to the evolution of herbicide-resistant Palmer amaranth.

As my colleague and I began our annual weed science gospel tour earlier this year, it was interesting that both of our presentations partially focused on the management of Benghal dayflower/tropical spiderwort (BD/TSW). 

 We did not consult each other prior to the tour and this was an obvious reflection of the number of inquiries we received about this weed in 2018.  As you might recall, BD/TSW was PUBLIC ENEMY NO. 1 prior to the evolution of herbicide-resistant Palmer amaranth in most of the southeast.  Since BD/TSW reared its ugly head again in 2018, I thought it might be a great time to review what happened and how this weed can be managed in peanuts.

It is my opinion that BD/TSW was such a problem in 2018 because of the biblical rainfall that occurred.  Here on the UGA-Tifton Campus where I reside, the rainfall total for the year was 62.77” (15.4” above the long-term average)!  Under soggy conditions, BD/TSW plants tend to grow very well, residual herbicides do not last as long, and timely POST herbicide applications can be delayed.  This trifecta is a great recipe for a BD/TSW nightmare.  Now I have no influence over the weather, but I do have a few suggestions for control that might be helpful.

Much like Palmer amaranth seed, BD/TSW seed does not like to be buried.  This is why tillage with a moldboard plow is so helpful in the management of this weed.  Research has shown that BD/TSW seed buried deeper than 4” in the soil will likely not emerge at all.  Other research has shown that BD/TSW seed viability is reduced to near 0% when buried 8” deep for at least three years.

I know that some folks prefer strip tillage to conventional tillage for very important economic and environmental reasons, but UGA research in 2018 continued to show that conventional-tillage peanuts out yielded strip-till peanuts by 8.6% to 13.3%, depending upon row configuration (single or twin row). 

Over the last several years, there has been some discussion on the continued need for twin-row peanuts with the development of newer, disease-resistant, and high-yielding cultivars.   That cerebral discussion might be above my pay grade.  However, I can say that BD/TSW control in twin rows is about 12% better than in single rows.  Also, do not forget that twin rows are very important in the management of tomato spotted wilt virus.

The use of multiple applications of residual herbicides (at least two apps) prior to BD/TSDW emergence is crucial for full-season control.  Historically, Dual Magnum (s-metolachlor) has been the residual herbicide of choice for BD/TSW, but other relatively new peanut herbicides are available including Warrant (acetochlor) and Zidua (pyroxasulfone). 

POST herbicide options for BD/TSW control in peanuts include Basagran (bentazon), Cadre (imazapic), Gramoxone (paraquat), and Strongarm (diclosulam).  

Do not forget that the peak emergence of BD/TSW in South Georgia is around June 1.  Thus, at-planting applications of Dual Magnum or Warrant with April sowed peanuts might not be the best place for these residuals.  I tend to prefer BD/TSW residuals in combination with “cracking” Gramoxone sprays AND later POST herbicide applications (2 apps of residuals).     

Mother Nature is very fickle and can be either friend or foe.  That’s entirely up to her.  All you can do is be prepared.  Didn’t someone more famous than I say “luck or chance favors the prepared”?  As with most weed problems, the best approach for managing BD/TSW in peanuts is to use a combination of tactics, including tillage, row spacing, multiple applications of residual herbicides, and timely POST herbicide applications. 

As always, good weed hunting!

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