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What happened with corn weeds in 2018 can guide us today

As the 2019 field corn season starts off, I would like to remind growers about a few things that happened in 2018.

At this time of year, I often think about a catchy phrase from one of my favorite James Taylor songs that says, “Well the frost is on the pumpkin and the hay is in the barn.” To me, this line heralds the end of one season and the beginning of another. 

Although not much can be done about the problems of last year, a lot can be accomplished now to help prepare for and/or minimize potential issues of the coming year. As the 2019 field corn season starts off, I would like to remind growers about a few things that happened in 2018.  For the record, many problems I see happen every year and more than a few are self-inflicted. 

One of the more frequent complaints I received in field corn in 2018 was related to sprayer contamination of Valor (Figure 1).  This can be a hard pill for some folks to swallow, especially when they fanatically believe that their sprayer is totally free from Valor residues.  In this situation, I will never claim to have all the answers.

It does not take much Valor residue to cause corn leaf injury and there are un-seeable nooks and crannies in rubber sprayer hoses to capture and release Valor at random times (even after cleaning).  My best advice for this situation would be to never leave Valor in your spray system longer than need be, follow the labeled Valor sprayer cleaning instructions completely, make sure that last 5 gallons in the bottom of the spray tank is really just water, and replace older hoses. 

Halex GT (glyphosate + mesotrione + s-metolachlor) has become a popular herbicide of choice for many field corn growers, but like many herbicides (and one weed scientist I know who trained at NC State University), it has some idiosyncrasies.  One of these is that Halex GT can form an unfriendly mass of precipitates in the spray tank when it is mixed with other agrichemicals in the wrong order.  The correct mixing sequence for Halex GT + Atrazine + NIS is as follows:  clean water ► good agitation ► NIS ► Atrazine ► Halex GT ► more clean water.  Increasing water volumes from 10 GPA to 15 GPA can also help alleviate some compatibility issues.

In 2018, I received more inquiries than normal about the lack of performance of one of our cheapest and most effective POST weed control programs in field corn: Roundup + Atrazine.  I cannot say with 100 percent certainty what happened in every one of these cases, but timing, weather, and resistance are always suspects. 

In 2019, the time might be ripe for corn growers to seriously consider using Halex GT, replacing glyphosate with Liberty, or tank-mixing something else with Roundup + Atrazine, such as Anthem Max, Dual Magnum, Impact/Impact Z, Laudis, Prowl, Revulin Q, Warrant, and Zidua. Plenty of good options here and glyphosate and atrazine are both dirt cheap these days. 

Now I purposely left this paragraph for last in response to the previous paragraph and Bob Kemerait’s recent Tailgate Talk article for Southeast Farm Press about Extension practitioners making potential costly recommendations.  I can assure you that this is something that I am very mindful of and do not take lightly.  Although field corn growers have historically been reluctant to spend much money on weed control, there is a ton of data out there to justify a reasonably priced herbicide program (~$20-25/A).   Yield data I have collected in Georgia over the last 12 years would suggest that spending this much money could easily save corn growers, who average 200 Bu/A, roughly $287 worth of lost yield due to weed competition.   Thus, one phrase you might here from me from time to time is “save a penny now, spend a dollar later.”

While the frost is on the pumpkin and the hay is in the barn, it is a great time to begin preparing for the upcoming field corn production season.  Many common problems can be avoided with a little forethought.  I look forward to visiting with you at an upcoming county production meeting in 2019. 

As always, good weed hunting!

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