By Darren Hefty
The post-emerge corn herbicide discussion begins with the topic of what your pre-emerge herbicide was. This puts you into one of three camps:
- I didn’t use a pre-emerge herbicide.
- I used a pre-emerge herbicide that also controls broadleaf weeds.
- I used a pre-emerge herbicide that mainly just controls grasses.
If you didn’t use a pre-emerge herbicide at all, you’ll definitely need to be back in the field early to spray for broadleaf weeds. If so, you need to use a herbicide that has some residual control to kill weeds that try to pop up later. Also, the timing will be important both for weed control (think about getting good coverage before some weeds get big and hide smaller weeds safely underneath) and yield preservation (it’s estimated that for every one inch in weed growth, you lose 4.7 bushels per acre off your corn yields).
If you did use a pre-emerge herbicide, it will impact which weed species grow in your fields early this growing season. If you have grass, Roundup (in tolerant hybrids) is the cheapest and most effective option. If you have conventional corn, Accent is the best choice.
If you have broadleaf weeds, you will likely be adding a tankmix partner if you intend on spraying Roundup. Here are the most popular choices.
Status has the broadest spectrum of weeds that it controls, and it’s good on nearly every major broadleaf weed. However, it has been sold out for months. So what else can you use?
The HPPDs (Group 27) are very popular and work well in most situations. Armezon, Callisto, Impact and Laudis are all fairly similar in how they work in the field. There are differences in formulations, rebates and the crop safeners they contain. The weaknesses of this chemistry are the vine weeds like wild buckwheat, as well as perennial weeds like Canada thistle. Strengths include pigweeds, lambsquarters, cocklebur, sunflower, velvetleaf and many more. Also, the HPPDs can be sprayed safely on taller corn than dicamba. We recommend adding ¼ to ½ pound of atrazine per acre to any of the HPPDs when used post-emerge if your soils and rotation allow.
Dicamba (Generic Banvel) is growing in popularity this year to fill the void left by Status being sold out. Banvel is certainly not Status, though. Keep in mind that Status has two active ingredients rather than just the one in Banvel. Also, Status has a crop safener and other improvements to reduce volatility. The strategy some are employing is to mix a lower rate of Banvel with one of the HPPDs and atrazine. It’s a three site of action approach that will definitely broaden the weed control spectrum.
Buctril is another choice for broadleaf weed control. Rather than being used on its own or in a combination with atrazine as it was in the past, most of the Buctril being used today is going out as a tankmix partner for Roundup. It heats the mix up and adds punch, especially on lambsquarters and wild buckwheat.
Whatever product or products you choose to spray in your corn this spring, be timely with your application to maximize weed control and your yield potential. If you have Roundup-resistant weeds, make sure you’re using a strong enough rate of your tankmix partner to kill those weeds all by itself because the Roundup in the tank will add nothing to your control.