Agronomic Answers

February 11, 2014 06:05 PM

AskAnAgronomistFind answers to a variety of crop pro­duc­tion questions on Farm Journal’s "Ask an Agronomist" blog. The Farm Journal agronomists and other experts respond to questions sent to based on their inde­pendent experience and in-the-field insight. Past questions and answers can be found at Here are three recent questions and answers from the blog.


Where can I get the planter calibration tool you talk about at the Corn College Planter Clinics?


The planter calibration tool can be a great help in calibrating seed and insecticide units on planters. You can purchase the tool at


What’s the difference between site of action for weed control and mode of action? I know figuring this out can help me address weed resistance.


Mode of action (MOA) tells us what effect the herbicide will have on the plant. Site of action (SOA) tells us what pathways the herbicide will use to inflict that damage. The goal in preventing weed resistance is to regularly change what pathways are being attacked within the plant by choosing herbicides with different SOAs. By choosing different SOAs, the mutated or resistant plants can be killed before they reproduce, stopping resistance from spreading.

It is important to note that choosing products with different active ingredients is not enough; you must make sure that your rotation of products contains varying sites of action. In an attempt to change up the MOA or SOA, applicators and farmers are going to be using products that have not been all that common in the past decade. When using different products, be careful you don’t increase drift problems or carryover issues, and follow all label recommendations.


I’m having problems with volunteer corn in my corn fields. How do I control it?


I’m not sure of your specific agronomic practices, seed traits etc., so I’m going to offer a couple of thoughts for your consideration.  If the previous crop you grew was conventional corn, you have more  options. The obvious one is to rotate to soybeans this year. Another option (depending on what seed you purchased) is to plant Roundup-tolerant corn and use Roundup herbicide in a postemergence application. If you grew glyphosate-resistant corn this past year, plant LibertyLink corn and apply a postemergence application of Liberty.

It gets tricky when you grow continuous corn with hybrids that contain both Roundup Ready and LibertyLink traits. Those traits stacked together can be good in a corn-soybean rotation, but in a corn-on-corn rotation, you really need to separate those traits, so you can use one or the other to clean up weeds.

Another option that is probably next to impossible for someone in the northern corn-growing areas is to plant corn later than normal after controlling the volunteer corn. Basically, you want to get your seedbed ready early. Level up that ground and then wait for the right soil temperature. Corn germinates at 50°F, and at 55°F it gets really active.

You want to let that volunteer corn sprout up to about two collars and then spray Fusilade or Poast or work the ground again with secondary tillage, such as a field cultivator. One caution: Be aware that today’s vertical-till harrows are not very good at removing volunteer corn and can make it worse. It can shatter those corn ears and cause reseeding.

I don’t know what your harvest was like in 2013, but if you had a 20-bu. or 30-bu. harvest loss when you went through the field, you might have a mess this spring. Even if 90% of it was killed by frost, that other 10% will have to be managed. Get on top of it as soon as you can.


I have been reading your series about making zone maps. It says to start with a soils map. Where can I get a good soils map?



You might be able to get a hard copy of your county soil survey from your local Natural Resources Conservation Service (NRCS) office. I’d also encourage you to visit the NRCS soil survey site at http://websoil




To read more crop production questions and answers or to submit your own questions, go to

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