This month I decided to switch things up just a bit by posing that question to several of my customers across southwest Illinois. The general consensus was that Weed Control is the #1 challenge. Here are a few of the responses I got: “Herbicide Resistant Weeds”, “The cost of having to use chemicals that are not working well”, “Waterhemp”, “Gramoxone didn’t work”, and “Weed Control is #1, but Liberty Link® has really helped with POST applications.  But now crop injury from the Pre’s is an issue”.

The responses I received did not work out quite as I had anticipated, as I was hoping for a broader range of comments. Therefore, I had to ask a slightly different question. This time it was: “What is your #2 problem with raising soybeans?” Here’s where things started to get interesting and here are some of those responses. “Expensive seed costs”, “SCN and SDS”, “Breaking the 45 bu/acre yield barrier”, “Machinery expenses to get everything done in a timely manner”, and “Marketing, when it seems so easy to lose out on $2 – $3 per bushel”.

I have a few thoughts or answers for some, but not all, of these challenges. Let’s start with the #1 challenge, Weed Control. Next month I will address most of the other challenges.

Above: Clean soybean field

Above: High waterhemp population soybean field

Currently in Illinois there is confirmed weed resistance to the ALS, PPO, HPPD, Amino Acid Synthesis and Photosynthetic inhibitor herbicides. I recently learned from Ron Krausz that there is a Growth Regulator (2,4-D) resistant population of waterhemp in Illinois. Ron is the manager at the Southern Illinois University – Belleville Research Center. He also went on to state that weeds such as waterhemp and Palmer amaranth can be controlled and there are three critical components.

1. Spray these weeds when they are 2 – 4 inches tall.
2. Use soil-applied herbicides with good residual.
3. Use over-lapping residuals.

 This year at the Belleville Research Center Field Day, Ron showcased a series of weed control plots that featured Roundup Ready®, Liberty-Link®, Enlist® and Xtend® soybeans.  As a side note, he had to get special approval to conduct the herbicide program on the Enlist and Xtend soybeans since the labels have not been approved.

All of these plots exhibited outstanding weed and waterhemp control, but were not completely weed free. Photos from the plots with running checks follow and I am intentionally not putting labels on them. The point to get across here is that the POST applications are only a portion of this success. The biggest part of the success on these plots was the use of the soil-applied herbicides and application timing on small, 2 – 4 inch weeds.  I cannot stress enough the phrase “2 – 4 inch weeds”.

In a separate study area at the research center there is a population of Palmer amaranth. This photo follows and here again the success of the weed control program is the use of the soil-applied herbicides and application timing.

To produce high soybean yields and combat herbicide-resistant weeds in the future growers need to be doing the following:

1. Scout your fields early and often to identify weed types, pressure and population density.
2. Use soil-applied PRE herbicides with good residual.
3. Spray weeds when they are 2 – 4 inches tall.
4. Use over-lapping residuals with the POST applications.
5. Spray weeds when they are 2 – 4 inches tall.  Yes, I put this in here twice.
6. Record all of the herbicides used, field observations, successes and failures.
7. Rotate your herbicide modes of action (MOAs) to reduce tolerance and resistance buildup.
8. Utilize crop rotation and cover crops when possible if it fits into your production system.
9. Learn to live with a few weeds. Repeated applications of the same MOAs in the same year further increases your chances of building resistance. Once a weed has been damaged by a herbicide, but not killed, the chances of killing it with another application are slim.
10. Rotate your seed technology traits. I observed a field this year that was switched to a straight Liberty soybean and corn program three years ago. Only Liberty has been applied now for three years and the waterhemp is showing signs of resistance development. Over the years with our herbicide applications we have been selecting for “survival of the fittest”. Now, waterhemp and Palmer amaranth have the potential to develop herbicide resistance in as little as 3 – 4 generations.
11. Talk with your neighbors. Share those successes and failures. The population dynamics of waterhemp can change rapidly simply through cross-pollination because of historical, cultural and differing management practices.  In other words, your success at controlling weeds is only going to be as good as the success of your neighbors.
12. Lastly, write down notes at harvest of any observed problems instead of trying to remember them.  A soybean field looks much cleaner after harvest (pun intended).

Terry Wyciskalla is an independent crop and soils consultant based out of Nashville, Illinois. He specializes in soil sampling, fertility recommendations, precision ag services and crop problem diagnoses. He serves a 12-county area throughout Illinois. He earned his 4R Nutrient Stewardship certification in 2015 and is happy to be a part of the 2016 Soy Envoy team.