Back to the Basics for Weed Control

The saying ‘all good things must come to an end’ is proving true for weed control in soybeans. Gone are the years of simply using Roundup to take care of everything (if they weren’t already for some acres). I confess that I was skeptical of weeds working around Roundup but should have known better since nature is geared to find a way to endure and overcome. Just like in the animal kingdom, survival depends on self-preservation. The same has happened with weeds, shifting their genetics to survive being sprayed with Roundup. 

The ‘Easy Button’ for weed control is over, not that we should ever have relied on straight Roundup as our sole option. We must now return to solid practices and ensure we use multiple modes to control problem weeds, which will help to stack the deck against further weed resistance and keep our herbicide options viable. 

Statistically, it is highly unlikely for any weed to simultaneously develop resistance to multiple herbicides. For example, say there is a 1 in 1,000,000 chance (much higher than the real world) for resistance to Roundup with a similar probability for resistance to 2-4D. The odds of finding both resistances in the same plant is 1/1,000,000 x 1/1,000,000 = 1/1,000,000,000,000, far worse than the minuscule odds of winning the lottery. 

The more logical path to multiple resistance is the weed population becoming resistant to one herbicide until the trait is locked in, and then using a non-resistant herbicide until that weed population develops resistance to that as well. 

In reflecting on the path to multiple resistance, we should hopefully see the error of single or even double modes of action. Using Xtend or Enlist soybeans on weeds that are already resistant to Roundup increases the danger of developing multiple resistance. With essentially one mode of control (the Roundup is doing nothing), you risk selecting plants resistant to Roundup and 2-4D or Dicamba. 

You should attack these weeds aggressively. Multiple modes of action will hopefully drive the population to nothingness, while using ineffective treatments will only allow them to spread to other fields. Even if you have no resistant weeds, it is still a strong policy to use multiple modes of action as a preventative measure in your fight against weeds. Remember that this is not a one-year fight; weed seed can sit in the soil for multiple years and come back to haunt you.

The basic program for weed control is starting with pre-emergence herbicide(s). This package can have several modes of action and prevent weeds from establishing in the first place. This will help the soybeans to get ahead of the weeds and allow post emerge spraying on a timely basis which eliminates having to come in when many of the weeds have grown beyond the size of the label. 

The University of Wisconsin has a very nice table of herbicides and their modes of action. It can be found at https://ipcm.wisc.edu/download/pubsPM/Herbicide-Mode-of-Action.pdf. It is important to match modes of action to the weeds you are trying to control. A good example is that group 2 (ALS Inhibitors) are not effective at controlling water hemp. 

After emergence, there are now several soybean options to control problem weeds: Xtend (Dicamba), Enlist (2-4D, Liberty), Liberty GT27 (Liberty) and coming next year XtendFlex (Dicamba, Liberty). Dicamba is probably the most effective and delivers some residual control and also has a great respray program for weed escapes. Unfortunately Dicamba has restrictions placed on its use due to some offsite movement during unfavorable conditions. 2-4D is a good spray and more forgiving but, just like Dicamba, can have the same offsite movement if the label is not followed properly. Liberty is my third choice as it is expensive and somewhat finicky when spraying. 

Though all three can be very effective, I lean towards Xtend as they have the clear lead in genetics and overall weed control. Enlist is next with its three modes of action that can be sprayed. I do like Liberty GT27 because they are genetically strong and allow for a mode of action beyond GT (Roundup). 

I cannot stress enough to follow the label on all three. These herbicides and soybean platforms are key weapons in our fight against weeds. There are many misinformed people that want to take them off the market in their zeal to ‘protect the environment’ and we don’t want to give them any reason to cite misuse. 

The easy days of Roundup being the magic bullet are gone but, with very minimal changes in our spray program, we can maintain the level of weed control we are accustomed to.

Saving Versus Earning for Seed Corn Inputs

I’m starting to get questions about costs this spring, which is not surprising given the recent COVID-19 effect on commodity prices. There are two significant components of the cost per acre equation: the number of trait technologies in the hybrid(s) a customer purchases and the plant population (which I’ll address at the end of this article).

Roundup Ready® hybrids cost roughly $30-/acre more than conventional hybrids (using 35,000 planting density and retail price for the technology, your mileage may vary). Most growers embrace the convenience of the technology and the “system” cost (trait + herbicide) is reasonable. Northern farmers (northern one half to two thirds of WI) have lower weed pressure and 70% of the time can use a single pre-plant or early post application of common tank mix herbicides where the system price is lower than the system price of Roundup Ready.

Corn borer protection, sometimes referred to as above ground insect protection, adds another ~ $20-/acre and is not available without the RR® trait in our lineup. Break even on this cost is a single corn borer in every plant (5% yield loss and $3-/bu) in 150 bu/acre corn. If yields or the commodity price increase, the number is more like one borer in every other plant. For growers in the I states (Illinois, Iowa and Indiana) plus Nebraska, it’s an easy decision: plant Bt corn.

Farmers in northern WI, MI, MN and the Dakotas will not likely see one borer per stalk where “not likely” is not the same as impossible. Growers in the southern one third of these states face a more difficult decision process and would generally be working right in the “break even” zone. Some considerations for these growers would include a scout and spray program probably costing the same as the trait technology, but used once every 5-7 years. Remember, the best spray program eliminates only two thirds of the pests which minimizes, not eliminates, damage. For the most northern growers, Renk Seed quietly has a “Dairy Dollars” program in Zone 3. Some Double PRO® hybrids are priced so the Bt portion of the trait fee is basically eliminated on the price list and can be purchased for virtually the same cost as RR products. This makes it an easy choice to have Bt on your farm (in Zone 3) and helps us with inventory management.

Corn rootworm technology (below ground protection) adds an additional ~$20-22/acre. When commodity prices were high, most growers planted fully traited hybrids for max protection which was our largest selling trait segment. VT2P® hybrids have been the largest selling trait segment for the past three seasons as farmers more carefully evaluate where they need to spend money. Rootworm beetle counts have been at historical lows the past two seasons and economic damage in wetter seasons would be hard to measure. On the other hand, there is no rescue treatment for corn rootworm, so the decision needs to be a sound one at the beginning of the season. If you need to control rootworm, the trait technology is the gold standard (review University of IL data). There are good soil-applied insecticide alternatives but are just as costly as the trait and less efficacious. There are numerous “cheap” insecticide alternatives in this space while, attractive from a cost perspective, deliver less than the price from a performance perspective.

Using an average trait technology mix, our customers spend ~$16- for 5000 kernels of seed corn – a great investment for the first 25-30,000 kernels/acre. Return per acre diminishes at some point and if you haven’t reviewed or updated where the density should be for your farm, current commodity prices and the hybrid you intend to plant, please do so before you go to the field. Honestly, most high-density recommendations are based on very high yielding research trials. If your farm doesn’t support high yields, get the density down where it makes sense. The following tables are copied from Extension publications from IL, WI and NE. I have included them so you can briefly review.

Summary Monmouth and DeKalb, IL data, two years (1990-91). Since this data is now 30 years old, I would increase the density response side of the graph by 5000 plants/acre.

Please remember that economic activity will return to normal, though I wish I could predict when. Consumers will have been cooped up for a prolonged period and I think there will be a rebound effect from pent up demand. Ideally this would occur before we get to harvest and the market starts reacting to supply. Another factor to consider when evaluating cost versus earnings is the possible price for this season’s crop, which has a good chance of being better than the virus-depressed price we are looking at going into planting.

Benefits of Scouting Fields Before Planting Corn

Weeds can become a major problem in crop production when not controlled prior to planting. This is especially important in no-till systems. Weeds emerging in late summer through fall can overwinter and flower to set seed in the spring and early summer. Identifying weeds before planting corn can be difficult, especially if plants are in the rosette state of development. But putting a little time and effort into killing them now is the easiest and most effective weed control you will do all year.

Scouting fields before planting can identify what weeds are present, their population and their growth stages. This information helps to determine what management practices and herbicides would be most effective for protecting the upcoming crop prior to planting and after establishment. 

Good weed control during the first four to six weeks after planting is critical for maintaining yield potential. A clean start helps to conserve moisture for the crop, promote good seed-to-soil contact and helps prevent weeds from binding up planters. 

Using the field scouting application in Climate FieldView™ provides a fast and easy way to drop a pin where weeds have emerged. Going straight to these spots for spraying can save time and money.

Considerations for No-Till Systems 

Winter annual weeds have become a larger problem in no-till fields due to the limited use of soil residual herbicides and the reliance on post emergence weed control associated with planting herbicide-resistant crops. Marestail has become a difficult to control weed for no-till fields because there are many populations that are glyphosate-resistant. It is important to control Marestail when it is small, which can require control as soon as equipment can enter the field. 

Plant debris in no-till fields can provide overwinter protection for germinated weeds, increasing weed populations. Fields that have been in no-till production for a few years may have a few scattered patches of weeds, which may not seem economically important to control. However, these patches may have enough time to seed out before a burndown application is made, creating problems in subsequent years. 

Stay safe and healthy during this upcoming planting season. You are an integral part of the best business in the world; American agriculture. Thank you for all you do.