Ag insiders have been warning for months that producers could face an unprecedented chemical shortage in the 2021/22 growing season. Unfortunately, the warnings have not subsided. If anything, they have grown more urgent as supply issues for the two most popular herbicides – glyphosate (Roundup, others) and glufosinate (Liberty, others) fail to subside. Where the herbicides are available, prices have increased substantially, a trend many fear will only continue.
Recently, a group of Extension weed scientists from Indiana, Kentucky, Michigan, Ohio, and Pennsylvania discussed the possible herbicide shortages and some of ways producers can overcome some of the challenges posed for corn and soybean production. Bill Johnson, a professor of botany and plant pathology at Purdue University, has been surveying pesticide retailers about their expected glyphosate inventories, with most expecting to have only 80% or less of their typical volumes. Many suppliers are reportedly only guaranteeing delivery to long-time customers, or regulating how many gallons per day a customer can buy.
While other chemicals are likely to experience inventory issues this year, glyphosate and glufosinate are expected to pose the most challenges. Dr. Mark Loux, OSU Extension Weed Scientist, says that as producers search for alternatives for these two herbicides, the weed control guides and technical guides produced by University Extensions as well as industry could prove an important tool in planning new weed management programs. In OSU’s latest C.O.R.N. Newsletter, Loux compiled a list of recommendations and guiding principals that were discussed with his Extension specialist colleagues, especially where glyphosate will not be in all applications. Below are some of the tips Loux shared. His full rundown, which is quite extensive and also provides links to other resources, is available HERE.
- Spring tillage is an option to replace herbicide burndown. Can cause long-term compaction problems if tilled when too wet. Waiting until weeds are large makes tillage less effective. Weeds that survive tillage will be difficult to control with POST herbicides. In other words, till when soil conditions are fit and before weeds are huge.
- Where it’s only possible to use glyphosate once, it may be needed most in the burndown. Saflufenacil can be added for enhanced control of rye and ryegrass, and marestail. ACCase herbicides (e.g. clethodim, quizalifop) can then be used for POST grass control in soybeans. Glufosinate, Enlist Duo, or XtendiMax/Engenia can be used for many broadleaf weeds, especially the glyphosate-resistant ones. Where residual herbicides are omitted, or do not provide enough control, we would expect POST treatments to struggle more in the absence of glyphosate with weeds such as lambsquarters. So use residuals. Glyphosate is still more than just a grass herbicide.
- If glyphosate is omitted from burndown, grasses become a bigger issue than broadleaf weeds. Options for annual grasses: Gramoxone; rimsulfuron – if small, corn only; ACCase herbicides – clethodim (wait 7 days to plant corn), quizalifop (soybeans only) – need 60 degree days, apply alone if possible, weak on winter annuals under cold conditions. Where trying to reduce glyphosate rates, a rate of 0.38 lb ae/A will control most annual grasses.
- Burndown programs typically contain two to three “burndown” herbicides in order to ensure control of a diversity of weeds under various environmental conditions. This is why glyphosate is not used alone in burndown programs, but mixed with 2,4-D, dicamba, or Sharpen. We suggest following this same strategy when glyphosate is omitted – try to have at least two herbicides with substantial burndown activity in the mix. Increasing rates of components of the burndown mix should be generally helpful, in accordance with label guidelines for soil type, weed size, time until planting, etc. There are also other herbicides that can improve control in some mixes although we don’t consider them “burndown” herbicides on their own – chlorimuron, atrazine, metribuzin.
- There are generally more options for burndown and POST applications in corn compared with soybeans, so it might make sense to save a limited supply of glyphosate and glufosinate for use in soybeans.
- Control of little barley and annual (Italian) ryegrass in a burndown requires glyphosate, ACCase herbicides are not effective enough in spring. For annual bluegrass – ACCase can work – 60 degree day, no tank mixes. High rates of metribuzin can provide fair control of bluegrass.
- For burndown of a legume cover prior to corn, clopyralid and dicamba are the most effective herbicides. For cereal rye, Gramoxone plus atrazine or metribuzin may be best option in the absence of glyphosate.
- It’s possible to chop and bale a cover, then use glyphosate POST to kill regrowth. The addition of an ACCase herbicide may help control regrowth in soybeans. POST corn herbicides will not kill the rye, including nicosulfuron, rimsulfuron, and Group 27 herbicides (Impact, Shieldex, Laudis etc).
- Mixing ACCase herbicides with dicamba or 2,4-D (no glyphosate) can cause reduction in grass control due to antagonism. Apply separately to avoid this.
- Increasing the number of applications can help with weed and herbicide management when certain products are short or glyphosate rates need to be reduced. For example, three applications instead of two: 1) Fall or early spring burndown when weeds are small; 2) residuals plus possibly additional low-rate burndown at planting; 3) POST.
- Best opportunity to omit glyphosate or reduce the rate will be: 1) in fields treated the previous fall, or those with a low population of small weeds; and 2) where the POST program is comprehensive enough to control weeds that escape the burndown – Enlist, XtendiFlex, LL GT27 (their effectiveness also depends upon whether glyphosate is being used POST).
- Take all necessary steps to maximize herbicide activity – optimize adjuvants and sprayer parameters (nozzles, volume, pressure, speed) per label guidelines.
- Check on availability of premix herbicides that may contain glyphosate or another herbicide that is unavailable as a single ingredient product. Examples that contain glyphosate – Sequence, Halex GT, Acuron GT, Extreme, Flexstar GT.