Rainfall prevented timely cereal rye termination in many parts of Eastern Nebraska this spring. These rain events also brought cool daytime and nighttime temperatures. All the while, cereal rye continued to grow. Three questions emerged relating to these events:
1) Why is cereal rye taking longer to die than normal?
2) How do I assess cereal rye terminated with glyphosate? 3) What are best practices for terminating cereal rye?
Time from Roundup® application to cereal rye senescence
Factors influencing cereal rye dry down following Roundup® application include weather and cereal rye size.
Daytime temperatures have remained mild this spring with considerable cooling off at night. Glyphosate is mobile within the plant; however, mobility varies with temperature. Daytime temperatures in the mid-50’s or above and nighttime temperatures above 40 degrees Fahrenheit favor glyphosate mobility, thereby improving rye termination.
The smaller the rye, the easier it is to terminate. Larger rye often coincides with warmer temperatures that promote glyphosate efficacy; however, the additional biomass poses a challenge. When using the same Roundup® rate on small rye versus large rye, the active ingredient to plant biomass ratio is smaller for large rye.
Additionally, canopy density increases as plant size increases. Dense canopies pose coverage challenges that may shield some plants. Protected plants receive less active ingredient that prolongs time to senescence or is sub-lethal.
Assessing stand termination
Roundup® blocks production of a specific amino acid in the plant, which slowly ‘starves’ the plant. Consequently, Roundup® requires time to work. Wait ten days before beginning assessments and do not consider re-spray decisions until at least two weeks following application.
Chlorosis, or yellowing, presents on new foliar growth first and progressively spreads. Yellow tissue eventually transitions to brown, necrotic tissue. Roots will often shrivel and discolor as the plant shuts down.
Best practices for terminating cereal rye
Northern areas within Eastern Nebraska continue to terminate rye stands. Some stands are larger than the intended termination size, however, temperatures are favorable if fields remain dry enough to spray. Following these guidelines will help with termination of large cereal rye:
- Use a full Roundup® rate
- Do not skimp on AMS, 17 lb AMS/100 gal
- Add AMS before Roundup®
- Increase carrier volume as rye size increases, 20 GPA for dense canopies
- DO NOT apply with liquid fertilizers such as UAN or ATS
Figure 1. Cereal rye terminated with Roundup PowerMAX® 3 on April 30th, 2024 near Columbus, NE. Plants (left to right) 1) cereal rye dug from field edge that was missed by the sprayer; 2) cereal rye dug from a dense cluster that likely did not receive adequate coverage. Note the chlorosis and developmental delay compared to the plant that was not sprayed; 3) cereal rye that was fully terminated. Note the chlorosis, necrosis, and stunting compared to the partially and non-controlled plants. Photos taken 12 days after application on May 12th, 2024.
