Photo credit: Bill Curran
Some winter annual weeds are easier to manage in the fall rather than waiting for spring. With small grain sowing happening in earnest this time of year, populations of winter annual weeds will be emerging and can potentially compete with wheat and barley in late fall and early spring potentially reducing yield. If winter annual weeds like common chickweed, henbit, Italian ryegrass, Bromus species, and others emerge with the small grain and are left unchecked, the potential impact on yield could be great. In these situations, it may make sense to kill these weeds in the fall rather than early spring. Harmony Extra (thifensulfuron + tribenuron) or a similar product is the most broad-spectrum herbicide for broadleaf control, but resistant populations of common chickweed are becoming evident in parts of the region. In addition, there are several herbicides labeled for grass control in wheat and fall is typically the best time to make an application. Make sure to include the necessary spray adjuvants. Remember that cool (less than 50 F) cloudy days can reduce herbicide activity. Also, if you plan to frost-seed or drill a companion crop such as red clover in early spring it may be best to make a fall herbicide application to avoid certain issues with herbicide residuals affecting their establishment. However, even if products such as PowerFlex HL, Osprey, and others are applied in the fall, recrop restrictions may still prevent seeding next spring, so check a current herbicide label for additional guidelines. The accompanying table summarizes the effectiveness of some small grain herbicides for control of specific winter annual weeds.
Relative effectiveness of POST-applied small grain herbicides for winter annual weed control.
Table compares the relative effectiveness of herbicides on individual weeds. Ratings are based on labeled application rates and weed size or growth stage. Results may differ with variations in weed size, temperature, rainfall, and soil moisture. Crop injury rating of VG or E is rarely significant.
|Weed control rating||Crop tolerance|
|10 = 95–100%||E = excellent; almost never any crop injury observed|
|9 = 85–95%||VG = very good; on rare occasion is crop injury observed|
|8 = 75–85%||G = good; seldom is crop injury observed as long as proper management practices are followed (e.g., seedling depth, seed slit closure, herbicide rate and application timing, adjuvants)|
|7 = 65–75%||FG = fair to good; occasionally crop injury is observed even with proper management practices; injury is often due to herbicide interactions with environmental conditions|
|6 = 55–65%||F = fair; some crop injury is commonly observed|
|N = less than 55% or no control|
|L = labeled but no university data|
-- = no information available
|Herbicide Group (Mode of Action)||Bluegrass, annual1||Bluegrass, roughstalk||Brome, spp.2||Buckwheat, wild||Catchweed bedstraw||Chickweed, common2||Corn chamomile||Groundsel, common||Henbit/purple dead nettle||Horseweed (marestail)||Knawel||Lettuce, wild||Mustard spp.||Pennycress, field||Ryegrass, annual2||Shepherdspurse||Speedwell spp.3||Vetch, hairy/annual||Crop safety|
- Annual bluegrass control is listed on Osprey and Olympus Flex labels. Fall applications are best.
- See the introduction of this chapter for more detailed information on these weeds.
- There are several speedwell (Veronica) species, including corn, common, ivy leaf, and others. Depending on the species, their life cycle is either annual or perennial. Many of the commonly used small grain herbicides provide little or no control of speedwell. Finesse has a few annual and perennial speedwells listed on its label and usually provides 80–90 percent control of them. PowerFlex has provided control of certain speedwell species in some university trials. Be cautious of crop rotation intervals if using Finesse. If speedwell is small, Aim provides some control/suppression.
- Will not control group 1 (ACCase) resistant annual ryegrass biotypes.
- 2,4-D ester provides better control of hairy vetch than 2,4-D amine.
- Crop safety with Glory/TriCor is dependent on weather at time of application and variety. Crop safety is improved if applications are made in the spring rather than in the fall.