Update: Pre-harvest weed control in wheat

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This year’s short, thin wheat crop, coupled with late-season rains has resulted in a lot of questions about the best approach to managing large weeds in mature wheat.  We did address this topic previously this year, but with the extended wheat harvest, it seems timely to share this information again. The weather will greatly affect how quickly the weeds will dry down to facilitate harvest. Because of the large size of some of the targeted weeds, there may not be complete control of the weeds and that can result in regrowth after harvest. In addition, there have been questions regarding the effect of some products, especially saflufenacil (Sharpen) on weed seed germination. We need to clarify that BASF data suggest that Sharpen does not negatively affect seed wheat and can be used on wheat that will be saved for seed.

Herbicides labeled for use as harvest aids in wheat are listed in Table 1. There are differences in how quickly they act to control the weeds, the interval requirement between application and grain harvest, and the level or length of control achieved. All of them will require thorough spray coverage to be the most effective. Paraquat is sometimes mentioned as a possible herbicide for pre-harvest application but is not labeled for pre-harvest treatment in wheat. Application of paraquat to wheat is an illegal treatment and can result in quarantine and destruction of the harvested grain, along with severe fines.
 

https://eupdate.agronomy.ksu.edu/lib/Filemanager/userfiles/05262022/4Fig1PreharvestWeedControlWheat.jpg

Figure 1. Weeds in wheat near harvest time. Photo by Dallas Peterson, K-State Research and Extension.


Table 1. Herbicides for use as pre-harvest weed control options in wheat.

Herbicide
and rate

Weeds controlled

Application timing

PHI* (days)

Comments

Metsulfuron
(Ally, others)
0.1 oz

Some broadleaf weeds

Hard dough stage

10

Kochia, pigweeds, and marestail may be resistant

Apply in combination with glyphosate or 2,4-D

Use 0.25 to 0.5 % v/v nonionic surfactant)

Do not use on soils with a pH greater than 7.9

12- to 34-month rotation interval for soybeans
 

2,4-D LVE
1 pt of 4lb/gal product or 2/3 pt 6 lb/gal product

Broadleaf weeds

Hard dough stage

14

Weak on kochia and wild buckwheat

Dicamba
0.5 pt

Broadleaf weeds

Hard dough stage and green color is gone from nodes

7

Do not use treated wheat for seed unless a germination test results in 95% or greater seed germination

Glyphosate
1 qt of 3 lb ae/gal product, 22 fl oz of 4.5 lb ae/gal product

Grasses and broadleaf weeds

Hard dough stage (30% or less grain moisture)

7

Kochia, pigweeds, and marestail may be resistant

Consult label for recommended adjuvants

Not recommended for wheat harvested for use as seed

Carfentrazone (Aim EC, others)
1 to 2 fl oz

Pigweeds, kochia, lambsquarters, Russian thistle, wild buckwheat

 

7

Acts quickly, usually within 3 days
Regrowth of weeds may occur

Use 1% v/v crop oil concentrate
 

Flumioxazin
(Valor)

1.5 to 2 fl oz

Broadleaf weeds

after wheat reaches the hard dough stage and g 30% or less grain moisture

10

Acts quickly, usually within 3 days
Regrowth of weeds may occur
Some residual activity

Use 1 qt/A MSO
May use UAN

Tank mix with glyphosate recommended

Rotation interval depends on rate and soil

Saflufenacil (Sharpen)
1 to 2 fl oz

Broadleaf weeds

Hard dough stage 30% or less grain moisture

3

Acts quickly, usually within 3 days
Regrowth of weeds may occur
Some residual activity

Use 1% v/v methylated seed oil + 1 to 2% w/v AMS or 1.25-2.5% v/v UAN

Rotation interval depends on rate and soil

*PHI = Pre-harvest interval, or days required between application and harvest.


For more detailed information, the “2023 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide is available online at
https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf or check with your local K-State Research and Extension office for a paper copy.

The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.

 

 

Sarah Lancaster, Weed Management Specialist
slancaster@ksu.edu


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