In previous eUpdate articles, we’ve discussed pre-harvest herbicide applications for winter wheat. However, we do occasionally need to consider weed management options to enable harvest of grain sorghum and other summer crops. In some cases, these products may be used to help the crop mature faster, but in most cases, herbicide applications are intended as a “rescue” treatment that will manage weeds to make harvest more efficient. In these situations, weeds are generally too large for control of Palmer amaranth or kochia. However, pre-harvest herbicide applications may improve weed control of perennial weeds such as johnsongrass in the next crop. Other factors to consider include maximum annual use rates for each product, crop damage caused by wheel tracks (if using a ground rig), and product approval for aerial application (if using an airplane, helicopter, or drone).
Some herbicides labeled for pre-harvest applications in corn, grain sorghum, and soybeans are listed in Table 1. All harvest-aid applications should be made after the crop reaches physiological maturity
Table 1. Selection of herbicides labeled for pre-harvest applications in corn, grain sorghum, and soybeans.
|
Active ingredient (Herbicide group) |
Herbicide |
Rate |
Preharvest interval |
Comments |
|
PRODUCTS LABELED FOR CORN |
||||
|
2,4-D (4) |
Several |
1 to 2 pt LV4 |
7 days |
Appy after denting, when silks are brown. Do not feed fodder for 7 days after application. |
|
Carfentrazone (14) |
Aim |
1 to 2 oz |
3 days |
Apply when the crop has begun to dry down. Apply with NIS or COC. AMS or UAN may be added. Contact herbicide that requires excellent spray coverage for control |
|
Glyphosate (9) |
Several |
Varies with product and type of application; up to 0.75 lbs a.e. |
7 days |
Apply when grain moisture is 35% or less. Will not control resistant populations of Palmer amaranth or kochia. |
|
Paraquat (22) |
Gramoxone, others |
0.8 to 1.3 pt of 3 SL product |
7 days |
Apply after black layer has formed. Apply with NIS. Contact herbicide that requires excellent spray coverage for control |
|
Saflufenacil (14) |
Sharpen |
1 to 2 oz |
3 days |
Apply when the crop has reached physiological maturity. Apply with MSO and AMS, or UAN. Contact herbicide that requires excellent spray coverage for control. |
|
PRODUCTS LABELED FOR COTTON |
||||
|
Carfentrazone (14) |
Aim |
Up to 1.6 fl oz |
7 days |
Apply at 60 to 70% open bolls. Apply with NIS or COC. AMS or UAN may be added. Contact herbicide that requires excellent spray coverage for control |
|
Paraquat (22) |
Gramoxone, others |
0.7 to 1.3 pt of 3 SL product |
7 days |
Apply when 75% or more bolls open. Apply with NIS. Contact herbicide that requires excellent spray coverage for control. |
|
Saflufenacil (14) |
Sharpen |
0.5 to 2 oz |
5 days |
Apply when the crop has reached physiological maturity. Apply with MSO and AMS, or UAN. Contact herbicide that requires excellent spray coverage for control. |
|
PRODUCTS LABELED FOR GRAIN SORGHUM |
||||
|
Carfentrazone (14) |
Aim |
Up to 1 fl oz |
3 days |
Apply with COC or MSO; AMS or UAN may be added. Contact herbicide that requires excellent spray coverage for control |
|
Glyphosate (9) |
Several |
Varies with product and type of application |
7 days |
Apply after physiological maturity. Will not control resistant populations of Palmer amaranth or kochia. |
|
PRODUCTS LABELED FOR SOYBEANS |
||||
|
Carfentrazone (14) |
Aim |
Up to 1.5 fl oz |
3 days |
Apply with COC or MSO. AMS or UAN may be added. Contact herbicide that requires excellent spray coverage for control. Do not feed treated plants to livestock. |
|
Dicamba (4) |
Several |
8 to 32 fl oz |
7 days |
Apply when soybean pods are brown and at least 75% of leaves have dropped. Apply with NIS or COC and AMS or UAN |
|
Glyphosate (9) |
Several |
Varies with product and type of application |
7 or 14 days, depending on the product |
Apply after 80% leaf drop and pods have lost all green color. Apply with AMS. May be applied with NIS. Will not control resistant populations of Palmer amaranth or kochia. Do not graze or feed within 25 days of application. |
|
Paraquat (22) |
Gramoxone, others |
5.4 to 10.7 fl oz |
15 days |
Apply when at least 65% of pods are brown or seed moisture is 30% or less. Apply with NIS. Contact herbicide that requires excellent spray coverage for control. Do not feed treated plants to livestock. |
|
Saflufenacil (14) |
Sharpen |
1 to 2 oz |
3 days |
Apply when greater than 65% brown pods and greater than 70% leaf drop with seed moisture of 30% or less. Apply with MSO and AMS, or UAN. Contact herbicide that requires excellent spray coverage for control. Do not graze or feed treated plants to livestock. |
For more detailed information, see the “2025 Chemical Weed Control for Field Crops, Pastures, and Noncropland” guide 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. Users should read and follow all label directions.
Sarah Lancaster, Extension Weed Science Specialist
slancaster@ksu.edu
Jeanne Falk Jones, Northeast Area Agronomist
jfalkjones@ksu.edu