By Dwight Lingenfelter
Late season weeds can cause issues with corn and soybean harvest. Consider some of these harvest aid recommendations to manage problem weeds.
As we move into harvest season, producers may notice some problem weed situations. Also, as soybean leaves start to turn yellow, problem weeds may become more noticeable. At this point in the season, it is difficult to do much except for a harvest aid prior to corn or soybean grain harvest. In corn, this type of application requires high clearance equipment or aerial application, so hopefully these fields are the exception and not the norm. Keep in mind, herbicide applications made during this late timeframe are used primarily to help desiccate green weed tissue in order to improve the harvesting process. Contact herbicides are usually better at this process; however, it can vary by weed species. Some of these herbicides are not that effective on large weeds or certain species. Harvest aids are not intended to (and usually do not) help speed up crop maturity. Below is a brief list of products available for late season application or harvest aid for corn and soybeans.
Corn
- Aim 2EC — May be applied 3 days before harvest at 2 fl oz/acre. Use as a harvest aid to desiccate certain broadleaf weeds. Apply in 10 gal/A water. Include necessary adjuvants and make sure spray coverage is sufficient otherwise poor control will result.
- Basagran — No restrictions.
- Defol 5L — Can be applied to desiccate problem weeds in early maturing corn. Apply 4.8 qt/acre, 14 days before harvest in 10-20 gallons/acre water and include appropriate adjuvants. Do not graze treated fields or feed fodder/forage until 14 days after application.
- Impact/Armezon — Can be applied up to 45 days prior to harvest.
- Glyphosate — Up to 0.75 lb ae/acre (32 fl oz of a 3 lb ae/gal formulation) to corn a week or more prior to harvest. Include necessary adjuvants to improve performance. Must be applied to grain when moisture is 35% or less and after maximum kernel fill.
- Gramoxone SL — Apply 1.2 to 2 pt/acre after black layer and at least 7 days before harvest. The higher rate can be used to desiccate mature broadleaves and grasses over 18 inches tall. Be sure to include a nonionic surfactant.
- 2,4–D LV4 — Apply 1 to 2 pt/acre after the hard dough or dent stage. Use higher rates on larger weeds and those under stress. Do not forage or feed corn fodder for 7 days after application.
Soybean
- Aim 2EC — Apply 1.5 fl oz/acre as a harvest aid to desiccate certain broadleaf weeds. Application shall be made when the crop is mature and the grain has begun to dry down and at least 3 days before harvest. Apply in 10 gal/A water. Include necessary adjuvants and make sure spray coverage is sufficient otherwise poor control will result. Do not feed treated soybean forage or hay to livestock.
- Clarity — Apply 8 fl oz to 2 quarts after soybean pods have reached a mature brown color and at least 75% leaf drop has occurred. Wait at least 7 days before harvest. Use a non-ionic surfactant or crop oil concentrate plus nitrogen solution in the spray solution. Do not feed soybean fodder or hay following a preharvest application.
- Defol 5L — Can be applied to desiccate problem weeds in early maturing soybean. Apply 4.8 qt/acre, 7-10 days before harvest in 20 gallons/acre water. No adjuvant is recommended. Do not graze treated field or feed treated fodder.
- Glyphosate — In Roundup Ready soybeans, glyphosate may be applied through flowering (R2 stage) for late season control. For pre-harvest, glyphosate may be applied to Roundup Ready and conventional soybeans after 80% leaf drop (loss of all green color). Apply up to 0.75 lb ae/acre (32 fl oz of a 3 lb ae/gal formulation) in 10-20 gallons of water/acre to control weeds that may interfere with harvest or to control perennials such as quackgrass or Canada thistle but will not control glyphosate-resistant weeds or dry down Roundup Ready varieties. Allow a minimum of 7 days between application and harvest. Use of a non-ionic surfactant plus ammonium sulfate in the spray solution may improve control. Do not graze or harvest the treated crop for livestock feed within 25 days of application. Do not use on soybeans grown for seed.
- Gramoxone SL — Apply 8 to 16 fl. oz/acre plus nonionic surfactant (1 qt/100 gallons of spray) to soybean plants that are mature (65% or more of the seed pods have reached mature brown color or seed moisture is 30% or less. Do not apply within 15 days of harvest and do not graze or harvest for forage or hay.
- Sharpen — Apply 1 to 2 fl. oz/acre after physiological maturity when greater than 50% leaf drop has occurred, and remaining leaves are yellow and at least 3 days before harvest. Include MSO plus AMS or UAN to improve performance.
- A special note on burcucumber
- With the wet weather we have been experiencing this summer in some parts of the state, conditions are ideal for late season burcucumber problems in corn and soybean. Under these conditions, burcucumber can germinate and emerge late into the season and it’s not until it gets above the crop canopy that it is often noticed. This late in the corn and soybean season, Gramoxone is probably the most effective of these options during this time.
Finally, if burcucumber can be harvested with silage and the seeds are immature or still green (i.e., cream or tan colored), the ensiling process will kill the seeds. If the corn or soybean is harvested for grain, the mature seeds will simply end up back in the field (or in the grain) making the problem worse for future years. Also, as you make plans for next season, include no-till in fields that are infested with burcucumber. Research suggests that no-till allows burcucumber seed to remain near the soil surface, thus allowing germination to occur over a shorter time period and reducing the number of germination flushes. This also improves herbicide effectiveness and performance. Also, two-pass herbicide programs are most effective at controlling burcucumber in corn.