Downed corn from the August 10 Derecho, which affected millions of acres in Iowa, will contribute to significant volunteer corn populations in crop fields in 2021. Volunteer corn ranging from 800 to 13,000 plants per acre can cause yield losses up to 54% in soybean and up to 13% in corn, according to the research conducted at SDSU, UMN, and UNL. In unharvested corn fields, establishment of 1% of the corn seed present would result in volunteer corn populations of more than 100,000 plants per acre. Besides crop yield losses, volunteer corn can increase the severity of corn rootworm and diseases. Therefore, it is important to develop proactive plans to control volunteer corn starting this fall.
Fall management: Much debate exists over the use of tillage or no-till to manage volunteer corn populations. Fall tillage operations to size residue in Derecho-affected corn fields can potentially increase the soil-seed contact and promote germination of corn seeds this fall. This strategy will expose emerged corn seedlings to winter kill, thereby help in mitigating volunteer corn in the following year. Any seed that is not incorporated into the soil and left on the surface is less likely to germinate due to lack of soil-seed contact and vulnerability to seed predation/decay.
Crop rotation: From a management standpoint, the best option for storm-damaged corn fields this year would be to rotate to soybean next year. Control of volunteer corn is easier in soybean compared to corn because a number of Group 1 herbicides are labeled for use in soybean (Table 1).
Preplant options in the spring: Non-selective herbicides such as Gramoxone SL (paraquat) can be used to kill volunteer corn (Roundup Ready/Liberty Link) before soybean planting. Shallow spring tillage (field cultivation) can kill emerged volunteer corn, but it will also move corn seeds into the soil causing emergence of volunteers later in the season. Delayed planting in fields with the potential for high volunteer corn populations will allow much of the seed to germinate prior to planting, therefore reducing populations that need to be dealt with after crop establishment.
Management in soybean: Below are the list of Group 1 grass herbicides (Accase inhibitors) that can be used to control corn volunteers in soybean.
|Select Max 0.97EC||6-12 fl oz|
|Clethodim 2EC||4-6 fl oz|
|Assure II/Targa 0.88EC||4-8 fl oz|
|Fusilade DX 2EC||4-6 fl oz|
|Poast||12 fl oz/a|
To reduce early-season crop competition, it is recommended to apply these products when emerged volunteer corn is 12 inches or less. Consult the product label for appropriate adjuvants (NIS, COC, MSO) to enhance the activity of these products for controlling volunteer corn in soybean.
Fields that were planted to Roundup Ready only or conventional corn can be planted to LibertyLink, stacked LibertyLink + Roundup Ready hybrid, or Enlist E3 soybean in the next spring as Liberty provides effective control of volunteer corn. Two applications of Liberty, each of 32-43 fl oz/acre, are recommended in LibertyLink soybean. Group 1 grass herbicides (Table 1) will be the only option for controlling volunteer corn in Roundup Ready or Roundup Ready 2Xtend soybean.
Management in corn: If a Roundup Ready only corn was planted this season, switching to LibertyLink or stacked LibertyLink + Roundup Ready hybrid would be an option for 2021. Liberty can be used to control Roundup Ready volunteer corn. Two applications of Liberty, each of 32-43 fl oz/acre, can be made in LibertyLink corn.
If the previous year’s corn was Roundup Ready + LibertyLink hybrid, Enlist corn can be a viable option to consider. Enlist corn is a new trait with stacked resistance to 2,4-D choline, glyphosate, and ‘fop’ grass herbicides. Assure II (quizalofop-p-ethyl) is the only grass herbicide labeled to control volunteer corn in Enlist Corn. It can be applied at 5 to 12 fl oz/acre in Enlist Corn for selective control of Roundup Ready + LibertyLink volunteer corn. Assure® II should include COC (1% v/v) or NIS (0.25% v/v) and should be applied to corn at V2 through the V6 stage.
Overcoming grass herbicide antagonism with broadleaf herbicides: For in-season weed control, grass herbicides listed in Table 1 are often tank-mixed with broadleaf herbicides, which may cause antagonism leading to inadequate control of grasses, including volunteer corn in soybean.
Antagonism generally can be avoided by applying a higher rate of the grass herbicide in the tank-mix or applying the grass herbicide one or more days before or 7 days after the broadleaf herbicide. In Figure 1, increasing the rate of clethodim or quizalofop-p-ethyl from 0.02 to 0.04 lb ai/acre overcame the decreased control of volunteer corn from adding dicamba (broadleaf herbicide) to the tank. In a research conducted at NDSU (Rich Zollinger), addition of adjuvants did not overcome the antagonism of clethodim with dicamba, except for AMS which is NOT labeled for use with Xtendimax or Engenia products.