October 1, 2010

Recent severe hail events in parts of Nebraska have left some fields with tremendous yield loss from hail stones beating down corn plants, knocking ears from plants, or shelling seed from the cob. Corn ears or seed that cannot be harvested may become a significant weed problem in the subsequent crop. For example, if a field was going to produce 175 bu/ac, and severe hail damage resulted in a 50% yield loss, there may be up to 7.1 million seed per acre on the ground as shelled seed or whole ears (assuming 81,000 seeds in a bushel and a 88 bu/ac yield loss). Of course, the number of viable seeds will be reduced before spring planting by fall germination, predation by insects and mammals, and fungal diseases. However, there will still be many viable seeds the following spring.

Earlier this year, we posted a CropWatch article about the competitive ability and control of volunteer corn. It also highlighted how volunteer corn may reduce the value of soybean as a rotational crop to break pest cycles. This current article discusses issues to consider so you are prepared to manage volunteer corn before it causes yield loss or excessive expense to your crop production in 2011.

A warm moist fall will encourage germination of volunteer plants and the first hard freeze will control them. Neither herbicide control nor tillage is recommended for control of volunteer plants in the fall. Shallow tillage in the fall or spring may “plant” the seed, increasing the problem in the subsequent crop. At a recent meeting of Extension weed scientists, a colleague described a situation where a producer had significant fall harvest loss of a Roundup Ready® corn variety. The producer did his normal tillage (field cultivation) the following spring and planted the field to Roundup Ready corn shortly afterward. While the tillage did kill emerged volunteer corn, it also “planted” other volunteer seeds, resulting in a Roundup Ready volunteer corn population of approximately 500,000 plants per acre. There was no way to remove the volunteer plants from the planted Roundup Ready corn crop and the producer eventually had to destroy his first planted crop.

Rotating to Soybeans

The first step in successfully managing volunteer corn in soybean is to consider the herbicide trait(s) of the volunteer seed and the herbicide trait of your soybean variety. Table 1 outlines the options for control when rotating to soybeans. Rotating to soybeans is highly recommended following extensive harvest losses in the previous corn crop because ACCase herbicides effectively control traited volunteer corn plants. Tankmixing an ACCase herbicide, such as Assure II®, Fusilade® DX, Fusion®, Select®, Select Max® or a generic equivalent should be done with the first postemergence application to minimize early season competition and yield loss from volunteer corn. ACCase herbicides cannot be used postemergence in corn or other grass crops because they will kill the crop.

Rotating to Corn

Control of volunteer corn in corn is more complicated. Again, knowing the trait(s) of the volunteer corn and the traits in the corn hybrid you intend to plant is essential (Table 2). Glyphosate will provide excellent control of conventional or Liberty Link® volunteer corn. Control of Roundup Ready or conventional volunteer corn using Ignite herbicide varies depending on volunteer corn size and environmental conditions. If the volunteer corn is stacked Roundup Ready and Liberty Link, inter-row cultivation is the only option for postemergence control.

When corn is planted two or more consecutive years in a no-till setting, it may be necessary to apply a burndown application to control Roundup Ready or Roundup Ready + Liberty Link volunteer corn prior to planting. The only ACCase herbicide labeled for burndown application prior to corn planting is Select Max (up to 6 oz/ac), which has a supplemental label allowing application up to six days prior to corn planting. While this can effectively control emerged volunteer Roundup Ready corn before planting, there are no selective postemergence herbicide options should the volunteer Roundup Ready corn continue to germinate after planting. The corn planting interval is four months after an Assure II application, two months after a Fusilade DX application, two months after a Fusion application, and one month after a Select, or generic equivalent, application.

Rotating to Sorghum

Volunteer corn control in sorghum is also difficult. There are no postemergence herbicide options to control any type of volunteer corn in sorghum. Inter-row cultivation is the only postemergence control option. If rotating to sorghum is necessary, a producer should allow the volunteer corn to germinate and then destroy it with preplant tillage, or with glyphosate if the volunteer corn is not Roundup Ready. Delayed planting may be necessary to allow time for maximum volunteer corn germination.

Volunteer Soybeans in Corn

Hail events are also capable of shattering soybean pods and scattering seed. Since over 90% of the soybeans planted in Nebraska are Roundup Ready, using an effective herbicide other than glyphosate will be necessary for control of volunteer soybean. Many of the common corn pre-emergence herbicides (products containing atrazine, mesotrione, or isoxaflutole) will control volunteer soybeans. An early postemergence application of a growth-regulator product (e.g. 2,4-D or dicamba) or HPPD (e.g. Callisto, Laudis, or Impact) herbicide also will effectively control volunteer soybeans.

Lowell Sandell
Extension Educator – Weed Science
Mark Bernards
Extension Integrated Weeds Specialist