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Extension > Agriculture > Crops > Corn Production >Pest management > Control volunteer corn for yield protection and corn rootworm management

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Control volunteer corn for yield protection and corn rootworm management

Lizabeth Stahl, Extension Educator – Crops; Bruce Potter, IPM Specialist; and Jeff Gunsolus, Extension Agronomist – Weed Science

Stalk lodging or breakage, dropped ears, and kernel loss during harvest can result in volunteer corn the following year. Volunteer corn populations can be significant in fields affected by storm damage, disease, root and stalk feeding insects, or environmental stresses. Improperly adjusted combines and header shatter losses of very dry grain can also create volunteer corn problems. Control of volunteer corn is important not only to help protect yield potential, but also to aid in the long-term management of corn rootworm (CRW).

Volunteer corn can affect yield

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Plants may not emerge uniformly from dropped ears, and coverage of all plants in clumps with a postemergence herbicide may be difficult.

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Volunteer corn can be a significant issue from not only a weed management standpoint but also a corn rootworm management standpoint.

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High populations of volunteer corn in corn may warrant control. Volunteer corn populations in corn needed to be at least 8,000 plants per acre before yield losses were reported in U of MN trials (2007-2008). Volunteer corn in corn may also play a role in selecting for resistance in corn rootworm.

Volunteer corn can significantly reduce soybean and corn yield, although research indicates that volunteer corn is less competitive in corn than in soybean. For example, researchers at South Dakota State University found that populations of volunteer corn ranging from 800 to 13,000 plants per acre resulted in yield losses of 0 to 54% in soybean and 0 to 13% in corn. Researchers from the University of Nebraska reported similar results where volunteer corn populations of 3,500 and 7,000 plants per acre reduced soybean yield 10 and 27%, respectively, while corn yields were reduced 2 and 5%, respectively.

Nebraska researchers also found that volunteer clumps were more competitive than individual plants. In soybean, 3,500 clumps of corn per acre reduced yield 40% while the same population of individual plants reduced yield 10%. In corn, a volunteer population of 7,000 clumps per acre reduced yield 14% while the same population of individual plants reduced yield 5%. Note that the total number of plants per acre would have been greater in the volunteer clump treatments than in the individual plant treatments, as numerous plants typically emerge from a volunteer clump.

In University of MN trials conducted in 2007 and 2008, volunteer corn populations had to reach at least 8,000 plants/acre before yield was reduced an average of 8%. Although this population did not consistently result in a yield loss, this level of infestation could be used as a guide to help determine at what point control of volunteer corn in corn is warranted to protect yield.

Even though volunteer corn in corn could potentially help offset yield losses by contributing to yield, University of MN researchers found volunteer corn plants typically lagged one to six leaf stages behind the hybrid corn and that volunteer plants at lower populations often had small ears, if any, with poor seed set. At high populations, volunteer plants were typically barren.

Volunteer corn can affect corn rootworm (CRW) management

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Volunteer corn plants that survive to silk will attract female CRW beetles into fields to feed and lay eggs, negating the beneficial effect of rotating out of corn in the management of CRW.

Most of the hybrid corn planted today carries traits for resistance to not only herbicides but also to insects such as CRW. Roughly 75% of the volunteer corn plants from a CRW-resistant hybrid can be expected to carry the Bt-CRW trait. This poses a challenge in the management of CRW and in the management of resistance to Bt-CRW traits.

Performance issues in Bt-CRW corn were first reported in MN in 2009, but the scope and intensity of complaints increased markedly in 2012. To date, these performance issues are confined to the western corn rootworm (WCRW). Significant Bt-CRW control issues with the more common northern corn rootworm (NCRW) have not been documented. Fortunately, the WCRW variant that lays eggs in soybeans has not been documented in Minnesota. Additionally, unlike NCRW, the WCRW does not exhibit significant extended diapause (egg hatch is delayed for one or more years).

While small CRW larvae may survive on the roots of seedling corn and some grassy weeds, the larvae require nodal corn roots to complete development. This is a key reason why rotating to a non-host crop such as soybean is the most effective CRW management option in fields with Bt-CRW performance issues.

Crop rotation, however, is only successful in managing CRW when volunteer corn populations are minimized the following year. In soybean, volunteer corn nullifies the benefit of crop rotation in CRW management. Larvae are able to feed and mature, and late- pollinating volunteer corn is very attractive as a feeding and egg-laying site for CRW beetles. As a result, the presence of volunteer corn in soybean creates the potential for CRW problems in the field the following year.

The current Bt-CRW events are considered low dose and allow some larvae to develop to the adult stage. Consequently, some CRW larvae should be expected to feed and survive on volunteer plants the following year. Not all plants will express the Bt toxin, but those that do have been shown to express the Bt toxin at variable and reduced levels.

Researchers from Purdue University demonstrated that WCRW larvae were able to feed on roots of volunteer corn testing positive for the Cry 3Bb1-Bt toxin at levels similar to plants testing negative for the Bt toxin. WCRW beetles also emerged from volunteer plants that expressed the Bt toxin.

Chronic exposure of CRW larvae in soybean and corn to sub-lethal doses of the Bt toxin also has the potential to hasten development of resistance to Bt-CRW traits.

Volunteer corn in corn reduces the effectiveness of rotating corn genetics. Additionally, volunteer corn in soybean minimizes the benefits of crop rotation. In addition to CRW, other insect and disease problems might be increased because of volunteer corn.

Early control of volunteer corn in soybean is critical

Controlling volunteer corn while it is small prevents soybean yield losses from competition and provides integrated pest management benefits as well. The nodal root system, needed for larvae to mature, begins to develop at the V6 stage of corn. Controlling volunteer corn by the V4 to V5 stage will result in the starvation and death of CRW larvae.

Early control will also remove volunteer corn before it can become a feeding and egg laying site for CRW adults later in the season. More than one herbicide application may be needed to control later-emerging volunteer corn.

Volunteer corn control options

Control of volunteer corn is complicated by the fact that most hybrids contain at least one herbicide resistant trait, if not more. For example, if a Roundup Ready (RR) hybrid was planted the previous year, glyphosate will not control volunteer corn the following year. Likewise, glufosinate (i.e. Liberty) will not kill volunteer corn where a hybrid carrying the LL trait was planted the previous year.

Many hybrids are now stacked with both resistance traits (LL/RR), so volunteer corn from these hybrids will not be controlled by glyphosate or glufosinate. However, volunteer RR corn can be controlled with glufosinate, and volunteer LL corn can be controlled with glyphosate. Volunteer conventional corn can be controlled with glyphosate or glufosinate.

Volunteer corn control in soybean

There are a number of effective options to control volunteer RR, LL, RR/LL or conventional corn in soybean (Table 1). Note that herbicide rates needed for control of volunteer corn are lower when volunteer corn plants are smaller at the time of application.

Activity of the herbicides listed in Table 1 is maximized by the use of crop oil concentrate (COC) or methylated seed oil (MSO) plus ammonium sulfate. Control can be more variable when these herbicides are mixed with a glyphosate product that contains surfactants in the absence of COC or MSO. In some cases control can be also be reduced when these products are applied with a postemergence broadleaf herbicide. Refer to the pesticide label or product literature for specific recommendations regarding additives and tank-mix partners.

Table 1: Postemergence herbicides for control of volunteer corn in soybeans.
Product Volunteer Corn Size Rate/acre

Source: Dr. Bill Johnson, Extension Weed Scientist, Purdue University.

Select Max Less than 12 inches 6 oz.
12 to 24 inches 9 oz.
Clethodim (Arrow/Section) 4 to 12 inches 4 oz.
12 to 18 inches 6 oz.
Assure II / Targa 10 to 12 inches 4 oz.
12 to 18 inches 5 oz.
18 to 30 inches 8 oz.
Fusilade DX Less than 12 inches 4 oz.
12 to 18 inches 6 oz.

To protect soybean yield and manage for CRW, control volunteer corn by the V4 to V5 Stage.

Volunteer corn control in corn

Control options for volunteer corn in corn will be limited if the volunteer corn contains the RR, LL, or RR/LL traits. Depending on what trait(s) were in the hybrid planted the previous year and the current year, cultivation may be the only viable option.



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