by Jourdan Bell, Assistant Professor and Extension Agronomist, Amarillo, Texas; Peter Dotray, Professor and Extension Weed Specialist, Lubbock Texas
Volunteer corn can be a significant problem in corn:cotton rotations under all tillage systems, but especially in no-till and limited tillage systems. Volunteer corn can result from grain loss at harvest due to poorly adjusted combines, late season hail damage, hybrid selection with poor ear retention, and/or lodged corn plants that dropped corn. If ear rots are present during the corn phase of the rotation, producers may opt to intentionally adjust the combine to discard low weight kernels during harvest. Low weight kernels will over winter and may still be viable to germinate the following spring.
In a cotton rotation, volunteer corn can become a significant challenge to the developing cotton crop. Like all weeds, volunteer corn uses water and nutrients in addition to shading young cotton plants all of which may affect cotton stand and reduce cotton lint and quality. Additionally, dense populations of volunteer corn may reduce cotton harvest efficiency by clogging harvest machines and even increase the risk of harvest equipment fires.
Volunteer corn begins to germinate in conjunction with cotton germination. In instances when the ears are poorly shelled, kernels often do not germinate until irrigation is initiated for cotton planting resulting in simultaneous emergence of both cotton and volunteer corn. Because Texas High Plains cotton is planted in May, there is not sufficient time to allow germination and termination of the volunteer corn prior to cotton planting. There are few herbicide options for control of volunteer corn in cotton. Most cotton and corn varieties are glyphosate (Roundup) and/or glufosinate (Liberty) resistant. Planting stacked herbicide traits results in the inability to control volunteer corn in a cotton crop using either a glyphosate or glufosinate herbicide. For producers who maintain a corn-cotton rotation, ordering corn hybrids without the Liberty Link trait would provide the opportunity to spray glufosinate to control volunteer corn. However, in many cases planting decisions change due to markets, environmental conditions, and even weather forecasts so in-season herbicide options must be evaluated. Trifluralin (Treflan) is a preplant herbicide labeled for volunteer corn in cotton. In no-till and limited tillage systems, trifluralin needs to be chemigated, but under conventional production, trifluralin is mechanically incorporated. Trifluralin provides good weed control, but in the event of a cotton crop failure, northern Texas High Plains producers have restricted plant back options. When using trifluralin in regions of Texas where annual irrigation plus precipitation is 20 inches or less, there is an 18-month plant back to grain sorghum and a 5-month plant back to corn.
A timely postemergence herbicide application is recommended when corn is 5- to 12-inches tall using a labeled herbicide with grass activity (Table 1). For labeled herbicides with grass activity, there are in-season rotational restrictions for grain crops, but rotational restrictions will not carry over into the following cropping season. Postemergence herbicides are the most effective option for control of volunteer corn in no-till and limited-tillage fields because preemergence herbicides are dependent on rainfall or irrigation to properly “activate” (move) the herbicide into the weed seed zone where they disrupt seedling development.
Table 1. Postemergence herbicide options for control of volunteer corn in cotton.
|Herbicide||Active Ingredient||Rate/Acre||Application Considerations||Rotational Restriction(s)*|
|Assure II (Targa)||quizalofop||5 to 8 fl oz||Labeled for 5 to 30-inch volunteer corn. Requires the use of a crop oil or a non-ionic surfactant. Tank mix with a broadleaf herbicide may reduce activity on corn.||120 days to corn, sorghum, or cereals|
|Fusilade DX||fluazifop||6 to 24 fl oz||Do not apply more than 48 fl oz/A per season. Requires the use of a crop oil or a non-ionic surfactant. A liquid nitrogen adjuvant enhances activity. Do not apply after boll set.||60 days to corn, sorghum, or cereals|
|Fusion||fluazifop + fenoxaprop||12 fl oz||Do not apply more than 24 fl oz/A per season. Labeled rate for volunteer corn in cotton west of I-35 in Texas. Labeled for 8 to 12-inch corn not to exceed 6-leaf corn.||60 days to corn, sorghum, or cereals|
|Select 2EC (Select Max, Vaquero)||clethodim||6 to 16 fl oz||Do not apply more than 64 fl oz/A per season. Use a crop oil concentrate. Use of AMS improves grass control. Tank mixing with a broadleaf herbicide may reduce (antagonize) grass control.||30 days to corn, sorghum, or cereals|
|Poast||sethoxydim||1.5 pts||In Texas, labeled for corn 12-inches or less. Incompatibility reduces grass control or may enhance crop injury. Do not tank mix Poast with other herbicides or insecticides. Use methylated seed oil or crop oil concentrate. Use AMS to improve grass control.||30 days to corn, sorghum, or cereals|
|*Refer to the label for additional restrictions.|
|Always carefully read and follow pesticide labels; the label is the law.|