No. 12/June 12, 1998
Postemergence Control of Volunteer Corn in Soybeans
High winds last fall caused a great deal of corn stalk lodging, which has resulted in many soybean fields with a significant volunteer corn problem in 1998. Several effective postemergence herbicides control volunteer corn, but you must know what type of volunteer corn you are dealing with to make the best herbicide selection.
The postemergence grass herbicides used in soybeans are very effective for volunteer corn control. These herbicides include clethodim (Select), quizalofop (Assure II, Matador), fluazifop (Fusilade DX) fluazifop + fenoxaprop (Fusion), and sethoxydim (Poast Plus, Prestige) and are collectively classified as the ACCase-inhibiting herbicides. These products are also very effective against a wide spectrum of annual and perennial grass species. However, if the 1997 corn hybrid was an SR (sethoxydim-resistant) hybrid, control of volunteer plants in 1998 may be only marginal with the postemergence ACCase-inhibiting herbicides. Research has indicated that clethodim may be the most effective ACCase-inhibiting herbicide on volunteer SR corn but may not provide an acceptable level of control.
What are other postemergence herbicide options for control of volunteer SR corn? Glyphosate (Roundup Ultra) is very effective for control of volunteer corn (including SR and Liberty Link) but may be broadcast only on soybean varieties designated as glyphosate resistant (Roundup Ready). Use of Roundup for control of volunteer corn in non-glyphosate-resistant soybean varieties requires selective application equipment (ropewick applicator) that restricts the herbicide from coming into contact with the crop. Several ALS-inhibiting soybean herbicides can also be used to control volunteer SR corn. Imazaquin (Scepter) is often applied at half rate for volunteer corn control. Imazamox (Raptor) controls or suppresses volunteer corn, and imazethapyr (Pursuit) canbe used to suppress volunteer corn. Pursuit also may be tank-mixed with a reduced rate of Scepter to enhance volunteer corn control.
What if the 1997 corn hybrid was an IMI (IR/IT) corn hybrid? In instances where volunteer IMI corn is a problem, Scepter, Raptor, and Pursuit will not provide adequate control. These products may be used for control of certain other grass and broadleaf species but will require a tank-mix or sequential partner to control the volunteer IMI corn. These products may be tank-mixed with one of the ACCase-inhibiting herbicides, but their (Scepter, Pursuit, Raptor) respective labels caution of potential grass antagonism when an ACCase-inhibiting herbicide is included as a tank-mix partner. Roundup Ultra also may be used to control volunteer IMI corn, as may various ACCase inhibiting herbicides.
If the 1997 corn hybrid was either a glufosinate-resistant hybrid (Liberty Link), or not a herbicide-resistant/tolerant hybrid, control of volunteer corn in the 1998 soybean crop can be achieved with the various herbicide options outlined above.
Aaron Hager (firstname.lastname@example.org) and Marshal McGlamery (email@example.com), Crop Sciences, (217)333-4424