Last August and September many were disappointed in the grass and vine infestations present at corn harvest in some fields. Often, these weed infestations emerged after PRE applied or early POST applied herbicides had played out. They grew very little until August and as the corn dried down and light became more available those established weeds started rapidly growing.
The vines in question are often ivyleaf and pitted morningglories and/or burcucumber. The grass species of note are junglerice, barnyardgrass, goosegrass and fall panicum. Since these weeds often establish after PRE or early POST herbicides have given out, a good strategy is to delay the typical POST application from V3 or V5 (< 12″) corn until V6 to V8 (>12″).
The herbicides of choice are those that can be applied to these later corn growth stages and provide residual control on these weeds. Two good options are Acuron GT and Capreno.
The strategy should begin with starting clean with either tillage or a burndown with Gramoxone 32 oz + Bicep 67 oz or Glyphosate 32 oz + Verdict 10 oz or Glyphosate 32 oz + Leadoff 2 oz. If no residual is used with the burndown consider applying a herbicide Group 15 (Dual Magnum II, Warrant, Zidua, etc) + atrazine PRE. Then….
Option 1. Acuron GT (Dual II Magnum + Callisto + bicyclopyrone + glyphosate) 3.75 pt. Can be applied up to 8 leaf tall corn. Be sure to add an NIS surfactant at a rate of 2 pts/100 gal. This herbicide is fairly new and is essentially Halex GT with the HPPD inhibitor bicyclopyrone replacing atrazine. The bicyclopyrone will provide better residual control of most weeds than one could expect from atrazine.
Option 2. Capreno (tembotrione + thiencarbazone) 3 oz + glyphosate 32 oz. Can be applied up to 7 leaf tall corn. Always add COC at a rate of 1.25 pts/100 gal. This herbicide has been around for a few years and has proven to have better residual control of vines than some other corn herbicide premixes. Much of that is provided by the thiencarbazone.
Atrazine is not a tankmix option since the corn is over 12” tall at V6 to V8. However, 4 ozs of Status tankmixed with either Acuron GT or Capreno will help both knockdown of existing vines and residual control of those weeds as well. Status can be applied up to 36” tall corn. Please keep in mind this strategy of later application can be easier to write than execute in the field. Applications after the label cutoffs can hurt corn pollination and grain set. In general, the later the application after the labeled maturity cut offs the higher the probability of poor pollination.