Many Iowa fields have significant volunteer corn problems this spring. If dry conditions continue, farmers will need to adjust combines to minimize harvest losses. Volunteer corn in a soybean field can be removed by spraying the right postemergence herbicide. But what do you do when you have volunteer corn in a corn-on-corn field?
"Many continuous cornfields across Iowa have significant volunteer corn problems this spring," says Bob Hartzler, Iowa State University Extension weed management specialist. "Unless this year's corn possesses a herbicide trait not present in the prior corn crop, there are no selective control practices available, other than cultivation. The lack of control options reinforces the value of adjusting combines to minimize harvest losses."
How much can volunteer corn in a cornfield affect corn yields?
That's a common question Hartzler is hearing from farmers this week. "As with any weed, the competitiveness of the volunteer corn is highly variable depending upon the specific situation," he says. He cites research in South Dakota found that volunteer corn densities of 800 to 14,000 plants per acre caused yield losses of 0% to 13%. Iowa State University research found that 1,700 plants per acre (1 plant/10 ft. of 30" row) caused 1.3% yield loss. "If the dry conditions that we are currently experiencing this spring in most of Iowa continue further into the month of June, the impact of volunteer corn on yields will increase," he says. ~~~PAGE_BREAK_HERE~~~ Beware of the dust—it can interfere with postemergence herbicide effectiveness
Beware of the dust—it can interfere with postemergence herbicide effectiveness
Here's another problem some farmers are having during these recent dry and windy days—it's dusty and dust can hinder the effectiveness of postemergence herbicides, says Hartzler. Airborne dust has been shown to reduce the activity of some foliar-applied herbicides; unfortunately, the remedies are few.
Dry soil conditions across many areas of Iowa, Illinois and other states have accelerated both planting of crops and spraying with post-emergence herbicides this spring. It is unusual for such a high percentage of corn acres to already have been sprayed with post-emergence herbicides at this point in the season, and one potentially adverse consequence of very dry soil is the often voluminous dust propelled into the air by application equipment.
"While planting an on-farm research location last week, we noticed a large cloud of dust in the distance," says Aaron Hager, a University of Illinois Extension weed control specialist. "Closer observation revealed that the cloud was being generated by application of a postemergence corn herbicide. The composition and size of the weeds in that field suggested treatment was justified, but reduced weed control could be an outcome of applications made during very dry, dusty conditions."
Airborne dust has been shown to reduce the activity of some foliar-applied herbicides, including glyphosate. Greenhouse research conducted at North Dakota State University (J. Zhou, A. Tao and C.G. Messersmith, 2006, "Soil dust reduces glyphosate efficacy," Weed Science, Vol. 54, pp. 1132-1136) demonstrated that control of nightshade species with glyphosate was reduced when dust was present on plant leaf surfaces.
Glyphosate performance is affected when sprayed in dusty field conditions
The reduced phytotoxicity occurred whether dust was present on the leaf surfaces before glyphosate application or deposited there within 15 minutes, notes Hager. If dust was deposited more than 15 minutes after glyphosate application, or if glyphosate was applied 30 minutes before dust was deposited, reduced phytotoxicity was not reported.
Dust generated from a silty clay soil tended to reduce glyphosate phytotoxicity more than dust generated from a loamy sand soil.
Glyphosate readily adsorbs to soil colloids, whether they are first encountered on the soil surface, suspended in the air (i.e., as dust) above the soil surface, or on the leaf surface of target weeds, explains Hager. Glyphosate adsorbed onto soil colloids is less able to be absorbed into plant leaves, which can result in reduced phytotoxicity.
Remedies for reduced herbicide phytotoxicity caused by dust are few. Spray booms mounted at the front of the sprayer can discharge spray solution before it encounters dust generated from the tires, but dust deposited on leaf surfaces shortly after application has been shown to reduce herbicide performance. Increasing the carrier volume and adding some spray additives to the herbicide in the tank have been shown to reduce, but not eliminate, the deleterious effects of dust. "It's advisable to scout fields that are treated with postemergence herbicides under very dusty conditions to determine the level of weed control," says Hager.