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27
May
2015
How effective are fungicides applied at early growth stages on corn in Arkansas?
Author: Travis Faske, Extension Plant Pathologist

Corn fungicides have been marketed for use on corn at early growth stages of corn (V5 – V7) for the past few years; however, based on university trials, fungicides applied at these early growth stages proved little or no benefit in regards to disease control or yield. Given that some growers may be considering such a fungicide application, now is a good time to review what was observed in the 2014 University of Arkansas foliar corn disease trials.

Figure 1.  Corn at early growth stage where some fungicides are market for use

Figure 1. Corn at early growth stage where some fungicides are marketed for use.

Typically, disease pressure on corn at these early stages of growth is absent, even in wet, cool years like 2014, in Arkansas. Some 18 commercially available corn fungicides were applied at V6, VT, and V6 fb VT application in replicated plots near Pine Bluff. NCLB was observed at low disease incidence at VT and southern rust at R3 stages of growth in these trials. Weather conditions were cool and favored NCLB development, which averaged 5% severity on corn ear leaf of the non-treated control at the end of the season. Fungicides applied at V6 growth stage provided NO benefit for disease control or yield (Fig. 2). Overall, fungicides applied at V6 averaged 2.8 bu/ac lower yield compared to the non-treated control whereas fungicides applied at VT in the presence of disease, protected corn yield potential and contributed to a 12.0 bu/ac yield benefit. Fungicides applied at V6 fb VT application provided a 2.5 bu/ac over the VT application; however, this small increase would not be economically beneficial based on fungicide and application cost at current corn prices. Fungicides applied at VT DO NOT guarantee a yield benefit as similar fungicides applied at VT in 2013 in the absence of any disease had a lower yield than the non-treated control.

Figure 2.  Response of corn yield to fungicides applied at V6, VT, and V6+VT stages of growth.  A low incidence of NCLB was observed at VT stage of growth and southern rust was observed at R3 stage of growth.  Bars with an * were significantly different from the NTC and V6 treatment.

Figure 2. Response of corn yield to fungicides applied at V6, VT, and V6+VT stages of growth. A low incidence of NCLB was observed at VT stage of growth and southern rust was observed at R3 stage of growth. Bars with an * were significantly different from the NTC and V6 treatment.

The TAKE HOME MESSAGE is that fungicides were effective when applied in the presence of a foliar disease and there was no benefit from fungicides applied at V6 stage of growth. The negative yield effect on V6 treated corn was due to yield loss caused by NCLB and southern rust that can in long after these plants were sprayed with a fungicide. Therefore, corn treated at V6 will need to be treated again if disease threatens at reproductive stages of growth as it did in 2014, which increases production cost and lowers profit. These trials will be repeated in 2015 to provide an additional data for final analysis; however, these data for V6 treatments follow the same trend as those observed in 2013 and by other university extension plant pathologists in the Mid-South. Support for these trials was provided by the Arkansas Corn and Sorghum Promotion Board. If you have any questions or comments, please contact Travis Faske (tfaske@uaex.edu).


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