In 2011, University of Kentucky set up 3 commercial-scale, on-farm fungicide tests in fields of yellow and white corn in West Kentucky. A single fungicide application resulted in 20+ bushel yield increases in 2 of the 3 tests. Improved stalk strength was also observed in one of the trials. Surprisingly, all of this occurred in the absence of significant disease pressure. It's important to note that in one of those 2 trials, the fungicide application included an insecticide, so researchers can't be sure how much of the yield increase was due to the fungicide. More information from those trials is available here. 

The researchers wanted to repeat those experiments to see how robust their results were. This past summer they completed 3 commercial-scale, replicated fungicide trials. Results for each trial are shown in the tables below. In order to interpret the tables, here are some facts:

  • “GLS,” “NLB,” and “SR” refer to gray leaf spot, northern leaf blight, and southern rust, respectively.  Foliar disease severity was assessed collectively in each trial, at black layer. 
  • “Error (%)”shows the risk of being wrong if you conclude that the application treatment was different from the untreated check. (This is the P-value X 100.)
  • “CV%” is a statistical measure of the amount of variation in the trial.  The higher the value the greater the variation.

Summary of Results

Trial I: The pesticide application, which included Headline AMP fungicide, Bio-Forge (marketed as a stress reliever), Silencer insecticide, and a spray adjuvant, provided an increase of 6 bushels per acre (with a 1% error rate), even though disease pressure was low (Table 1). In this trial, the costs of the several spray products plus spray application would very likely exceed the income from the additional corn, if the price of corn is at $4.00 per bushel.  

Figure 1. Trial I, yellow corn (Pioneer P2088YHR) on 20-inch rows, following wheat/double-crop soybeans. Pesticide application at brown silk (R2) included Headline® AMP 10 fl oz, + Silencer 3.2 fl oz (insecticide) + Bio-Forge 8 fl oz (antioxidant) + Frontpage 1 fl oz (spray adjuvant).

Trial II: An increase of 12 bushels per acre was observed from the pesticide application (Table 2). That conclusion is based on a high — though not unreasonable — error rate of 16%. Trial II included Headline AMP fungicide, two insecticides, a foliar nitrogen product, Bio-Forge, and a spray adjuvant. While it is not clear which component(s) in the pesticide application may have contributed to the yield difference, disease pressure was moderate in this trial. Thus, it seems reasonable that the fungicide played a significant role in contributing to yield, by protecting the crop from losses due to fungal diseases of the foliage. If corn is at $4.00 per bushel, it seems possible that the added income of an additional 12 bushels per acre might exceed the cost of all products used plus the application cost, but not by much.

Figure 2. Trial II, yellow corn (Pioneer P1498HR) on 20-inch rows, following wheat/double-crop soybeans.  Pesticide application at late silking (R1) included Headline® AMP 10 fl oz, + Prevathon 14 fl oz (insecticide) + N-Spire 128 fl oz (slow-release foliar N; includes salicylic acid) + Silencer  3.2 fl oz (insecticide) + Bio-Forge® 8 fl oz (antioxidant) + Frontpage 1 fl oz (spray adjuvant).

 

Trial III: An increase of 10 bushels per acre resulted from the pesticide application, with an error rate of 7%. Trial III included Headline AMP fungicide, insecticide and surfactant. As in Trial II, it is not clear which component(s) of the spray mix affected yield. However, a disease severity of 11% in the untreated check at black-layer is certainly enough to impact yield negatively. Thus, it seems likely that the fungicide had a positive impact on yield by protecting against foliar diseases. Because of the premium associated with white corn, the yield increase may have offset the cost of the products plus spray application.


Figure 3. Trial III, white corn (Pioneer P32B10) on 30-inch rows. Pesticide application at R1 included Headline® AMP 6 fl oz, + Protyx 0.5 fl oz (surfactant) + Warrior with Zeon 1.5 fl oz (insecticide).

Conclusion

Across the country, corn pathologists agree that fungicides are most likely to provide a benefit under conditions of moderate to severe pressure from key disease diseases. University of Kentucky's results from 2013 affirm that guideline. This is because 2 of the 3 trials had enough disease pressure that fungicide application very likely provided an economic benefit in corn grown for grain, especially for the test in white corn. In contrast, researchers saw in 2011 that substantial increases in yield and stalk health were sometimes (but not always) possible from a fungicide application even in the absence of significant disease. This is consistent with the experience of some producers, who believe they are getting substantial agronomic benefits rather consistently.   

If a producer is still undecided about whether fungicide applications have a place in their production system, they should consider leaving several untreated strips in an otherwise treated field. This will help them see for themselves whether yield is increased under their farming conditions.

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