Foliar fungicides in corn

By Kirk Reese, Agronomy Research Manager for DuPont/Pioneer

The use of foliar fungicides in corn production has become a more common practice in recent years. This is largely due to the increased value of the crop and the subsequent interest in protecting or enhancing grain or forage yield. There are factors where the value of corn yield can be enhanced by a foliar fungicide application, which we will discuss in this agronomy update.

During years 2007 to 2011, 475 on-farm trials conducted by Pioneer have shown an average 7-bushel grain yield increase in the presence of a foliar fungicide compared to an untreated check when applied between tassel emergence and brown silk. The economic benefit, or the point where the value of the yield increase was greater than the cost of the fungicide application, occurred 80% of the time when calculated at a corn commodity price of $4 per bushel and application cost of $28 per acre.

Small plot research conducted by Pioneer agronomists showed similar results to the on-farm trials with an 8.9-bushel increase when compared to an untreated check. However, yield results ranged from 0.6 to over 22 bushels per acre, largely dependent on the level of disease pressure at tested locations. Higher levels of foliar disease pressure resulted in increased yield and vice versa. One related factor that influences corn yield response to foliar fungicides is the genetic resistance level to the disease that infects the crop in the field. For example: hybrids with relatively low tolerance to gray leaf spot showed a significantly higher yield response to a foliar fungicide application when compared to other hybrids with a moderate or high level of gray leaf spot resistance.

However if disease pressure is high enough, even the most resistant hybrids will benefit from a fungicide application. Since there are varying levels of disease resistance among corn hybrids, it is important to have the corn product information available from your seed supplier. That will help target fields that may potentially benefit from a fungicide application.

Other considerations are the rotation and tillage practices of each farm and field. For example: disease pressure in continuous corn tends to be higher than fields that were rotated out of soybeans the previous year. Diseases that overwinter in fields, such as northern corn leaf blight, tend to be more prevalent in continuous corn and a labeled fungicide application will provide a greater benefit to the crop at harvest. There are other diseases in corn, such as common rust, that do not survive the winter season and are blown up as spores from the southern U.S., and can infect a corn crop regardless of what crop was grown in the previous year.

Research studies have shown there is an inverse relationship between the intensity of tillage and disease inoculum load, where yield benefits from fungicides were greatest in no-till or reduced tillage and decreased with conventional tillage. This was largely due to the amount of corn residue left on the soil surface, which in turn reduced the amount of disease in the field. Diseases can occur at any time throughout the growing season and in our Eastern Corn Belt environment it is important to scout fields regularly.

It has been observed that with fungicide use there is an increase in grain harvest moisture. Among the on-farm trials conducted by Pioneer, there was a slight increase in moisture (0.3 points wetter) when treated with a fungicide. One reason for increased moisture in fungicide treated corn is that disease pressure of untreated corn may be high enough to cause premature death of the plant. In these cases, the yield increase was high enough to more than offset drying costs at harvest. Hybrid maturity and planting date also have an influence on foliar disease pressure. Later planted fields tend to be more vulnerable to late season foliar diseases since timing of grain fill occurs more closely to the time that disease pressure is greatest later in the growing season. As always, please read and follow all fungicide label directions. Some fungicides have specific application timings that if not followed, could result in a negative impact on yield.



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