Since 2005, the more typical corn fungicide application timings have occurred when corn begins to tassel, between VT and R1. However, over the past few years, aggressive marketing campaigns have shifted application strategies to vegetative-stages that range between V4 and V7 (depending on the literature and more specifically when the last over-the-top herbicide application may occur). Data from university plant pathologists throughout the U.S. is lacking regarding earlier application timing strategies. During 2012, the Mississippi Corn Promotion Board funded a project whereby fungicides were applied at vegetative timings (V6) in two different corn production systems. Applications were made in Stoneville, MS in a field where continuous corn had been produced for five seasons but disease pressure has been limited. The second location was west of Greenwood, MS and has had continuous corn production for more than six years with excessive gray leaf spot (GLS) pressure.
Seven different fungicides were applied (3 strobilurin products (Evito (4 oz), Headline (6 oz), Quadris (6 oz)), 3 pre-mix (strobilurin + triazole) products (Headline AMP (10 oz), Quilt Xcel (10.5 oz), Stratego YLD (4 oz)), and a 1 triazole product (Tilt (4 oz))) representing the major fungicide products used in corn production systems throughout the Mid-southern U.S. Fungicides were applied both with and without glyphosate (22 fl oz/A of Roundup PowerMax) to serve as the adjuvant at the vegetative timing since the specific formulation is a “loaded” herbicide. All applications were made at a general application rate of 15 gallons per acre. Two different strategies were employed: one whereby the full rate of the product was applied in a vegetative application and one whereby a half rate of the fungicide was applied at the vegetative timing followed by a half rate at the traditional tassel timing. Applications were also made to compare the differences between a vegetative application (V6), a tassel application (R1), and a vegetative followed by a tassel application (V6 fb R1). This update will only pertain to the vegetative stage application timing and a second piece will cover the effect of a vegetative application on green snap.
Stoneville, MS Location:
In general, when averaged together, yield differed between fungicide treated and the control. Fungicide performance at the Stoneville location (Figure 1A, 1B Figure 1 – Stoneville, MS corn fungicide project) was not consistent between products applied either with glyphosate at V6 or without glyphosate. Disease incidence during the 2012 growing season in Stoneville was low. However, limited disease pressure from common rust, northern corn leaf blight, and southern corn rust was observed in plots but generally speaking was less than 5%.
Greenwood, MS Location:
Similar to the Stoneville location, trials conducted west of Greenwood with the same products applied using the same two application strategies did not produce consistent results (Figure 2 Figure 2 – Greenwood, MS corn fungicide project). One major difference at the Greenwood area location had to do with the level of disease throughout the season. The location was chosen due to the consistent, no-till corn production system and several consecutive years of excessive gray leaf spot (GLS). Plots were rated shortly after having received a fungicide application and the products chosen significantly reduced observable symptoms of GLS even at vegetative growth stages. Rarely is GLS observed at vegetative timings. Even in a situation where heavy disease pressure was present fungicide applications made at a V6 timing did not consistently improve yield compared to the control.
Fungicides are an important tool. Maintaining the technology they provide is incredibly important for the future of agriculture. Utilizing a fungicide to prevent yield loss as the result of a foliar fungal disease is a scenario whereby the product provides the most consistent response. The “plant health” benefits following a foliar fungicide application reported across the U.S. by university scientists have proven to produce sporadic responses. I realize that many different reports regarding the influence of an early fungicide application on: drought tolerance, stalk integrity, a reduction in aflatoxin accumulation, general plant health, and many other physiological impacts of the fungicide on the plant have been made over the past two seasons. All of the suggested impacts are regardless of the presence of a particular foliar disease. In addition, in most cases the previous crop is not considered to be an important issue when prescribing a vegetative stage fungicide application on a large number of acres. Keep in mind, the results included in this post are from a single year of trials conducted at 2 locations (4 total trials). In my opinion, and based on almost 7 years of trials conducted on corn in MS, I believe fungicides perform best when they are applied to affect a particular foliar disease.
Based on the information contained in the figures attached, fungicides did not provide a consistent response during the 2012 trials. Additional trials will be conducted during the 2013 season at the same two locations to produce more data and attempt to answer important questions regarding the most efficient application timing and strategically place fungicides vegetative application timing situations where they could provide a benefit, such as in a situation where continuous, no-till corn with a prior history of foliar disease has occurred.