I have had many conversations recently, over whether we should spray our corn with a fungicide. One of the main concerns is that fungicides delay the maturity of the corn crop. This is not true; fungicides keep the corn crop healthy so it will reach physiological maturity and not die prematurely from yield robbing leaf diseases.
Leaf diseases
Disease development in corn around tassel can result in yield loss, particularly if environmental conditions favor infection of leaves around and above the ear. Corn on corn rotations with heavy trash residue and temps ranging from 18 to 27 Celsius with extended periods of wetness or frequent rain are ideal for Northern Corn Leaf Blight (NCLB) development. The earlier foliar diseases occur the greater the yield loss. Begin scouting fields for leaf diseases just before tasseling and continue through grain fill.
Thresholds for fungicide use for (NCLB) do not exist, however it is important to protect the ear leaf and those above it as corn plants enter reproductive stages of growth. NCLB symptoms are large cigar shaped lesions approximately 2.5-15 cm in length. NCLB can reduce yield by as much as 25 per cent if left untreated.
Northern Corn Leaf Blight
Common rust infections beginas light green to yellow spots on leaves and develops into reddish brown raisedpustules that rupture the leaf epidermis and contain rusty brown powderyspores. Rust development occurs under high humidity with night time temps 15 to21 C and moderate daytime temps. Yield loss is usually minimal.
Common Rust
Grey Leaf Spot shows up asgrey or tan rectangular lesions on leaf, sheath or husk tissue. Spots areopaque and long (up to 5 cm) Lower leaves are affected first, usually not untilsilking. Grey leaf spot has become more prevalent with reduced till practicesand corn on corn situations.
Grey Leaf Spot
If we are only concerned with controlling leaf diseases then Stratego Pro, Acapela, Priaxor, Headline Amp, or Trivapro are all excellent choices for controlling leaf diseases in corn. However, I think everyone remembers the high DON levels we experienced last year and don’t want to repeat this year so, our spray program this year is targeted to include ear mold.
Gibberella Ear Rot is the most common corn disease in Ontario. Symptoms of Gibberella Ear Rot is most readily identified by the red or pink color of the mold starting at the ear tip. Gib ear rot pathogens overwinter on corn and wheat debris. Spores produced on the debris lead to infection during silking.
Gib ear rot is more prevalent when cool wet weather occurs during the first 21 days after silking. Extended periods of rain in the fall, which delays dry down, increase the severity of the disease. The most severe cases of Gib will occur in corn on corn rotations or after wheat that had a high level of Fusarium head blight which is caused by the same pathogen.
Gibberella Ear Rot
Applying a fungicide to reduce the level of vomitoxin in your corn is a good approach to protecting your investment and producing a more marketable crop.
Fungicides that will reduce the DON levels are from the Triazole group 3 fungicide family. Proline from Bayer Canada, Caramba from BASF Canada and the new Miravis Neo from Syngenta Canada.
These products for best application results must be applied at early silking with adequate water and pressure to ensure the fungicide gets driven down to the silks. For more information contact your AGRIS or Wanstead Farmers Co-operative crop sales specialist today.
