Healthy Corn Leaves Power Yield Potential


   Around the tasseling stage in corn development, presence of foliar disease may lead to yield loss. Yield potential may be impacted if the top eight to nine leaves above the ear show disease symptomology – these leaves contribute around 75 percent of the energy needed to add carbohydrate, and grain, to the ear.1 Much of a corn plant’s energy from photosynthesis is produced by the foliage at and above the primary ear, so it is important to protect the integrity of those leaves from damage.
   As corn matures from the vegetative stage to the early reproductive stage, symptoms of foliar diseases may start to appear in fields. Foliar disease in corn is a concern when pathogens develop early and progress up the plant before grain fill completes. Primary fungal diseases to scout for are Northern corn leaf blight, Gray leaf spot, Common or Southern Rust, Anthracnose leaf blight and bacterial diseases such as Goss’s or Stewart’s wilt. 
   While fungicides can help manage foliar fungal diseases, planting less susceptible hybrids are the best protection against bacterial diseases.
   Evaluating fields at risk for disease should occur prior to tasseling, particularly fields with susceptible genetics, acres farmed continuously corn-on-corn, or fields with a history of disease. The decision to apply a fungicide should be based on field evaluations, environmental conditions, management practices, disease pressure, and economic thresholds.  Fungicide applications may also help with late season standability, although this is hard to put an economic value on. Contact a Channel Seedsman in your area to help you evaluate your need for fungicide.

   For the best economic return, in most situations, fungicide applications should between R1 and R3 stages. If an application is planned prior to the tasseling stage, avoid using adjuvants. The purpose of adjuvants is to make the fungicide adhere better to the plant surface which impacts pollination. Foliar fungicides are typically active for 14 to 21 days and an optimal application can protect leaves from fungal diseases through grain fill.
   Visit the for an article titled “Managing Early Onset Diseases in Corn” with photos and descriptions of corn diseases.  For information about the effect of stress on corn yields, read “Managing Corn Plant Health to Maximize Yield Potential”. ∆
1 Rees, J.M. 2008. Gray leaf spot of corn. G1902. University of Nebraska.
   Cathy Soanes: Channel Agronomist

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