Foliar Fungicides in Corn for 2011

Seed Type: 
Corn
Corn Row

Foliar (leaf) fungicides are proven to arrest the development of yield limiting fungal diseases.                                                                                                                                                            

  • These diseases reduce photosynthetic area in leaves that affect yield directly and stalk quality and harvest efficiency indirectly. 
  • Hybrids yield more today so value per acre has increased. Fungicides return investment in the right situation but can be wasted in the wrong situation.
  • Several factors need to be considered before a decision is made for fungicide applications.
  • A good decision involves understanding hybrid susceptibility to disease, disease risk factors, scouting, disease identification and application timing.  
  • When to spray is the question.

Fungicide application in field corn has gained popularity in recent years. Improved fungicide products in the strobulurin family (Quilt®, Quadris®, Headline® and Stratego®) and sterol inhibitor family (Tilt®, Folicur®; package mixes Headline AMPTM, Statego YLDTM) have increased efficacy of disease control. Corn grain commodity prices have increased to improve economic feasibility for applications. In addition, yield potential of hybrids is improved and increased value per acre can be conserved. This article describes multiple factors to consider for profitable fungicide application in corn.

Disease Risk Factors
Hybrid susceptibility. Corn hybrids vary in their susceptibility to major foliar diseases. Hybrids with susceptibility to disease respond better to fungicides, disease resistant hybrids do not. Fungicide response ratings (likelihood for yield protection) are listed for each hybrid in a table following this article, 9 = high response, 8 = moderate response, 7 & 6 = lowest response.

  • Previous crop. Fields that are corn followed by corn with heavy corn residue are most at risk for severe disease outbreak. Corn foliar disease pathogens over season in the residues.
  • Tillage. Minimum tillage fields are at a higher risk because of existing residue on the surface where disease inoculum is launched.
  • Weather. Rain and high humidity levels favor disease development. Extended wet periods increase disease potential. Extended dry periods reduce disease potential.
  • Field location and history. Fields that are in river and creek bottoms are usually more prone to attack and establishment of foliar diseases. Also fields with a history of disease should be considered more at risk for disease development.
  • Planting date. Hybrids in later plantings are also subject to more disease pressure due to more time in warm and wet conditions when disease outbreaks are at a peak. 

Scouting and Disease Identification
Scout corn fields in the week before tassel emergence, the time when one fungicide application is most effective. Look for lesions and signs of foliar disease. Diseases controlled are gray leaf spot, southern rust, northern corn leaf blight, southern leaf blight, northern leaf spot, common rust, and eyespot. Goss’s wilt and Stewart’s wilt are bacterial diseases and not controlled with fungicides. Information about specific corn diseases is found on LG Seeds Agronomy Web page at http://www.lgseeds.com/agronomy_resources/corn/diseases.

  • Susceptible hybrids. Look for lesions or disease symptoms on the third leaf below the ear. If lesions are on 50% of the plants or more then an application may be justified.
  • Moderately Susceptible hybrids. Look for lesions on the third leaf below the ear and if 50% or more plants are affected and if a high risk field and history of disease or with corn residue on surface or in a river or creek bottom and weather patterns are expected to be warm and humid then a fungicide application may be justified.
  • Hybrids with resistance. A fungicide application is not warranted.

Application Timing
Usually one fungicide application is economically feasible. Best timing is just before VT (tassel) to the R1 (silking) growth stage when disease is present. Most foliar fungicides have an active range of 14 to 21 days. Applying at this growth stage is likely to protect leaves in important upper canopy leaves especially the ear leaf. Consider all disease risk factors before a decision are made, including label restrictions.

Early applications at growth stage V5 (five visible leaf collars) and V6 (six visible leaf collars) are also being advocated. Results from one application at this stage are inconclusive. Sometimes there is a yield benefit but these factors are not clearly identified. Disease pressure is low at V6. Diseases such as anthracnose are targeted but plants are infected well before V6. When one application is used the R1 application is more responsive than the V6. However, largest responses are observed when V6 applications are followed by R1 applications. So if you have made a V6 application based on disease risk then consider following with another application at R1.

Summary
Fungicide applications provide a return on investment but must be judicially used. Decisions to use a fungicide should consider factors that include hybrid susceptibility to target diseases, field history, and risk factors related to surface residue then future weather patterns for disease development. Fungicide products introduced into the market in recent years are very effective in controlling target diseases. Improved grain commodity prices are allowing better economic return for these applications, especially for susceptible hybrids in high risk fields that have surface corn residue and/or corn following corn rotations.

Download full Technical Bulletin containing charts and list of LG Seeds' hybrids response ratings.