Stripe rust and leaf rust have been confirmed by crop consultants at low levels in several wheat fields in far southern Indiana, near Gibson County. Producers should be aware of these diseases and scout fields to determine if rusts are present, and at levels that may warrant fungicide application.
The diseases can be differentiated by the color and pattern of the pustules on the leaves. The fungus that causes stripe rust (Puccinia striformis) produces a yellowish or orange spore, and pustules appear in a row on infected leaves, giving it a “striped” appearance (Figure 1). Leaves infected by the fungus that causes leaf rust (Puccinia triticina) have brownish pustules that are scattered on the leaf (Figure 2). Purdue Extension Bulletin BP-79-W, “Identifying Rust Diseases of Wheat and Barley” is available to aid in diagnosis of these diseases, and can be found at the following link: <https://mdc.itap.purdue.edu/item.asp?itemID=19349>.
Both rust fungi prefer humid, wet weather and moderate temperatures to infect wheat and develop disease. However, the stripe rust fungus can infect under cooler conditions, which may be problematic in Indiana wheat fields with the recent weather. Each disease has the capacity to cause yield loss if infections occur prior to heading and environmental conditions favor disease development and spread.
Fungicides are available to manage both leaf and stripe rust. Products and their ratings for efficacy against rusts are listed in the following table, developed by the North Central Regional Committee on Management of Small Grain Diseases or NCERA-184 committee: <http://www.ppdl.purdue.edu/ppdl/wise/NCERA_184_Wheat_fungicide_table_2012.pdf>.
The decision to apply a fungicide should depend on crop growth stage, application cost, and weather conditions prior to application.