Stewart's Wilt of Corn -
"The Tale of Two Models"

Disease forecasting models have been proven to a very effective "tool" in predicting and limiting producer losses from disease. One of the oldest and most widely used disease predicting models is for Stewart's wilt of corn. The initial model was developed in the 1930s but has gone through various transitions over the years and is referred to as the Stevens-Boewe Stewarts wilt disease forecasting system. This model (Table 1) adds the average monthly air temperatures for December, January and February which is used to predict disease severity for the upcoming season. Based on the Stevens-Boewe Model, Essex county (Windsor-Leamington) and west Chatham-Kent would be at higher risk (moderate to severe) of the disease developing in 2007 (Table 3). For areas North and East of these, the model would suggest trace levels except for the Sarnia (light to moderate).

Table 1. The Stevens-Boewe disease forecasting system fo Stewart's wilt disease of corn (Model 1).

We have been validating a newer model developed at Iowa State University which also uses air temperature from the same three months but interprets the data differently. Each month's average winter air temperature is given a point score if the average was below - 4.4°C (°24 F) and the point scores are added up for each of the months. For example, if over the winter 3 points were accumulated then your risk of Stewart's wilt is high. If you accumulate fewer points, the risk of Stewart's wilt decreases. Using the IOWA model in 2007, it also predicted that the risk to Stewart's Wilt would be moderate to high from Windsor through to Niagara and London (Table 3).

Table 2. The Iowa State Method (Model 2) for disease forecasting for Stewart's disease of corn
(Nutter et al)

Table 3 - Comparison of the Two Models and Stewarts wilt predictions in 2007

This should be a good year to evaluate the different Stewarts wilt computer prediction models. These two computer model outputs are very similar to what Michigan State University is predicting for Michigan. Corn disease surveys conducted by OMAFRA (Ridgetown) and AAFC (Ottawa) found Stewart's wilt disease was more frequent in 2006 across the province on commercial corn and as expected in seed corn production fields in Essex and Chatham-Kent.

The bacteria overwinters in the gut of adult corn flea beetles, which hide through the winter in protected areas. Mild winters can result in beetles successfully overwintering and therefore an increased number of beetles the following spring. Overwintered adult flea beetles feed on corn in the seedling-to-whorl stage and susceptible varieties will develop a stem wilt resulting in complete plant loss. This occurs rarely in corn hybrids but can be devastating in seed corn inbred parents. The next generation of adult beetles emerge after corn silking and cause leaf wilting symptoms, which are commonly seen in many hybrids. Seed transmission is rare. Most often, late infections after silking are associated with high beetle populations. Sweet corn is often more susceptible than field corn and can serve as a reservoir for the bacteria. The disease is often found in the best fields and fertility seems to play a part. Susceptibility to the disease increases in fields that have high nitrogen and phosphorous levels.

The ability to accurately predict Stewart's wilt of corn allows for better management of the disease and the corn flea beetle. If you have a recent history of Stewart's wilt in your field, arrange for resistant hybrids or seed corn inbreds, if possible. Most field corn hybrids are resistant but there are few susceptible ones out there. The use of Gaucho, Poncho (low rate) or Cruiser seed treatment will control the flea beetles and potentially reduce the transmission of stewart's wilt this spring. Keep in mind that Gaucho is only available for use on seed corn. And do not graze or feed livestock on Cruiser treated areas for 45 days after planting. If a susceptible hybrid or inbred is planted, plan to scout early for flea beetle damage.

This survey and prediction model was supported by the Seed Corn Growers of Ontario which obtained funding through contributions by Canada and the Province of Ontario under the Canada-Ontario Research and Development (CORD) Program, an initiative of the federal-provincial-territorial Agricultural Policy Framework designed to position Canada's agri-food sector as a world leader. The Agricultural Adaptation Council administers the CORD program on behalf of the province.

| Top of Page |