Leaf rust is causing problems for some wheat producers in Kansas this fall with reports of wide spread infections in volunteer wheat and the early planted fields in western and central regions of the state. In some cases, the leaf rust is severe enough to cause significant discoloration of the young plants (Figure 1). The disease likely survived the summer months on volunteer wheat that is also prevalent this fall.
Figure 1. Wheat with severe leaf rust infection developing this fall (Photo by Jeanne Falk-Jones, K-State Research and Extension).
Many producers are asking if fungicide applications are needed control leaf rust infections yet this fall. When the wheat is intended for grain harvest, the answer to this question is often “No”. Fall fungicide applications are rarely needed to control leaf rust and preserve grain yield potential. In many years (60%), leaf rust does not survive the winter in Kansas and the disease must be reintroduced from areas in the southern U.S. or Mexico where the fungus is able to persist. However, growers should be monitoring their wheat for signs of rust throughout the winter. It is particularly important to check for signs of rust as the crop “greens-up” and begins to grow in March and February. During these months Leaf rust fungus must move from the overwintering leaves to the new growth. If the fungus fails to move, the local disease population will decline rapidly as the old leaves (the food source for the fungus) deteriorate and the plant redirects resources to the new growth.
If the fungus does survive locally, fungicide applications may be needed in the spring. Fields with overwintering leaf rust are candidates for fungicide application just prior to the jointing stages of growth. These treatments are most effective when combined with a second fungicide application between flag leaf emergence and heading. When diseases are not present or remain at low levels prior to jointing, a single fungicide application protecting the flag leaves is generally enough to maintain yield potential.
Some consultants recently suggested that the value of fall applied fungicides may be greater for wheat intended for grazing pasture than it is for grain only production systems. Their observations suggest that the amount and quality of forage is negatively influence by severe leaf rust infestations. The statements seem logical, as leaf rust damages the leaf tissue we would expect a reduction in total forage, protein content, and moisture. We would also anticipate an increase in fiber content if the forage as well. While these facts are supported by field observations, it should be noted that K-State does not have research data to address the role of fungicides in preserving forage yield and quality. Growers attempting protect forage yields of wheat should also carefully evaluate fungicide product labels for grazing restrictions. Some fungicide labels prohibit grazing for between 6-30 days after application (Table 1).
Table 1. Sample of fungicide label restrictions for grazing wheat or harvest for forage
|
Product (active ingredient) |
Grazing or Forage Restriction |
|
Folicur (tebuconazole) |
Do not graze of feed green forage for 6 days after application
|
|
Prosaro (tebuconazole + prothioconazole) |
Do not graze of feed green forage for 6 days after application
|
|
Tilt (propiconazole) |
No harvest for forage or hay within 7 days after application
|
|
Qult Xcel (propiconazole and azoxystrobin) |
No harvest for forage or hay within 7 days after application
|
|
Approach Prima (picoxystrobin and cyproconazole) |
No harvest for forage or hay within 21 days of application |
|
Absolute Maxx (tebuconazole and trifloxystrobin) |
Do not graze or harvest for forage within 30 days of application
|
Erick DeWolf, Extension Wheat Pathologist
dewolf1@ksu.edu
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
Tags: wheat rust wheat disease