Mississippi Wheat Disease Update

Wheat leaf rust

Wheat stripe rust

Currently, the wheat crop continues to be mostly disease free. The majority of the wheat crop is heading to flowering depending on the geographic location within Mississippi. At present, the two most prevalent diseases are leaf and stripe rust. The two diseases are fairly easy to tell apart. Leaf rust will develop in a non-uniform pattern on the leaves. Sporulating pustules are typically more orange in color when compared to stripe rust. In addition, like the name indicates, stripe rust will be present on leaves in a pattern. Areas surrounding the more yellow sporulating lesions will be brown on the leaf. The brown areas, in addition to the pattern of the ruptured pustules will look like a stripe.

Low levels of leaf rust were detected in a wheat field in Winston County last Friday. Leaf rust is also present at low levels around Cleveland and Shaw, MS. In addition, several fields with mostly low levels of stripe rust have been identified, predominantly south of Leland and immediately north of the Shaw area. However, since the vast majority of the wheat present in MS has reached flowering, a fungicide application for leaf or strip rust management once flowering has initiated is off-label. Stripe rust can be the more damaging of the two rust diseases encountered in MS. However, as I stated in a previous posting, the majority of the varieties planted in MS have some level of tolerance to the rust diseases. Based on research that has been conducted nationally, including in the Mid-south, fungicides applied to a tolerant variety typically will not result in a positive economic response.

In addition, I have received a tremendous number of calls since December regarding Fusarium head blight (FHB).  FHB can also be commonly referred to as scab.  Frankly, I’m surprised at the amount of interest in this disease as well as the number of calls.  In the past we have not observed much FHB in MS.  In fact, on an annual basis it would be a struggle to detect a single wheat head in one field of wheat that could be deemed caused by FHB.  FHB can be more of a problem in fields where corn has been planted since the fungus that causes FHB can cause disease in corn and would likely overwinter on stubble present in the field.  However, an incredibly specific environment would be necessary for infection of wheat to occur.  Moreover, with the amount of glyphosate drift that we’ve received this season deciding if the characteristics are specifically related to glyphosate injury (i.e. a “blanked” or white head) or FHB would be difficult.  Currently, there is a website that is available to follow whether or not a conducive environment is present for the development of FHB.  Based on the model, available at http://www.wheatscab.psu.edu/ (click on Risk Map Tool, Click “ok” on the next page for the model, then make sure that Winter Wheat is checked, and then click on the state of MS) a “high risk” area for the potential of disease development is present in a small area in Simpson and Smith counties.  In fact, based on the model, limited areas of “high risk” (to the potential of infection and development of the disease….not necessarily the disease) have been present in limited areas throughout the state for the past several weeks.  None of the “high risk” areas have been present in the Delta and in most cases low numbers of wheat acres have been impacted by a conducive environment.  In addition, not much wheat was planted in some of the areas where a high risk was predicted.  The risk map that is available at this site is simply a guide as to the level of risk that could be associated with the environment and is predictive in nature.  In no way should it be considered to be a tool to indicate where disease is present.  While the model has been extensively tested, the majority of the research and data involved have been gathered from across the northern wheat producing areas.