Source: Erick DeWolf, Kansas State University Extension plant pathologist (from K-State “Plant Disease Alert” April 5, 2010).
Evaluation of wheat near Manhattan, Kan., indicates that powdery mildew and tan spot have both increased significantly this past week. As expected the tan spot is most evident in locations where wheat was planted into wheat residues.
Leaf rust and stripe rust
We continue to hear reports of leaf rust and stripe rust in Texas and Oklahoma. These reports are indicating that leaf rust and stripe rust remain at low levels in most fields. The reports of stripe rust on varieties previously thought to be resistant to the disease have continued to flow from College Station, Texas. At this location, it appears that stripe rust has moved to the flag leaves and is still causing significant damage. Many varieties grown widely in Kansas previously thought to be resistant to stripe rust are being affected, including Jagalene, Jagger, Fuller, Art, and Santa Fe. These reports reduce my hope that adult plant resistance will stop the spread of the disease. Stripe rust is also severe on TAM 112 and Endurance, but these varieties were already known to have considerable vulnerability to the disease. The stripe rust resistance in TAM 111 is still holding.
Another significant report this past week came from Bob Hunger, OSU Plant Pathologist, indicating a low level of stripe rust in Jagalene near Stillwater, Okla. My communications with Bob indicate that the stripe rust is at very low levels and only in the lower levels of the canopy.
What does this mean for Kansas?
Although it is too early to make a definitive call on the risk of foliar diseases in Kansas this year; I think these reports confirm that Kansas still has a moderate risk for yield losses to stripe rust and other leaf diseases. In most years, outbreaks of leaf or stripe rust at College Station will tend to move east; therefore the stripe rust at this location may not directly impact Kansas. It is also possible that "adult plant resistance" or some other factor will slow the progress of disease.
Producers should continue to monitor disease activity carefully. If additional reports of "disease hot spots" occur in Oklahoma, we need to be prepared to respond with fungicides that can protect those fields with enough yield potential to justify the additional inputs. The additional value of seed production fields makes them a high priority. Fungicide costs range from $4 to over $20 per acre, suggesting it could be important to start planning early.
Wheat Soilborne Mosaic and Wheat Spindle Streak Mosaic
The Plant Disease Diagnostic Lab at K-State has also received numerous samples of wheat that appears to be infected with Wheat Spindle Streak Mosaic and/or Wheat Soilborne Mosaic (tests are currently underway to confirm). These diseases are most commonly observed as yellow patches in fields that follow the soil drainage patterns. Closer examination of the infected plants will reveal a blotchy or streaked mosaic of yellow on otherwise green leaves. The intensity of the symptoms will vary with cultivar susceptibility to these viral diseases. Most varieties grown in central Kansas are considered resistant to spindle streak and soilborne mosaic; however, TAM 111 and TAM 112 are considered susceptible. These varieties hold a large portion of the acres in western Kansas where these diseases tend to be rarer, but do occur in some fields.