By Erick DeWolf, Extension Plant Pathology, Kansas State University
Stripe rust was observed in North Central Kansas last week. The disease was found at low levels in research plots near Belleville and was present in the varieties Jagalene, Jagger and Santa Fe. The size of the lesions and position in the canopy suggests that the inoculum resulting in these infections likely arrive three to four weeks ago. Wheat at this location was at the end of jointing with flag leaves emerging over the next week to 10 days. This is the first report of stripe rust in Kansas for 2010.
Since this initial report, low levels of stripe rust have also fond near Hays and Manhattan. These additional finds suggest that stripe rust is established at low levels in many areas of north central and northeast Kansas.
Leaf rust was observed in Reno, Cowley and Ellis county Kansas during the last seven days. The disease is still at low levels in all reports. Powdery mildew and tan spot were also active in many fields.
Bob Hunger, Plant Pathologist at Oklahoma State University, is also reporting leaf rust and stripe rust near Stillwater, Okla.
What do these reports mean for Kansas?
These reports of multiple disease threats are important for wheat producers in Kansas. All evidence to date suggests that stripe rust, leaf rust and other diseases are likely reach levels that can be damaging to wheat yields. The biggest threat to may come from stripe rust because variants of this fungus have emerged that can overcome the resistance of some widely grown cultivars in the state, including Fuller, Santa Fe, Overley, PostRock, Jagalene and Jagger. All of these varieties should now be considered susceptible to stripe rust.
Research suggests that the best time to apply a foliar fungicide to wheat is between flag leaf emergence and anthesis (flowering). Most product labels will prevent application to wheat that has reached the fully headed or flowering stages of growth. Wheat in many parts of the state will be at critical growth stages during the next few weeks.
Wheat in southern Kansas is now at flag leaf emergence and some fields may already be in the boot stage of growth. Wheat in central Kansas will likely reach these stages during the next week. Wheat in northern Kansas appears to be jointing but has not yet reached the flag leaf emergence. The prognosis for western Kansas is mixed. The stripe resistance in TAM 111, one of the most common varieties in this region, has been holding in Texas. However, the TAM 112 is known to be susceptible to stripe rust and is showing severe disease in research plots in Texas. Growers with TAM 112 or the varieties mentioned above should be carefully monitoring their fields for signs of stripe rust. Both TAM 111 and TAM 112 are susceptible to leaf rust.
The current weather forecast for this region includes temperatures near the 70 F and scattered showers. Growers should be on alert for potential development of stripe rust and other diseases in their fields, and be ready to apply a fungicide if warranted. Finding even low levels of stripe rust or leaf rust prior to flag leaf emergence is cause for concern.
The average yield response to fungicides is approximately 10 percent, but can exceed 20 percent when disease becomes established early. The decision to apply may rest on price of grain. With the price of wheat hovering around $4, the price of the fungicide will strongly influence the decision to spray for disease control. Seed production fields should be a top priority.
Fungicide costs this spring ranged from $4 to $20 per acre depending on the product choice and rate. Nearly all fungicides currently marketed in Kansas provide very good to excellent control of leaf rust and stripe rust. Folicur and generic forms of tebuconazole will be the least-cost option where available. The choice of fungicide is more important when stripe rust is already present in a field because this fungus has the potential to spread systemically within a leaf. Products containing a triazole fungicide, or pre-mix of a triazole with a strobilurin, are the best option when stripe rust is present in a field because these products are known to have stronger curative activity. More details on fungicide products can be found at: http://www.ksre.ksu.edu/library/plant2/EP130.pdf