Stripe Rust alert for Southern Alberta wheat
Jul. 24, 2009
Stripe rust is a significant disease of both wheat and barley world-wide. Stripe rust has been in Alberta for decades; however, since 2003, the incidence and severity has increased dramatically in wheat some years.
The disease is caused by the fungus Puccinia striformis tritici. Infections were first observed in the Lethbridge winter wheat nurseries on June 30, 2009 and conditions have favoured secondary infection. Infections were noted on the spring wheat nurseries on July 3, 2009. The rainfall on July 13, 2009, in southern Alberta favours continued sporulation and secondary infection.
This fungus can over-winter in Alberta. However, the greatest risk is from air-borne spores carried from wheat producing regions in the U.S. Upon landing on a suitable wheat plant, the spores produce fungal strands which grow beneath the leaf surface only to re-emerge within 10 days as a distinctive raised orange or yellow stripe on the surface of the leaf. If ideal conditions persist, the fungus consumes the leaf and the released spores re-infect other portions of the plant and ultimately the entire crop. In the end, the field takes on an orange shade prior to the release of trillions of spores onto crops both near and far. Once the leaves lose their photosynthetic capacity, the grain fills poorly and shrivelled kernels result in yield reductions as high as 30 per cent.
Generally, this disease prefers cool temperatures, but strains do occur that are less sensitive to temperature. The rainfall experienced in Lethbridge combined with cool days and cold nights have allowed the disease to progress with a number of repeating cycles since first observed on June 30.
There are a number of spring and winter wheat varieties that offer very good resistance to stripe rust. Radiant, the most commonly grown winter wheat in the Lethbridge region, has adequate stripe resistance whereas the number two variety, Bellatrix, is very susceptible.
With the large number of spring wheat varieties available to producers, the best course of action is to consult the seed guide to determine variety susceptibility. Rust may still occur on these varieties but should not require protection with a fungicide. For some varieties, the stripe rust reaction is not known. A number of effective fungicides are available but label directions should be followed in terms of timing for effective control and preharvest interval, following diligent crop scouting. Stripe rust generally favours thick stands of wheat where the dew will persist on the lower leaves for a long period.
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