Wheat Disease Update, 26 April 2013
The black fruiting bodies associated with stripe rust lesions are telia of the stripe rust fungus and signal and end of the stripe rust epidemic.
I evaluated plots near Kibler, Rohwer, and Mariana on 24-25 April. At Kibler, maturities ranged from early boot to flowering, and only low levels of leaf blotch were found on lower leaves. At Rohwer, maturities ranged from boot to past flowering. Stripe rust did not increase much since last week, and the stripe rust fungus was producing telia (see attached photo) that produce spores involved in the sexual cycle of the fungus on its alternate host instead of uredinia that produce spores infecting wheat. This early production of telia may be a characteristic of the contemporary strain of the fungus and signal an end of the epidemic in southeast Arkansas. Stripe rust is attacking the same varieties as last year, so there does not seem to be any new races so far this year. Leaf blotch was widespread but still low in the canopy. Barley yellow dwarf was widespread and easy to see. I specifically looked for leaf rust but did not find any. Blackbirds were showing interest in the wheat, so there may be some armyworms. At Marianna, varieties ranged from boot to early flowering. A few recent stripe rust lesions were seen on upper leaves. Leaf blotch was at low levels on lower leaves. Downy mildew was evident in low spots near the plots and in fields along the way.
Flowering is the latest growth stage to apply fungicides to wheat. Research in Arkansas has shown that fungicide applications are most profitable when certain diseases are present at or above threshold levels when the application is made. Currently, disease levels seem to be below thresholds south of I-40 where some fields are at or near flowering. Septoria and Stagonospora leaf blotches seem to be the diseases to scout for at this time if a fungicide application is being considered. Furthermore, the weather has not been favorable for head blight (scab), so a fungicide application specifically for head blight is not necessary at this time.
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