From Gene Milus, plant pathologist:
The most serious disease at this time is stripe rust on susceptible and very susceptible varieties where the disease overwintered and formed hot spots. Fields with hot spots should be sprayed with a fungicide as soon as possible. Fields of varieties with a susceptible reaction type (abundant yellow sporulation surrounded by green leaf tissue, see photos below) but without hot spots at this time should be the next highest priority for being sprayed. Fields of varieties with only resistant to moderately resistant reactions (little or no yellow sporulation surrounded by yellow or tan leaf tissue, see photos below) are not likely to have significant losses from stripe rust, and applying a fungicide may not be necessary to control stripe rust.
There have been no new reports of leaf rust since the previous newsletter. Recent dry weather is keeping Septoria leaf blotch and Stagonospora blotch confined to the lowest leaves that were infected last fall or earlier this spring. Frequent rains will be needed for these diseases to move to upper leaves.
The overall incidence of barley yellow dwarf appears to be low. If symptomatic plants are scattered and not stunted, then the infection likely occurred during the spring, and yield losses should be insignificant. If symptomatic plants are in stunted patches, then infection occurred last fall and yield losses likely will be significant in the stunted areas.
The risk of scab remains low across Arkansas south of I-40 where wheat has flowered or is approaching flowering. Flowering is the most favorable time for scab infection, and dry conditions are not conducive for spore production or infection. Given the recent dry conditions, several rainy periods will be needed to elevate the risk of scab.
Syngenta recently registered Alto 100 SL fungicide (Cyprocanazole) for use on wheat and it has been used this season on wheat in southwest Arkansas. Recommended rates are 3 to 5.5 fl oz per acre. It likely is effective on rusts, Septoria leaf blotch, Stagonospora blotch, and powdery mildew but not effective for scab.