Carrington Research Extension Center
North Dakota State University
NDSU Extension Service
North Dakota Agricultural Experiment Station

Ag Alert


July 29, 1999

ASTER YELLOWS IN CANOLA

As canola is inspected to determine time of swathing, you may observe widely scattered plants that are abnormal or malformed. The problem may be aster yellows, a disease transmitted by the aster leafhopper. Infected plants produce distorted and sterile inflorescences. Pods are replaced by round to oval, blue-green, hollow, bladder-like structures. The disease has been observed in canola fields in counties including Eddy, Foster, and Wells. Levels of incidence are very low. The disease is not considered of economic importance.

LEAFSPOT IN YOUR CORN?

Leaf samples from a Carrington area corn field were recently diagnosed as having a fungal disease called northern corn leaf spot. The leaf spots were oval, about 1/4 to inch in length, and were light tan in the center, with a darker border. The tips of the leaves were severely infected and tattered or torn looking. This corn leaf disease is favored by moderate temperatures and high relative humidity. Fortunately, this disease is considered of minor importance and of little threat to hybrid corn. Control is limited to use of resistant hybrids.

SUNFLOWER RUST

Area sunflower are beginning to bloom. This is the time to start scouting fields for seed weevil, as well as continue monitoring for the presence of other insects including sunflower beetle, midge, and moths. While in fields, don't limit your observations to only insects as sunflower rust should also be on your scouting list.

Our recent warm day and night temperatures, and high humidity have been favorable for the development of sunflower rust. Rust spore production is best at 68-95 F and germination is best at 60-80 F. At 77 F, over 90% of spores germinate if the leaf stays wet for only 3 hours; but at 68F, the leaf must stay wet 8 hours for 90% of the spores to germinate. Rust cycles in only 8 days when day/night temperatures are 85 F/75 F. It cycles in 14 days when day/night temperatures are 65 F/55 F. In addition, pustules are larger at high temperatures, so that up to 80% more spores are produced.

If sunflower rust severity in the top four leaves averages at least 3% before ray petal wilt, a fungicide application is likely to provide an economic return. Ray petal wilt occurs approximately 12 days after the plant begins to bloom. Folicur has emergency section 18 registration for use on sunflower (confection and oilseed) in North Dakota. Folicur can be applied at 4 fl oz/A up to 50 days before harvest, which is usually about ray petal wilt. Folicur cost is about $9/acre plus application costs.

Refer to NDSU Extension Service circular PP-998 'Sunflower Rust' for details on rust symptoms, survival and spread, severity estimation, and management.


Greg Endres, Area Extension Specialist/Cropping Systems, Email: gendres@ndsuext.nodak.edu
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