ISSUE 10 July 6, 2006
Loose smut in wheat appears to be quite common in many fields across the state this year. The spores of this fungus seen on grain spikes are now being wind-blown to adjacent flowering wheat heads. New infections only occur during flowering, and are favored by humid weather. Last year’s weather conditions were ideal for loose smut infections.
Loose smut infected wheat heads - 2006
Following infection last year, the fungus survived as dormant vegetative strands within the embryo (see figure) of the wheat seed.
Wheat seed embryo with vegetative strands of loose
smut fungus visible on left, healthy embry on right.
This infection is not visible to the naked eye. However, when the infected seed is planted and germinates, the fungus also begins to grow within the plant, and at heading, the fungus is at the growing tip and produces smut spores where the grain kernels should be.
Management of loose smut is through seed treatment fungicides registered for loose smut control. See NDSU Fungicide Guide (NDSU Ext. Circular PP-622) for Seed Treatment Products with efficacy against loose smut.
In barley, growers may take this year’s grain and have it tested for loose smut infection levels at the ND State Seed Department. Unfortunately, a reliable test is not available to check for loose smut infection in wheat. Growers with considerable loose smut should consider seed treatment on this grain next year, if grain is kept or sold for seed. In barley, infection levels of 2% or greater are considered high enough to warrant seed treatment. In wheat, 2% or greater would also indicate that seed treatment would be economic. Infected wheat fields in our survey are now averaging slightly higher than 4% infection.
WHEAT AND BARLEY DISEASE OBSERVATIONS, June 26-30
Wheat: NDSU IPM’s summer field scouts surveyed 115 wheat fields and 9 barley fields during the week of June 26-30. The average growth stage of these crops during that week was Zadoks 59 = head emergence complete, with 44 of the 115 fields not in the heading stage yet. Tan spot was found in almost every field, with average severity remaining below 5%, although a few fields had severities up to 28%. Leaf rust was observed in less than 10% of the surveyed fields, and average severity of leaf rust in infected fields was 3%. Loose smut was found in 39% of post-heading wheat fields, with an average incidence of infected tillers in these fields at 4.4%. Other diseases were observed very infrequently.
Barley: Leaf spots were commonly found by field scouts, but were not severe. The barley growth stage averaged Zadoks 55 = head emergence stage at that time.
Fusarium head blight has NOT been detected in the surveyed fields, in either spring wheat or barley. A few observations of this disease were made in some winter wheat plots, but at low incidences.
Extension Plant Pathologist