Recap of Small Grain Diseases 2011 (8/25/11)
Wheat streak mosaic virus (WSMV): This virus disease, vectored by the wheat curl mite, appeared early in the season, and frequent confirmations were made by the NDSU Plant Diagnostic Lab on samples submitted, primarily in winter wheat, but also in spring wheat. The source of the virus and mite frequently was volunteer wheat that had not been completely controlled prior to planting of the new crop. Management of WSMV is entirely dependent on the breaking of the green bridge for virus and mite survival. Grass hosts, such as volunteers and grassy weeds, must be destroyed at least two weeks prior to planting, and appropriate planting dates must be used (mid to late Sept. for winter wheat, early spring for spring wheat).
Tan spot and Septoria species: Tan spot: This fungal leaf spot developed early in the wheat crop because of all the spring moisture, and continued to develop in the canopy all growing season. Early season application of fungicide alone probably wasn’t enough to prevent the heavy infections seen later in the season in some crops. Infections of the fungi in the Septoria species complex were observed most readily once crops entered the heading stage, and also were common. Net blotch or the spot form of net blotch was the most common fungal disease observed in barley. Fungicide treatments helped control all these fungal leaf spot diseases, but other, non-fungal, problems may have overtaken fungicide response.
Barley yellow dwarf virus (BYDV): This virus infection became apparent early in the season, with the fairly early appearance and common occurrence of the small grain aphid vectors. Some commercial fields had fairly severe and widespread BYDV infection, and these infections would lower yield and test weight of the crops. Insecticides could be used to control the grain aphid before virus transmission, but no pesticide can control the virus per se.
Bacterial leaf streak and black chaff: Bacterial infections were severe and widespread this year in wheat and lesser so in barley. The frequent rains and storms really favored leaf wounding and spread of the causal bacteria. The head infection caused by the bacterium, called black chaff, was very apparent is some fields, as well. Bacterial infections are not controlled or managed by any fungicide treatments commonly used on small grains. Yield losses due to bacterial infection will be variable depending on extent of infection and damage seen, and kernels may be shriveled, as well.
Root rot: Although less commonly observed than expected because of water-logged soils, root rot symptoms were visible in some fields, where patches of grain heads turned prematurely white and contained no grain. The affected plants easily pulled from the soil. Some seed treatment fungicides alleviate early infections from root rot pathogens, but in 2011, the soil conditions may have been overwhelming favorable for continued infection in some fields.
Fusarium head blight (FHB): FHB or scab was more common in 2011 than in the past five years. The full extent of this disease is not known yet, as very few yield and DON (vomitoxin) reports are in, but the disease symptoms were noticeable in many fields, and some harvested grain is now showing the scabby kernels or tombstones. In years very favorable for FHB, fungicides provide, on average a 50-60% reduction in FHB disease severity, and a 40-50% reduction in DON. Greater disease reductions have been seen in years when conditions were less favorable for infection. This year, fungicide use might seem disappointing; however, because of the prolonged favorable conditions for FHB infection, and because some severe problems, ie. barley yellow dwarf, root rot, and bacterial streak, were not affected by any foliar fungicide use.
Leaf rust and stripe rust: The one area of good news for ND producers in 2011. Rust infections were very infrequently observed in winter and spring wheat crops and in barley in 2011, and only at trace levels were observed in commercial fields. Rust infections did not develop in states to our south, so few spores moved into our area. The heavy stripe rust infections in Montana did not appear to be carried into ND, except perhaps along the very western border counties.
Overall, the diseases were just too plentiful in 2011 for many producers, and many were not manageable once observed. Once data comes in from research plots, more information should be available on variety performance and fungicide performance in this strange year.
Marcia McMullen - Extension Plant Pathologist, Cereal Crops