ISSUE 10  July 16, 2009

NDSU IPM FIELD SURVEY UPDATE - JULY 14

NDSU IPM field scouts surveyed 130 wheat fields and 32 barley fields across the state for the week ending July 10th. Average growth stage over all wheat and barley fields surveyed was "head half-emerged".

Wheat: Tan spot continues to be the most common disease observed in wheat, with some flag leaves consumed by this disease in more mature fields planted onto wheat stubble. Leaf rust, at trace levels, was found in two commercial fields surveyed. On July 13th, disease evaluations at Lisbon, ND, showed that leaf rust had developed in winter wheat plots, with susceptible, non-fungicide treated varieties showing up to 40% severity on the flag leaf. Application of Prosaro fungicide at the flowering growth stage resulted in almost 100% control of leaf rust. The fungicide also effectively reduced fungal leaf spots, at about an 80-85% reduction. The winter wheat crop in these plots was in the soft dough stage.

Loose smut was observed in 15% of the surveyed wheat fields, with an average incidence of heads infected at 6%, well above the threshold indicating the need for seed treatment. Saving seed from infected fields and reduced use of seed treatment is contributing to the steady rise of loose smut infections being observed in wheat in our state. (See image). Loose smut spores will be wind blown to adjacent flowering heads. With wet weather, the spores can infect the uninfected heads and move into the kernel’s embryo. At harvest, the seed looks uninfected, but the fungus will reside in the embryo. At planting, an infected seed will germinate, the plant will look normal, but the fungus is growing along with the growing point of the plant, and at head emergence, the seed tissue is replaced by the loose smut fungal spores. Effective seed treatments are the only way to control this disease.


Loose smut on wheat

Head scab was found in 8 (6%) of the fields, and 6 of these were winter wheat. The highest field severity was 12% in one winter wheat field.

Wheat streak mosaic virus (WSMV) symptoms were observed in 12% of the wheat fields surveyed. Scattered wheat virus symptoms are common across ND this year, often those of WSMV, but barley yellow dwarf also is easily observed. Most fields won’t be seriously damaged by viral infections this year, but some late planted fields with viral infections are looking very yellow and have some stunted plants, and their yield will be affected.

Bacterial stripe was observed in 10 fields, with some fields also showing the head infection phase of this disease, called black chaff.


Bacterial stripe in wheat


Black chaff on wheat

Bacterial infections have been seen more commonly on certain varieties (such as Freyr and Granite spring wheat and Jagalene winter wheat), and generally are more common in ND in the Red River Valley area (or on sandy soils) if wheat crops are planted onto bare, well-tilled soil. Soil particles are then moved readily about in wind and rain storms. Moving soil particles cause small wounds for bacteria to easily enter the tissue. I rarely see bacterial stripe in crops planted into good crop residue because the residue provides some protection from widespread soil particle movement, at least within the field, if not along field margins.

Fungicide applications for wheat fungal diseases do not control bacterial infections. At this time, NDSU does not have a rating system for variety response to bacterial stripe because of the inconsistent occurrence of the disease in research plots. Hopefully in the future we will have a better understanding of this disease and the yield effects it may have.

Barley: Net blotch, spot blotch or Septoria infections were the most common diseases observed in barley. Severity of infection on the flag leaf ranged from 1 to 20%. Head scab has not been reported yet from barley.

Marcia McMullen
NDSU Extension Plant Pathologist
marcia.mcmullen@ndsu.edu

 

PULSE DISEASE SURVEY UPDATE

Last week, as intensive survey of pulse crop diseases was done in North Dakota. Infected root and foliar tissue and soil from each field were collected for disease identification (or confirmation) and processing in the laboratory. In total, 38 pea fields, 24 lentil fields, and 10 chickpea fields were surveyed and sampled in Bottineau, Divide, McLean, Mountrail, Ward, and Williams Counties. Although identification and processing take time, some general observations were made. Ascochyta was found in all crops, and in most fields. The severity was generally lower in the western counties surveyed, and tended to increase in the eastern counties. Root rots were found in nearly every chickpea and pea field and in approximately 40% of lentil fields. Damage was generally light; however, patches in some fields were severe. Although confirmation is needed, Fusarium species are most likely the pathogens causing the root rot. The information and pathogen cultures generated in this survey are critical for the development of resistant varieties, rotation recommendations, fungicide strategies for disease management, and detecting and documenting fungicide resistance. Specific information will be available at winter meetings, and if possible, included in the last issue of the Crop and Pest Report. This survey was funded by the Northern Pulse Growers Association, and coordinated by Dr. Goswami’s research team. Most of the surveying was done randomly throughout the state, so we also thank the numerous growers whose fields we happened to survey.

Rubella Goswami
Pulse Crop Pathologist
Rubella.goswami@ndsu.edu

Sam Markell
Extension Plant Pathologist
Samuel.markell@ndsu.edu


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