Scouting & Management of Sunflower Rust

Rust in sunflower is caused by the fungus Puccinia helianthi, which overwinters on plant stubble and produces five spore‐stages throughout the year. Early in the season, orange rust pustules appear on the upper surfaces of cotyledons of seedlings and volunteer plants, with later infections moving to the underside of the leaf (Figure 1).  The most yield-damaging stage occurs in late July to early August, when symptoms of infection show up as dusty, dark brown pustules on leaf surfaces, petioles and flower bracts (Figure 2). As the disease develops, black teliospores form, overwintering on the crop residue.

 

Figure 1: rust on leaf underside (photo: MB Ag)

 

Figure 2: Rust on leaves, stem. Wilting plants (photo: MB Ag)

Sunflower rust becomes a more severe issue in later-planted crops, or crops with weaker genetic resistance. Warm, moist weather favours rapid multiplication of rust spores, and windblown spores can travel quickly from field to field.  Early stages of sunflower rust in 2018 have been observed in the Cypress River area the week of July 3rd.

High plant populations and dense, leafy canopies allow humid conditions to remain in the crop throughout the day, compounding injury from rust spores.

Scout sunflower fields regularly to monitor the development and stage of rust infection. Watch for dense clusters of brown, powdery pustules scattered over all plant surfaces.  Orange-brown ‘dust’ on clothing after being in a sunflower field is a key indicator that rust is present, and more careful scouting is needed. Withered lower leaves are an indication that the surface is heavily infected.

Controlling rust after infection is primarily done using triazole-based and strobilurin-based fungicides. Recommended action in rust-infected crops is to use a fungicide from the triazole group after the first onset of symptoms, at the 2-3% pustule coverage on the upper four leaves at flowering (R5).  Strobilurin-based fungicides act more as a ‘protectant’, applied earlier before widespread infection occurs.

See more information on sunflower rust at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp

See Guide to Field Crop Protection for more information on fungicides registered at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp

National Sunflower Association of Canada information on Sunflower Diseases: http://www.canadasunflower.com/wp-content/uploads/2012/11/Disease.pdf

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Manitoba Insect & Disease Update – Issue 5: June 15, 2016

The Manitoba Insect and Disease Update is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-06-15.html

SUMMARY:
Insects: Cutworms continue to be an issue in some areas. Flea beetle feeding continues, although foliar use of insecticides for flea beetle management has not been widespread. In many fields plants are now getting to stages more tolerant to feeding by flea beetles. Alfalfa weevil is being noted at high levels in some alfalfa fields.

Plant Pathogens: Rust diseases in cereal crops and sunflower have been observed in Manitoba. Root rots in soybeans have also been reported from various locations in Manitoba. Scouting and monitoring progression of disease symptoms in the field will help in making fungicide application decisions.

Several samples of soybeans showing root rot symptoms have been submitted to Manitoba Agriculture’s Crop Diagnostic lab. Root rot is soybeans are caused by pathogens like Fusarium spp, Phytophthora sojae, Rhizoctonia spp and Pythium spp

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
Manitoba Agriculture on YouTube: www.youtube.com/ManitobaAgriculture
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