Heat and dry conditions in southern Alberta have encouraged development of several crop diseases.
Wheat streak mosaic, aster yellows and bacterial leaf streak have been spotted on spring wheat, and Goss’s wilt has been found on grain corn.
Plant pathologist Michael Harding of Alberta Agriculture’s crop disease centre in Brooks issued an alert June 30 about the occurrence.
He advised diligent crop scouting to determine disease presence, although few control measures are available.
Information on the areas affected and their relative severity were unavailable at press time.
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Wheat streak mosaic disease is caused by a virus that enters the leaves and spreads throughout the plant. It first appears as light green streaks in leaves, indicating chlorophyll destruction.
Those streaks later turn yellow, with blotchy patches that give a mosaic appearance.
The disease is spread by a mite, but Alberta Agriculture fact sheets say no effective control measures are available.
Aster yellows is a parasitic bacteria transmitted by insect species, most commonly the aster leafhopper. Insects carrying the bacteria can spread on the wind.
An outbreak in 2012 caused considerable crop damage, though it generally has minimal effect on prairie crops. Symptoms include stunting, excessive branching, smaller leaves and poor seed set.
Insecticide treatment will not improve crop prospects once a crop is infected, said Alberta Agriculture data. Spraying is considered impractical because there may be multiple waves of leafhoppers, and the chemicals would kill beneficial insects.
Bacterial leaf streak appears as translucent water-soaked streaks on leaves. These streaks later turn dry and brown. It can cause significant yield loss.
The pathogen is seed-borne and no effective treatments are available beyond the initial use of clean seed.
Goss’s wilt, also caused by a bacteria, shows up as dark green to black water-soaked spots. It was first confirmed in Alberta in 2013.
The degree of damage to corn depends on weather and crop conditions. The disease favours high humidity.
Genetic resistance is the best management method. Fungicide is not effective.
