Aster Yellows

A mycoplasma-like organism (MLO)

Biology

This virus-like disease can attack barley and other crops including canola. The MLO is transmitted by a leafhopper, Macrosteles fascifrons. Aster yellows do not occur naturally in field grown oats or wheat but has been transmitted experimentally with leafhoppers. There may be some confusion between the symptoms of aster yellows and barley yellow dwarf.

Each spring, inoculum is brought into western Canada by infected leaf hoppers that migrate in from the United States. Barley may also become infected by leafhoppers that overwinter locally and acquire the MLO from infected perennial weeds.

When leafhoppers feed on an infected plant, MLOs are taken up by the insect vector. After 8-10 days, leafhoppers become infectious and can transmit this organism to healthy plants for the remainder of their life span, which lasts up to a few months.

Damage Description

Chlorotic blotches appear on the older leaves, and leaf margins of younger leaves curl under. Blotches coalesce and the entire leaf becomes chlorotic. Plants appear dwarfed and bushy because internodes are shortened. Heads of infected plants may have distorted awns or floral parts resembling leaves.

Reduced photosynthetic area plus head sterility causes yield reductions. Severity of this disease varies from year to year depending on the size of the population of migrating leafhoppers. The disease is cyclical and only occasionally is of economic significance on barley.

Diagnosis

To positively diagnose this disease a complex procedure involving leafhopper vectors and electron microscopy must be used. However, general symptoms will probably identify the problem.

Management Strategy

Seed crops early. This allows the crop to mature before the MLO can be spread by leafhoppers and cause extensive damage.

Text and captions courtesy of Dr. Ieuan R. Evans
Images courtesy of I. R. Evans and WCPD