Environment
There are hardly any conditions that directly impact the development of Aster yellows, but there are a few indirect factors that strongly influence the rate of transmission by the leafhopper. Conditions that favor movement and spread of the leafhopper and encourage feeding assist in the spread of the phytoplasma.
Transcontinental migration begins in the spring when the prevailing winds and jet streams help carry the leafhoppers from their overwintering sites in the South to the Midwest. Upon arrival in the Midwest they begin feeding. The leafhopper may have migrated into the region already carrying the phytoplasma, which it could have acquired from infected plants along the migration or while still in the South. The leafhopper could have also arrived not yet carrying the phytoplasma. If this is the case, it could feed on perennial weeds that are infected to acquire AYP. Weather conditions greatly influence leafhopper flight because they are poor flyers. Temperatures below 15 degrees Celsius or rainfall will temporarily halt their migration and delay the time of infection. The leafhoppers will then feed all summer long until they migrate back to their overwintering sites in the fall.
Weather conditions of the region also greatly influence leafhopper feeding patterns. If conditions are hot and dry plants do not appear as lush and nutrient rich to the phloem feeding leafhopper whereas seasons with abundant rainfall allow the plants to have much more lush growth. This means that hot and dry conditions are less conducive to the spread of Aster yellows than times of abundant rainfall.
In the Western United States, there is no migration of the vector leafhoppers. This allows for transmission of the phytoplasma year round.
Read more about this topic: Aster Yellows
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