About Aster Yellows
Aster yellows is a disease caused by specialized bacteria called phytoplasma. The disease is mainly transmitted by an insect called Aster Leafhoppers as they feed on plants. After feeding on an infected plant, the leafhoppers will become infected for the remainder of its life (one month or more). It takes two to three weeks after infection for the aster leafhoppers to be able to transmit the phytoplasma to plants. Transmission occurs when insects are feeding on plants, which causes them to distribute phytoplasma cells into the phloem of the plant. This causes the infection to spread relatively quickly throughout the plant. Once infected, phytoplasma manipulate host plants for increased odds of survival and distribution. Some of these symptoms include stunted growth and producing attractive foliage for insects to infect, just to name a couple. Symptoms will generally be visible after 10 to 40 days. At the end of the season, phytoplasma are capable of overwintering in plant roots, which then grow in the spring season.
Aster Yellows Identification and Habitat
A condition called chlorosis is common in plants affected by aster yellows. This condition causes leaves to turn yellow as a result of a lack of chlorophyll. Often the host plant’s growth is stunted, causing plants to be shorter and smaller than they would typically be. Some symptoms cause the plant to develop extra foliage to attract more insects. Sometimes this foliage is curled. Abnormal green coloration also occurs in structures of the plant that are not normally green. In some plants, purple discoloration is common, such as purpling of pods in canola. Furthermore, it is possible that diseased flowers will not produce any seeds. Random tufts of leaves inside or instead of a flower may develop in certain hosts. Be aware that symptoms are very dependent on the strain of phytoplasma and/or the species infected.
Spread of aster yellows is very conditional on suitable weather for insect populations. Aster Leafhoppers will not take flight unless air temperatures are higher than 15°C. Cool and wet temperatures do not favor spread of the disease due to the unsuitability for leafhoppers. Overly hot and dry weather conditions are also unfavorable for the disease for similar reasons. Areas with little to moderate rain and warm temperatures will allow leafhoppers to feed on plants and, in turn, transmit the disease.
Aster Yellows Management and Control Methods
The main strategy in reducing aster yellows is monitoring leafhopper populations. Many farmers choose to utilize sticky traps and sweep nets to detect insect populations. Both of these methods can be useful to find out if insect populations in crops are low or high. Monitoring should begin in May and end around mid-August. Detecting insect populations early on can greatly reduce yield loss later in the season. Moreover, infected plants and weeds can serve as shelter for leafhopper and/or their eggs, so removing infected plants upon detection is vital. If planting in an area with high leafhopper populations, planting less susceptible crops can help reduce the spread of aster yellows. Because aster yellows is not a soil-borne disease, crop rotation will not be effective in reducing further infection of plants.
First off, fungicides are not effective when treating aster yellows because it is a bacteria-like disease. Insecticides can be useful if applied shortly after migratory leafhoppers are detected. Leafhoppers are capable of transmitting the disease in about 8 hours, so quick action must be taken. Once a host is infected, insecticides are no longer effective. Early insecticide applications, along with some cultural controls, are good ways to manage aster yellows.