Aster Yellows Has Arrived in Edina

There has been a lot of chatter on the University of Minnesota master gardener network lately about a disease that is widespread throughout Minnesota this year—Aster Yellows. You may have noticed it on your Echinacea spp (coneflowers), other flowers, and even some vegetables. 

What does it look like?

Aster Yellows can infect many types of flowers. One sign is that your flowers are partially to completely green. The plants may have strange-looking green growths coming from the center of the blossom. Some people refer to these distorted growths or the “shape” of the flowers as “witches’ broom.” 

According to Michelle Grabowski, a UMINN Extension Educator, Aster Yellows is “caused by a tiny bacteria-like organism known as a phytoplasma.” This group of phytoplasmas can infect more than 60 families of plants, including a wide range of your perennials, vegetables, and even weeds. While coneflowers have been the most reported plant infected, aster yellows can attack other plants such as cosmos, golden rod, and carrots. 

The leaves of infected plants can be discolored yellow to red. The bacteria affects the normal growth and development of the plant, which results in clumps of weak shoots developing throughout the plant or on the flower stalk itself. Typically, flowers are the most affected part of the plant. 

Where does it come from?

Aster Leaf Hoppers transmit the bacteria. Leaf hoppers are insects that suck up plant sap, which has the phytoplasma bacteria. This in turn allows the bacteria to live and reproduce within the leaf hopper. As the insect feeds from plant to plant, some of the bacteria is released into the plant, starting another infection. 

The bad news is that there is no cure once a plant is infected with Aster Yellows. The good news is that the leaf hoppers do not overwinter in Minnesota. The outbreak this year could be the result of our mild winter and early spring. We were about three weeks ahead of schedule this year, which could account for the leaf hoppers migrating into Minnesota earlier in the growing season. With more time to spread the disease, more plants were infected, with more people having noticed the strange growths and discoloration on their plants. 

What should you do?

Your perennial plants can survive multiple years with the bacteria and can serve as a future source of the disease. If you have Aster Yellows in your plants now, remove the entire plant. You can bag and toss them in your weekly yard and garden waste removal service. You can recycle the infected plants in your compost pile. You can bury them in your garden. The phytoplasma will not survive once the plant dies. It needs a living host to carry on its dastardly deed. 

Removal of the infected plants does not, however, guarantee that the disease will not return. If you do not remove the infected plants, it is fairly certain that you will have the disease next season. Leaf hoppers and infected perennial weeds can be a source of new infections. That said, removal of all infected plants is still recommended.