A Summary of Late Summer and Early Fall Pests
Symptoms of aster yellows are apparent now on Echinacea (coneflower) (Figures 1 and 2 below). Thepathogen that causes this disease, a phytoplasma, is a bacteria-like microorganism spread by leafhoppers, primarily the aster leafhopper (Macrosteles fascifrons). Over 300 plant species can be hosts for this disease, including ornamentals such as asters, zinnia, Echinacea, and chrysanthemum, and vegetables such as lettuce, carrot, and tomato. Symptoms of aster yellows include stunting, chlorosis (yellowing), and abnormal flower development (green petals, clustered mini-flowers instead of a single blossom, green petal-like tissue in center of flowers). There is no cure for infected plants, so they should be removed. Echinacea flower distortion can also be caused by an eriophyid mites.
Controlling Leafhoppers and Planthoppers
In the previous section on aster yellows, Karen mentions that leafhoppers are one of the major vectors of this disease. Plan now to deal with these sucking insects next season. I would suggest making a root drench application of either Altus (Bayer Company) or Mainspring (Syngenta Company) early in the season right after you plant, or in early summere. Mainspring should provide 12 weeks of control when applied at 8 oz/100 gallons of water. Altus is long lasting but I have not yet had enough experience with this newer material to tell you how long a soil drench would provide control. If you prefer to spray, I would use either Endeavor or Aria, which are both stylet blockers. When the leafhoppers feed, their stylet is blocked and they cease feeding. It takes a day or two for the insects to die from starvation.
Stanton Gill and Karen Rane
In July, a dahlia grower in central Maryland experienced heavy damage from a fleahopper (Halticus sp.). This insect quickly caused damage to plant foliage, in some cases hitting just about all of the foliage. We checked with other dahlia growers, and they were not experiencing this pest. If you are seeing it at your operation, please contact me at [email protected].
For sucking insects like fleahoppers, three excellent materials to use are stylet blockers under the names Aria, Altus, and Endeavor. They stop the insect from feeding pretty quickly, but it takes a couple days for the pest to die.
Thrips usually start to build up in August, when they head to dahlia flowers, where they love to feed on pollen. Mainspring works very well on thrips and is very soft on beneficial organisms and pollinators. It is a little expensive, but safe and effective.
The sunny days and cool nights near the end of July created perfect condition for powdery mildew on dahlias. Check your plants for early leaf symptoms. There are a number of fungicides, including myclobutanil, propiconazole, strobilurins, and potassium bicarbonate products, which effectively manage powdery mildew, but phytotoxicity may occur if sprays come in contact with open flowers.
Aster yellows on Echinacea
Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]