I first saw aster yellows last year on a solitary cone flower bloom. The odd growth pattern of the bloom had me mesmerized, delighted and a little stumped. Was this bloom that looked like fireworks a good find, or a sign of something terrible? Turns out it was not good, not good at all.
Aster yellows is a plant disease caused by the aster yellows phytoplasma, a bacterium-like organism that lives in the food-conducting tissue (phloem) of plants. The disease affects 300 species in 38 families of broad-leaf herbaceous plants, primarily in the aster family, as well as important cereal crops. Entire stands of plants can be affected. The disease occurs across North America.
Transmission of the Disease The disease is transmitted by the aster leafhopper, Macrosteles quadrilineatus. When a leafhopper inserts its stylet into the plant to feed on the phloem of an aster yellows infected plant, it acquires the phytoplasma. The phytoplasma goes through an incubation period during which it multiplies within the leafhopper and then moves to the salivary glands. The leafhopper then transmits the phytoplasma via its saliva when it feeds on a new plant. The newly transferred phytoplasma is deposited into a healthy plant, and within 8 to 12 hours the phytoplasma moves into the host plant’s phloem.
Signs of Aster Yellows:
• vein clearing, the loss of chlorophyll or green pigment in the leaf veins
• yellowing of newly formed leaves
• sporadic bushy growth
• erect growing habit
• stunted growth habit
• stems and flower stalks may be numerous and spindly
• flowers often remain green and become distorted
• seeds and fruit do not develop
Take Action There is no cure for asters yellow. Upon noticing signs of the disease, immediately remove and dispose of the plant.
Submitted by Lucinda Reynalds
The Plant Health Clinic has received numerous samples of tomatos with severe leaf damage. Septoria Leaf Spot caused by Septoria lycopersici is one of the most damaging diseases of tomato foliage. Septoria is favored by warm temperatures and high humidity.
Symptoms of Septoria generally appear on the lower leaves after the first fruit sets. Lesions are circular, about 2.6mm in diameter, with dark brown margins with tan to gray centers. A narrow yellow halo may often be observed around the lesion. Small black fruiting bodies of the fungus (pycnidia) may be observed in the centers of the lesions using a hand lens. Lesions may coalesce to form large blighted areas. Foliage turns yellow, then brown and dry. The plant has an almost burned appearance. There are no resistant cultivars available.
Control measures include crop rotation with a non-host, control of weeds in tomato crops, removal of all crop debris, and avoidance of night watering and overhead irrigation. Protective fungicides at regular intervals during the growing season will be necessary for most growers. Quadris, Cabrio, Flint, Bravo, Mancozeb, and Gavel are labeled for Septoria leaf spot control. Homeowners may use Ortho Garden Disease Control, or Fertilome Liquid Fungicide, or Bonide Fung-onil Multipurpose Fungicide Concentrate, or Garden Tech Daconil Fungicide Concentrate, or Bonide Mancozeb Flowable w/Zinc, or Hi-Yield Maneb Garden Fungicide, or Green Light Tomato and Vegetable Spray. Organic Gardeners may try Bayer Advanced Natria Disease Control, or Bonide Liquid Copper Fungicide Concentrate, or Kaligreen, or Bonide Remedy, or Bonide Copper Dust, or Hi-Yield Bordeaux, or AgraQuest Serenade.
University of Arkansas Plant Health Clinic Newsletter
Baxter County Master Gardener Program • University of Arkansas System • Division of Agriculture • © 2013 BCMG