Aster Yellows & Blight

• A condition called aster yellows, brought on by the pathogen Phytoplasma, afflicts the coreopsis and approximately 300 other species of plants, causing them to be twisted, stunted and yellowed. The disease is rarely lethal and is transferred by the aster leafhopper (Macrosteles fascifrons). Botrytis blight, caused by the pathogen Botrytis cinerea, kills leaves situated on the lower section of the plant and covers them with a white or gray fungal growth that serves as the reproductive center of the disease.
  
  

Rot & Mildew

• Crown rot, produced by Sclerotium rolfsii, forces the plant to wilt, brown and eventually die with a white, fungal growth developing at the base of the coreopsis. Infected plants should be removed and destroyed to avoid transferring the disease to adjacent specimens. Downy mildew caused by the bacteria Plasmopara halstedii displays as a collection of black spots on the upper surface of coreopsis leaves and a white, fuzzy growth on the bottom of the foliage.
  
  

Leaf Spots

• Several different fungi including Cercospora, Septoria, and Phyllosticta produce fungal leaf spots on a coreopsis. The problem first displays as purple or tan spots on the leaves. The likelihood of the planting contracting these diseases can be minimized by ensuring that leaf surfaces remain dry when watering. Powdery mildew caused by the pathogen Sphaerotheca macularis produces a white, fuzzy covering on the upper surface of coreopsis leaves. It can be controlled by applying copper sulfate.
  
  

Root & Stem Rot

• Root rot is a lethal problem that causes a coreopsis to yellow, wilt and die. Fungicides are helpful in controlling this disease of the pathogens Phymatotrichopsis or Rhizoctonia. Meanwhile, stem rot can force significant sections of a coreopsis to collapse and die, preceded by a browning of the stem. Infected plants should be removed and destroyed. Verticillium wilt is a soil-borne fungus that survives in the earth for lengthy periods and is capable of causing the coreopsis to wilt and die.