Mysterious green blobs on my coneflowers :(
I have coneflowers in my northern cottage in the woods and everything is so dry here. I just noted some green blobs about 1-2 mm circular and slightly elevated with dark discoloration around them on my coneflower leaves and it is spreading to the others and the black eyed Susan’s. Is this a virus or an aphid infestation and what can i do about it? I depend on coneflowers so muc as nothing else really grows where I am. Thank you......
Kalkaska County Michigan
I believe this damage is being caused by an small insect called a rudbeckia psyllid. It appears to have a single lifecycle each season in Michigan. You can see similar damage in the photo on page 2 of the document found at this link:
I was only able to find a general recommendation for insecticide treatment, at this source: https://content.ces.ncsu.edu/rudbeckia-triozid. Several non-university resources recommended Neem oil, but I would be cautious about application with the hot weather we have been experiencing. Please read all label instructions when using a pesticide.
I contacted Howard Russell, the entomologist at the MSU Plant and Pest Diagnostics Lab, to see if he could tell us anything else about this pest. His response follows:
This is what I send out to people...probably not much different than the 2010 article.
Rudbeckia psyllid galls, Bactericera antennata (Hemiptera: Triozidae (Psyllidae in part)).
The insect is reported to have considerable morphological and color variation. The mature nymphs I have observed are about 1/8 inch long, flattened and very colorful with a light green abdomen, red-orange head and thorax, and white wing pads. The eyes are large and the nymph is completely fringed in white hairs. The adult is very small and has two pairs of transparent wings and red eyes. The body is mostly black with brown highlights on the dorsal aspect of the thorax. The legs are two-toned with the bases black and ends tan.
The nymphs feed by inserting their needle-like mouthparts into lower surfaces of the leaf and sucking plant fluids. The nymph’s saliva appears to have systematic effect throughout the leaf. First, a shallow but distinct depression develops at feeding site on lower leaf surface. The tissue surrounding the feeding site turns deep purple on both leaf surfaces. However, the top surface of the feeding site remains green in most cases. The veins may turn purple over much of the lower leaf surface.
The nymphs are heavily parasitized (over 90%) by a small black and red wasp. There appears to one generation per year in Michigan. Their overwintering habits remain a mystery. They occur throughout North America and well into Central America.For homeowners, the best products for controlling the psyllid are cyfluthrin (sold as Bayer Advanced Vegetable and Garden Spray), bifenthrin (sold as Ortho Bug B Gon) and malathion. Be sure to read and follow all instructions.