For many years, the most common aphid that greenhouse growers have encountered has been the green peach aphid. However, in recent years, Tom Dudek of Michigan State University (MSU) Extension says he has noticed more foxglove aphids (Aulacorthum solani) showing up on a wide variety of plant material.
According to MSU Extension, foxglove aphids have been found on herbaceous perennials like foxglove, hardy mums, perennial geraniums, dianthus, and viola. In annuals, they have been noted on calibrachoa, petunia, peppers, pansy, and salvia. On an international scale, they have been found worldwide on more than 95 different plant species, and can transmit more than 40 different plant viruses.
The foxglove aphid can be distinguished from other species by their large, dark-green patches found on the abdomen near the base of their cornicles (exhaust-like pipes) at their rear end. Growers can see this feature, along with dark spots on their antennae and their legs, with the aid of a hand-lens.
Most aphids feed by sucking plant juices from the host plant so that if enough aphids are present, they can reduce plant vigor. Foxglove aphids also inject a toxic saliva into the plant while feeding, causing leaf twisting and curling, which will lead to necrosis and eventual leaf drop.
Recent research by Sarah Jandricic while at Cornell University found that foxglove aphids actually produce more immature aphids at cooler temperatures than other greenhouse aphids. Her work stated they produce more offspring at 50°F to 60°F than at 77°F. This substantiates what scouts in Michigan report, that foxglove aphids are observed more on greenhouse crops earlier in the season than later in late spring or summer when temperatures are above 80°F in the greenhouse.
For growers using biological controls to defeat this pest, Jandricic recommends Aphidus ervi, as it is much better at control than Aphidus colemani. As for chemical controls, MSU entomologist David Smitley recommends using one of the following materials with good spray coverage: Aria, BotaniGard, Distance, Endeavor, Kontos, or Orthene. Neonicotinoids may also be applied if your buyer allows them to be used, including Imidacloprid, Safari, Flagship, or Tristar. They can be sprayed on the foliage or applied as a soil drench.