Foxglove aphids: Gear up to deal with this cooler temperature greenhouse pest
Recent research sheds new light on a more commonly occurring aphid in greenhouses, the foxglove aphid. Understanding host plants, identification and biology will help you deal with this pest.
Greenhouse growers have battled aphids in their operations for many years. In the past, the most commonly encountered aphid was the green peach aphid. However, in recent years I have noticed more foxglove aphids (Aulacorthum solani) showing up on a wide variety of plant material. According to Michigan State University Extension, they have been found on herbaceous perennials like foxglove, hardy mums, perennial geraniums, dianthus and viola. As for annuals, they have been noted on calibrachoa, petunia, peppers, pansy and salvia, to name a few. The literature states they have been found worldwide on over 95 different plant species. In addition, they can transmit over 40 different plant viruses.
This aphid can be distinguished from other species in that they have large, dark green patches on their abdomen near the base of their cornicles (exhaust-like pipes) at their rear end. You can see this feature with the aid of a hand-lens. In addition, you should note that they have dark spots on their antennae and their legs (see photo).
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 50-60 degrees Fahrenheit than at 77 F. This substantiates what scouts here 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.
Other good news, if you are using biological controls to defeat this pest, Jandricic recommends you use 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 Imidicloprid, Safari, Flagship or Tristar. They can be sprayed on the foliage or applied as a soil drench.