Dr. Richard S. Cowles is an agricultural scientist at the Connecticut Agricultural Experiment Station and the owner of Humming Grove Farm in East Windsor, CT. He has conducted extensive research on aphids and wants Christmas tree growers to be aware of just what they are and the damage they can potentially cause to an evergreen crop.

Aphids, insects with sucking mouthparts, feed on the phloem sap inside plant tissue. Phloem is the tissue which conducts the sap back from the foliage downward to the root system. Aphids target the sap, enriched with carbohydrates and sugars, to consume the amino acids contained therein.

Aphids are often parthenogenic, meaning they can reproduce without sex, with many young aphids already have embryos forming within them at the time of their birth.

“This is one of the reasons that aphids can have such extraordinarily quick reproduction,” said Cowles. “This explains how many farmers notice how quickly their trees can become dripping with aphids.”

Cowles added, “Usually, one of the distinguishing features of most of the aphids are what are called cornicles. They are colloquially called ‘tailpipes’ because that’s what they look like – dual exhaust pipes sticking out at the back. But what’s kind of a strange thing about the aphids that feed on Christmas trees is that they do not have long, conspicuous cornicles.”

Aphids damage Christmas trees by producing honeydew as they feed, which dries and supports the growth of sooty mold fungi which forms a black layer on the needles. The honeydew also attracts ants to take hold of the leaves.

Dr. Richard Cowles, a scientist at the CAES and owner of Humming Grove Farm in East Windsor, CT. Photo submitted by Richard Cowles

Cowles outlined the main types of aphids that feed on Christmas trees:

• Balsam twig aphids – These aphids are native to North America. They can be found on Canaan, Fraser and most balsam firs in the Appalachian Mountains. These aphids feed primarily on the needles.

Unlike most other aphids, the Balsam twig aphid is not tended by ants. Balsam twig aphids have numerous wax pores and produce a wooly-looking discharge which results in shortened needles closely pressed to the sides of the shoot. “Conventional insecticides for Balsam twig aphids include Diazinon, chlorpyrifos and Dimethoate,” Cowles said.

• Giant conifer aphids – These aphids are soft-bodied and notable for their large size. They feed on many species of conifer, particularly junipers. When it comes to feeding, these aphids target the stems. During the growing season, all giant conifer aphids are females that give birth to live young. The last summer generation develops into males as well as females. They mate, and then females lay eggs on needles or bark.

“Giant conifer aphids are usually controlled when sprays are applied to manage Balsam twig aphids,” Cowles noted.

• Conifer root aphids – These aphids feed on trees’ root systems. They can be identified by a reddish head that contrasts with their body. The primary host of conifer root aphid is thought to be ash trees.

“One of the things that’s nice about this aphid is that it has no economic consequence for Christmas tree growers,” Cowles said. “Even if these aphids are present on your spruce trees, they don’t cause deformation of the growth, and they are not present when the trees are harvested in late fall. You ought to know about them, but they are not a pest that’s worthy of making any insecticide applications to manage.”

Cowles also advised on inhibiting agricultural insects: “Ants are farmers too! Much like humans raising dairy cows for their milk, ants ‘farm’ aphids for their honeydew.”

Controlling the ant population on your Christmas tree farm will help to control the aphid population.

by Enrico Villamaino