Aphids

In addition to the crown and root aphids, which are discussed separately, other species of aphids are found on carrot. These aphid species have soft bodies and vary in color, size, and shape. Winged aphids form under specific conditions of overcrowding or plant stress and disperse to other plants or fields. Species can be distinguished by color and examination of the cornicles, tubercles, and cauda using a hand lens.

• Bean aphid: A dark olive-green to black aphid with a dull appearance. Hairs on the cauda give it a bushy appearance. Winged and wingless forms have a similar appearance.
• Cowpea aphid: A dark olive-green to black aphid with a shiny appearance. A relative lack of hairs on the cauda gives it a more naked appearance compared to bean aphid. Winged and wingless forms have a similar appearance.
• Cotton (melon) aphid: Small to medium-sized and highly variable in color, ranging from lemon yellow to blackish green, often within the same colony. Color may change with temperature fluctuations, being lighter when the temperature is hotter.
• Green peach aphid: Medium-sized, uniformly pale green or pinkish with prominent cornicles. The frontal tubercles at the base of the antennae are very prominent and are convergent. This is the most common type of aphid found on carrot. Winged forms have a distinct dark patch on the abdomen.
• Honeysuckle aphid: Wingless forms are grayish green with dark features and may have a fine white wax dusting. Winged forms have a mottled green abdomen and a dark patch around the base of each cornicle.
• Willow carrot aphid: Pale green wingless forms with elongate oval bodies and a second tail-like process called the supracaudal process. Winged forms have a black head and thorax with a pale green abdomen. The antennae are black. The legs are pale in color and black at the tips. The cornicles are somewhat swollen near the tip.

Aphids that feed on the tops of carrots are rarely of concern due to the removal of tops at harvest. Exceptions can occur if aphids transmit viruses during early stages of development. Virus infected carrots typically have curled or distorted leaves that can lead to stunting. Most aphid species can transmit one or more different viruses. Some of the more serious viruses include carrot motley dwarf, carrot red leaf, and parsnip yellow fleck that are transmitted by willow carrot aphid.

Species of aphids can be controlled by predators, parasites, or entomopathogenic fungi. Common aphid predators include green lacewing, lady beetles, and syrphid fly larvae. Many predators are commercially available but efficient release rates are not known.

Parasitized aphids can be identified by their tan color and bloated appearance. Bean aphid is attacked by a very prolific parasitic wasp, Lysiphlebus testaceipes. Cowpea aphid is commonly attacked by Lysiphlebus spp. and Diaeretiella spp. Several parasites of cotton aphid and green peach aphid are present in California and can provide effective control. Little is known about parasites of honeysuckle aphid or willow carrot aphid.

Bean aphids and green peach aphids are also attacked by a fungal disease that leaves the aphid body flattened and with the appearance of being glued to the leaf.

Field sanitation is important in reducing the number of aphids in and around carrots. Sanitation is also important in slowing the spread of the viruses that willow carrot aphid vectors. Disc all crop residues into the soil as soon as harvest is complete. Keeping fields, ditch banks, and fence lines weed-free may also help to reduce virus inoculum.

Carrots planted next to aphid-infested cotton or melon are at risk of becoming infested with cotton aphid particularly in fall following cotton defoliation or termination of the melon crop. Carrots should be planted a safe distance from both, if possible.

Use biological and cultural controls in a certified organic crop.

Monitor fields for aphids weekly during spring and summer by examining the upper and lower surfaces of leaves. Also, look for evidence of predators and parasitoids and their impact on aphid populations.

No treatment thresholds for aphids in carrot have been established.

For bean aphid, cowpea aphid, cotton aphid, and willow carrot aphid, insecticide treatments are not effective in preventing virus transmission and these aphids rarely cause economic damage through direct feeding.

For honeysuckle aphid, insecticide treatment is generally not advisable as economic damage is rare.

For green peach aphid, small colonies occasionally develop on carrot leaves and may reach treatable levels, but no treatment thresholds for green peach aphid on carrots have been established. Green peach aphid has developed a high level of resistance to many pesticides and may be hard to control.