Another cool, wet spring is unfolding, similar to last year, creating ideal conditions for a buildup of aphids. Last fall, large numbers of these small insects caused a nuisance along the Wasatch Front and beyond. One of the aphid types was identified as the bird cherry-oat aphid. In northern Utah, this aphid alternates between its primary winter host, trees in the genus Prunus(cherry, peach, apricot, plum) and summer hosts of many grasses, including wheat, barley and oats. Entomologists have seen large numbers of aphids on Prunus fruit trees this spring and suggest that homeowners monitor fruit and ornamental trees for an increase in aphid populations. Consider this information.

 

• Despite their small size and limited mobility in the non-winged stages, aphids have evolved into one of the most destructive pests of cultivated plants in temperate regions. They can be a bane to farmers and gardeners. There are more than 4,000 described species worldwide with about 250 of these causing economic losses.

 

• Also known as plant lice, aphids have straw-like mouthparts that suck sugary sap from the phloem vessels of plants. They can produce copious amounts of sticky “honeydew,” which drips down onto sidewalks and cars below aphid-infested trees and promotes the growth of a black fungus called sooty mold. Some aphid species feed on one type of plant throughout the year, while others feed on several or many species of plants.

 

• Some aphids have a mutualistic relationship with ants. Certain types of ants will “farm” aphids, protecting them from predators and harvesting the sugary honeydew to feed their own colony. The presence of ants climbing into plants can signal an aphid infestation. Exclude the ants by placing a band of tacky substance, such as Tangletrap, around the base of the plant. This will allow natural aphid predators to move in and reduce the aphid infestation.

 

• Common symptoms of aphid infestations are curled leaves in the new growth, yellowing and stunting of plants, a lack of vigor, the presence of honeydew, and for gall-forming species, galls or abnormal swelling of plant tissue. Aphid saliva can have toxins that cause deformities in plant growth. Also, some aphids transmit plant viruses that cause diseases such as curly top virus in tomatoes and iris yellow spot virus in onions.

 

• In the home landscape and garden, a few aphids generally will not cause substantial harm, but if the population increases quickly, control measures may be necessary. For woody plants, an important control is the use of dormant oil spray in the spring. Coat the overwintered aphid eggs and young nymphs with the suffocating oil just as the buds open, but before leaves or flowers expand. Another key time for control is in the late spring to early summer when plant injury is noticeable, but before leaves are tightly curled. Application of a lighter oil, such as horticultural oil, or common garden insecticides, such as bifenthrin, esfenvalerate, insecticidal soap, malathion, neem or permethrin may prevent plant injury or the loss of vegetable crops. Dinotefuran and imidacloprid are systemic insecticides that can be applied to tree roots and will be taken up and transported to the leaves. They can be especially helpful in treating aphid infestations in trees that are too tall for easy spray application.

 

• Always read the label of a pesticide product to determine on which plants the product is registered. Never apply a pesticide to a site or plant for which it isn’t registered. The pesticide label is the law, and plant injury can occur from incompatible pesticides. Be aware that insecticide options will differ for landscape versus edible garden plants.

 

• If aphid infestations are mild to moderate, hose down the infested plant with as hard of a spray of water as it can withstand every three to five days until the aphid population subsides. Natural biological control from common aphid predators, such as lady beetles, lacewings, hover flies and others can play a major role in suppressing aphids. To preserve predators, avoid toxic insecticides. For more information on management of aphids and other pests, visit the Utah Pests website at www.utahpests.usu.edu. Look for links to fact sheets, image galleries, newsletter articles, slideshows and advisories to find out which pests are currently active in the landscape and garden.