GARDENING
Aphids are one of the most common garden pests. These tiny, soft-bodied, pear-shaped insects range in size from 2-4 mm in length and can be found in a variety of colours — black, green, brown, yellow, white and pink — as well as on a variety of plant types.
The green peach aphid (Myzus pericae) is one of the most common types found on more than 200 species of herbaceous plants.
The potato aphid (Macrosiphum euphorbiae) is also generally green in colour but can sometimes have a hint of pink. As the name suggests, the potato aphid is common on potato plants but also prefers tomato and cabbage plants in the garden.
The Honeysuckle aphid (Hyadaphis tartaricae) is very small (pinhead-sized) with a green, soft body covered with a whitish, powdery covering. The saliva released from the honeysuckle aphid during feeding causes dense deformities (often called witch’s broom) on the honeysuckle branch with the tip of the branch curling over into a crook.
The Smoky-winged Poplar Aphid (Chaitophorus populicola) and the Conifer aphid (Cinara spp.) are examples of aphids that attack the stems, branches and sometimes even the roots (Conifer aphid) of plant species. Heavy infestations of the caragana aphid (Acyrthosiphon caraganae) can completely defoliate an entire shelter belt of caraganas; however, if the shrubs are otherwise healthy, they will recover.
Some aphids will form growths, referred to as galls, on trees for overwintering and laying eggs. The Poplar Vagabond Gall Aphid (Mordvilkoja vagabunda) forms galls on branches and stems of poplar trees.
The woolly elm aphid (Eriosoma americanum) is a bluish-black, flattened oval soft-bodied insect with a white, woolly coat. These aphids emerge from eggs laid in the cracks of the elm bark and feed on elm leaves early in spring, causing the leaves to curl up. By midsummer, winged females are produced which fly to small saskatoon berry shrubs and feed on the fine roots of the saskatoon bush. Depending on the degree of infestation and the size of the bush, the root loss can be severe enough to damage or even kill the plant.
Aphids are extremely prolific. Wingless female aphids hatch in early spring from overwintered eggs. These female aphids bear live young without mating. A newborn aphid becomes a reproducing adult within one week. That reproducing adult can produce up to five offspring per day for about 30 days.
It’s easy to see how a few aphids can lead to a large infestation in a short amount of time. When aphids experience stress due to hot weather or high numbers, they will produce wings, allowing them to spread over a wide area. Although aphids typically are not good flyers, they have been known to ‘fly’ on wind currents for thousands of kilometres from one area of infestation to another. In fall, male and female aphids mate: eggs are laid on a host plant or in the soil to overwinter.
On larger plants, it can be difficult to find the tiny aphids. One of the signs of an aphid infestation is the presence of a dark, sticky, sooty mould on plants, furniture, cars or sidewalks under the infected plant. This substance is the excrement from the aphids, known as ‘honeydew.’
Another sign of aphid infestation can be the presence of large numbers of ants on a plant. Ants eat the aphid honeydew. The relationship between ants and aphids is symbiotic: ants ‘farm’ aphids. Aphids provide food for ants while the ants provide protection for the aphids. Ants have been known to ‘milk’ the aphids by stroking the abdomen of the aphids while the ants provide protection for the aphids from predators such as ladybugs and lace wings.
Aphids will rarely kill a plant outright; however, distorted shoot growth, sticky excrement and an excessive number of ants in one’s garden are never welcome. Because aphids are piercing and sucking insects, they are capable of spreading diseases in plants, especially viruses. Viruses will eventually kill plants. Controlling large outbreaks of aphids is recommended.
Next week’s column will discuss aphid control and predators. This column is provided courtesy of the Saskatchewan Perennial Society (SPS; saskperennial@ hotmail.com). Check our website (saskperennial.ca) or Facebook page ( facebook.com/saskperennial) for a list of upcoming gardening events: Drought Tolerant Perennials by
Sara Williams — Oct. 23, 7:30 p.m., Emmanuel Anglican Church, 607 Dufferin Avenue, Saskatoon. Free and open to the public.