Compared to wheat fields, canola fields are rich in insect diversity and abundance. While some of these insects may reduce canola yield, a number of these species are beneficial. The most common pest insects in canola are flea beetles, wireworms, and cabbage seed pod weevils. Canola hosts a wide spectrum of beneficial insects including pollinators and predatory insects. Pollinators can benefit canola yields and predatory insects can help control some insect pests. When developing an insect management plan it is important to consider the potential benefits of insects as well as the damage cause by pest insects.
Adult flea beetles are a type of leaf-feeding beetle. They get their name from having enlarged hind legs and will “spring” or “jump” like a flea when disturbed. These insects are small, less than 2.5 millimeters and have an overall elliptical or oval-shaped body shape. Some species are entirely shiny black or can have yellow markings hence the name “Striped” flea beetle. Despite their size, these insects have been known to destroy entire crops when numbers are extreme.
Wireworms can damage cereal grain crops, resulting in increased weed pressure and reduced stands, yields, and profits.
Wireworms are the immature larval stage of click beetles, and these beetles can spend several years in this larval stage feeding on germinating seeds and young seedlings, resulting in thin crop stands and lower yields. Crop damage is not detected until after planting when it is too late to make preventive pest management decisions. This situation makes wire worm scouting prior to planting essential.
Cabbage Seedpod Weevils, if left unchecked, can reduce canola yields by 50%. Adult feeding on developing flower buds can cause them to abort, also known as “bud-blasting.” Larval feeding can destroy several, if not all, of the seeds within an individual pod. With the combination of damaged and developing seeds during pod-fill, pods will become misshapen or distorted and are subject to premature shattering. Therefore, scouting and being able to recognize adult CSPW’s is essential. Adults like many weevil species, have a prominent, curved snout with elbowed antennae. Two round black eyes at the base of the antennae make up the head. The entire body is covered with very fine white hairs. Hairs on the hard wing covers(elytra) form distinct lines. Overall color is ash-grey with the underside and legs a little lighter in color. They measure 3 to 4 mm.
Cabbage aphids are small green, gray with a white, waxy coating soft-bodied insect. They can be distinguished from other insects by having 2 cornicles which are appendages at the rear-end of the abdomen which resemble “exhaust pipes”. They have piercing-sucking mouthparts and prefer to feed on the newest plant growth and thus are generally found in dense colonies at the tops of plants. Large colonies can stunt or kill small plants.
Diamond back moths typically do not reach levels of economic concern. However, there have been outbreaks recorded of this pest causing many millions of dollars in lost revenue. Adults lay eggs on leaves of canola, usually during the rosette stage. Larvae or caterpillars are usually greenish to sometimes yellowish in color. They have a rounded-brownish head capsule and overall are “cigar-shaped” in appearance at maturity. Larvae can reach lengths of nearly 0.5 inches. Feeding damage can occur at leaf margins but typically larvae like to feed on the underside of leaves where they consume the lower leaf epidermis thereby leaving the upper cuticle. This damage is known as “window-paning” as one can see through the damaged portion of the leaf.
Nymph and adult grasshoppers can be a problem during seedling emergence. During years of high populations, grasshoppers migrate into emerging stands and can devour entire cotyledons. Damage is usually limited to the field margins, but total stand loss there can occur. An economic threshold of 7 to 12 grasshoppers per square meter is recommended for treatment.
Tarnished Plant Bug
Tarnished plant bug (TPB) adults are approximately 5 mm (1/5 inches) in length, mottled, yellowish-to-reddish-brown in color and have a small triangle shape on their back. Feeding on flowers can cause flower abortion. Feeding during pod stages results in scarring, malformation and dimpling or pitting of the pods. Sap may ooze from the feeding sites on the pods, which increases the risk of pod disease development. TPB can also drill directly into the seed thereby reducing seed quality. Yield losses of up to 20% have been observed.
There are a number of beneficial insects in canola systems. Beneficial insects can be classified as predatory, parasitoid, or pollinator insects. As with small grains production, predatory and parasitoid insects benefit crops by controlling pest insect populations. Unlike small grain production systems, pollinators are an important aspect of canola production
Canola is an attractive plant to many types of pollinators such as Honeybees, Bumble bees, Mason bees, and various types of Butterflies and Moths. Beekeepers have been known to bring up hives and place them next to fields. Therefore, if pests rise to levels that require an insecticide application, try to apply insecticides later in the day towards the evening hours or at night when bees are less active, or during the early morning hours before bees start to actively forage.
Parasitic and Predatory Insects
As for pollinators, care should be taken anytime an insecticide is to be applied to a crop. Oftentimes, natural enemies such as ladybird beetles, lacewing larvae, syrphid larvae or parasitic wasps can be found feeding on or parasitizing Cabbage aphids or other pests of canola. Insecticide treatments should only be applied if pest levels have reached or surpassed “Action-Thresholds.” Both insect pest and beneficial presence and numbers can be determined through sampling with an insect net or beating tray.
For more information on insects contact: