Tom A. Royer, Extension Entomologist
I have received scattered reports of cabbage aphids infesting canola racemes and low levels of green peach aphids feeding on canola leaves. Cabbage aphids are small, 2.0-2.5 mm (1/12 inches) blue-gray aphids with short cornicles. They are usually covered with a powdery wax coating. They are often found clustering on the developing panicle (Figure 1). They can cause plant stunting, distortion of growth, and flower abortion.
Green peach aphids are pale green to yellow (and sometimes pink) with long cornicles and antennae and measure 1/8 inch. They are found in winter and spring on leaves (Figure 2). Their feeding can cause stunting and defoliation. They can also transmit plant disease-causing viruses such as cauliflower mosaic and turnip mosaic viruses.
Scout for aphids by looking on the underside of the leaves, and racemes. For cabbage aphids, research conducted in Australia suggests that an insecticide application is justified if 20% of the racemes are infested with cabbage aphids.
For green peach aphids, research conducted by Dr. Kris Giles at OSU found that and average of one green peach aphid per plant can reduce seed yield by about 0.5 lb per acre. Thus, if the cost of an application is $10 per acre, and canola is bringing $0.2 per pound (quote from ADM Farmer Services 04/08/2016 www.adm.com), an infestation of 100 aphids per plant would cause yield loss of $10.00 (50 lb, x $0.2/pound) which is equal to the cost of the application. This is known as the ECONOMIC INJURY LEVEL (EIL). We typically set the ECONOMIC THRESHOLD (ET) below the EIL, in this case at 80% of the EIL (80 aphids per plant) to give time to schedule an application before the EIL is reached. Below is a set of suggested ECONOMIC THRESHOLDS, based on the cost of the application.
Application Cost Economic Injury Level Economic Threshold (Application cost/
0.5 lb/aphid x $0.2/lb (0.8 x EIL)
$8.00/acre 80 aphids/plant 64 aphids/plant\
$10.00/acre 100 aphids/plant 80 aphids/plant
$12.00/acre 120 aphids/plant 98 aphids/plant
$14.00/acre 140 aphids/plant 112 aphids/plant
Current recommendations for control of aphids in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola which can be obtained online at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-3045/CR-7667web2009.pdf.
Transform® insecticide is no longer registered for use in canola as of November 11, 2015. Only existing stocks that have already been purchased and delivered to the grower before the cancellation can be applied according to the label.
Remember, green peach aphids have a history of developing resistance to pyrethroids, which are the primary registered insecticides for use in canola. Thorough coverage of an insecticide application is necessary to obtain optimal control.
If you notice natural enemy activity, especially lady beetles, and want to preserve their activity, keep several things in mind. Our research shows that Beleaf® insecticide is particularly benign to natural enemies because of its slow acting efficacy on aphids, which allows aphid-feeding beneficials to continue to eat them with little to no consequence on their biology. That being said, cabbage aphid may contain toxins that they acquire through their feeding which make them less palatable to some predators, and reduces their effectiveness as natural controls.
With all pesticides, review label restrictions for applications during bloom, as honeybees can be killed if exposed to several of the registered products. One registered product, Beleaf® (FMC Corporation) does not have any restrictions for application during bloom.