Oklahoma canola producers need to scout for aphids

Monday, February 27, 2017

Substantial numbers of turnip and green peach aphids were recently found in Oklahoma’s Canadian and Tillman counties, so winter canola growers need to be increasingly vigilant and protect their investment by scouting for aphids now.

“Turnip and green peach aphids tend to feed on the underside of canola leaves, so producers need to flip the leaves over and check, especially those leaves closest to the ground,” said Heath Sanders, Oklahoma State University Cooperative Extension area agronomist for the state’s Southwest District.

To sample for turnip or green peach aphids in winter canola, walk diagonally across the field and stop 10 times. Check three plants at each stop. Be sure to count the aphids on three consecutive plants. Note other spots with dead or dying plants as well as other areas of the field that do not look vigorous.

Turnip aphids are a pale grayish green with short, swollen cornicles. They measure about 1/16 inch in length. Winged adults can be recognized by the presence of transverse dark bands on the last two abdominal segments.

Green peach aphids typically are pale green to yellow in color – though some are pink – with long cornicles and three dark lines on the abdomen. They measure about 1/8 inch in length.

“The feeding of these aphids can cause stunting and defoliation,” Sanders said.

Canola growers also need to be aware green peach aphids have a resistance to pyrethroid insecticides, which are the primary registered insecticides for use with canola. Thorough coverage of an insecticide application is necessary to obtain optimal control. With that being said, increasing the carrier volume at application will provide better overall coverage.

“It is important to delay insecticide use until aphids approach operational economic injury levels because the use of insecticides on very low populations will result in net dollar losses to the producer,” Sanders said. “Also, the longer a producer can viably delay the first insecticide application reduces the chance on needing a second or even third application.”

Research conducted by entomologist Kris Giles of OSU’s Division of Agricultural Sciences and Natural Resources found an average of one green peach aphid per canola plant can reduce seed yield by about 0.5 pound per acre.

“If the cost of an application is $10 per acre and canola is bringing 20 cents per pound of seed, an infestation of 100 aphids per plant would cause a yield loss of $10, which is equal to the cost of the application, “Giles said. “We typically set the economic threshold below the economic injury level to give growers time to schedule an application before EIL is reached.”

To help safeguard against economic losses, insecticide applications should be employed per the following recommendations:
● If canola is bringing 30 cents per pound of seed, manage aphids when they reach 50-100 pests per plant;
● At 25 cents per pound of seed, manage aphids when they reach 60-120 pests per plant;
● At 20 cents per pound of seed, manage aphids when they reach 70-140 pests per plant;
● At 15 cents per pound of seed, manage aphids when they reach 80-160 pests per plant; and
● At 10 cents per pound of seed, manage aphids when they reach 90-180 pests per plant.

As with all insecticides, always follow label directions in regards to proper use.

“Even if you have used a specific insecticide in the past, it’s a good idea to read the label again to make sure you’re applying it correctly,” Sanders said. “Airplane pilots employ a checklist before every flight, no matter their level of experience, just to make sure they haven’t overlooked anything. Insecticide applicators need to do likewise.”

Control guidelines and information on registered insecticides are available online at http://osufacts.okstate.edu and the OSU department of plant and sol sciences’ Okanola webpage at http://canola.okstate.edu/cropproduction/insect.

Canola growers needing additional assistance should contact their OSU Cooperative Extension county office, typically listed under “County Government” in local directories.