Agricultural News
Producers Need to Check Canola for Effectiveness of Seed Treatments on Aphids
Fri, 21 Oct 2011 13:36:47 CDT
Last week, we talked about some seedling canola that was being infested with diamondback moths and cutworms and stressed the importance of regular scouting, preferably 1-2 times per week to avoid problems while the seedlings are vulnerable. This is also a good time to check and make sure your insecticide seed-treatments are working. We recommend treating canola seed with an insecticide/fungicide treatment to protect seedlings from aphids and seedling diseases. Registered insecticide active ingredients include imidacloprid (Dyna-Shield Imidacloprid, Gaucho 600), thiamethoxam (Acceleron IDL, Helix Lite, Helix Xtra), or clothinaidin (Poncho 600, Prosper).
Products like Gaucho XT and HelixXtra include an insecticide and a fungicide, but it is not a given that a seed treatment will include one of the aforementioned insecticides. For example, Allegiance FL, Dynasty and Sebring are fungicide seed treatments that don't include an insecticide in the formulation. Even more confusing, is that Dyna-Shield Metalaxyl 318 is a fungicide seed treatment registered for canola that does not include an insecticide, but Dyna-Shield Imidacloprid 5 is an insecticide seed treatment that does not contain a fungicide. Seed treated with an insecticide is effective in controlling aphids through the fall, but if the seed was treated with a fungicide only, it is critical to watch for aphid infestations because they can quickly infest a field and take out stand.
We suggest that producers use their field-time to evaluate whether the seed treatments are working as expected. Three aphids are commonly found in canola: the cabbage aphid (Brevicoryne brassicae), the turnip aphid (Lipaphis erysimi), and the green peach aphid (Myzus persicae). Don't confuse these three aphids with the greenbug, which attacks wheat but does not infest canola.
Cabbage aphids are a medium-gray. Turnip aphids are bluish-green. Green peach aphids vary in color from medium green to yellow and, in cool winter months, reddish-brown. Mild fall and early winter temperatures can allow aphids to rapidly increase in number.
OSU's canola research program has not established treatment thresholds for aphids in untreated seedling canola, but recommendations from the University of Georgia suggest a threshold of 2 aphids per plant at seedling stage. Later in the winter, once the seed treatment is diminished, our suggested threshold for aphids in rosette stage canola that was protected with an insecticide seed treatment is 100 to 200 per plant. If the seed was not treated with an insecticide, the threshold suggested by the University of Georgia is 5-10 per plant. The difference between the thresholds is that aphid buildup will be delayed if the seed had already been treated with an insecticide and the plants will be larger and more able to tolerate a small infestation.
Green peach aphids and diamondback moths have something in common. Both are notorious for developing resistance to insecticides, particularly pyrethroids, which are the primary registered insecticides for use in canola. The only other non-pyrethroid insecticide registered for aphid control is methyl parathion. Therefore, select the high end of any labeled rates AND apply at maximum gallonage insure thorough coverage. This will reduce the possibility poor control. Also, rotate between insecticide classes to avoid selecting for resistant aphids.
Current recommendations for control of aphids in canola are listed in CR-7667, Management of Insect and Mite Pests in Canola.
Our thanks to Tom Royer and Kris Giles with Oklahoma State University for providing this article over checking aphids in canola. This article was sent out as part of the Extension News from Oklahoma State University's Department of Plant and Soil Sciences. Click here for more Extension News articles.
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