Chemical Control for Aphids: Spring 2024

For those of you relying on chemical control for aphids in spring crops, some of you might have observed that Beleaf (Aria in the U.S.) has not been working as well recently, especially in green peach aphid (Myzus persicae). This post will fill you in on what we know about potential resistance to flonicamid in aphids, and which chemicals are working.

Is Resistance to Beleaf/Aria a Thing?

Green peach aphid. Photo by OMAFA.

Beleaf has long been relied on as the main control for aphids in greenhouse crops in Canada and the EU, given it’s relatively “soft” nature on natural enemies. However, overuse of a single active ingredient often leads to resistance.

Resistance to flonicamid in melon/cotton aphid (Aphis gossypii) has already been reported 16 separate times, in both the U.S. and Asia, according to the Arthropod Pesticide Resistance Database (run by Michigan State University and the Insecticide Resistance Action Committee (IRAC)). Resistance in this aphid species was first reported in 2013.

Although it looked like we had dodged a bullet when it came to green peach aphid (Myzus persicae) becoming resistance to Beleaf for the past decade, that time may be over. Koppert rencently reported the presence of a more “aggressive strain of Myzus persicae” in Dutch sweet pepper greenhouses. Research by Wageningen University Research Centre confirmed that certain strains or “lines” of green peach aphid found in these greenhouses were much less sensitive to flonicamid (see Figure 1, below). These strains were dominant (more common) in greenhouses that regularly sprayed flonicamid.

Figure 1. Responses of Myzus persicae to flonicamid. This graph shows the average mortality of nine different aphid lines, when exposed for 96 h to five concentrations of flonicamid (2, 4, 8, 16 and 32 mg/L). The black line represents the average mortality of all aphid lines together. Graph taken from Beekman et al. 2024.

Myzus persicae and other aphids are prone to developing resistance to chemicals, party as a result of reproducing mainly by cloning. A separate 2024 research report from the Netherlands showed that aphids collected from disparate greenhouses in 2019 actually all shared the same common ancestor, illustrating that resistance genes can easily spread to different farms.

Currently, if you are finding Beleaf still works well for you, then keep using it. One caveat to the study above is that the maximum rate of active ingredient tested is somewhat lower than that in the actual product at the label rate (e.g. 32 mg/L vs. 50 mg/L of a.i. in the EU). Further, resistance is likely to vary widely by country, region, and possibly even by farm. But given the new research results above, which indicate less-susceptible strains exist and can proliferate, a wise course of action would be to always rotate Beleaf (IRAC group 29) with a chemical in a different class.

If you DO think you have a Beleaf-resistant population of green peach aphids and you’re in Ontario, then contact myself (sarah.jandricic@ontario.ca) or Cara Mcreary (greenhouse vegetable IPM specialist; cara.mccreary@ontario.ca) and we’ll come collect samples for research!!! (Please let us collect live samples before you nuke them with another chemical!)

Alternatives to Beleaf for Aphid Control

If you are one of the unlucky ones finding Beleaf isn’t working well on your farm, the easiest way to look up alternatives to Beleaf in Canada is to go to OMAFA’s Crop Protection Hub and check out the Greenhouse Ornamentals module.

In Crop Hub, you can search for “aphids” as a pest using the drop-down menu on the right side. By clicking on the “view efficacy breakdown” button on the card for each pesticide, you can see how effective a product is as either a foliar spray or a drench.

A screen shot of the efficacy information available in Ontario’s Crop Protection Hub.

Depending on your needs, you can also change the way information is sorted. If you’re most concerned with compatibility with natural enemies, the default sorting will list chemicals by their compatibility with both insect and mite natural enemies first, then by chemical group. Products with good efficacy against aphids that are considered “soft” include Ventigra (afidopyropen) and Ference (cyantraniliprole).

The default sorting method in Crop Hub lists chemicals by compatibility with natural enemies first. Other selections include sorting by trade name or IRAC group. Sorting by efficacy will be a feature in the next few weeks!

If application method is your main limitation, you can also choose drench, foliar spray, or other methods via the “application method” filter on the right hand side. Non-neonic products that can be drenched – and therefore tend to offer longer-acting control – include Kontos (spirotetramat), Altus (flupyradifurone) and Ference (cyantraniliprole).

Oleander aphid on mandevilla. These aphids are not good candidates for biocontrol, and can also be difficult to control chemically.

For more difficult-to-control-aphids in ornamentals, such as oleander aphid (Aphid nerii) or potato aphid (Macrosiphum euphorbiae), your best bet might be a one-two punch of a Rycar (pyrifluquinanzon) spray with a Kontos (spirotetramat) drench. This has been working well in crops where aphids are one of the main pests (e.g. oleander aphid in mandevilla), and there are fewer concerns with Kontos potentially affecting natural enemies.

Here’s wishing you an aphid-free Spring!