by CAAHP Ornamental Horticulture Educator, Lindsey Christianson
Many of you have already seen and possibly already treated for aphids in your greenhouses, but with the cool weather keeping everything closed up, interiors are perfect for aphid populations to rebuild. If you use biological control agents for aphid management, you’ll want to release them as soon as possible.
How do you decide which beneficial bug to release?
First things first: Are you finding green peach, melon, or foxglove aphids? Cornell University’s Dr. John Sanderson put together a quick guide (pdf) to help identify these three aphids that will probably be the most likely to show up in your greenhouses.
I found these foxglove aphids on fuschia in a greenhouse on May 1. This species can be distinguished from green peach aphids and melon aphids by 1) the antennae that are longer than their body, and 2) the dark green patches on their posterior, around the cornicles.
Melon aphids are generally the smallest of the three, and range in color from a very light yellow to a dark green/almost black. The easiest way to distinguish these from foxglove and green peach aphids is that the entire length of their cornicles are black.
Green peach aphids exhibit a range of colors also, but have shorter antennae that don’t extend the full length of their body.
The predatory midge Aphidoletes aphidimyza is a great way to get started in aphid management without necessarily having to know which kind of aphid you have. The larvae aren’t picky about which aphids they’re eating, and they’re voracious feeders.
Native lady beetles, Adalia spp. and Hippodamia spp., are also recommended. However, as generalist predators that are fairly large, they’ll eat just about anything, including each other and other beneficial bugs, so you may not want to add them to your biocontrol mix if you’re using midge larvae.
Parasitoid wasps hold a special place in my heart as I used to work with a number of them for invasive species management. But there are a few things to take into consideration before you release them into your greenhouse. You typically want to start releasing wasps prophylactically. Many of these wasps have a difficult time stinging if aphids are crowded on a leaf, or they can get stuck in the honeydew of aphid populations that have been around awhile. Wasps are pickier about the species of aphids they attack, so these may not be a good place to start if you’re not sure which aphids you typically find in your greenhouses. If you know that you usually find green peach or melon aphids, you’ll want Aphidius colemani. If you have had more issues with foxglove aphids, go with Aphidius ervi. If you’re not sure, you can release both species at the same time and they won’t interfere with each other. Make sure to at least temporarily take down your sticky cards around the release date because, like other hymenoptera, they’re attracted to blue and yellow.
For more biological control options, check out Dr. Lily Calderwood’s factsheet “Getting Started with Biocontrol”.
If you need to knock down a large aphid population and need to go the chemical route, UMass has a table of active ingredients that are effective against aphids and approved for use on greenhouse ornamentals. Since this information is out of Massachusetts, there may be some that aren’t registered in New York, so be sure to check on NYSPAD to make sure these products are okay to use in New York.
On the NYSPAD homepage, search “Products”.
Then you can search by the product’s trade name, or Advance Search to look up by active ingredient.
If you’ve already released biological control agents into your greenhouses, chemical applications will knock them back too, so you’ll have to keep a close eye on your aphid populations since those tend to bounce back more quickly than the beneficial insect populations.