The spring bedding crop season is over, so now’s the time to reflect on what worked, and what didn’t, for foxglove aphid control. This way we can prepare for their re-appearance in the fall.
To recap, foxglove aphid (Aulacorthum solani) is a “cool weather pest”. It prefers temperatures between 15-25 C, and can’t survive in the greenhouse in summer (1). Unlike other aphid pests, foxglove aphid tends to feed in hidden locations – primarily the lowest leaves of plants – making it difficult to detect and treat.
And, unlike green peach and melon aphid, biological control of foxglove aphid is definitely a challenge.
Some growers and consultants have been trying both Aphidius ervi and Aphidius matricariae for foxglove aphid. But, as demonstrated by the Buitenhuis Lab here at Vineland, foxglove aphid is a terrible host for A. matricariae, and this wasp will barely parasitize it (see graph). Further, using A. matricariae for foxglove aphid can actually end up spreading this pest, and it’s damage (2). This is because the wasps simply pesters the aphids to the point where they drop of the plant and go find a quieter place to eat. So it’s pretty clear that releasing A. matricariae is simply a waste of money and effort if you’ve got foxglove aphid.
- Parasitism rates of foxglove aphid by different Aphidius species. Wasps were offered 50-60 2nd instar aphids. Tests were done in small plastic containers.
But what about A. ervi? Although parasitism rates were high in the lab (73%), results were not as good in practice. Tested in the greenhouse, A. ervi was able to offer about 50% control of foxglove aphid after 1 release. Repeated releases may offer greater control, but this is still not reassuring when you’re talking about a pest where populations can explode quickly.
Why A. ervi does a great job of parasitizing foxglove aphid the lab, but not the greenhouse, is something we’re currently investigating. But until we have an answer, it seems that pesticides may currently be the best option for control of foxglove aphid in floriculture IPM programs. With the current limitations on neonicotinoids, growers will want to turn to Beleaf or Endeavor. (But, since these two chemicals have similar modes of action, and it usually takes several sprays of either to provide complete control, you may want to consider rotating these chemicals with Enstar II to prevent resistance).
If you’ve had infestations of foxglove aphid in your greenhouse, and have anything to say about it’s control, feel free to leave me a comment!
I just discovered some foxglove aphids in our gerbera crop again. We could not control them in the spring using banker plants with aphidius matricariae and colemani and even ervi didn’t do much. Beleaf worked well so I think I’ll use that again for now. I was surprised to see them so soon since it hasn’t been that cool yet.
Hi Matthew; thanks for the comment! This is the first time I’ve heard of foxglove aphid on Gerbera! Cut or pot? If it’s cut, I’ve often wondered if a few sneaky ones can hide out when it’s hot (maybe near the soil surface, where it’s coolest), then to re-emerge suddenly when the temp drops a bit. I’d love to come see them sometime.
Potted gerbera and you can stop by anytime. We had to deal with them in the spring but up to that point I had not seen them in the gerbera crop for years. Usually, we mainly have to deal with the peach morph of the green peach aphid which can be very successfully controlled with matricariae. The foxglove aphid are difficult to spot because the hide underneath the leaves so you really have to scout for them.
Hello,
have you evey try larger predators as chrysoperla? I know that the big challenge is to keep them in the greenhouse but if more and more and released, don’t you think it could have an impact? We have tried them but few times and no real success but I keep confident!
I currently have observed that foxglove aphid makes up 75 percent of aphids in my cold houses where potato aphid Macrosiphum euphorbiae around 25 percent. I find ahidius colemani works very well on the smaller instars of these aphids. I have witnessed colemani being able to perform in very cold environments provided the canopy is dense. They begin working in early February , as for aphidius ervi, I have spotted them in small numbers in a house that dips to 45 degrees, there are much less ervi than colemani which are more abundant. But I have good control when I introduce both of these ahidius in the early spring. Remember that both of these aphids will produce winged forms in the fall and in spring (well before numbers increase as when you usually see this winged forms appear) which allows them to spread to many areas of the greenhouse. Scouting in winter in my houses , I will see a lone alate with a couple nymphs in semi diapause just waiting for light increase causing production to increase significantly. The aphidius winter over and I know this because before release of fresh wasps in early spring I find parasitization already occurring.
I do believe that fresh aphidius should be released as soon as temps permit though. Current information does hint at colemani paraisitizing the smaller instars of both these large aphids but correctly state that they may add to control. I have found this to be true for colemani in this case.