Battling aphids with biologicals

“Certain parasitoids attack certain aphids,” says Raymond Cloyd, professor and extension specialist in horticultural entomology/plant protection at Kansas State University. “For example, aphidius colemani attacks green peach and melon aphid but will not touch potato or foxglove aphid. Those aphids require a different parasitoid.”

 

Cloyd recommends the use of parasitoids and green lacewing when battling aphid populations. Both insects are aggressive predators. He says that ladybugs will work in the greenhouse, but require a larger population of aphids to satiate themselves. Frequently, the aphid population reaches too great a number before ladybugs are fully effective.

 

To keep parasitoids and green lacewings sated, growers should consider adding a banker plant system, plants that will attract and feed natural predators of aphids.

 

“Parasitoids work very well in, what I would call, inoculated releases or with banker plant systems,” he says. “A number of our growers use both and they’re very happy with the results. The key is making sure they get the aphid identified correctly, so they can release the proper parasitoid.”

 

He notes that aphids feed on terminal leaf growth, making them fairly easy to spot.

 

“What you’re looking for are insects with two tubes on their butts, called cornicles. In a lot of herbaceous material, aphids are obvious because they feed in such large numbers. Unfortunately, when you get to that point, it may be too late,” he says.

 

He adds that color is not a way to identify aphid species, which is why growers should seek external help. Once aphids are spotted, growers should capture a few and send them to a lab for identification.

 

Cloyd says growers can look for aphids’ indirect effects in the greenhouse as well. The insects leave molting skin behind, as well as the honeydew they produce. To spot those effects, or to find the insect themselves, growers must physically examine their plants.

 

“You should also know the plants you grow and which ones are susceptible to aphid populations. One of my favorites is variegated sweet potato vine, but it’s always getting aphids,” Cloyd says. “You can use those as indicator plants, to let you know that aphids are up and coming, which will help you time the release of your beneficials.”

 

 

The mantra for biological control is prevention.

 

“You really have to get your parasitoids, your predators, out there early enough that you’re not going to have to deal with outbreak populations,” Cloyd says. “In the case of aphids, you have to do visual observations. If you catch flying adults on sticky cards, you’ve already lost the game. That means the population levels are extremely high and biologicals will not provide any suppression that will save or salvage the marketability of a crop.”

 

To properly set up your biologicals program, Cloyd says growers should be sure there is a food source present. So there must be some aphid population to sustain the biologicals. That’s where banker plants can come in handy. Then, once a grower has spotted aphids, they should order parasitoids. Place the container near the population, so that when the parasitoids emerge, they’re directly next to the aphids.

 

“The thing about using parasitoids is that you have to make sure you take down your yellow sticky cards. The parasitoids will be attracted to the yellow. Take the cards down for about a week and then put them back up. Then, continue to scout on a regular basis,” he says.

 

Cloyd adds, with emphasis, that to contain aphid populations with biologicals, growers need to act preventively.

 

“You really have to get your predators out there early enough that you’re not going to have to deal with outbreak populations,” he says.