Avoiding aphid angst

Aphids are little insects that can make a big impact on produce yields, sucking out crops’ vitality and spreading plant viruses. Hard to spot until it’s too late, they’re one of the most destructive pests on cultivated crops.

“Aphids are a pest because they develop very quickly,” says Hugh Smith, assistant professor of vegetable entomology at the University of Florida. “They have a complex lifecycle. … It’s a really accelerated production, and in some cases some species don’t even need to mate; the females produce babies on their own. So they’re very well adapted to build up quickly … and when you’re in a greenhouse, they’re protected from a lot of their natural enemies.”

The key to protecting your production is to take steps to catch an aphid threat as early as possible and mitigate impact. Knowing what to look for and how to respond will make a difference to your operation’s bottom line.

Identifying a threat
There are many different types of aphids, which are known as plant lice. Some are plant-specific, while others attack a wide array of plant material. Color for these pear-shaped pests varies, including green, yellow, orange, brown and black. Common species affecting produce growers are green peach aphids, potato aphids and bean aphids.

At low population levels, warning signs are few and far between. Yellow sticky insect cards can be used to detect the aphids’ winged form if present, and you can train your team to look for the pest in key spots on crops. They’re attracted to new growth cells, such as topside growing spots or shoots off the side. They are also common on the underside of leaves.

“Implement as rigorous a scouting program as you can to detect as early on as you can,” Smith says. “Have a good scouting program looking twice a week, with a trained crew.”

As an aphid population builds up, you’ll spot a sugary, sticky excretion called honeydew on your plants. This honeydew often promotes sooty mold growth. Because the aphids suck sap from plants and distribute poisonous saliva (as well as often carry viruses), crops typically show signs of stunted growth, wilted and curled leaves, and discoloration in a bad infestation case.

Key risk factors
First and foremost, realize that if you’re a greenhouse grower, regardless of region, you are going to get aphids. Aphids will get in from the outside, and there’s no way around it.

“There’s no way you can really keep aphids or other pests out,” Smith says. “You may raise the walls on your structure or have a porous roof structure. Even if you have a tightly sealed operation, they can still sometimes get in through ventilation openings and things like that.”

You can reduce your risk for contracting this insect by diligently avoiding contamination from new material.

“If you’re getting your material and seedlings from somewhere else, you want to be in communication with your supplier and make sure your supplier is someone who follows good practices in terms of giving you the cleanest material possible,” Smith says.

Identifying how prevalent ants are in your operation can also alert you to your risk level. Some ant species actually farm aphids, a mutualistic relationship in which the ants provide protection for them on leaves to reap the dietary benefits of aphids’ honeydew excretion. The more ants you have, the more encouraging an environment aphids may find.

Mitigation and management
There are several measures you can take to manage an aphid infestation among your crop yield. In addition to your human scouting crew, employ a cavalry of beneficial control insects. Lady bugs, lacewings and parasitic wasps (they don’t sting humans) are common predators of aphids.

Insecticides can also be effective, particularly newer systemic insecticides taken up by the plant roots or from foliage.

“(Aphids) have this sucking, piercing mouth like a couple straws put together that they use for sucking the sap out of a plant,” Smith says. “So when aphids are actually sucking on the plant’s sap or juice … they’ll be sucking up the insecticide.”

But Smith warns that many insecticides can be too harsh for greenhouse use, particularly with food crops.

“There are protection issues; you don’t want to spray something toxic in an enclosed area,” Smith says. “Switch to more selective, softer insecticides if that’s what you’re going to use.”

Some growers support organic alternatives to synthetic insecticides. Such options include insecticidal soap, pyrethrin, and neem oil, although opinion on effectiveness varies.

You can also take a simple, hands-on approach by wiping off or removing leaves with aphid colonies by hand and spraying down plants with pressurized water to dislodge clingers.

Keeping your food crops clean of aphids is key to maintaining fruitful stock and providing pest-free plant shipments, which is critical to maintaining a positive bottom line.

“They’re a very common pest,” Smith says. “In vegetable production, people need to be concerned about them just about everywhere. Any grower should get familiar with what pests they’re expecting.”

Jessica Hanna is a frequent contributor to Produce Grower magazine.