Yellow sticky cards can be a great tool for any gardener. They’re used to help monitor insect populations, as well as to collect insects for identification. They can also be used to a lesser degree for population control; however, they’ll only work for adult insects, as only adults will have developed wings, enabling them to fly into the cards. (Immature insects or mites would have to crawl onto the cards – a much less likely scenario.)

Aphid on sticky card

Most insects are attracted to the color yellow.

Photo Credit: Most insects are attracted to the color yellow.

Sticky card

Sticky cards can be a great tool for gardeners.

Photo Credit: ©2004 Buglady Consulting

How do sticky cards work? As the adults are flying around, they “see” the yellow and are attracted to it, flying right into the card. They immediately begin to struggle and become trapped on the adhesive, often in a twister-like position, just like fly paper. From here you can use these stuck insects to help identify them. To do this you’ll need a magnifying lens from 5X-10X magnification. (They can be purchased through the Internet or at a hobby store.) Use the lens to help identify the parts that are visible. Once done, you can discard the card or put it back. Remember pests stuck on the card may be long gone, so keep the cards fresh. Change about once a week.

Fungus gnats are probably the most common pest that these cards are used for, but other pests can also show up on them. As you examine your cards, keep an eye out for insects like shore flies, whiteflies or even aphids. It’s very important to be able to tell them apart on the cards so you know what to target when developing your pest management program.

Common pests attracted to yellow sticky cards include:

Fungus gnats

These are small (2.5 mm), grayish to black flies often found buzzing around the soil of houseplants. Fungus gnats resemble tiny mosquitoes with long legs and long, skinny antennae. Their two wings (not four, like other insects) are shades of smoky gray. The larvae live in the soil, eating plant roots. Because the larvae are generally not above the soil line, they can be difficult to monitor. Don’t forget: Not only are these guys a visual pest problem, they can also spread plant diseases.

Whiteflies

Adult whiteflies are tiny insects that resemble moths, but they’re covered with a white, waxy powder. They’re rarely more then 1-3 mm long and are typically found on the underside of leaves. Whiteflies can be a garden pest on tomatoes and other flowers. If you have sticky cards, the adults will head straight for them. The immature stage of whiteflies is also found on the underside of leaves, and can be easily confused with scale insects. The immature stage can be easily controlled with insecticidal soap or horticultural oil.

Aphids

Now these girls (Aphids don’t have to mate in order to have babies!) are a little different. Just because they’re adults, it doesn’t mean they necessarily have wings. Only when aphid populations get high enough do you find some fliers. If you do find winged ones on your sticky cards, you know there’s a serious aphids problem around. Aphids are round, soft-bodied insects usually 1-3 mm long. Keep in mind once they stick to the cards their bodies will dehydrate, causing them to look more shriveled. Colors may vary from black to brown, green, yellow, red and even pink. The key to identifying an aphid is to look for structures called cornicles. They’re tubelike structures found on the backside of the body.

To control aphids you can simply manually wash them off your plants or treat with an insecticidal soap or horticultural oil.

Other random insects may show up on your cards – just keep in mind only a small percent of insects are actually pests, and some of what you’re trapping may in fact be beneficial insects.