Greenhouse growing, while truly great for many reasons, is not without its fly in the ointment, so to speak. Because it’s a closed environment that means  that natural predators are prevented from entering (unless deliberately introduced). So populations of pests can explode. There are several pests that are relatively common in greenhouses, including: aphids, fungus gnats, whiteflies, and spider mites.Recognizing what you have is the first step toward control and eradication. This step is critical, because you don’t want to treat pest problems indiscriminately with chemicals (or even biological controls), especially if you are growing edibles. Even though the word “pesticide” implies that it works on everything, the truth is that virtually all pesticides are very specific regarding what they target. Aphids: Aphids are soft-bodied, sap-sucking insects. Their pear-shaped bodies can come in a range of colors (green, orange, red, yellow). Aphids not only suck plant juices, weakening plants, but they excrete a substance called “honeydew” that can cause a condition called sooty mold. Treat by releasing lacewings or ladybugs (also called lady beetles). Insecticidal soap also works well, as does spraying with water and pruning off affected stems. Fungus gnats: Fungus gnats are tiny, blackish to grey flies. They don’t live very long, but they reproduce massively! Fungus gnats can transmit plant viruses, such as Fusarium wilt, and Botrytis. These are not good. Two organic controls are Bt (Bacillus thuringiensis) or Neem oil (as soil drenches). Don’t overwater. Whiteflies: Adult whiteflies look like tiny white moths. They also breed like crazy. The juveniles suck plant juices, like aphids. Also like aphids, whiteflies excrete honeydew, which promotes sooty mold. You can handpick heavily infested leaves (and throw them in the trash) or release lacewings or ladybugs. Spider mites: Important: spider mites are mites—not insects. These tiny creatures, hard to see with the naked eye, live on the undersides of leaves. They feed on leaves, bruising them so the leaves look speckled. The two-spotted spider mite is the one that most often infests greenhouses. Treat with insecticidal soap being particularly careful to get the undersides of leaves. There are actually predatory mites that feed on spider mites. Yellow sticky cards can also catch many insects, especially flying ones. Aphids, whiteflies, and fungus gnats are attracted by its yellow color and they get stuck on the sticky surface. |
