Essentially, all crops we grow in Hawai‘i could be attacked by an insect or mite pest. They feed on the leaves, stems, roots, fruit—every part of the plant is fair game. Pests can reduce your garden’s yield significantly. In some cases, the entire crop can be lost to a plant disease transmitted by insects.
Of the most significant pests infesting our Islands, many are very small, and some barely resemble insects. So how does one go about fighting scale insects, mealybugs, whitefly, and thrips? It’s important to be able to recognize the pest, or the specific damage it causes, so you can take corrective action.
Mealybugs and Scale Insects
Mealybugs and scale insects are sap suckers that barely resemble insects, since they’re either covered by a protective shield or have a waxy covering. Most don’t have wings or even move. They suck fluids out of their food (plants), and excrete a sugary “honeydew” solution onto leaves. A black sooty mold grows on the honeydew, often the most noticeable sign of these insects. Another way to detect their presence is by looking for malformed leaves or stems.
Effective biological control agents are available in Hawai‘i for most species of scale insects and mealybugs. However, if something goes wrong – e.g., the beneficial insects are being killed by the insecticide – other pest-management options will be needed. Regular, manual sanitation (removing the infested parts by hand) does require time and energy, but it can be highly effective.
For widespread infestations of scale insects and similar pests, there are soap- and light oil-based insecticides such as Safer Soap®, PureSpray Green®, and Safe-T-Side®. (Please note: my mentioning any brand name or commercial product does not imply that UH/CTAHR endorses it). These products are less likely to impact creatures other than target pests, and should be safe to use. (Please follow all label directions when applying and storing the product, as well as disposing the empty container.)
Closely related to mealybugs, with similar biology—but as the name implies, the adults are winged and can fly. They feed on a wide array of crops and cause physical damage. Some also transmit pathogens like the Tomato Yellow Leaf Curl Virus.
Whitefly populations can become huge, producing large clouds of insects. Natural enemies usually keep their numbers under control, but if an outbreak occurs, you can buy pesticides similar to those used for scale insects and mealybugs. Or you can get tomato varieties that are resistant to the Yellow Leaf Curl Virus; some perform very well in Hawai‘i.
These small (less than 2mm in length) and potentially devastating insects are almost transparent as juveniles; adults have feathery wings. Thrips feed on the underside of leaves and on flowers and young developing fruit. They feed by breaking open plant cells, which are never replaced as the leaf or fruit develops. Instead, a silvery feeding scar develops. Severe infestations can result in badly deformed fruits, twisted and malformed.
Thrips transmit the Tomato Spotted Wilt Virus, which similarly can be combatted by growing disease-resistant varieties of tomatoes, which are available in Hawai‘i. We’ve also found that reflective mulches (almost like aluminum foil), laid in strips over planting beds below plants during the seedling transplant process, can deter thrips and whitefly. This mulch also may protect plant varieties that are susceptible to viruses carried by these insects.
For more information on pest insects, please visit our Crop Knowledge Master website. It’s currently being updated, but it still has lots of useful information!
Mark G. Wright, Department of Plant and Environmental Protection Sciences, UH College of Tropical Agriculture and Human Resources