Kale seems to be all the rage among those who want to live healthier. Most have referred it a “superfood with staying power.” That’s quite a statement in support for this leafy green that has been around since Roman times.
Customers often buy kale because of its vitamins and minerals, such as vitamins A, C, K and B (in the form of folate), and the minerals such as phosphorus, potassium, calcium and zinc, according to WebMD. It also has few calories, only 33 in one cup of raw kale. Two more benefits include nearly 3 grams of protein and 2.5 grams of fiber. Importantly, kale has alpha-linolenic acid, which is an omega-3 fatty acid that is supposed to help lower cholesterol. Additionally, kale contains the nutrients lutein and zeaxanthin that give this green its deep, dark color.
No flies, please
Keeping kale dark and green in the field and maintaining vitamins and minerals in the plant mean growers must control insects that feed or suck on this leafy vegetable. One such pest includes the whitefly. Entomologists with the Integrated Pest Management (IPM) program at the University of California describe the whitefly as a very small insect that likes to suck the plant’s sap. It can eat too much without fully digesting it all, causing it to release sticky honeydew. This substance can either kill the plant or, unfortunately, turn the leaves yellow, losing that dark color that is so attractive to customers at farmers markets.
There’s more bad news for customers and growers – management of whiteflies becomes difficult once their numbers increase to uncontrollable levels, according to the IPM entomologists at the University of California. Whiteflies especially like to build up underneath the leaves, where they want to lay their oblong eggs. So, growers are wise to learn how to identify these pests. The adult whitefly usually has a yellowish-colored body and four white-colored wings. However, depending on the species, a few may appear wingless and leg free. Nymphs range in color from light yellow to white and sometimes black colored.
Whiteflies prefer to come out during the daytime when the sun is out and temperatures are warm, according to Bruce Barrett with the Division of Plant Sciences at the University of Missouri Extension. If growers want to inspect their kale leaves for whiteflies, all they need to do is touch the leaves and watch for large numbers that may quickly fly away. Adults stretch 1/10-inch to 1/16-inch long. Females can lay between 200 and 400 eggs! In a week’s time, eggs hatch. Out come flattened nymphs that scatter around the plant. Before long, they start feeding and continue for about four weeks. Once they leave a pupa stage, adults emerge.
Adult whiteflies carry four wings and can colonize a host plant, according to Carlos Bográn and Kevin Heinz, entomologists at Texas A&M University. Adults can fly about, traveling long distances, and the wind can carry them on its air currents. Adults can lay their eggs underneath kale leaves, usually randomly. The adults and nymphs can feed by punching their mouthparts into kale plant tissue then sucking out the sap. This feeding can stunt plant growth. Indirectly, the sticky honeydew left from whitefly feeding also can damage the plant. Mold can grow where the feeding occurred, reducing light and photosynthesis taken up by the plant. Besides the aforementioned damage, whitefly damage can encourage viral diseases.
Growers are wise to try an IPM approach when dealing with whiteflies. Bográn and Heinz advise growers to implement cultural control practices so they can limit whitefly colonization, monitor populations frequently, identify species of whiteflies accurately and use effective pest management tools such as insecticides to control them and to limit exposure to natural enemies.
Entomologists advise growers to avoid a population buildup of whiteflies. Natural enemies can help control them, but if insecticides should disrupt or kill these enemies, then control is lost and could lead to large numbers of whiteflies. For more management, growers can remove leaves with high populations or hose down leaves with water. Reflective mulches and yellow sticky traps may help as well, although commercial growers may need quite a few. Natural control may also involve insecticidal soaps or oils. Commercial growers can apply systemic insecticides, understanding that these may kill beneficial insects.
Some beneficial insects or natural enemies of the whitefly are lady beetles, lacewings and spiders, Barrett noted. He likes sticky traps for inside greenhouse use. Growers can build their own by taking a 12- by 6-inch strip of cardboard or posterboard. He suggested painting both sides a bright yellow to attract adult whiteflies. If growers apply a sticky substance on the board such as a petroleum jelly, mineral oil or heavy grade motor oil, whiteflies will stick to this trap. Barrett advised growers to hang the manmade trap over the kale plants. Put out the traps when whiteflies first start appearing. If populations decrease, remove the traps so natural enemies won’t become stuck. Growers who want to spray with an insecticide are warned that it may take four to five applications during a 5- to 7-day interval, spraying directly to the lower part of the leaf. Besides those mentioned, growers can apply pyrethrin, permethrin, imidacloprid or a malathion. Make sure to follow label directions.