The unmistakable clusters of purple flowers and distinctive, fragrant scent of wisteria (Wisteria spp.) are readily linked to the onset of spring. Not a fussy plant, wisteria grows well in most environments, is considered invasive in some, requires only a modest amount of water and takes to most any type of soil. Given plenty of sun and a good pruning to encourage growth, it will return season after season. Continued growth hinges, however, on the plant surviving being eaten by one of its four pests.
According to the University of California Agriculture and Natural Resources' Integrated Pest Management Program, the bean aphid often eats woody ornaments like wisteria. The insects are small, black and as its name implies, shaped like a bean. To prevent the pest from feasting on the plant, check wisteria often in the early growing season when temperatures range between 65 and 80 degrees Fahrenheit. The UCIPM also recommends watching for large amounts of ants, because they are a strong indicator of an aphid infestation. Aphids can be controlled naturally by its enemies, the parasitic wasp, lady beetle, soldier beetle and syrphid beetle. For chemical control, use an insecticidal soap or oil, either of which smothers the pest. Spray the leaves on both sides liberally, and when possible spray pests directly. The University of California Agriculture and Natural Resources recommends mixing 1 to 2 percent oil with water and spraying onto both sides of the leaves. Repeat the application if necessary as the product only rids aphids spayed at the time of application. Carefully follow the manufacturer’s instructions for mixing the proper amount of water with the oil.
Armored scales also eat wisteria. These insect pests are often hard to identify because they look like a physical abnormality of the plant. Yet, sticky honeydew it excretes makes the pests’ presence known. The parasitic wasp can control scale population. For a severe scale infestation, treat with a horticultural oil. Because mixing varies with each manufacturer, carefully follow the label instructions. Spray the oil just after crawlers have emerged, usually in spring or summer.
Soft scales are also a threat to wisteria. About one quarter of an inch or smaller, soft scales are waxy, smooth or cottony. Like the armored scale, soft scale is best controlled by natural predators and parasites. Horticultural oil may provide the best defense against a heavy infestation. As with armored scales, soft scales should be sprayed in early spring or summer. Be sure to follow the manufacturer’s instructions for proper mixing.
Unlike scale, the longhorned beetles are easy to detect. The pests are brightly colored and have long antennae. They also leave marks of their handiwork behind creating holes in bark or seeping liquid from trunks or limbs. The University of California Agriculture and Natural Resources points out that longhorned beetles largely attack dying or damaged plants. The best defense against this pest is a healthy tree or vine as pesticides are not generally effective. Wisteria is kept healthy by pruning in early summer or late spring and applying fertilizer to young wisteria once a year. Mature wisteria typically only needs fertilizer to address conditions brought on by drought. When pruning, disinfect your tools, wiping them with rubbing alcohol.
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