Wisteria Borers Control: How To Fix Wisteria Borer Damage
By: Bonnie L. Grant, Certified Urban Agriculturist
Wisterias are magnificent winding vines that perfume the air lightly when flowers are present. The ornamental plants are hardy, fast growing, and prey to few pests or disease problems—most of the time. However, an important pest of the plant, the wisteria borer, is a beetle that tunnels into the woody stems of wisteria, causing interruption of the flow of water and nutrients. Knowing how to control borers on wisteria at an early stage will help protect the plant’s health and appearance.
Wisteria Borer Damage
Damage to the appearance of a wisteria is one of the obvious problems, but the issue goes deeper. The holes open up the plant to introduction of rot and disease, as well as other insect invaders.
The most important issue is the girdling of crucial meristem tissue on the interior of the stems. This tissue is responsible for ferrying nutrients and moisture to all parts of the plant. When the tunnel cuts through this tissue, the food and water are stopped from traveling to the rest of the stem.
Wisteria borer damage is the most problematic in young trees which have few reserves to help them battle back from infestations.
Types of Wisteria Borers
Boring beetles attack many varieties of plants and trees. The main types of wisteria borers are the long-headed borer or round-headed borer. These are actually beautiful beetles with vibrant coloring.
The long-headed borer has lengthy antennae and their larvae are called round-headed borers. These appear as chubby yellowish-white grubs with brown heads and evident mouth parts. Round-headed borers on wisteria cause the majority of the damage as they feed and tunnel into wood.
Some of the most common varieties that may become pests on wisteria are the Asian long-horned beetle and the spotted tree borer. Wisteria borer control begins before the adults lay eggs and prior to tunneling activity.
How to Control Borers on Wisteria
The first step to helping your wisteria is to keep it healthy. Healthy vines grown in good soil, with adequate nutrient and moisture supplies are able to withstand some of the boring activity.
Vines that are infested need to be removed so the borers can’t move into unbothered real estate.
Chemical wisteria borer control with residual sprays must be applied prior to adults laying eggs. The larvae will hatch and eat the poison as they feed, effectively killing them before they can reach the sensitive interior of the stems.
If larvae are visible, spray spinosad or Bacillus thuringiensis for non-toxic control. This must be done when the round-headed borers on wisteria are young to be effective.
“Low-Tech” Wisteria Borer Control
When all else fails, try the “pick and crush” method in early spring as larvae emerge to feed. Not only is this satisfying but it is non-toxic and requires no special equipment.
Another way to combat the pests is by fishing them out. Use a length of thin wire and twirl it around in the borer hole. You can skewer the larvae and then slowly, gently pull it out of the tree.
Some gardeners swear by putting a drop of a petroleum based product in the hole to coat the larvae and suffocate it.
Try any of these quick easy controls before you spend a lot of money on chemical solutions. They just might work!
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How to Manage Pests
Wisteria—Wisteria spp. Family Fabaceae (Pea family)
Wisterias are attractive deciduous vines that are often grown as trees and shrubs. They have large green leaves divided into many leaflets. Clusters of blue, white, or pink flowers bloom in spring, often all at once followed by pea-shaped pods. Foliage yellows in fall.
Optimum conditions for growth
Wisterias are very adaptable plants. Most do well in areas with full sun and require little to moderate amounts of water. They can tolerate many soil types but need good drainage. Prune and train to control the shape and size of the plants and to encourage bloom. Fertilizer is generally not needed.
- Armored scales
- Wisteria scale
- Longhorned borers
- Spotted tree borer
- Soft scales
- Calico scale
Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California
Aphids are small insects found in a variety of colors that use mouth parts to pierce tender plant parts and suck out fluids. Small numbers of aphids are generally not cause for alarm, but large populations can cause the wisteria leaves to curl, yellow and become distorted. Additionally, aphids secrete a sticky, sugary substance known as honeydew that acts as a food source for sooty mold. Aphids can be controlled naturally by predatory insects like ladybugs, lacewings and the syrphid fly. Prune out heavily infested leaves if the aphid population is extremely localized or knock off aphids with a strong spray of water. Horticultural oils, insecticidal soaps and a number of insecticides can be used to treat aphid infestations.
Japanese Wisteria (Wisteria floribunda)
Capable of growing to a height of 35 feet, the woody vine Japanese wisteria has been found to be invasive from mid-Atlantic to southeastern states. Japanese wisteria can girdle and kill trees and choke out the light in a forest setting. Both the Chinese and Japanese species are extremely invasive, smothering and choking out every plant in their path, yanking down trees and creating dense thickets if left unchecked.
No doubt, these spectacular vines are coveted for their breathtakingly fragrant, pendulous blossoms in lavender, pink and white. But gardeners seeking to add one of these gorgeous vines to that newly built arbor or pergola first need to consider the bigger environmental picture — not just their own little backyard snapshot.
Rustic Entryway with Wisteria and White Garden Plants
American wisteria climbs above an arched front door and stone entrance.
Photo by: Alex Smith Garden Design
American wisteria climbs above an arched front door and stone entrance.
How to Grow Native Wisteria
Give your American wisteria a spot with well-drained, moist soil and full sun (where the plant will get at least six hours of direct sunlight every day). They can take some shade too, but if you want to see hundreds of flowers every spring, planting in full sun is the way to go.
Do your planting in the spring or fall. You'll need to dig a hole that’s as deep as the root ball in its nursery container, and two to three times as wide. If you're trying to create your own version of a wisteria tunnel with multiple plants, space them at least 10 to 15 feet apart so each one has plenty of room for its roots to develop. Once you’ve filled in the hole, water well to help the soil settle around the plants, and add a layer of mulch on top to hold in moisture and prevent weeds.
Wisterias are drought-tolerant once they've settled into your garden, but you might still need to water them once a week if you don’t get at least an inch of rain. And for the best blooms, be sure to prune your plant every year in late winter. Wisterias flower on new growth and pruning encourages more stems to sprout on the plant. You can also prune the plant back in late summer after it blooms if you’re trying to keep it a certain shape or height.
The right wisteria vines can be a beautiful addition to your yard, but the wrongs one will quickly become pesky, problematic weeds. Pay close attention to plant tags when you’re shopping for a wisteria, and look for varieties of the native species they'll add gorgeous flowers to your yard without becoming a nuisance.
Damage caused by roundheaded borers and longhorned beetles
Roundheaded borers are commonly found in firewood, and the longhorned beetles may emerge from wood brought into the house. These beetles may also wander into houses by mistake as "accidental invaders." Longhorned beetles crawl about the house creating a nuisance but they cannot bite, sting, attack furniture or damage the house structure. They do not infest cured lumber (such as in the house structure or in furniture) nor dried firewood.
Wisterias are gorgeous climbing plants, perfect for covering walls and fences or grown over pergolas and arches where their flowers can be appreciated cascading overhead. They flower from mid-spring into early summer, producing delightfully scented flowers in shades of purple, white or pink.
How to grow wisteria
Wisterias need a sunny, sheltered position to flower well. They can be grown in very lightly shaded positions, but won’t flower as well.
They also need a soil that retains plenty of moisture in summer, but doesn’t become overly wet or waterlogged. If grown up against walls, the soil can become very dry, as can light, sandy soils, so may need watering during prolonged, dry periods – and certainly while plants are establishing. Give the soil a 7.5-10cm (3-4in) thick mulch to conserve soil moisture.
Types of wisteria
There are two main species of wisteria commonly grown in gardens:
- Wisteria sinensis is vigorous and only really suitable for covering large areas. It produces its flowers before the leaves appear.
- Wisteria floribunda is more compact and more suited to growing in smaller areas. It produces its flowers and leaves at more-or-less the same time.
Interestingly, the stems of Wisteria sinensis twine anticlockwise, whereas those of Wisteria floribunda grow clockwise – useful to know if you want to distinguish between the two.
Be wary when buying wisteria plants! Cheap, seed-raised plants can take many, many years to start flowering and the flowers are often a disappointing size and colour.
Grafted plants on the other hand, will reliably flower at even a young age. You can tell if the plant is grafted by looking for the graft union (a visible bulge) near the base of the main stem. Named varieties are nearly always grafted. Grafted plants are also much more expensive.
Wisterias are one plant that it is a good idea to buy in flower if at all possible, so you know it will flower early and you can see the size and colour of the flowers.
Suggested planting locations and garden types
Walls and fences, pergolas and arches, patios, containers, city and courtyard gardens, cottage and informal gardens.
How to care for wisteria
For best results, feed wisteria plants every spring. You can use Miracle-Gro Growmore Garden Plant Food or Miracle-Gro® Fish, Blood & Bone All Purpose Plant Food, but a rose or flowering shrub feed will generally give better results. In very well-drained soil, also feed with sulphate of potash in summer.
Wisterias don’t need pruning – but they can grow out of control and and the flowers hidden by the foliage, and they will flower much more profusely if you do. The aim is to build up lots of short flowering spurs.
Initially, it is more important to train the plants to produce a main framework of main branches, and tie them in to their support to ensure they fully cover the support evenly, than worry too much about flowering.
Once the framework has been produced, you can start pruning for flowers – which needs to be done twice a year. In summer (July or August) shorten the current year’s shoots to around 30cm (12in) long, or 5-7 leaflets from the main stem/framework. Then in winter (December - February) cut back the shoots that were pruned in summer to around 2.5-5cm (1-2in) or a couple of buds.
Wisteria may be susceptible to the following pests, diseases and problems: Birds, frost damage and graft failure.