Control of root rot is difficult. P: 888.472.7748 Descriptions cover five root weevils that cause most damage on rhododendrons in the Pacific Northwest. Every Nematop® Weevil-Stop trap contains around 2.5 million tiny pathogenic nematodes for the effective control of adult black vine weevils. You can also hand pick the adults off the plant at night while they are eating. Selection of chemicals should be based on local expert advice. Control of adult root weevils is accomplished in several ways. Recently, we developed a mass rearing system for these pests and … Weevils feed for about 4 weeks after emerging from their underground pupal chambers. Least-toxic root weevil control. In fact, one larva/plant has been reported to kill cyclamen, whereas three larvae killed a rhododendron plant. Root weevils primarily chew on broadleaf evergreen shrubs. Common Sense Gardening: Root Weevils, Thurston County. You can help prevent insect damage to your existing plants with proper care. Beneficial nematodes seek out and kill all stages of harmful soil-dwelling insects. The flower buds of rhododendrons affected by bud blast disease fail to open, so ruining any chance of a colourful spring display of flowers. Jun 17, 2018 - Q: What can I do to control root weevils in my rhododendrons? One of several types of root feeding weevils, the black vine weevil is the most destructive and widespread. The black vine weevil, Otiorhynuchus saleatus, feeds on rhododendron plants throughout its life cycle. Pest description and damage Identification is important: species differ in susceptibility to pesticides. Photo: Jim Baker, North Carolina State University, bugwood.org. The weevil feeds on leaves creating a C-shaped notch around the leaf margin. This feeding detracts from the appearance of the plant but rarely causes serious injury. Characteristic damage includes notching of leaf edges by adults and minor to severe root and bark damage by larvae. Otherwise, organic material like leaves or dirt will collect on the substance and form a bridge for the root weevil. Root weevils need to travel along branches to get to the leaves. They are effective against a number of serious pests that live in the soil, including weevil larvae. Plant resistant types of rhododendrons. Gardeners with vine weevil should keep up their guard because stopping control measures after the apparent disappearance of the weevil can allow numbers to build up again. Weevils – The adult black vine weevil is a night-feeding insect that is about 1/5 to 2/5 (5 ml. These especially include Rhododendrons and Yews (or Taxus). The larvae live in the soil and feed on roots and may also girdle the plant at the root crown, causing the plant to wilt and die. If it’s dry and hot out, the nematodes won’t survive in the soil very long. Root weevils feed and develop on a wide variety of plants. Root Weevil Control on Rhododendrons. You can usually achieve control of root weevil populations by using Sevin products. It is also needed to be used over and over and over. The Root Weevil Life Cycle An adult root weevil will lay its eggs in the soil under your favorite rhododendron in mid-summer. Proper timing is critical to successful root weevil control and the best time to initiate control is when the adult beetles start to emerge from the soil in late spring/early summer. Since plant stress is related to susceptibility, make sure you are using the right amount of water. Control of Root Weevils on Plants. Vine weevil is a very widespread insect in Britain. Root Weevils Adult black vine, woods and obscure root weevils have elongated heads and wingless, brown or black bodies. Check susceptible plants frequently onwards so action can be taken before a damaging population has developed. Controlling root weevil is possible. The adult weevils feed at night, notching leaf margins. Leaves that have a slight roll on the edges tend to be avoided by weevils because the roll creates an edge too wide for the root weevil’s mouth. Although the damage is not attractive, it presents no serious risk to the bush. Application of beneficial nematodes which kill the larvae. Reducing watering around building foundations may limit root weevil migrations, as the adult insects appear attracted to shade and moisture. Root Weevils: Troublesome Rhododendron Pests, American Rhododendron Society. Weevils attack over 100 different plant species in addition to rhododendrons. Adult root weevil notching. The least toxic method to control weevils is to treat them in the larval stage, using beneficial nematodes, Rosetta said. If leaf holes are large, scooped out bites, damage is Organic mulch, such as compost or arborist chips, helps keep your shrubs healthy. Because broadleaf evergreens take a while to lose their leaves, the notching will stay visible for at least a few years. A guide to root weevil control for the earth-friendly gardener. Few insects are serious pests of rhododendrons, but a type of weevil leaves foliage tattered from its feeding. Hank Helm Bainbridge Island, Washington. Non-Chemical Management. Root weevil stages and damage shown in color. I seem to remember the notches from the root weevil as being larger than these. Using chemicals to get rid of root weevils is definitively not the way to go. The technicians look for recent damage to the leaves and apply nematodes if they see damage. Proper timing is critical to successful root weevil control and the best time to initiate control is when the adult beetles start to emerge from the soil in late spring/early summer. Information about physical, chemical and biological control methods. During the early development of rhododendron plants, there is insufficient root tissue on an individual plant to support the development of black vine weevil larvae, leading to plant girdling (Cowles, 1995). These are microscopic organisms that attack the root weevil larvae as they grow in the soil below the shrubs. The easiest way to prevent root weevil damage is to choose plants that are naturally resistant to root weevils. It is most prevalent from May through September. Organic root weevil control methods include purchasing parasitic nematodes or predatory beetles can be bought to hunt down the weevils. Those eggs will hatch into larvae in late summer to early fall where they will over-winter in the top layer of soil, feeding on the fine root mass of the plant. Descriptions cover five root weevils that cause most damage on rhododendrons in the Pacific Northwest. The three weakest ones have a lot of tiny notches in the leaves. Buglogical natural organic gardener's reference catalog provides solutions to pest problems, ladybugs, praying mantis, beneficial nematodes and beneficial insects. The list of species resistant to root weevils can be found in the WSU Extension Bulletin #1229– see further reading. Loose, coarse mulches (wood chips, shredded bark, oak leaves or pine needles) can be applied to a depth of no more than 3", keeping the mulch a few inches away from the main stem to prevent rodent damage. Buglogical natural organic gardener's reference catalog provides solutions to pest problems, ladybugs, praying mantis, beneficial nematodes and beneficial insects. In particular, they seem to love rhododendrons, azaleas, pieris, viburnums and laurels. Nematodes are nontoxic to plants and other animals. © 2020 In Harmony Sustainable Landscapes. Root weevils need to travel along branches to get to the leaves. A: I am sure that you have weevils, little beetles with long snouts that come out at night to chew notches out of the edges of Rhododendron leaves. For more information on root weevils in general refer to the Pacific Northwest Pest Management Handbook, The Pacific Northwest Nursery IPM and The American Rhododendron Society website. Copyright © 2020 Extension Publications. Your email address will not be published. Includes extensive list of species and hybrid rhododendrons resistant to adult root weevil feeding. They are used as a soil drench in moist soils over 52 degrees … The nematode hatchlings will eat the larvae. The least toxic method to control weevils is to treat them in the larval stage, using beneficial nematodes, Rosetta said. 2. Root Weevils: Troublesome Rhododendron Pests Hank Helm Bainbridge Island, Washington Perhaps the worst insect pests that attack rhododendrons are the several species of weevil, found in nearly all areas of the world. UC Master Gardeners of … There are two optimal timings, one in the late spring to early summer targeting late-stage larvae, pupae, and adult weevils prior to emergence. Three different types of root weevils chew on evergreen shrubs. We do not recommend the use of insecticides. inch in length. Have you seen notching along the edges of leaves on your rhododendrons, azaleas or other broadleaf evergreens? Adult weevils prefer to feed on young new growth. Chemical and cultural controls. Everyday low prices and free delivery on eligible orders. Prune up branches that touch the ground to reduce access. Descriptions cover five root weevils that cause most damage on rhododendrons in the Pacific Northwest. Description. The adults are very difficult to find during daylight hours, preferring to hide away and using the cover of darkness to move from plant to plant. NOTE:Pesticides registered for root weevil control will normally reduce aphids and many other leaf feeding insects as well. They usually crawl up the trunk and move out to the branches to chew on the leaves. Perhaps the worst insect pests that attack rhododendrons are the several species of weevil, found in nearly all areas of the world. Descriptions cover five root weevils that cause most damage on rhododendrons in the Pacific Northwest. The larvae live in the soil and feed on roots and may also girdle the plant at the root crown, causing the plant to wilt and die. Root weevil stages and damage shown in color. All Rights Reserved. Root weevils are challenging to control since they feed on a wide variety of plant materials besides rhododendrons. inch in length. Vine weevil is a very widespread insect in Britain. Mild to severe notching of new leaves is mainly an aesthetic nuisance and will usually not damage the plant’s overall health. Prune up branches that touch the ground to reduce access. Organic root weevil control methods include purchasing parasitic nematodes or predatory beetles can be bought to hunt down the weevils. There are several species of weevils native to B.C. We recommend sticky or teflon barriers and beneficial nematodes. They must be replaced or replenished frequently. Root weevils primarily chew on broadleaf evergreen shrubs. Also, many rhododendron and azalea varieties or species demonstrate considerable weevil resistance. P: 425.486.2180 These include black vine weevil, strawberry root weevil, woods weevil, and clay-colored weevil. About a dozen kinds of root weevils attack rhododendrons and azaleas with only five of them being of significance. There are several species of this insect that damage rhododendron leaves and roots, black vine weevil, Ortiorhynchus sulcatus, strawberry root weevil, Otiorhynchus ovatus, and obscure root weevil, Sciopithes obscurus. Pour a 1-inch layer of coffee grounds around the base of the shrub. Because these plants take a while to lose their leaves, the notching will stay visible for many years. 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