Vine Weevil belongs to the family Curculionidae under the Order Coleoptera. The Female reproduces offspring without the involvement of the male sex. The larva remains subterranean and feeds on the plant roots and cambium region near the base of the tree trunk. Vine Weevil larvae are highly damaging pests for the herbaceous plant especially containerized plants, and the plants that grow in small gardens where the soil is compact or the plants have poor growing conditions. Usually, heavy infestation leads to root demolition resulting in plant death. In fall, the larva feeds on the small roots of the targeted plants. Whereas, well-established roots in the spring. Overfeeding leads the stem to the girdle under the soil surface. Initially, leaf yellowing is observed that leads to stunting and death of the plants occur. Comparatively, larval feeding causes more injury than adults.
The vine weevil is native to the UK and Europe and has been established in nurseries, greenhouses, and gardens throughout Australia and North America. They attack an extensive range of host plants and the recently proven that it could damage more than one species of horticultural and ornamental plants in the United States of America. Whereas the areas where higher infestations are could include Northeastern and north-central parts of the US, neighboring part of eastern Canada, and from Alaska south to California.
The larva, also called grub, may grow up to 1 cm in length. Larva possesses a slightly curved body without the legs. The body color is off-white with a dark brown head. The most distinctive identification feature remains the absence of thoracic legs, and it observes a slightly C shape. If someone finds it after digging into the soil, their resting position also appears like a "C" alphabet. The larva passes the entire six instars under the soil, and this period could extend up to 8 months depending on the varying soil temperature and the availability of moisture. This period remains the most damaging period of larval life, and the damages reduce on becoming an adult.
Usually, Vine Weevil adults live about three months, and during this period they could lay up to 200 eggs. Under optimum conditions, the eggs hatch in two weeks or could delay up to three weeks at maximum. The result is the emergence of a "C" shaped larva without legs that feeds on the smaller roots of the plants. The larval growth is usually slower in the summer, and it passes six instars over this period. It matures in the late fall and enters into a dormant pre-pupal stage. The roots feeding activity ceases, and the larva builds up an earthen case round itself to pupate in the coming spring. Under warm conditions, the pupated larva converts to an adult earlier, especially on indoor and containerized plants whereas, it could delay in the outdoor gardens. The duration of larval development remains a minimum of about 74 days under good conditions and a maximum of 225 days when winter freeze interrupts them.
Generally, the larva feeds on the tender roots and secondary growth, rhizomes, tubers, suckers, and lower stems of several herbaceous and ornamental plants. It destroys the nutrients uptake system that parts of the plants assimilate for transporting to the upper ground parts of the plants. Stem lodging occurs that leads to yellowing of the foliage, occasional wilting could appear, and death of the plants occurs, finally. Larval subterranean damages are difficult to notice, and their detection and control also remain a challenge for the growers. Vine Weevil Larvae are considered pests for container gardeners especially, in a greenhouse and other climate control environments. The damage continues from mid-summer to late fall and again in early spring. If there is a shortage of feeding sources underground, the larvae could feed on the foliage reducing the vigor of the plants more speedily.
Both the temperature and relative humidity are the basis of their arrival in your garden or a greenhouse. Since most greenhouse cultures adopt a temperature range between 60-77°F, So there is always a chance that they could trigger growth at any time of the year. Similarly, whenever the temperature falls in the same range, look them around. They don't come from anywhere but, these are the conditions that allow them to hatch rapidly. Additionally, the greenhouse culture may have infestations from the stuff that was brought from the external source. Anyhow, the larva entering the pre-pupal stage could die upon experiencing a surface temperature of about 81°F for three consecutive days or more.
Besides following the preventive measures if Vine Weevil larval infestation goes beyond your control, here are the most authentic ways to keep their population suppressed using the biological, organic, and chemical methodologies;
BotaniGard contains 11.3% Beauveria bassiana strain GHA that can disperse when released in any hydroponic growing culture or a garden. The product is compatible with other biological controls and comes in an easy-to-mix emulsifiable suspension. Beauveria bassiana are fungal spores that germinate on the bodies of the host and weaken their skin. A larva or an adult vine weevil can't molt to reach the next instar. Upon weakening their chitin, they enter the bodies of the larva and kill them. These spores also release some toxins that work as a natural insecticide that kill larva and the adults together. The best time to release them in any culture is on the first appearance of larva or adults. Overall, it takes 7-days to kill any sort of pests that live on the plants' foliage.
Add half an ounce of suspension per gallon of water and apply using a low-pressure sprayer on the foliage of the plants.
Although this product holds registration for controlling Fungus Gnats, it contains naturally occurring insect-parasitic nematodes, Steinernema feltiae, and research proves that these are entomopathogenic nematodes that are highly effective in controlling the Vine Weevils at larval and adult stages. They are released in an infective juvenile condition that searches and destroys the larvae, quickly. Once inside the body of the pest, Steinernema feltiae kill them rapidly. Another generation of nematodes reproduces inside the body of the larva that provides extended control. When applied in the soil for larval control, Steinernema feltiae not only provides prolonged control But, stops re-infestation as well. Its applications are needed during the initial stages of larva growth.
50-million nematodes are good for controlling larva in 1000 square areas and adults in 550 square feet.
3-in-1 Plant Guard is multipurpose and a broad-spectrum product in a powdery form that contains seven natural oils extracted from Garlic, Cinnamon, Clove, Castor, Rosemary, Peppermint, and Spearmint which makes an excellent Tar and Latex-free tree paste for applying around the stem of the plant. It also protects the plants from scorching sun besides stopping the Vine Weevil larva from climbing the stems. The addition of Diatomaceous Earth makes it difficult for the grubs and larva to survive if applied directly to the soil
Adding water to the powdery contents depends on the method of application, either you want to make a paste, direct soil, or a foliar spray.
The application of Diatomaceous Earth initially stops larval feeding, starves, and dehydrates them. Diatomaceous Earth is safe for organic gardening and leaves zero residues on the foliage, the environment, or the soil. It stops larval movement when they attempt to tree stems. The product is best applied once when larvae hatch from the eggs in early summer or late spring and then when they try to reach foliar using the stems. It contains 85% Silicon Dioxide and OMRI listed.
DE applies in a dry powder form on the surface when the soil is pretty dried and contains zero or little moisture for the effective control of Vine Weevil larvae.
These granules contain 9.3% Trichlorfon from the organophosphate group of insecticides that directly affects the nervous system of insect pests on ingestion. However, the product chemistry remains toxic for all birds, mammals, and pollinators, toxicity varies for all individual species. On application, the Vine Weevil larvae stop feeding and are controlled within 24 hours. It works well when the granules get thinly spread on the surface of the soil and watered after application, immediately.
pound granules are for covering 500 square feet of Vine Weevil larvae affected area.
Although this product is recommended for controlling grubs in turfgrasses, it also performs well when an edible garden is not a target because Bifenthrin and Carbaryl leave prolonged residual effects on vegetables and fruits. Especially, Vine Weevil larval infestations need heavy dosage besides incorporating them into the soil and watering the plants, immediately. The product comes in ready-to-use chemistry and kills subterranean larvae besides penetrating the plants' foliage. However, the results are quick that could prolong up to 3 months.
Application rates vary depending on the types of infestations and the pest species in the target. However, it applies 8 pounds per 1000 square feet of the garden if the infestation cause is Vine Weevil larva only.
Check out our other guides on common garden bugs.
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