Black vine weevil control with beneficial nematodes in fall, Digi Mart USA News: Gardeners who notice wilting or damaged rhododendrons, azaleas, hollies and other prized plants may be dealing with black vine weevils. The pest often goes unnoticed because its larvae feed underground on roots, and as few as three larvae can destroy a young rhododendron.
Black vine weevils are often introduced through nursery plants and nursery material, and the larvae keep feeding after plants are moved into containers or garden beds. Adults later feed on leaves above ground, but the root-feeding young cause the most harm to new plants.
The source notes that roughly 200 plant species are affected, including geraniums, hostas, cyclamens and begonias.
One non-chemical option described in the source is beneficial nematodes, tiny soil worms that include species parasitic to insects. Some nematodes prey specifically on black vine weevil larvae and are described as posing no harm to plants.
The source says summer through fall is the best time to apply them to soil against weevil larvae.
For black vine weevil problems, the source advises choosing prepackaged products that list black vine weevils as a target pest or that contain a Heterorhabditis or Steinernema species. Prepackaged live nematode products are available at garden centers and online, and the source cites a Steinernema-based product as an example.
Application involves choosing a period in fall when the long-term forecast predicts warm weather, mixing the product with distilled, cold water in the amount listed on the package, and watering it into damp soil around the plants. The soil should stay at or above 60 degrees Fahrenheit during this period and remain moist for about two weeks, since the nematodes need moisture to work.
The source warns that neem oil and similar organic products can repel beneficial nematodes, so gardeners should wait before using them.
