BYGL Industry Insight May 15, 2008 BLACK VINE WEEVIL DIAGNOSTIC CHALLENGE
| BLACK VINE WEEVIL DIAGNOSTIC CHALLENGE |
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 Randy Zondag reported observing an astilbe in a 3 gallon container that had wilted and had browning leaves indicating a watering problem; either too little, or too much. He also noted the plant would easily tip-over as though it had only been recently upsized from a much smaller container. Improper watering was not an issue, and the plant had been in the container long enough to produce a root system to keep it upright. The true problem was revealed when Randy dumped the container to find over 60 black vine weevil (BVW)(Otiorhynchus sulcatus) larvae among the destroyed root system.Randy's report demonstrated three challenges with diagnosing a BVW infestation. First, although the weevil is most commonly associated taxus and rhododendrons, it can feed on over 100 different plant species. BVW may be overlooked on plants that are not commonly thought of as being hosts to this pest. Second, adults feed on foliage and produce notches on the leaf margins. The leaf-notching damage is easy to see on leaves with smooth edges, but hard to detect on leaves with serrated edges. Third, the cream-colored, legless, grub-like larvae consume roots. The damage mimics symptoms caused by other problems including: too little, or too much water; root-rotting fungi; and vole damage. Bottom line: growers should conduct thorough whole-plant examinations of dead or dying plants before drawing diagnostic conclusions. BVW is currently in the late instar larval stage and insecticides will have little effect on these large-sized larvae. Also, the larvae are nearing pupation. Traditionally, insecticide applications in field production have targeted the adult stage; however, adults are active for an extended period during the growing season, so multiple applications are required. Foliar applications of bifenthrin (e.g. Talstar) or permethrin (e.g. Astro) can reduce the aesthetic impact of adult leaf-notching damage, but there is a risk that some adults will escape treatments to lay eggs. A BVW management program should also include a mid-August soil drench with imidacloprid (e.g. Merit, Marathon). The application timing targets a "bottleneck" in the life cycle of the weevil: in mid-August, a high percentage of the population is in the first instar larval stage. Management of BVW in container production can be accomplished by using preplant potting mix incorporation treatments of synthetic insecticides, such as bifenthrin (e.g. Talstar 0.2 G) For more information, see: 
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| Last Updated ( Wednesday, 14 May 2008 23:16 ) | ||
