Landscape - White Pine Weevil

The following is information in whige pine weevil, a common pest in Delaware landscapes.

WHITE PINE WEEVIL (Pissodes strobi).

I have almost missed the opportunity again to address white pine weevil (WPW). With one of the earliest seasonal habits of all landscape pests, control of WPW is difficult or missed entirely. WPW feeds on spruces (Colorado Blue, Norway, etc.) firs, and white pines. Damage is a very characteristic “burning out” of the branch terminals that looks like a “shepherd's crook”. Unfortunately, this damage is apparent in early summer, after the insect has completed its development for the year. Affected trees are robbed of their dominant central leaders and over time grow to be uncharacteristically bushy.

WPW overwinters as an adult in the soil near hosts. On sunny spring afternoons they'll fly/climb to the tops of trees, feed on current season terminals, and lay eggs into them. Egg hatch occurs 1-2 weeks later and larvae (grubs) tunnel into the terminals. They'll feed for a month or two, eventually forming a “chip cocoon” (pupal chamber) and emerging after 2 weeks pupation. Adults feed on host plants before going dormant until next year. Scout closely NOW for the signs of WPW. Feeding leaves small droplets of resin/pitch flow on the terminals and infestations can be detected while damage is minimal. Chip cocoons left behind after adults emerge can be detected but terminal dieback is well underway by that time.

Chemical control is directed on younger, developing trees where proper branch structure is critical. Resin/sap flow is also a good indicator for when to time adult flight sprays of pyrethroids two applications 3-4 weeks apart. Another control option is neonicotinoids drenches/sprays. If using Merit, it must be applied ASAP in the spring because it takes around a month to get up into the terminals and it may be too late already. Faster translocated neonicotinoids such as Safari may still have some use this year if the weather stays cool. For cultural control, prune out the damaged central leader and select a new one. Some growers select the Northwest leader preferentially prevailing winds will allow this branch the greatest success of forming a straight leader.

Information from Casey Sclar, IPM Coordinator, Longwood Gardens