For professionals working in nurseries or Christmas tree plantations, it is time to be on the lookout for the European pine shoot moth, Rhyacionia buoliana. Although European pine shoot moth attacks several different types of pines, including red, mugo, Scots, and Austrian, the insect prefers Austrian and mugo pines. Repeated infestations of European pine shoot moth can distort trees to the point of reducing their marketability. So it is critical that spray applications of insecticides be performed before the larvae or caterpillars bore into the growing shoot because once inside the growing tips they are well protected from any insecticide application.
It is during early spring (right now!!) that the overwintering larvae of European pine shoot moth crawl onto new shoots and tunnel into the base of buds or shoots. The larvae eventually undergo a pupal stage within the shoot tissues. In late May to early June, the European pine shoot moth adult female deposits small, flattened eggs on new pine shoots near the base of needles or bud scales during a 2- to 3-week period. The eggs hatch in early June into larvae that tunnel into the needle sheaths and then mine needles at or near the base. Early injury symptoms include yellowing needles near the tips of twigs and masses of pitch near the base of new bud clusters. The mined needles eventually turn brown and die. The larvae kill terminal and lateral growth when tunneling into the base of needles, shoots, or buds. Infested trees may eventually appear reddish due to an abundance of dead tips. Additionally, European pine shoot moth larvae commonly cause the candle to form a “shepherd’s crook” shape. Small trees growing in nurseries and landscapes may be killed under heavy infestations. In Christmas tree plantations, repeated infestations may result in trees appearing distorted, unsightly, and potentially unmarketable.
Resin-coated webbing may be present near wounds or entry sites created by larvae. In later summer to early fall, larvae discontinue feeding for the growing season and prepare to overwinter in needles near shoot tips mined during the summer. The larvae, which are 1/12 to 1/8 inch long, turn a deep black, covered with resin-coated webbing. European pine shoot moth has one generation per year in Illinois.
Management of European pine shoot moth primarily involves pruning or using insecticides. Normal shearing or pruning of Christmas trees in mid-July provides some measure of control in Christmas tree plantations. Insecticides recommended for controlling European pine shoot moth include permethrin (Astro or Pounce) or phosmet (Imidan). These insecticides should be applied before larvae enter the growing shoot, which is normally in early spring, as well as late June or when hills-of-snow hydrangea (Hydrangea arborescens ‘Grandiflora’) is in early bloom. Concentrate spray applications on branch ends, where the larvae are most likely to be located.
Pheromone traps, which are used to detect male moth activity in June, can be used to help time spray applications. After the peak trap catch, spray 7 to 10 days later. It is important to irrigate trees during extended drought because dry weather and poor soil conditions may lead to increased susceptibility.