White pine needle blight:
All that glitters isn't gold

Remember last year's report of needle discoloration of white pines?  At the time, we did not find any disease organism associated with it and reported that is probably was a physiological problem, ?semi-mature tissue needle blight?.  This year, eureka!, fruiting bodies have been found on the needles affected last year. 

Needle blighting of white pine has been reported since the turn of the century and various causes ascribed to it, most recently, semi-mature tissue needle blight and ozone damage.  In 1996, the casual fungus was finally pinned down and  identified as Canavirgella banfieldii.  See the reference below for further information.

This needlecast fungus causes an early season blighting of current needles.  In late June or early July, the infected needle tips turn yellowish-tan, later turn brown and then fade during the fall and winter to a grayish-tan. Not all needles in a fascicle are affected, affected needles retain a green base, and, the proportion of needle killed is variable. Fruiting bodies (hysterothecia) begin to form in late fall and winter and mature spores may be released from budbreak through shoot elongation.  The mature fruiting bodies are dark grey and run along the length of the needle.  Some are over an inch long. 

Needles attacked by C. banfieldii are nearly always infested with other secondary fungi, especially, Meloderma desmazieresii, some of which inhibit the development of the pathogen and appear to be natural control agents of the needlecast fungus.

Reference:  Merrill, W., N. Wenner, T. Dreisbach. 1996.  Canavirgella banfieldii gen. and sp. nov.: a needlecast fungus on pine. Can. J. Bot. 74: 1476-1481.

Red turpentine beetle

Red, white, and  jack pines, firs, and spruces  stressed by home and road construction, nearby logging and other land-clearing activities, drought, fire, lightning, flooding, or various insect or disease damage may become infested and killed  by the red turpentine beetle, Dendroctonus valens.  It is the largest (l/4 to 3/8 inch) and most widely distributed bark beetle in North America.  Despite the abundance and wide distribution of this beetle, outbreaks have not been extensive or severe because the insect is usually in competition with more aggressive species. In general, it is a secondary pest, but on occasion, can attack and kill apparently healthy trees.

A few generations of red turpentine beetle can girdle and kill large, old conifers.  The presence of this forest insect in standing trees can be confirmed by observing one or more pitch tubes extending from the bark on the basal six feet of the trunk, or an accumulation of boring dust with or without some pitch pellets on the ground close below the trunk.  The pitch tubes are l/4 to l/2 inch long, up to two inches wide,  white to reddish in color, and they mark the entry and exit points of the adult beetles through the bark.  They are composed of resin that flows from the outer sapwood and inner bark as the beetles excavate galleries, but the resin becomes mixed with body wastes and boring particles.  Since fir and spruce produce little resin during beetle feeding, there may be no pitch tubes formed, but boring dust and small pitch pellets can be found around the base of infested trees.  Larval galleries of the red turpentine beetle often extend below the ground line and along larger roots.  They are in the cambium and inner bark and are up to twelve inches wide and several feet long.

In Minnesota, there is one generation per year.  Each female can lay from a few to more than a l00 eggs within the inner bark of a tree, and she may bore out, attack and lay eggs in other trees before she dies.  The adults that eventually develop from these eggs remain in the galleries  a few days to several months and over winter.  As the weather warms in the spring, they bore out through the bark and fly to other host trees. 

Preventative control of the red turpentine beetle can involve maintaining tree vigor, minimizing damage to stands or individual trees through improved logging and construction practices, and removing trees infested with other insects.  Where trees are infested, the use of beetle pheromone traps and spraying the basal six feet of the trunks with a persistent insecticide once a month from spring to fall may reduce beetle numbers.  Fertilizing with granules or tree spikes, coupled with watering, may allow improved resin defenses and tree recovery.