The Black Stem Borer (Xylosandrus germanus) (BSB) has been found infesting 3-5 year old slender spindle trees (variety Zestar) in a second Hudson Valley site, this time in Columbia County (observations by by Dan Donahue, CCE ENY Horticulture Team – Tree Fruit Specialist). Tree decline with yellowing leaves, discolored bark, 1mm entry holes and toothpick frass provide indicators of BSB infestation that growers and scouts should be looking for this week.
Infected trees should be removed and burned. Treatments directed to the trees post infection have not been shown to kill the developing larva, however management measures will reduce subsequent infestation in remaining trees. Presently there are no recommendations for management other then the use of labeled insecticides, such as Lambda-cyhalothrin for tree borer species. The tree nursery industries have relied on a two-week scheduled pyrethroid program for control.
Troubling in this particular find is infestation of the beetle 3″ below the graft union and 5′ above the soil line in lower scaffold limbs. Unlike Dogwood Borer management in which applications are made above the graft union and below the scaffold limbs, treatment of BSB will require graft union drench and canopy applications to limit the adult infestation during emergence.
Deb Breth and Art Agnello have first brought this insect to our attention in a recent scaffolds article on black stem borer. As they have been monitoring populations over the past two years they have found increasing WNY orchards with BSB infestation. Results have shown tree decline and loss of a significant numbers of trees in locations where standing water and conversely, lack of water in non-irrigated blocks, contribute to tree stress and BSB infestation.
Induced tree stress, especially from wet soils, causes trees to undergo anaerobic respiration. This process produces ethanol, highly attractive to the family of ambrosia beetle to which BSB belong. Tree stress reduces tree defense, increasing beetle survival and reproductive success. Once the female beetle bores through bark cambium into the wood, she creates a gallery, brings in fungal spores that grow and plug the vascular tissue of tree, causing decline. The adult lays her eggs, larva hatch and feed on fungus until maturity. The female will then plug the hole with her body and die there. A link to a powerpoint of the history, biology and WNY perspectives of infestations with excellent imagery can be found here.
Anna Wallis, ENY Horticulture Team Tree Fruit Specialist, has found BSB in all of the 9 northern commercial orchard trap sites. All of the captures have been confirmed as BSB. Traps captures indicate adults are present along the wooded edge / orchard borders as well as within the orchard. However, none of the apple trees in and around the location of the traps have been found to be infested in these sites. This indicates that presence of the insect does not warrant control measures at this time in NNY. However, it does signal the need for monitoring orchard signs of tree stress, and upon a find, requiring increased level of detailed observations. Again, tree decline with yellowing leaves, discolored bark, 1mm entry holes and toothpick frass provide indicators for management.
