Overview: Black stem borer (BSB) female beetles were found in traps placed at the HVRL research orchard in Highland, NY and in Walden, NY on April 9th. Using ethanol (ETOH) soaked branches, we can determine the time at which BSB begin attacking apple. Presently, ETOH soaked apple bolts placed in Ithaca NY are seeing the onset of attack by female beetles and trunk boring activity (USDA-Lindsey Milbrath). Droplets of sap have been observed on apple trunks from 2020 infestation sites this season.
We are nearing the point at which apple trees are at risk from BSB infestation. The upcoming cool weather will delay adult emergence, flight and attack of apple tree trunks. Applications of directed trunk sprays up to the 1st scaffold limbs (3-4′) of chlorpyrifos (Lorsban) or labeled pyrethroids prior to bloom should be considered if blocks had BSB infestations in 2020. Options provided in Cornell guidelines for NYS labeled for BSB management include chlorpyrifos (Lorsban Advanced) and the pyrethroids Danitol 2.4EC and Warrior II 2.08CS.
In-Depth: The black stem borer (BSB), Xylosandrus germanus is a forest pest in the U.S. introduced from Eastern Asia and first detected in New York in 1932. It has since been detected in most parts of the U.S. detected in orchard sites throughout the Lake Ontario and Hudson Valley fruit growing region of New York. These beetles have been responsible for the decline and demise of newly planted blocks and developing young apple trees in western New York.
In recent years, BSB have been found to attach apple trees across the Hudson Valley Highland, NY in 2nd leaf Pink Lady on M9 – Nic29 rootstock (1st observed by John Whiteman-CPS, Highland). The young trees were not in a location of standing or excessive water last season nor under irrigation.
Research in Ohio and North Carolina have shown that trees growing in saturated soils (producing water stress) tend to develop and release ethyl alcohol as the root zone goes into anaerobic respiration during wet periods. The ethyl alcohol (ETOH) acts as a host finding mechanism to an insect complex known as Ambrosia Beetle of which the black stem borer is one of many species in this beetle group.
The black stem borer is a concern as it attacks apparently healthy plants that have undergone this form of ‘root zone anaerobic stress’.
Adults emerging in the spring locate stressed trees and begin burrowing entrance holes through the bark. The round entry holes are approximately 1 mm in diameter, often having long toothpick-like strings of frass or compacted boring dust emerging from these holes. Beetles tend to borrow directly into the center of the wood and begin forming small chambers for egg laying and rearing of their young.
During a tour in Long Island by the CALS tree fruit program work team, we came upon Macoun on M-26 rootstock on a site that appeared to be on well drained soil, planted on a slope with good air drainage. There was no sign of herbicide injury such as cankered, flaking or scaling bark or winter injury. Yet the tree was completely yellowed with browning fruit.
The tree had completely shut down and was dying. The orchard had experienced two hurricanes over a three year period, with standing water. These conditions led to stress induced ethanol (ETOH) production that acted a signal for BSB to invade the tree. Over the course of a single season the tree appeared to suffer multiple invasions with development of galleries and introduction of fungal spores, which develop and wall off the transport capacity of nutrients to the canopy of the tree, causing its decline and death.
Biology: It takes about 30 days for development of black stem borer egg to adult, and the beetles produce 2 generations per year with the ratio of females to males about 10:1. Late summer the beetles migrate to a hole lower in the trunk to overwinter with as many as 100 beetles in one chamber. The beetles go into diapause, becoming active again next spring.
Tree symptoms can include blistering of bark, oozing sap or fireblight ooze from entry hole, toothpick frass from entry hole ‘weather permitting’ as frass extension crumbles in rain and wind. The female cultures a fungal food source utilizing Ambrosiella hartigii and possibly Fusarium as food for the larvae and adults. She lays her eggs (tiny, ~1mm white, football shaped) in the chamber.
Larvae are white, undergo 3 instars prior to adult emergence.
Monitoring: Young tress showing leaf yellowing, poor extension and shoot growth, tip die-back, cankering or bark discoloring should be examined for BSB entry holes and toothpick frass.
To effectively monitor the insect, the use of bucket trapping for newly emerged adults should be used beginning at green tip employing ethanol solution as both a lure and killing solution, changed weekly (see image below). Beetles captured in the ETOH can be easily observed and as needed, identified by HVRL staff.
Females take flight from overwintering sites to infest trees when temperatures exceed 68°F, typically beginning in mid-late late April in the Hudson Valley with boring activity shortly there after.
In one study BSB flight occurred approximately 4 days after first bloom on Norway maple, and full bloom on border Forsythia. A second generation occurs in late July or early August, based on literature from Ohio. Yet trap captures have shown overlapping adult presence, and as such, generations have been difficult to separate by distinct flight peaks.
Management: The damage thus far has been observed primarily to young trees planted in tall and slender spindle plantings, in wet or very dry shale loam soils.
To control BSB in newly budded trees, the ornamental nursery industry employs pyrethroids on a two-week schedule to reduce injury from the insect.
Warrior II 2.08CS (lambda-cyhalothrin; 2.56 fl.oz./100 gal. water), and Danitol 2.4EC and also requires a 2EE label , applied at (16-21 fl.oz./A) are presently labeled for tree borer species. Efficacy data is presently unavailable as trials in tree fruit are on-gong. The points of entry can be as high as 4 feet above the ground into the tree scaffold limbs, which may preclude the use of post bloom Lorsban used in graft union burr knot control of dogwood and trunk borers.
Generally, the neonicotinoids, anthranilic diamides (cyazypyr, acelepryn), and tolfenpyrad, have not been found to be effective in controlling BSB.
