Overview: The Black Stem Borer (BSB), Xylosandrus germanus a species of ambrosia beetle, continues to challenge newly planted and young apple trees. When planted on heavy soils in wet years and or planted in shale well drained soils during years of drought BSB will use them as reproductive hosts. In response to these environmental conditions the trees undergo stress that leads to the production of ethanol (ETOH). The BSB uses ETOH as a cue to find and invade the host tree with a compromised defense system. Adult females burrow into the trunk, creating galleries to rear grubs, harvesting ambrosia fungal spores to grow within the gallery with which to feed on. The tree responds to this invasion by walling off the cambium layer and dying.
The use of insecticides, specifically chlorpyrifos (Lorsban-Dow/DuPont) pre-bloom can be used in a single trunk application. Applied at the first sign of tunneling of trees, often beginning in late April into May, would likely reduce early BSB invasion of apple trunks during periods of weather extremes causing tree stress.
In-Depth: In New York State the use of chlorpyrifos (Lorsban-Dow/DuPont) is limited to a single application per season. Two types of applications can be made, either directed to the tree canopy to manage scale, beetles including borers and plum curculio, aphid, lepidopteran and plant bug or Lygus pests, or course trunk spay directed to the lower 4’ of the tree to manage trunk boring pests such as dogwood borer and black stem borer. Lorsban can still be used in NY up to July 31, 2021.
On April 30th, 2019 NYS legislators approved Senate bill S5343 and Assembly bill A2477B, which brought about the ban on chlorpyrifos in New York beginning in 2021. This legislation is part of a larger environmental package and requires the approval of Gov. Andrew Cuomo’s (D) to put the new law into effect. The bill would ban all use of chlorpyrifos except for on apple tree trunks by Jan. 1, 2021 and ban the pesticide altogether by July 31, 2021. The loss of this tool is very unfortunate.
The DEC cancelled the registration of 29 pesticides containing chlorpyrifos on Dec. 31, 2020, and is cancelling the registration of the remaining 15 pesticides as of July 31, 2021. Following cancellation, a pesticide can no longer be sold, distributed, or used in New York State. In addition, these canceled pesticides cannot be stored after the manufacturer’s container has been opened.
Effective control options for pests managed by chlorpyrifos are available for all but one of the pest complex.
The ambrosia beetle, the black stem borer (BSB), Xylosandrus germanus (Blandford) (Coleoptera: Scolytidae) is the one Asian invasive insect pest for which we have no Lorsban replacement. Finding a solution for BSB prior to the loss of chlorpyrifos by 2021 will be critical to maintain orchard productivity and sustainability.
To date hundreds, possibly thousands of young apple trees have been killed by this one insect pest in orchards throughout the Eastern US tree fruit growing region. (see prior post on this topic)
This BSB is attracted to young apple plantings under environmental or biotic stress. Stress include drought and heavy rain conditions, such as we’ve been experiencing over the past few years in the Hudson Valley. During these conditions the tree emits ethanol (ETOH) to which the BSB is highly attractive.
ETOH is an indication of tree stress and reduced defense mechanisms within the tree physiology, leading to greater insect infestation and higher levels of insect reproductive success.
The female first flight began 16th April in the Mid-Hudson Valley in 2021. The female emergence will be monitored using bottle traps with ETOH pouch lures, while burrowing into apple wood will be monitored using cut bolts of apple wood soaked in ETOH. The early onset of BSB attack of stressed apple trees can often be found from pink and bloom through petal fall and into the early season. A second generation occurs during mid-late summer. Given the cool spring, BSB beetle activity may be delayed this season.
A trunk application of Lorsban prior to bloom should be considered to reduce the boring activity of BSB into stressed newly planted or young apple. Following pest management options include Danitol 2.4EC at 16-21.3 fl.oz./A or Warrior II 2.08CS at 2.56 fl oz/100 gal water. Frequent applications may be required using the pyrethroid class of insecticides during the BSB attach cycle.
