Overview: Withdrawing registration for agricultural uses of Chlorpyrifos must be strongly considered by stakeholder groups, given the complexity of insect and disease pest management contending with shifting biotic and abiotic forces. This decision should weigh the dramatic expression of change in climate impacting food production practices. Both drought and flooding impose significant plant stress in agricultural systems to reduce agricultural resilience while increasing vulnerability to pests.
Global trade has contributed to our ever-increasing invasive insect pest complex, while inducing unpredictability in insect behavior modeling and subsequent management programming. Invasive pests often require intensive research efforts to develop monitoring and threshold management decision making to combat outbreaks while production leans heavily on broad spectrum, long residual tools to retain food quality and farm profitability during conditions of extreme susceptibility.
Insecticide resistance management practices for agricultural pest with multiple generational periods per season require seasonal rotation of effective and diverse tools with specific modes of action targeting a variety of biochemical sites within the insect to retain efficacious management. The loss of effective tools tools such as Chlorpyrifos reduces sound resistance management strategies. This will likely increase agricultural risk given the pending losses of our newer, highly effective insecticides in the neonicotinoid class, many of which replaced older, more disruptive insecticide uses since the advent of the Food Quality Protection Act, placing greater risk on food production systems.
Lastly is our need for balanced environmental regulations to sustain a healthy environment and safe food production practices to retain sustainable food security in our nation, at times at odds with food production concerns.
Uses in Apple: At present, the active ingredient Chlorpyrifos (IUPAC name: O,O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate), in the organophosphate insecticide class of insecticides, is limited to foliar applications to tree fruit for use against the insect pest complex during pre-bloom tree phenology stage and seasonal trunk applications against invasive boring pests during the pre and post bloom stage. The key insects controlled on tree fruit include the dormant phase of San Jose scale, early development of the aphid complex including rosy apple aphid, overwintering larval stage of the obliquebanded leafroller, larval stage of the dogwood borer, and migrating phase of adult ambrosia beetles and members of the Buprestidae family of apple trunk borers.
With the advent of insect growth regulators (pyriproxyfen and buprofezin), lipid biosynthesis inhibitor (tetramic acid: spirotetramat) and dormant or delayed dormant applications of horticultural oil, Chlorpyrifos has, for many orchards, fallen out of favor for San Jose scale management. Neonicotinoid use at petal fall has greater efficacy in management of rosy apple aphid with very effective newly developed lepidopteran insecticides including Methoxyfenozide, Emamectin-Benzoate, Spinetoram and Chlorantraniliprole are being used against the overwintering obliquebanded leafroller larvae to alleviated the need for pre-bloom Chlorpyrifos.
Increasingly, the development of alternate technologies, including mating disruption (MD) for lepidopteran pests (adult moth species), and specific granulosis virus (Cyd-X) have reduced the need for directed applications of residual insecticides against developing larva of codling moth and oriental fruit moth. This is also true for MD of dogwood borer, a trunk boring insect pest for which Chlorpyrifos is used successfully. However, MD decreases in effectiveness in orchards less then 10 acres in size and is relatively ineffective in orchards of less then 5-acres, and ineffective in one-acre blocks (Jentsch, 2016). Many sites where wind conditions and airflow are dynamic enough to reduce the flood of pheromone needed to keep the male from finding the female, inhibiting successful mating and viable egg hatch also reduce the viability of this management strategy. In these cases Chlorpyrifos is an essential tool that would not easily be replaced for this pest. Studies by Cornell faculty have been underway to test the efficacy of replacement insecticides for dogwood borer management. To date only Acetamiprid is labeled for use against dogwood borer.
Although there is a shift away from the older classes of chemistries with the advent of newer, less environmental disruptive insecticides, there remain conditions and circumstances in which specific chemistry modes of action with long residual and broad-spectrum insecticides are necessary for the survival of the tree fruit industry in the northeast. This is especially true if replacement insecticides come under greater constraints, and more likely, if they are lost due to revelation of toxicity not previously observed in the chemistry. A current example includes the targeted pressure placed on the Neonicotinoid group, cited in playing a increasingly important role in reducing native pollinators and considered a viable suspect in contributing to honeybee colony collapse disorder.
Black Stem Borer Management: The high degree of efficacy found in Chlorpyrifos is in due to multiple modes of action including feeding, contact and fumigant activity combined with long field residual life. The black stem borer, Xylosandrus germanus (BSB), a trunk boring pest of deciduous trees in the ambrosia group of beetles is a cyclical invasive pest of apple that has contributed to the demise of thousands of young apple trees in NYS since 2011. As a forest pest it resides along the orchard edge of forested woodlands and hedgerows. During severe weather events such as excessive rainfall or drought apple tree metabolic function begins to stress, causing the tree to produce ethanol. The BSB uses ethanol as a host finding trigger for invasion into orchards undergoing stress, allowing the adult female to borrow into tree trunks of stressed trees, creating a gallery in the heart of the tree, which provides a brood chamber for her young. She will bring fungal spores of plant pathogens into the tree to feed her young. Spores develop to invade the tree vascular system, causing decline and death of the tree, often within a single season. The long life residual and multiple modes of action of Chlorpyrifos have been shown to be the only effective insecticide to effectively manage this pest as a prophylactic and post infection management tool. Until tools of comparable efficacy can be developed, the use of Chlorpyrifos will remain vital to the tree fruit industry.
Research conducted by Cornell University faculty and staff Agnello, Breth, Cox and Jentsch has documented the widespread destruction of trees in NYS. Referenced studies on management of BSB using Lorsban (chlorpyrifos) include:
I. In May, 2014 by Deborah Breth, Cornell Cooperative Extension Lake Ontario Fruit Team in preliminary trials employing high-density tree fruit planting. The insecticide control trial was conducted in a commercial orchard having a history of X. germanus infestation, which involved insecticide applications to the trunk and central leader of trees using a motorized mist blower. Lorsban (chlorpyrifos), Danitol (fenpropathrin), and Cobalt (chlorpyrifos+lambda-cyhalothrin) were each applied to a group of trees in early May; a grower standard consisting of sequential airblast applications of chlorpyrifos and lambda-cyhalothrin was also included. Inspections of the trees to determine active black stem borer infestations later in the season showed the least amount of damage in the Lorsban-treated trees, although the trial setup prevented proper statistical analysis (Table 1).
II. In 2015 Arthur Agnello, NYSAES Cornell University entomologist tested the efficacy and practicality of trunk sprays using chlorpyrifos and two pyrethroid products (lambda-cyhalothrin and gamma-cyhalothrin), evaluated against infestations of ambrosia beetles including black stem borer, Xylosandrus germanus, (BSB) on two commercial farms having documented infestations (Sodus, NY and Medina, NY). All treatments were replicated in randomized complete plots at each of the individual test sites. Potted 2-yr. old Mutsu trees from the nursery were placed in turn into larger pots, which were then flooded to induce stress and promote ethanol production. These potted trees were placed in the rows between the orchard trees, with 5 pots per replicate, and 4 replicates per treatment at each site. The trunks of the potted trees plus the orchard trees were sprayed using a handgun sprayer (Rears Nifty Pul-Tank) on May 7 and 8, before the start of major BSB flight. The treatments were: chlorpyrifos (Lorsban Advanced); 1.5 qt/100 gal lambda-cyhalothrin (Warrior II); 2.56 fl oz/100 gal gamma-cyhalothrin (Declare); 2.05 fl oz/100 gal Untreated Check (potted trees only; orchard trees in Check plots sprayed with chlorpyrifos) Grower Standard (Lorsban 1.5 qt/100 gal applied by grower using airblast sprayer) Treatment efficacy was assessed for evidence of new infestations by preliminary inspection of treated and untreated trees on July 9, after termination of the first flight. A final evaluation of the potted trees was conducted on August 19; these were destructively sampled to document all occurrences of holes, galleries, adults, and brood in the treated trees. In the Preliminary Evaluations, efficacy of the handgun treatments in the potted trees was not consistent between the two sites, with the Lorsban plots tending to have lower levels of infested trees than the Warrior plots at the Sodus site, but the opposite trend occurring at the Medina site. Damage in the Lorsban airblast (Grower Standard) treatment was low at both sites; however, because these plots were situated in a different part of each orchard (to prevent the airblast application from interfering with the handgun treatments), there was almost certainly a site variability factor introduced in regard to BSB population pressure, so it is difficult to make any reliable inference about comparative treatment efficacy as a result. There were no significant treatment differences in percent-infested trees in the established orchard trees. Results of the Final Evaluations varied somewhat between sites. At Sodus, there was a slight trend toward lower infestations (infestation holes, presence of galleries, gallery contents) in the sprayed vs. Check treatments; however, there was no real separation among the handgun treatments. The Grower Standard was lower in all categories. At the Medina site, the Lorsban handgun treatment generally had the lowest infestations, with the pyrethroid products not performing as well. The Grower Standard was again lower in all categories. Reference: Detecting & Responding To Ambrosia Beetle Infestations In New York Apple Orchards
III. In spring through summer of 2015, we surveyed 7 commercial Hudson Valley orchards suffering from severe dogwood borer infestation expressing severe feeding injury with additional black stem borer infestations. Injury to trees led to decline, collapse and death of hundreds of newly planted and young apple trees ranging from 2 to 8 year old plantings in 4 eastern NY counties including Orange (Crist Brothers Orchards, Campbell Hall), Ulster (Dressels Orchard, New Paltz; DuBois Orchard, Highland; Porpiglia Orchards, Marlboro), Dutchess (Mead Orchard, Tivoli) and Columbia counties (Fix Brothers Orchards, Hudson; Yonder Farms, Valatia, NY). In one 500-tree block of 7-year old Fuji in a commercial apple orchard surveyed in Marlboro, NY we found 54% of the trees in decline, 61% of the trunk cambium removed by DWB larva feeding, combined with 23% BSB infestations in synergy to cause severe cankering, sudden apple decline, tree collapse and death of the tree. The stress induced by drought and DWB feeding is the likely cause of increased ethanol production to attract black stem borer adult females to initiate boring and egg laying in wounded trees. This scenario was repeated throughout orchards in the Hudson Valley in 2015.
IV. In 2015 a remediation study was conducted by Peter Jentsch, entomologist at the Hudson Valley Research Laboratory in Highland, NY, in a newly planted orchard block of Honey Crisp on M-9/Nic 29 rootstock in Milton, NY infested with black stem borer. The 0.5 acre block in its third leaf from Willow Drive Nursery, Washington, planted on a 5% slope. Trees did not experience heavy rainfall yet were not provided irrigation on gravely loam soil during the 2014 year of planting and as such experienced low or inadequate soil moisture. During the 2014 growing season the grower did not find extension shoot growth. Significant limb dieback, discoloration and cankering occurred toward the end of the season. Black stem borer infestations began appearing in April of 2015 as new boring sites were evident. Infestations occurred in 15% of the trees in the southwest corner of the block showing symptoms of ‘toothpick’ frass and entrance holes with 1% of the trees appearing to be dead. Upon individual tree removal and dissection, BSB galleries and adult female plugging the entry holes were observed at which time a single application of Lorsban at 1.5 qt/100 gal. was applied by grower using a conventional airblast sprayer. On November 11th, 2015 tree assessments were made to the trunk and lower scaffold limbs. No re-infestation of the trees was observed and new extension growth from limbs previously showing symptoms of severe dieback showed significant growth. From this study it appeared a single application of Lorsban protected the trees from re-infestation during the emergence of the summer generation. http://rvpadmin.cce.cornell.edu/uploads/doc_396.pdf
V. In 2015 42% of growers responding to a Cornell Cooperative Extension pest management survey acknowledged finding infestation of BSB in apple plantings. Over 80% of the growers sited tree losses of up to 100 trees with 9% seeing between 100 and 500 tree losses, 5% experiencing 500-1000 trees infested and 2% with over 1000 trees infested with BSB. In follow-up assessment of infestation, 37% growers reported removing and burning infested trees, 28% reported making Lorsban applications to manage infestations with 9% making pyrethroid applications and 27% using traps to monitor follow-up infestations. http://rvpadmin.cce.cornell.edu/uploads/doc_388.pdf
In Summary: The invasive insect complex continues to cause unprecedented injury to crops, requiring significant time to determine best management practices while broad spectrum management tools are employed to reduce losses. Although newer, reduced risk technologies and products are available for use in tree fruit production, they are not without concerns, recently evidenced in the reduced risk OP replacement neonicotinoid insecticide class. Insecticide resistance management, by design, requires rotation of multiple classes of insecticides. The OP class has only a few tools available for use in tree fruit after FQPA reductions of this class. Limiting the use of Lorsban during the pre-bloom period for black stem borer management, employing a single trunk application, would significantly reduce the risk to pollinators and the predatory insect complex while reducing the potential for introduction to ground water and residue on fruit, yet would optimizing the efficacy in timing to reduce significant losses to the tree fruit industry by boring pests.
