Final report for FNE23-044
Project Information
This project sought to evaluate the effectiveness and logistics of border trap trees for plum curculio management, both from the perspective of the grower and of an orchard IPM consultant. Apple trees around the perimeter of the entire 85-acre orchard were selected and baited with fruit-mimicking and aggregation lures for plum curculio adults. The intent was to compare a grower standard vs two methods using the trap trees: border treatments determined by the occurrence of fresh curculio injury on trap trees, or treatment of trap trees only; unfortunately, a severe freeze that destroyed the crop in 2023 also resulted in very low curculio activity in 2024, and we were unable to assess effectiveness. We did determine that the time needed to set up and continue weekly or twice-weekly monitoring was not a barrier to adopting the practice, and likewise the cost of less than $15 per acre was acceptable. Three other growers adopted the practice voluntarily, and the results were presented at multiple meetings of growers and Extension and consulting colleagues, with favorable response.
Evaluate the effectiveness and cost, in time and money, of using border 'trap trees' to intercept immigrating plum curculio on an entire commercial orchard.
Compare the results of either using border traps as a monitoring technique or a control technique against a grower standard program.
The plum curculio (Conotrachelus nenuphar) is one of the most important insect pests of apples in the Northeastern United States. Adult female curculios lay eggs in developing fruit shortly after petal fall, which causes fruit blemishes and sometimes fruit loss if adults and/or larvae are not controlled by insecticide sprays. Most of the adult curculio beetles overwinter outside the orchard, and migrate in as fruit blossom, set, and begin to grow. The first flush of beetles are controlled by an insecticide shortly after petal fall that also helps control other insect pests, but additional immigration, feeding, and egglaying may occur for several weeks after that, meaning that multiple insecticide applications may be needed for effective control.
Monitoring and control of these insects is difficult – they are not very susceptible to biological control (though work on using entomopathic nematodes is in progress), and they do not respond well to trapping methods. It has been found, however, that using apple trees baited with synthetic fruit odor (benzaldehyde) and a pheromone (grandisoic acid) can intercept and collect immigrating curculio adults into a limited area, allowing much more efficient monitoring, and even the possibility of using insecticide only on the baited trap trees, instead of the entire block, or the entire border of the orchard. Finding a fresh curculio feeding or egglaying scar on a trap tree would be a trigger for a border or spot treatment; if no fresh injury is found, no insecticide should be needed. This has been shown to greatly reduce the number and volume of insecticide used for curculio control.
This method has been well established in small experimental plots and in a few small-scale cider orchards, but has yet to be adopted on a wider basis, largely due to cost ($4 per benzaldehyde lure, with 4 lures per tree needed, plus another $4 for a single grandisoic acid dispenser per tree = at least $20 per tree). In addition, growers and consultants have some uncertainty about scaling up from a few small blocks to an entire good-sized commercial orchard; how much additional time might be needed in setting up and continuing to monitor the trap trees. Technical Advisor Kathleen Leahy has been particularly eager to learn how well the trap tree approach might be integrated with the rest of the orchard scouting and pest management program.
Our proposal is to do the trap tree method across the entire orchard, demonstrating the effectiveness of this approach, identifying any shortfalls that might come along because of scaling up, and tracking the amount of additional consultant and grower time needed to set up and maintain the trap trees over the course of the curculio immigration period, from early May through late June. From earlier work done at UMass Amherst by Dr. Ronald Prokopy, it appears that trap trees spaced at about 60 meters along the border should be sufficient to intercept beetles flying in to the orchard. We will monitor all traps twice a week during that period, and compare the results of border insecticide applications, trap-tree-specific applications (sometimes called 'bomb trees'!), and a grower control.
We believe that using this approach successfully would encourage other growers to try it on a larger scale, even if the cost of the odor baits is several hundred dollars per orchard, given that it could reduce the need for one or more full-orchard or border applications. In addition, work currently under way under Dr. Jaime Pinero at UMass Amherst is showing promising results using apple trees grafted with varieties that seem to be especially attractive to curculio adults, instead of the synthetic odor baits; if this turns out to be a practical method, it could reduce costs. Finally, if use of the odor baits is adopted on a sufficiently wide scale, it's possible that the price could be reduced.
Located in the hills above the village of Putney, VT, Green Mountain Orchards is one of Vermont's largest apple orchards and is managed by the Darrow family. Four generations of the Darrow family have farmed the hills that make up Green Mountain Orchards. We grow primarily apples and blueberries for the wholesale market and boast over 125 acres of apples in production and nearly 18 acres of blueberries. We also grow raspberries, peaches, pears, plums, pumpkins and Christmas trees!
Cooperators
- - Technical Advisor
Research
Using aerial maps of the orchard, we selected trees along the outer rows of the orchard at roughly 60 meters apart as the designated trap trees. We estimated that about 40 trap trees will be selected using this method; 48 traps trees were actually used. During bloom on May 12, we set out the odor baits in the designated trees. Four dispensers of benzaldehyde were set out, one in each quadrant of the tree, using a colored plastic drinking cup to protect the benzaldehyde from degrading in sunlight. One dispenser of grandisoic acid was set out in each trap tree. Both types of lures were obtained from Agbio, Inc. in Westminster, Colorado. For each of the two large sections of the orchard (Main and Temple), we designated part of the block as 1) trap tree monitoring; 2) trap tree control; or 3) grower standard. All traps trees were checked twice a week (once by KL as part of her regular weekly scouting, once by CD) from petal fall until curculio activity declined, using the Cornell NEWA plum curculio model. After an initial full-orchard insecticide at petal fall, in the monitoring section, insecticide was planned to the border rows if fresh curculio 'stings' were found; in the control block, only the trap tree and one tree on either side of the trap tree were treated with insecticide, and the grower standard block were treated according to typical orchard practice. Time spent on monitoring was recorded.
Harvest assessments was conducted in early September on all blocks/sections, with 25 fruit sampled in each trap tree or adjacent tree, and 400 fruit sampled randomly from the interior of each section, for a total of 1200 fruit in the Main block, and 1200 in the Temple block for the interior fruit, and roughly 1000 for the trap tree fruit. Data were intended to be entered onto a spreadsheet and analyzed using ANOVA with the R statistical software.
In 2023 a spring freeze wiped out 95% of the apple crop here in May, so the project was postponed until 2024.
There was virtually no plum curculio activity in this orchard in 2024 -- likely owing to the previous year's freeze having damaged the wild fruit that curculio usually migrate from. While this lack of insect activity did mean that no additional insecticide was needed for curculio in any study sections (fruit injury by curculio was zero in the entire harvest sample), it meant that we were unable to evaluate the accuracy of this method in predicting and controlling curculio activity and injury.
However, an additional goal of the proposed project was to assess the logistics and cost of the practice, and we were able to follow through on that. For the 85 acres of Green Mountain Orchard, we deployed bait on 48 trap trees; the total cost of the bait, protective cups, hangers, and flagging tape was $876, which works out to about $18 per trap tree, or $10.30 per acre. The positioning of the baits in the trap trees was done by Kathleen Leahy, and it took a total of 2 hours, which was additional to the “normal” 2.5 hour scouting time for this orchard at blossom time.
A primary point of interest was in how much time the curculio monitoring would add to the “normal” weekly monitoring done by Kathleen as an IPM consultant. It was found that no additional time was needed to observe 25 fruit clusters for signs of fresh curculio injury at each trap tree, and both normal and additional scouting were accomplished in the time frame of 2.5 hours that has been typical in this orchard. Similarly, Casey Darrow found that virtually no time was added to his normal checking for fruit set, pest injury, etc.
We were disappointed that we were not able to evaluate the effectiveness of this method in predicting curculio activity (although not entirely unhappy about the lack of curculio!), but its effectiveness has been confirmed elsewhere, in multiple small-block and small-orchard settings over the past two decades. The ability to withhold additional insecticides after the petal-fall application without seeing any increase in curculio injury did result in a significant saving of cost and time. The materials needed would likely cost between $10-20 per acre for materials, depending on orchard configuration, and the setup time is likely to be an hour to several hours at pink or early bloom. This additional time is something to take into consideration, especially for consultants who might be doing this at multiple orchard sites, but it seems unlikely to present a great obstacle. The weekly or twice-weekly monitoring time is minimal for any grower or consultant who is checking trees on a regular basis.
We both felt that neither the cost nor the time element involved in this practice were a deterrent to using the baited trap trees, so we believe that it is an option for growers who would like to use trap trees for either monitoring or control of plum curculio. This work will be continued
Education & Outreach Activities and Participation Summary
Participation Summary:
Presentations were made at two winter meetings of Extension workers and consultants, the Northeast Tree Fruit IPM Working Group, which had about 40 in attendance, and the Northeast Crop Consultant Conference, with about 15 attendants (many of whom overlapped with the first group). There was a good deal of interest and discussion by the group.
Presentations were also made to the Vermont Fruit Growers Association annual meeting, and the New Hampshire Fruit Growers Association annual meeting, with about 40 and 60 attendees respectively.
Learning Outcomes
General positive response and interest at 2 grower meetings but no evaluations done.
Project Outcomes
By demonstrating the relative ease of using this method, we believe that this project will reinforce other work being done in the region using trap trees at various densities, grafted trees, and other innovative techniques. Several growers have expressed interest in using this practice on at least part of their farm. We will continue to work with the baited trap trees in the future.
We only partially answered the question we set out to study, because of the lack of curculio pressure. Using the trap trees with 4 benzaldehyde and 1 grandisoic acid dispenser is the most conservative method available for border interception of curculio, so we are reasonably confident that it would succeed under much greater curculio pressure.
Something that had not been done previously was assessing the time and effort needed to use this method on an orchard-wide scale on a substantial acreage, and we are pleased that it fell well within the range of normal scouting and monitoring activities. The material cost is not prohibitive. We believe that this information is useful to apple growers and consultants in the Northeast, where plum curculio is traditionally most problematic.