April 16, 2003
Vol. 5 No. 2
Monitoring Codling Moth
Codling moth (CM) is a key pest for most Northwest apple and pear growers. Few orchards pass a year without using some control measures, commonly involving several sprays and, increasingly, mating disruption (MD). Too often, CM controls are used with little or no information about CM populations. Extra sprays are applied, wasting money and possibly disrupting biocontrol, or needed sprays are missed, leading to unwanted surprises at harvest or before.
Increased CM damage in many Washington orchards, together with the increased use restrictions and the pending loss of organophosphate cover sprays, makes effective CM monitoring even more important. Pheromone traps have been used successfully as part of a CM monitoring program for over 25 years. They remain central to CM monitoring programs but their use has become more complicated in the now close to 50% of the Washington apple acreage treated with MD. The increased use of more selective, expensive and time-critical CM insecticides (e.g. Intrepid, Esteem, Assail) also calls for better knowledge of CM in individual orchards so that growers can respond in the proper manner and at the proper time.
Pheromone Lures for Mating Disruption Orchards In MD orchards a lure releasing a high rate of codlemone (codling moth pheromone) is recommended, allowing the male codling moth to detect the lure and navigate to the trap amidst the high levels of codlemone released in the orchard by the MD dispensers. Even with the high load lure, pheromone traps are not as reliable indicators of CM populations in MD orchards as are standard (1 mg codlemone) lures in non-MD orchards. In both orchard situations, pheromone trap efficiency declines in the second CM generation, increasing the risk of false negatives (no moths caught but fruit damage occurs in the area).
Several lures are available for use in MD orchards:
- Superlure (or "bubble lure"), manufactured by Phero Tech of Delta, BC. Phero Tech recommends a change interval of 50-60 days in the spring and 35-45 days in the summer. In the AWII project these lures are changed every 6 weeks.
- Megalure, manufactured by TrÈcÈ, Inc., of Salinas, CA. Recommended change interval is 10 weeks.
- Biolure CM10x, by Suterra, Inc. of Bend, OR. Recommended change interval is 8 weeks (spring) and 6 weeks (summer).
- The 10X lure, with various manufacturers. A red rubber septum, containing 10 mg of codlemone. Recommended change interval is 3 weeks (spring) and 2 weeks (summer).
The 10X has been a standard in the industry and has been used extensively in research as a standard for comparison. However, it only provides consistent attraction of CM with frequent changes, something that is too easily overlooked by busy growers and consultants. The first three lures all allow less frequent changes. Their effectiveness has been compared in many trials with the 10X changed at 10-14 day intervals.
The Superlure often provides the highest initial CM catches in the weeks after placement. Its effectiveness declines after 45-55 days in most trials. The Megalure is a gray rubber septa; codlemone is much more stable in this rubber than in the red rubber used in the 10X. It generally catches less than other lures in the cooler spring conditions, but catches similar numbers in summertime trials. The Biolure has performed well in recent trials, catching as much as the standard 10X for at least 8 weeks.
Pheromone Lures for non-Mating Disruption Orchards
Several lures are widely available commercially:
- The 1X lure, with many manufacturers, contains 1 mg of codlemone in a red rubber septum. It has been the standard for many years, but for consistent performance must be changed every three weeks in the spring, and two in the summer. Longer intervals will result in reduced or no catch.
- The L2 ("Long Life") lure, by TrÈcÈ, has looked good in trials, maintaining a high level of attraction for at least eight weeks; the company recommends a change interval of 12 weeks.
- Biolure CM1x, by Suterra. Recommended change interval is 8 weeks (spring) and 6 weeks (summer).
- The DA lure can overcome the problem of male catch being suppressed in pheromone traps in MD blocks.
- The DA lure can detect the emergence and numbers of female codling moths, not just the males found in pheromone traps. The females lay the eggs that produce the larvae that cause fruit damage, so female numbers may be a better indication of fruit damage potential and the need for supplemental sprays.
- The DA lure may allow the development of a model based on female CM emergence; an improved phenological model could permit more precise timing of cover sprays, which becomes increasingly important with the use of more selective, and less effective, insecticides like the IGRs.
The type of trap has a significant effect on the number of CM caught. To a certain extent, a larger sticky, catching surface will catch more moths. The triangular, or delta, trap has largely replaced the wing trap (e.g. Pherocon ICP) as the trap of choice by orchard consultants in Washington. The plastic trap body is usable for 2-3 or more seasons, and the sticky insert is easily replaced as needed. Trials in several states have shown that the delta trap catches 50% or more moths than the wing trap. Other traps are available, including small and large disposable diamond-shaped traps (e.g. Pherocon IIB and IIC, respectively). Sticky surface area is important to trap performance with these as well, with the smaller trap catching fewer moths in most trials.
There is no one best trap type. However, for the best ability to detect the low CM populations often found in Washington the larger surface area traps are preferred. Likewise, use the same trap type in the orchard, between orchards and from year to year so that good relative comparisons can be made.
Trap Placement and Maintenance
Proper use and maintenance is crucial to optimize catch and is often neglected. In conventional blocks, traps should be hung securely in the middle third of the tree height, not below head height, and near the outer perimeter of the canopy. Traps in MD blocks need to be placed higher in the tree canopy, within the top third of the tree. In a block with a tree height of 12 to 14 feet, that would mean traps should be 8 to 10 feet from the ground. An easy way to do this is to affix a 4-6' bamboo pole to the wire of the trap, allowing the trap to be hooked over a limb at the appropriate height. To maintain the stickiness of the trap bottoms, stir up the "stickum" periodically when it becomes fouled or coated with dust, and replace the sticky surface when accumulated moth catch has exceeded 30 per trap or at the end of the first generation, whichever is first. Remember to remove the old lures when the new ones are inserted. In MD blocks make sure that traps are not placed within 5 feet of a pheromone dispenser.
Trap Numbers and Interpreting Catch
The number of traps needed per orchard depends upon your objective in trapping. If your only purpose is determining biofix, for use with the codling moth phenology model, then placing a few traps near known hot spots may be enough. Check these traps daily, beginning shortly before full bloom on Red Delicious, until a consistent catch is found. If you want to follow CM flights through the season, monitor relative CM pressure through your orchard and/or determine the need for sprays, then more traps are needed. Place traps in the block to represent all of the borders, staying at least two tree rows in from the edge, and through the block interior. Bias trap placement towards known or suspected CM sources and "hot spots".
Using higher densities of traps will give more accurate information on CM population levels and distribution. In non-MD orchards, many consultants have found that using traps at a density of one per 5 to 8 acres has given them adequate catch data on which to base a control program. In MD orchards, traps attract moths over a smaller area, even with the use of high load lures. Trapping in MD blocks should be at a higher density, with one trap per 2.5 to 4 acres, to provide a similar level of accuracy. The reliability of moth catch declines in the second (summer) CM generation in both conventional and MD orchards, although considerably more in MD blocks.
Growers and consultants have used moth catch action thresholds successfully for many years to determine whether to spray. This approach is very dependent upon proper trap use and maintenance, and the density at which traps are placed. In MD orchards with traps at one per 2.5-3 ac, and conventional orchards trapped at one per 5-6 acres, applying supplemental insecticides may be needed when cumulative CM catch reached 4 or more moths per trap. A cumulative catch of 10 or more moths indicates a clear need for supplemental sprays. As trap catch efficiency declines in the second generation, these suggested action thresholds should be halved in the summer.
Visual Inspections for Damage
Trapping should be used together with visual inspection of fruit for CM damage, particularly within mating disruption blocks. In the first generation, do a fruit inspection near the end of CM egg hatch (mid to late June in most parts of Washington). Concentrate your search, from the ground, on fruit in the upper canopy of the tree, focusing on orchard borders, known hot spots (near bin or prop piles, the top of slopes, and near packing sheds), and on more susceptible varieties like Golden Delicious. Be alert for any CM stings or entries that are found during hand thinning. These exams can help determine the need for and location of sprays, especially in the following generation. Be sure to examine fruit in the bins at harvest for damage by CM, as well as other pests; although this is a busy time, this information can be invaluable to planning pest control measures for the following year and focusing efforts on hot spots. If a harvest exam is not possible, then do a second exam of fruit on the tree just prior to harvest to pick up any concentrations of damage.
The DA Lure
High load pheromone lures are the standard means of monitoring CM in mating disruption orchards, but there are problems with their use. They are less apparent to CM in the pheromone-rich atmosphere of a MD orchard than are standard pheromone lures in a non-MD orchard. The risk of false negative trap catches is greater in MD orchards than in non-MD orchards. The DA lure may help address this problem.
The attractive chemical in the DA lure is ethyl(2E,4Z)-2,4-decadienoate, a volatile compound derived from the odor of ripe Bartlett pears. Dr. Doug Light, of the USDA-ARS lab in Albany, CA, identified this chemical in 1998. He found it to be specific to codling moth, attracting both males and virgin and mated females. DA is a stable compound, no more expensive than codlemone to produce, and easily loaded into rubber septa to make a lure that is attractive to CM for two months or more.
Dr. Alan Knight, of the USDA-ARS lab near Wapato, WA, has done extensive research in both the lab and field with this compound for four seasons. He sees several advantages that this new, non-pheromone lure offers:
Dr. Knight's work has shown that DA traps have caught up to 3-4X more moths in MD apple blocks than Megalure baited pheromone traps, in both CM generations. In non-MD apples, the DA caught less than the standard pheromone lure. Work conducted by Dr. Jay Brunner and in the Areawide II project showed similar results in non-MD blocks. In MD blocks the DA traps caught less than Superlure baited pheromone traps in the first CM generation and equal or greater numbers in the second. Although the absolute attractiveness of the DA lure declines later in the summer, it may not decline as much as pheromone lures do and thus could be a more sensitive measure of CM populations and damage risk at that time. Like the pheromone lure in MD blocks, it has a very limited area of attraction and can't be expected to reflect the CM population of a large, multi-acre area.
Some of the variability in catch may be due to cultivar effects, probably related to the production of competing fruit volatiles by the crop. Dr. Knight found higher catches with DA relative to pheromone in some late season apple cultivars, especially Granny Smith, and less catch in earlier cultivars, including Gala and Golden Delicious. Understandably, it is even less effective in pears. (The DA lure looks especially good in California walnuts using CMMD; codling moth is a pest of walnuts and there are no pear fruit volatiles to be found in those groves!) This cultivar effect may influence treatment thresholds for supplemental sprays.
Research with the DA lure is continuing in several areas in 2002 by Drs. Knight, Brunner and others, investigating catch relative to pheromone lures and fruit damage, cultivar effects, ways to improve lure attractiveness and more. Dr. Knight is also pursuing the use of DA in an "attract and kill" product that could take out females as well as males, even in MD orchards (more on this novel approach in a later newsletter).
The DA lure will be available commercially for the first time in 2002. TrÈcÈ, Inc. is selling the lure in a kit only (three lures and six Pherocon IIB traps) for about $31.00. TrÈcÈ is developing protocols for its use and will provide an "IPM Partner" sheet with purchase. The recommended change interval for the lure is eight weeks. Its best fit at this time is in apple MD blocks (not pears) and it should be used only in conjunction with pheromone traps. It may be of particular value in suspected hot spots and along orchard borders.