The Newsletter of Pheromone-based Orchard Pest ManagementVol. 1, No. 4 -- May 1, 1996
The recommended treatment thresholds are based upon a trap density of one per 2.5 acres, with traps maintained as described in the April 15 issue of Areawide IPM Update. Trapping at lower densities, one trap per 5 to 6 acres, has been successful for consultants and growers when similar thresholds are used. Keep in mind that lower trap densities increase the risk of failing to detect "hot spots" within a block.
First generation: The treatment threshold is a cumulative catch of 5 moths per trap. Apply an insecticide at the standard first cover timing of 250 degree-days (°D) if the threshold is reached anytime prior to 250 °D. Reset moth catch to zero when a cover is applied. Apply a second spray if 5 moths are again caught in the next 14 to 21 days, or within whatever the residual activity of the first spray is considered to be. A third cover may be required if flight continues and the threshold is again reached. If 5 moths have not been trapped by 250 °D continue accumulation to 350 °D. Reset moth catch to zero at that point if the threshold has still not been reached. No first generation sprays are required if cumulative trap catch never reaches 5 moths.
Second generation: Reset moth catch to zero at 1000 °D, the start of second generation flight. Reduce the threshold to 3 moths as pheromone traps are less efficient at this time. Apply an insecticide at the standard timing of 1240 °D if cumulative trap catch exceeds the threshold. Reset moth catch to zero in treated orchards and follow the same guidelines outlined above for applying additional sprays.
Insecticides may be applied to only those parts of the orchard where trap catch has exceeded the threshold, but treatment boundaries should not be drawn too finely. For example, if low catch traps are intermixed with traps exceeding the threshold then it may be best to treat the entire area. Deciding NOT to treat portions of a block requires confidence gained through experience with pheromone traps and good knowledge of CM history for the block. Whenever treatments are not applied in a marginal trap catch situation, you should spend time examining fruit for CM damage, particularly high in the tree and on more susceptible varieties like Golden Delicious.
Mating Disruption Orchards
In moderate and high CM pressure situations, MD will not stand alone. Trap catch thresholds can be used in mating disruption blocks for determining the need to supplement MD. Brunner and Gut, based on work in Washington orchards, suggest treatment thresholds for high-load traps placed at mid-canopy position at a density of one per 2.5 acres. A cumulative moth catch per trap of 4 or less indicates that MD will provide good CM control without supplemental control. When cumulative catch is between 4 and 10 per trap an insecticide may be needed, but growers with MD experience may wish to delay treatment and monitor for CM fruit injury before making a decision. Trap catch exceeding 10 per trap is a clear sign that a supplemental spray is needed at the appropriate timing.
Trap catch efficiency declines during the second CM generation, in MD blocks as in conventional blocks. Therefore the treatment threshold is halved. Cumulative moth catch of 2 per trap indicates that a supplemental treatment is probably needed. A catch of 5 or more indicates a definite insecticide need.
Codling moth monitoring: Pheromone traps for monitoring CM have not been used with the same degree of confidence in MD blocks as in conventional blocks. This project attempts to develop a better understanding of trap catch within MD blocks, and better correlate trap catch with CM damage. Pheromone traps will be selected across project sites, representing a range of CM pressures. Each trap included will be characterized by many qualities, including trap height, tree canopy height, dispenser height, trap proximity to dispensers, to block edge and to bin or prop piles, and trap position on slopes. Fruit damage from CM will be rated each generation in the area represented by each trap. Work will also be done on how to make the pheromone trap, with a lure containing 10 mg of codlemone, more "apparent" to CM males. The pheromone concentration around traps will be modified by varying the distance from the trap to the nearest dispenser, from 0 to 10 to 25 feet.
Leafroller monitoring: Visual monitoring for leafroller larvae is costly and often unreliable. Standard leafroller pheromone traps are often too attractive, attracting males from outside the orchard. High trap catch may result, whether leafrollers are a problem in the particular block or not. Pheromone traps baited with lures containing lower amounts of pheromone will be used in an attempt to better correlate trap catch with the population present in the particular block.
Colpoclypeus florus: This parasitic wasp can be a very effective parasite of leafrollers, with parasitism rates exceeding 90% in unsprayed blocks. It may provide considerable help in MD blocks with low or no insecticide use. C. florus will be introduced at several release levels in sites with considerable leafroller populations. Releases will be made once each generation, timed for the presence of mid-sized to larger leafroller larvae.
Guthion resistance in codling moth: Levels of resistance have increased greatly in recent years. CM populations with greater resistance have been identified in California, Oregon and Washington. In this project, male CM will be trapped and treated with varied amounts of Guthion (azinphosmethyl) to determine the concentration needed to kill half of the population (LC50). Results will be compared with other sites and previous years, monitoring how Guthion resistance changes with the use of mating disruption and changes in insecticide use.
Monitoring secondary pests and natural enemies: With the use of mating disruption and a reduction in broad-spectrum insecticide use, changes occur in levels of secondary pests (e.g., leafrollers, leafminers, psylla) and natural enemies (e.g., ladybird beetles, predatory bugs, parasitic wasps). An intensive monitoring program will document these changes over time. Sites for this monitoring have been chosen both within the CAMP sites and in nearby conventional blocks for comparison.
Codling moth is the key pest of pear orchards in the Pacific Northwest and California. Currently, the broad spectrum insecticides applied for control of codling moth in pear orchards reduce chances for improving biological control of pear psylla, spidermites and, possibly, grape mealybug. If shown to be effective, mating disruption could help to increase the potential for integrated control in pear orchards by improving the chances for the survival of beneficial insects.
However, certain challenges exist. First, colonization of pear orchards by beneficial insects varies depending on the type of vegetation surrounding the pear orchard. Mating-disrupted orchards located in areas of conventionally-treated apple and pear orchards are not colonized as quickly or in as great numbers as pear orchards bordering native or riparian habitat. These differences must be assessed on an orchard-by- orchard basis and managed accordingly. Secondly, while pears are inherently less susceptible to codling moth than apples, little work has been done to determine if the same density of mating disruption dispensers is required in pear as in apple orchards. This is critical to pear growers, as reduced susceptibility often results in lower internal codling moth populations, allowing for a reduced treatment schedule using conventional insecticides. Pear growers in this enviable situation view the difference between their conventional treatment programs and the higher cost of mating disruption as a deterrent to implementation of mating disruption.
Can these challenges be overcome? Can mating disruption become a more important tool in integrated control of the pear pest complex?
We do not have all the answers. Some of the earliest codling moth mating disruption trials were initiated in California's Lake County by UC farm advisor Rachel Elkins. The longest continuously running large-scale mating disruption trial in pears is the Randall Island, California, project initiated in 1993 by UC entomologists Steve Welter and John Dunley. This was reviewed in the April 15 Areawide IPM Update. In this trial, while growers have been able to reduce or eliminate treatments for pear psylla and mites in half the acreage, mating disruption remains an expensive program due to heavy codling moth pressure. This pressure results from 3 to 4 generations of codling moth each year coupled with the highest levels of codling moth resistance to azinphosmethyl in the West. Growers at Randall Island must make two applications of mating disruption dispensers, along with supplemental application of insecticides in many years.
Research in Washington by Drs. Larry Gut, Jay Brunner and Tom Unruh, using a single dispenser application, demonstrated a similar trend to a reduction in pear psylla, mites and grape mealybug but was highly variable. About half of the orchards studied required treatment for control of pear psylla in the first two years of the study and soft controls such as soap or diatomaceous earth were not always sufficiently effective, likely because of the differences in colonization by beneficials discussed earlier. Orchards which were colonized by generalist predators early in the growing season had the greatest potential for successful biological control. The use of Comply (fenoxycarb) as a pre-bloom pear psylla control in the last year of the study resulted in fewer orchards treated for pear psylla that summer.
In two of the study orchards which had low codling moth pressure, 250 dispensers per acre performed as well as 400 dispensers per acre and did not result in an increase in codling moth damage over a three-year period. This data may indicate that in carefully chosen low-pressure pear orchards the cost of mating disruption may be safely reduced, making the technology more competitive with conventional insecticide applications. Leafrollers, boxelder and stinkbugs also caused detectable-to-severe damage in certain orchards, reinforcing the need to carefully scout mating-disrupted orchards for nontraditional pests.
Codling moth mating disruption is currently being tested in many other pear-growing districts from Mendocino County to Medford and Hood River on to the Canadian border in Washington. While the definitive answer as to the role of codling moth mating disruption in pear orchards is not available, sufficient evidence exists to suggest that along with careful monitoring and judicious insecticide use, mating disruption could be a useful tool in many pear orchards throughout the West.
The CAMP site at Carpenter Hill (Medford) established CM biofix on April 8. The weather has been cool since then, and they are planning on their first oil spray at 200 D, probably May 5-10. CM catches are higher this spring than last, particularly for one grower who opted to not apply a late OP in 1995. Pheromone traps have been placed high in the trees this year, which may account for some of the increased catch. Psylla counts are somewhat higher this year in the Medford area but are lower within the CAMP site.
The West Parker Heights site has determined April 15 to be CM biofix. Isomate-C Plus pheromone dispensers were installed at 400 ties per acre to close to half of this site, with Checkmate-CM dispensers, at 120 to 160 per acre, applied to the remainder. Weather has been unseasonably cool of late, and CM catch has been very low. Growers with leafroller concerns are hoping for warmer weather to apply Bt.
The Howard Flat site installed Isomate-C Plus dispensers the week of April 22. While most blocks are using 400 ties/acre, some growers have decided to reduce rates in pears, young trees and other low pressure areas. Most growers are applying these dispensers using "The Hoop," instead of the clips they used last year. This device, developed by Bill Fleming of Brownfield Orchards, is a 6" circle of PVC that has two holes to accept each end of the "rope" and a slot cut in it to permit passage over a limb. Mounted on a pole, this has allowed the installation of the dispensers in 2-2.5 man-hours/acre, without the time and expense associated with clips. (A good example of how new approaches are continually being tested and improved upon. I think we'll look back in five years and shake our heads at how far we've come. - Ed.) As of April 29 no CM had been trapped.
The Lake Osoyoos site, near Oroville, expects full bloom on apples soon after May 1. Pheromone dispensers will have been applied in the week prior to that. Intensive monitoring for leafrollers is underway, as this site had a big increase in this pest in 1995. Few have been found by early pink in apple blocks. Leafrollers will be easier to locate closer to bloom and beyond. High numbers have been counted in cherry blocks, particularly young, non-bearing blocks. Several Bt sprays are planned by most growers; full rates are needed.
AREAWIDE IPM UPDATE
The Newsletter of Pheromone-based Orchard Pest Management
Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
Partial Funding provided by: Washington State Tree Fruit Research Commission, U.S. Department of Agriculture-Agricultural Research Service,International Apple Institute, and U.S. Environmental Protection Agency
WSU Cooperative Extension, Chelan County
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Wenatchee, WA 98801