The Newsletter of Pheromone-based Orchard Pest ManagementVol. 1, No. 3 -- April 15, 1996
There are several leafroller species present in Washington but only two species, pandemis and obliquebanded, are known as pests in commercial pome fruit orchards. While their life stages look similar it is possible to learn how to differentiate between them with a little practice. Usually these two leafrollers do NOT occur in the same orchard. The life histories of the pandemis and obliquebanded leafrollers are similar and for the sake of this discussion will not be differentiated. Consult "Orchard Pest Management, a Resource Book for the Pacific Northwest," available through Good Fruit Grower, for more detailed information on these and other leafroller pests of tree fruits in Washington.
Spring Control: The best strategy for controlling leafrollers is to attack the overwintering larvae as they emerge from winter hibernacula and start to feed on opening buds. Most pandemis leafroller larvae have left their hibernacula by the half-inch green tip (HIG) stage of apple flower bud development. Obliquebanded leafroller larvae may continue to emerge after HIG. Timing of spring chemical controls targeted primarily for leafroller should be made at HIG. The combination of insecticide with oil also provides suppression of aphids and mites. Lorsban 4E is the best product to use at this time.
Other registered insecticides do not provide good control or have a high potential to cause spider mite outbreaks because they are toxic to the western predatory mite, Typhlodromus occidentalis. Good coverage of the foliage is critical to good control. Delaying the spring control for leafrollers until the tight-cluster to pink stage of apple bud development has also provided good leafroller control but these later timings should not be accompanied with oil. Multiple applications of Lorsban in the spring are NOT recommended because of the higher potential to disrupt biological control of leafminers and aphids, and selection of resistance in leafroller populations. If leafroller populations remain too high (greater than 2% of infested flower clusters) following the HIG sprays, the use of Bacillus thuringiensis (Bt)-based products (e.g., Dipel, Javelin, Biobit, MVP) provides a "soft" means of control that will not disrupt the activities of biological control agents or bees present in the orchard at this time. Two applications of a Bt product applied between pink and petal fall have provided 80 to 90% suppression of leafroller populations. However, this is only true if:
Summer Control: Lorsban 50WP along with Penncap-M (encapsulated methyl- parathion) represent the two most effective chemical control products against leafroller in summer. While both will kill leafroller adults, the best and recommended target for control is the young larvae. A single Penncap-M or two Lorsban applied at the beginning of the egg hatch period (3 to 4 weeks following the start of moth flight) provide probably the most consistent suppression of leafrollers. However, Bt products can also be used effectively to control leafroller larvae during summer. Because Bt products have a short residual life, 3 to 5 days in summer, multiple applications are required to cover the egg hatch period. The advantage of using Bt products is that they will not disrupt biological control of leafminers, aphids, or other pests and they are completely safe to pesticide applicators and farm workers.
Conventional blocks: Several types of lures containing the CM pheromone are available commercially. The industry standard has been the red rubber septa containing 1 mg of codlemone, produced by Trece, Inc., and others. Research in 1995 showed that to maintain consistent attractiveness lures should be replaced every 3 weeks in spring and every 2 weeks in summer. Note this change from the previous recommendation of changing lures at 4 week intervals. Lures are also available from Consep, Inc. (the "Biolure," a plastic membrane-type) and Hercon, Inc. (a "luretape"). Both of these remainattractive much longer than the red rubber septa, through the entire first generation or longer, and capture as many or more CM than the standard.
A standard wing-type trap (Pherocon® 1CP or equivalent) should be used, with replaceable sticky bottom. Make sure that the top and bottom fit together snugly. Attach the trap securely to a limb within the middle third of the tree canopy height, and not below head height. Traps should be in place before full bloom of Red Delicious, when first flight generally occurs. Check traps weekly and change the bottoms when accumulated moth catch exceeds 40/trap, when dirty and less sticky, or at the end of the first generation, whichever is first.
The number of traps needed per orchard depends upon your needs. If determining biofix (first sustained male flight) is your only purpose, then placing a few traps near known hot-spots may be enough. Check these daily until a consistent catch is found. If you want to follow CM flights throughout your orchard, and determine the need for sprays, then more traps are needed. Place traps in the block to represent all the borders, staying at least three tree rows in from the edge, and through the block interior. Bias your trap locations toward areas of known or suspected higher CM risk, e.g., near bin piles and where damage was seen the previous harvest. Using higher densities of traps will give more accurate information on CM population levels and distribution. Traps placed at one per 5-6 acres has given growers and consultants accurate catch data on which to base a control program. We will review the use of catch thresholds in the next newsletter.
Mating disruption blocks: Monitoring CM adults is more difficult in blocks under mating disruption (MD). Traps baited with standard 1 mg septa are almost useless because they attract moths poorly when high levels of pheromone are present in the orchard. Traps baited with a high load red septa (10 mg of codlemone) have been used with greater success in MD blocks. Their proper use varies some from trap use in conventional blocks.
In pheromone-treated orchards, high load traps do not attract moths from an area as large as do 1 mg traps ina conventional orchard. Therefore, trapping at higher densities is crucial to accurately monitor the CM population. Recommendations call for placing one trap for every 2 to 2.5 acres. In addition, these traps are much more effective when placed in the upper third of the tree canopy. High traps capture about three times more moths in the first generation and almost seven times more in the second generation when compared with mid-canopy traps. Change lures on the same schedule as for 1 mg septa (every 3 weeks in spring, every 2 weeks in summer).
At this time, we do not have the same confidence in the accuracy of these high load traps in MD blocks as we do with standard traps in blocks without pheromone treatment. Research is being done this year on how to further improve their attractiveness.
Trapping in MD blocks should be used along with visual inspection of fruit for CM damage. Examine at least 50 trees per orchard twice each generation. In first generation examine apples when hand thinning begins, and again in late June. Concentrate your search on fruit in the upper canopy of the tree, along orchard borders, in known hot spots (e.g., near prop or bin piles), and on more susceptible varieties like Golden Delicious.
CAMP Site Profile: Randall Island The Randall Island site consists of 760 acres of Bartlett pears situated in the Sacramento River Delta region, near Courtland, California. The area has hot summers and full bloom on pears comes in mid-March, allowing for three full codling moth (CM) generations and often a partial fourth. This site has had very high CM populations, with seasonal pheromone trap catch in some areas of 400 to 800 or more! This pressure, combined with levels of Guthion resistance that can be more than eight times higher than in susceptible populations, created a situation that required a new approach if CM were to be brought under control. Growers were applying the maximum legal rates of Guthion (4 sprays @ 3#/application) and still suffering damage in areas.
An areawide approach to CM control involving mating disruption began here in 1993, two years prior to the other CAMP sites. Drs. Steve Welter and John Dunley, of the University of California-Berkeley, joined with pheromone industry representatives, fruit industry leaders, the site's growers and pest management consultants to develop a codling moth management program that would be economically viable for the growers. At the same time, they hoped to limit or reduce thedevelopment of Guthion resistance and allow for the potential use of "softer" alternatives to high rates of organophosphates. Isomate-C Plus pheromone dispensers were applied (400 per acre) at the beginning of the first CM generation (mid- March) and re-applied in early to mid-June.
In the first year (1993), two Guthion applications were made to all orchards. In 1994, 60% of the acreage received no Guthion and total usage was reduced by 85% from the pre-mating disruption period. In 1995 Guthion use increased slightly and less than 30% was Guthion-free. The increased use reflected a better understanding of the threat posed by strong codling moth flights late in the life of the pheromone dispensers. Infestations along borders and roadsides, extending about 5 rows into the orchard, have been a problem and border sprays are recommended. Average CM damage remained below 0.8% all three years. There does not seem to be an overall decline in the CM population at Randall Island over the period, in contrast to many experiences in the Pacific Northwest. High CM pressure remains, in part due to infestation of "rat-tail" fruit by 3rd generation larvae that develop and mature after the crop is harvested.
Resistance levels to Guthion have been monitored each year at Randall Island. A 20% decline in resistance was found in 1994 from 1993. More extensive Guthion use in 1995 apparently resulted in resistance levels returning to where they were at the beginning of the project, even though most growers only sprayed once, if at all. With the continued high CM pressure here, two applications of Isomate-C Plus are needed to maintain enough pheromone in the orchards for control. It also appears that, in this area, some application of insecticide will be needed many years to supplement mating disruption for CM control. All in all, not a cheap program.
Other pests and beneficial insects have been monitored within these orchards. Low but increasing levels of obliquebanded leafroller infestations were found sporadically in 1995. Treatment was required in only one small block but some controls may be required in 1996 to prevent significant damage. Psylla and mites generally pose less of a problem here than in Pacific Northwest pear blocks. Treatments for these pests have been reduced or eliminated in almost half of Randall Island.
In 1996, research within the Randall Island project will focus on finding a more economical approach to CM control, comparing treatments involving 1 or 2 pheromone dispenser applications combined with sprays of Guthion or Penncap-M. It has been shown that Penncap is more toxic to CM populations that are more resistant to Guthion (negatively-correlated resistance). Several approaches to resistance management will be tried. Different rates and application timings of pheromone dispensers will potentially be combined with insecticide treatments that are varied in time and location across the acreage, to avoid placing uniform selection pressure on a large proportion of the CM population. A new areawide management project using mating disruption has begun this year on 400 acres of pears near Ukiah, in Mendocino County, with direction provided by Dr. Lucia Varela and assistance from Steve Welter.
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
400 Washington St.
Wenatchee, WA 98801