The Newsletter of Pheromone-based Orchard Pest ManagementVol. 1, No. 6 -- June 1, 1996
Orchards with high leafminer populations generally can trace this problem to one of two things: high overwintering populations or disruption of biological control. Leafminers often approach the onset of winter with most of the population in a larval stage, and freezing temperatures destroy most of them. The rare year when leafminer pupae predominate as winter approaches may set the stage for very high populations in the spring. The more common source of a leafminer problem stems from the use of insecticides and timings that kill Pnigalio. Both Lorsban and Penncap-M are highly toxic to adults of this parasite. Their use in June for leafroller control has been associated with outbreaks of leafminer later in the season.
Today, although treatment for leafminer is less common, some blocks will need to use insecticides to prevent serious damage. June is the time when the main treatment decision is made; let s review briefly the monitoring and treatment criteria.
Because biological control can be quite successful it is important to assess the extent of parasitism of the first leafminer generation. About the time that first generation leafminer pupae appear (late May to early June in central Washington this year), collect tissue-feeding mines and tear them open to determine if the larva or pupa within is alive. Look for the parasite egg, larva or pupa to determine if death is due to parasite attack. Immobile larvae have probably been stung by the parasite and should be counted as parasitized. If the percentage of parasitized mines exceeds 35% the likelihood of biological control is good. If finding leafminer mines is very difficult then you may not need to be concerned with leafminers in the next generation.
Assess the second generation leafminer population in late June to early July, at the time the first tissue feeding mines appear. From at least 10 trees in a block, collect leaves from the basal to mid-portion of vegetative shoots, and count the number of sap-feeding mines found. Treatment should be applied if mines average more than two per leaf, particularly if first generation parasitism is less than 35%. The threshold should be lowered if the second generation develops early, with sap feeders present in early June. A binomial sampling plan for the second generation is presented in the resource book, Orchard Pest Management. For a thorough presentation on leafminers, refer to the section in this book.
Agri-Mek (abamectin) has recently received a registration for the control of leafminers on apples. Tests have shown this material to be very effective in controlling the second generation. Agri-Mek is less disruptive of biological control than Vydate, as tests with Agri-Mek have shown it to have residual contact toxicity for only a few days. It is taken up by the leaf where it remains for some time, even providing suppression of third generation leafminers when applied at second generation timing. Note that the Agri- Mek label for apples at this time requires the addition of spray oil at a minimum of 1 gallon per acre.
In 1994 a grassroots movement, initiated by fieldmen from several fruit packing and orchard supply warehouses in the area, was organized into an approximately 300-acre codling moth management project, using mating disruption as the principal means of control. In 1995, this existing organization of growers and fieldmen at Howard Flat became one of the five sites of the federally funded codling moth areawide management project. By the summer of 1995 there were 34 growers participating, with 176 separate blocks. In 1996, one more grower joined the project, and bearing acreage under mating disruption is 1093 acres.
Management of the project is by the Howard Flat Management Board, which consists of five fruit industry fieldmen and three growers from Howard Flat. A Technical Advisory Committee of tree fruit entomologists provides technical and scientific input. Kelly Denton serves as the project coordinator, overseeing daily project activities and supervising much of the work within the project. Information is made available by mounting weekly data summaries on a bulletin board within the project site, and by placing it on the Electronic Bulletin Board of the WSU-Tree Fruit Research and Extension Center.
In 1995, more than 3,000 moths were trapped during the first three weeks of monitoring. This high level of pressure was anticipated based upon the history of codling moth and the fruit damage reports from the 1994 harvest. In 1994, codling moth catch averaged 32.3 per trap in 155 traps on the Flat, an indication of the significant pressure. All growers were advised in 1995 to apply a cover spray for codling moth control. Codling moth trap captures dropped dramatically following the cover spray and remained low for the rest of the first generation. Second generation codling moth catch was lower still, and limited cover sprays for codling moth were planned for some high pressure orchards. The catastrophic hailstorm that hit Howard Flat on July 9th changed those plans, however, as most of the orchards had their fruit reduced to juice quality at best. Even without further covers, mating disruption alone provided good codling moth suppression in most orchards, even in those with severe hail damage.
Bin samples were taken at harvest from as many blocks as possible to quantify fruit damage by codling moth and other insects. Overall fruit damage from codling moth averaged 0.55%. Many blocks had no detected damage, and 71% of the bins examined were free of codling moth. Significant cullage was limited to a few areas with the highest pressure, and some block borders. Without hail, some growers would have applied an additional cover, as indicated by pheromone trap catch, and damage would have been lower still.
Leafrollers are a potential pest problem on Howard Flat. Pheromone traps placed across the area in 1995 showed significant catch of both pandemis leafroller and obliquebanded leafroller in a few areas, and some fruit damage was noted at harvest. With this knowledge, a more intensive trapping and sampling program for leafrollers is in place this season, and some growers will be including specific sprays for leafrollers in their control programs.
Other pests were also monitored, as were many beneficial insects and mites. Campylomma were found in a few blocks, and leafhoppers were found in most blocks, but no specific controls were applied for either pest. The leafhopper parasite Anagrus was present in most blocks; with few organophosphate insecticides used, this natural enemy may be able to reduce leafhopper populations. Aphid and aphid predators were low throughout the area in 1995, both within and outside Howard Flat. Spider mites were monitored; predatory mites kept them under control and no miticides were required.
In 1996, nearly 1100 acres are under mating disruption at Howard Flat. Isomate-C Plus dispensers have been applied by growers to 850 acres. Crews under the supervision of Kelly Denton treated the remaining 250 acres, at a charge to the grower of $15/acre. Codling moth pheromone traps, using 10mg lures, are in place in the upper-third of tree canopies throughout the site, at a density of one trap per 2.4 acres. Pheromone traps for both pandemis and obliquebanded leafrollers are also used but at a density of one trap per 10 acres.
At the Carpenter Hill site near Medford the spring weather has been more cool and wet than usual, raising concerns with scab, but in general most pear varieties appear to have a good crop. Codling moth catch continues to be higher than at this point in 1995. This has been attributed in part to the higher placement in the trees of traps this year, but has many of those involved concerned. One 20-acre block of pears with high trap catch has had azinphosmethyl applied to supplement the use of mating disruption. The effect this has on disrupting the biological control that has been developed will be followed closely. All pear blocks have applied their first horticultural spray oil, at close to 200°D, and plan on later applications at 400°D and 600°D. Control of mites and psylla with the soft program used at this site again appears very good. Obliquebanded leafrollers are being monitored more extensively this year, and are present in the areas seen last year. Many blocks with leafroller concerns have been treated with Bt sprays this spring but only one, an apple block new to the project in 1996, used a Lorsban in conjunction with the delayed dormant oil spray.
The West Parker Heights site has seen first cover timing come and go, with only about 10% of the blocks receiving a cover spray. First covers were applied around Memorial Day weekend. Codling moth catch per trap in the CAMP blocks is less than half of the 1995 catch, despite the higher placement of the pheromone traps this year. Trap catch in the conventional comparison blocks is quite high, several traps at this point having a cumulative catch exceeding 50 per trap. White apple leafhoppers are present at higher levels in only a few blocks and no sprays targeted at them are planned. With the cool and wet weather this spring there are concerns that leafroller control may not be as good as hoped for, but monitoring indicates no problems at this time. Apple scab has been a concern with this weather as well, and appropriate controls have been applied. Winter damage is widespread in the Yakima Valley, particularly in many stone fruit and Bartlett pear blocks, but this site, with its generally good slopes, has experienced less damage. There are no pressing concerns at this point but, as Brad Higbee says, "Diligence is the byword!"
Howard Flat determined biofix to be May 6 on the Flat this year, and somewhat earlier down by the River. Degree-day accumulation on the Flat was close to 150°D by May 29. First covers should be applied here by the end of the first week of June. Codling moth trap catch at this point is well behind last year's, with 277 moths caught this year (0.6/trap) compared with close to 3000 (>6/trap) at this point in 1995. Leafrollers are being monitored extensively in the post-bloom period, and have been found, at very low levels, in less than 20% of the blocks. Most growers included Lorsban in their delayed dormant application and did not apply Bt in the period around bloom. Both pandemis and obliquebanded leafrollers are present. Leafroller pheromone traps are being placed across the project the week of May 28. The Lake Osoyoos site determined codling moth biofix to be May 6. Trap catch has been heavy in some nearby conventional blocks used for comparison, but almost nil within the mating disrupted blocks of the project. By May 29, with degree-days standing at close to 190°D, a total of only 42 moths has been caught in 168 traps (0.25/trap) within the CAMP site, with 85% of the traps showing no catch. At his stage of development last year catch averaged 1.2 moths/trap. Where first covers are needed it is anticipated that they will be applied within the first week of June. Leafrollers became a big concern in 1995, so in addition to a delayed dormant Lorsban spray most growers applied two Bt's. A very thorough monitoring program found leafrollers to be present at low levels, with only one apple block having more than 1% infested terminal shoots. Campylomma surveys showed them to be a problem in one block within the CAMP site and one within the conventional blocks. Echoing the other Washington sites, Glenn Richardson says, "We need good weather!" -- for fruit growth, chemical thinning and spray applications.
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
400 Washington St.
Wenatchee, WA 98801