A monitoring plan to assess the efficacy of control programs after each CM generation should include:
- visually examining fruit for signs of CM injury;
- monitoring trap catch to help determine the size and distribution of emerging populations;
- and monitoring phenology models (in DAS) to ensure that sampling and spraying activities are carried out at the appropriate time.
Using these tools to assess control programs throughout the season will allow the opportunity to make any adjustments that are necessary to ensure clean fruit at harvest and can also save time and money by eliminating unnecessary spray applications or limiting the size of the area that is treated.
Visual inspection for CM injury does not have to take a great deal of time. It is more important to look at more trees than spend a lot of time looking at more fruit on a few trees. In most cases, visual inspections can be focused on problem areas or areas with high CM trap catch. On-tree sequential field sampling protocol for export to Taiwan should be done within 14 days of harvest. However, this sampling protocol can also be used earlier in the season to assess CM damage and success of CM control treatments.
Begin on-tree samples in the area of highest CM pressure and examine 60 half-fruits per tree for CM entries. A half-fruit is a fruit of which an entire half plus the calyx can be seen. Begin at the top of the tree and work down until a total of 60 fruits have been examined. Trees should be randomly selected, but separated by roughly 70 feet. Record the successful CM entries in a sampling form (below). The number of trees sampled will depend on the amount of CM injury that is found. A clean orchard block may require sampling as few as 21 trees to complete the evaluation.
CM damage is primarily found on orchard edges, which is likely caused by females migrating into an orchard from outside, poor spray coverage on the orchard margins, and lower concentration of pheromone in mating disruption plots. Therefore, optimal sensitivity is obtained by at least initially sampling the orchard perimeter, where you recorded the highest trap counts or where you expect migration is coming from, then moving to the center. The majority of CM migrate in the direction of prevailing wind.
Outside sources of CM populations can become problematic during the summer generations. When first generation populations are left uncontrolled, as in abandoned or poorly managed orchards, summer populations can grow exponentially. Extra traps should be placed along orchard boarders when outside sources are suspected. Bin piles can be another outside source of CM populations. A good monitoring program can help pinpoint these problem areas so that controls to protect fruit can be applied when necessary.
Pheromone traps are less effective in the summer months. Treatment thresholds based on trap catch should be reduced by half for summer generations. Pheromone lures do not last as long in warm summer months and may need to be replaced more often (do not exceed manufacturers recommendations). If trap capture from first generation was not representative of fruit injury found during visual inspections, changes should be made to improve the monitoring program. False negatives (i.e. no trap capture but fruit injury occurred) can be the result of using too few traps, poor trap maintenance, or inappropriate lure choice. The Combo lure has shown to be more attractive and can be a good option for use in areas that have a history of false negatives. The DA Combo lure contains a low pheromone load plus pear ester which is attractive to CM males and females.