Movement of codling moth and leafrollers into your orchard can be the start of serious damage. Both CM and leafrollers can easily fly 5-7 miles in a single night and their reproduction is as high as those that do not fly. Although 5-7 mile flights are common, the likelihood of the moths coming to your orchard in high numbers is directly related to wind speed, distance from the source, and the environment in between the source and your orchard.
Impact of wind speed and direction
Our studies have shown that CM rarely fly at wind speeds above 3.3 mph and that they are unable to locate lures (or mates) at those wind speeds. Wind speed in orchards with high tree density tends to be lower than in low-density orchards. This suggests that moths may be able to fly further in a high-density orchard where wind velocity would be less than 3.3 mph a greater percentage of the time. Studies with marked CM have also shown that the majority of adults migrate in the direction of prevailing wind.
Impact of migration on reproduction
In lab studies we let CM and oblique-banded leafroller (OBLR) adults fly over a distance of approximately 6,200 feet (1.17 miles) and then looked at their reproduction in comparison to moths that did not fly. CM reproduction was not affected by this flight distance. OBLR reproduction even increased 2-2.5 fold after the flight. This means that migrating OBLR can produce 2-2.5 times more offspring when they arrive at a new location compared to moths that do not fly before mating. This is critical information for resistance management, as migrating individuals carrying a gene for pesticide resistance should be able to easily pass that on in the area where they settle. The flight distance of 6,200 feet translates into an area of more than 2,772 acres that moths can infest without a reproductive disadvantage. Our studies further suggest that mated moths fly further than unmated ones and that the flown distance decreases with moth age.
Impact of cover sprays on flight distance
We tested the effects of sublethal doses (LD10) of Assail and Guthion on flight of CM and OBLR in the lab with flight mills (a cheaper and more sensitive method to evaluate these effects compared to field trials). After CM females and males received a sublethal dose of Assail, they flew shorter distances, less frequently and for shorter periods of time. Guthion did not significantly change flight patterns of CM adults. OBLR females exposed to sublethal doses of Assail and Guthion showed significant reductions in flight distance, number of flights and flight duration. Males were unaffected. Our data suggest that migration of CM and OBLR may be reduced due to sublethal effects, however, those effects vary depending on the pesticide used, the pest species and sex.
Impact of kaolin on CM migration
Our studies showed that a border spray of 3 rows with kaolin can reduce CM migration significantly, even in the face of high population pressure, as long as the coverage is thorough and without gaps. Kaolin works as a deterrent as females do not lay their eggs on surfaces covered with kaolin. We suggest to treat only border rows as the kaolin can flare spider mites and interferes with natural enemies (they spend more time cleaning themselves than attacking pest insects and mites). CM migration into an orchard from outside decreases sharply after the first few rows. In sloped orchards, however, CM may be able to fly over the top of the orchard border rows (instead of from tree to tree), thus migrating further than in flat orchards.