Summer leafroller control 2010: Gather the information needed to make a sound management decision
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The 2010 “early growing season” has resulted in an unusual and close to parallel pattern of obliquebanded leafroller and codling moth adult emergence. Whereas in most years codling moth adult emergence is much earlier than obliquebanded leafroller, this year the biofix dates of codling moths and obliquebanded leafrollers have been very close on farms where adult flight for both species has been monitored. As a result leafroller egg hatch is likely to overlap with late first generation insecticide sprays targeting hatching codling moth larvae. [(Enviro-weather forecast for June 14 in southwest Michigan; see Obliquebanded leafroller emergence graph.)] This is rather unusual, but may provide an opportunity to select materials that will control both pests with one spray. Growers should be actively monitoring both pests to best determine if and when control actions are necessary.
Monitoring with pheromone traps
Moth captures in pheromone traps provide valuable information to the scout and grower, including the establishment of biofix, but are not a reliable indicator of leafroller abundance or potential damage. Obliquebanded leafroller traps have a large active space, potentially catching moths that originate not only from within the trapped orchard, but also from neighboring or more distant orchards and native habitats. Thus, high moth catches may or may not indicate that the orchard being monitored has a leafroller problem. On the other hand, very low catches of less than five per week strongly hint that obliquebanded leafrollers are not a problem. In either case, assessing larval activity is highly recommended to determine if a treatment is warranted.
Assessing larval abundance to determine the need for control measures
Scouting growing terminals for obliquebanded leafroller larvae is the best way to judge whether intervention in the summer is likely to be needed. Larvae are green with brown to black head capsules and are about 25 mm long when fully grown. Often, a scout will detect signs of leafroller activity rather than the actual larva. The name leafroller comes from the larva’s habit of rolling leaves to form a shelter. These feeding sites are most often found at the tips of growing shoots. Larvae will use silk webbing to attach two leaves or a leaf and fruit together to form a shelter. The presence of webbing is a good clue that leafrollers are around. Orchards in which less than 2 percent of the terminals were infested should be monitored in the summer, but controls may not be warranted. Inspect the undersides of leaves within the fruiting canopy, especially where fruit are clustered. Higher levels (greater than 2 percent) of shoot infestation by overwintering larvae are cause for concern and control measures are likely needed to prevent fruit injury.
Table 1. Obliquebanded leafroller GDD model and insecticide timings
| GDD° base 42 (Post Biofix) | Event | Action |
| Tight cluster | Majority of larvae have emerged from shelters | Examine fruit buds for larval activity |
| 0 GDD° = biofix ("*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*~ />
|
