Summer leafroller control 2010: Gather the information needed to make a sound management decision
Editor’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 (~900 GDD° after Jan 1)||1st sustained moth captures||Set DD° = 0|
|220-250 GDD°||Peak moth flight - overwintering generation|
|400-450 GDD°||Start of egg hatch||Timing for scouting-based treatment w/larvicides (egg materials applied earlier)|
|1,000 GDD°||End of egg hatch|
|2,300 GDD°||Peak moth flight - 2nd generation|
|2,750 GDD°||Start of 2nd generation egg hatch||Timing for scouting-based treatment|
Timing control measures
Degree-day models are essential tools to be used in timing insecticide sprays. Optimal timing for summer sprays varies according to the life stage or stages that are targeted by the product of choice. For conventional insecticides, like organophosphates (OPs), pyrethroids, and carbamates, the first sprays should be targeted between 400 and 450 GDD (Base 42°F) after biofix to control hatching larvae before they can damage fruit. Obliquebanded leafrollers are resistant to OPs in most apple growing regions of the state and are generally not the best option for control. The newest options for growers, Proclaim, Delegate, Belt and Altacor, require ingestion by larvae, but have shown excellent activity against obliquebanded leafrollers. The first sprays should be targeted between 400 and 450 GDD after biofix to control young hatching larvae. Good, thorough coverage is key to leafroller control with materials requiring ingestion to be effective.
If Bt products are used, the latter timing (450 GDD) may be the better choice because they have a short residual, which must be present to control the larvae at the time and location they are actively feeding. If the first application is applied too early, it may take four or more sprays to keep the active ingredient on the foliage throughout the long period of larval activity. Bt’s are most effective when applied during warm weather conditions (daily highs in the 70’s). Additionally, they are generally more effective with a lower tank pH.
SpinTor has been a very good leafroller management option for a number of years. It primarily acts through ingestion, but also provides some contact efficacy. The latter activity will help kill larvae as they move to the actively growing terminals. SpinTor is also a good choice for leafroller control in cherry blocks where control with OPs and pyrethroids is failing to provide adequate protection.
Intrepid is another good leafroller material that can be applied both early to target coverage of eggs or later to target older larvae. If Intrepid is used early, it should be targeted to cover obliquebanded leafroll egg masses around 350 GDD post-biofix, so that larvae will consume the chemical as they eat their eggshells upon emergence. The later timing (400-450 GDD) protects fruit against damage from older larval instars. Upon application, Intrepid has a long residual effect, but should be reapplied where necessary on a 14-day interval to insure coverage of new terminal growth. The addition of an agricultural adjuvant to Intrepid 2-F is recommended to improve spray deposition.
Rimon acts by suppressing development within the egg, as well as larvae that consume it. Hatching of eggs laid by treated adults will also be inhibited. Eggs are particularly susceptible to these products when laid on top of sprayed residue, thus application of sprays should be timed for 100-200 GDD after obliquebanded leafroller biofix. Similarly, Esteem applied at leafroller egg laying timing will also provide some control, though it is more typically used for the overwintering generation.
As with many of our key apple pests, obliquebanded leafrollers have a track record of developing resistance to insecticides. Currently, there are some good options for control of this pest. Practicing good resistance management should help conserve their efficacy. We encourage you to rotate materials with different modes of action (Table 2). For example, if Rimon was the material of choice for control of overwintering larvae, opt for Delegate, Altacor, SpinTor or Intrepid if a summer treatment is warranted. During periods of warm weather, Bt is an excellent option and a good resistance management strategy.