Summer leafroller control
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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.
This past week marked the beginning of the first of two flight periods of adult obliquebanded leafroller in Michigan. The first flight typically begins in mid-June and lasts about six weeks. The second flight takes place from early August to mid-September. Obliquebanded leafroller flight can be tracked through the season using pheromone-baited traps. Moth captures in pheromone traps also are used to initiate a degree day model, base 42°F. First sustained moth catch (catch on two successive dates) in pheromone traps is used as a biofix. Key events in the life history of obliquebanded leafroller can subsequently be predicted using the degree day model. For example, egg hatch begins around 400 degree days after biofix.
Although moth captures in pheromone traps provide valuable information to the scout and grower, they are not a reliable indicator of leafroller abundance or potential damage. Obliquebanded leafroller traps have a large active space. In other words, they potentially catch moths that originate from within the trapped orchard, 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. Very low catches of less than five per week strongly hint that obliquebanded leafroller is not a problem, but assessing larval activity is highly recommended to confirm this.
To get the information needed to make a sound management decision, a scout must look for leafroller larvae, or at least signs of their presence. 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 also 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.
Finding young larvae in the early spring is difficult, thus most growers take preventative measures at this time. If they were successful, fruit damage will be avoided and few larvae will survive and move to the shoot tips to feed. Scouting orchards for surviving larvae in growing terminals is the best way to judge whether intervention in the summer is likely to be needed as well. Orchards with less than 2% of the terminals infested should be monitored in the summer, but controls may not be warranted. Higher levels of shoot infestation are cause for concern and control measures are likely needed to prevent fruit injury. This investment of time could result in saving several sprays.
Obliquebanded leafroller GDD model
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GDD42 (Post biofix) |
Event |
Action |
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Tight cluster |
Majority of larvae have emerged from shelters |
Examine fruit buds for larval activity |
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0 DD° = biofix ("*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*"*~>
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Esteem
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IGR (juvenoid)
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Eggs, Larvae
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Biofix + 100 DD Residue under eggs
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10-14 days
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L |
