Summer leafroller control

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.

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

GDD42 (Post biofix)

Event

Action

Tight cluster

Majority of larvae have emerged from shelters

Examine fruit buds for larval activity

0 DD° = biofix (~900 DD° after Jan 1)

1 st sustained moth captures

Set DD° = 0

220-250 DD°

Peak moth flight - overwintering generation

0

400-450 DD°

Start of egg hatch

Timing for scouting-based treatment

1000 DD°

End of egg hatch

0

2300 DD°

Peak moth flight - 2 nd generation

0

2750 DD°

Start of 2 nd generation egg hatch

Timing for scouting-based treatment

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 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 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. Bt’s are most effective when applied during warm weather conditions (daily highs in the 70’s F). 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 active ingredient on the foliage throughout the long period of larval activity. Bt products are generally more effective with a lower tank pH. SpinTor has a similarly short residual (seven to ten days), but provides some contact efficacy, which 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. Proclaim, a new material (Avermectin class) has also shown very good activity against obliquebanded leafroller and requires ingestion by larvae.

In contrast, if Intrepid is used early, it should be targeted to cover egg masses around 350 GDD post biofix so that larvae will consume the chemical as they eat their eggshells upon emergence. Intrepid can also be used later to protect 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. Good, thorough coverage is key to leafroller control with materials requiring ingestion to be effective. 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 sprays should target 100 to 200 GDD after biofix. Similarly, Esteem applied at egg laying timing will also provide some control, though it is more typically used for the overwintering generation.

It should be noted that treating the summer generation of obliquebanded leafroller with SpinTor, Rimon or Proclaim would also provide some control of codling moth, Oriental fruit moth and spotted tentiform leafminer. Intrepid applied at the earlier summer obliquebanded leafroller timing would also assist in controlling codling moth and tufted apple budmoth. Esteem will provide control of San Jose scale crawlers and some added control of codling moth. Bt’s can also be expected to control other leafrollers when applied in the summer for obliquebanded leafroller control.

As with many of our key apple pests, obliquebanded leafroller has 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. For example, if Rimon was the material of choice for control of overwintering larvae, opt for Proclaim, 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.

Compound Trade Name

Chemical Class

Life-stage Activity

Optimal Spray Timing for OBLR

Residual Activity

Mite Flaring Potential

Guthion, Imidan

Organophosphates

Larvae

Biofix + 400-450 DD

10-14 days

L - M

Lannate, Sevin

Carbamates

Larvae

Biofix + 400-450 DD

5-7 days

M - H

Asana, Warrior, Danitol, Decis

Pyrethroids

Larva

Biofix + 400-450 DD

7-10 days

H

Deliver, Dipel, Crymax

Bt’s

Larvae

Biofix + 450 DD

5-7 days

L

Spintor, Entrust

Spinosyn

Larvae

Biofix + 400-450 DD

7-10 days

L

Rimon

IGR

(chitin inhibitor)

Eggs,

Larvae

Biofix + 100-200 DD

Residue under eggs

14+ days

M*

Proclaim

Avermectin

Larvae

Biofix + 400-450 DD

7-10 days

L

Intrepid

IGR (MAC)

Eggs, Larvae,

Adults (sublethal)

Biofix + 350 DD

Residue over eggs

14+ days

L

Esteem

IGR (juvenoid)

Eggs, Larvae

Biofix + 100 DD

Residue under eggs

10-14 days

L

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