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Monitoring Obliquebanded Leafroller in Sweet Cherry Orchards
Written by Lynn E. Long, Mike Omeg, and A. Knight
Wasco County Extension Agent and OSU Entomoloty Dept.
Photos by Helmut Riedl, OSU MCAREC
- OBLR Life History
- Strategies for Controlling OBLR
- Delayed Dormant Bloom
- Trapping Adult Moths
- Scouting Method
- Monitoring Overwintering Larvae
- Monitoring Summer Generation Larvae
OBLR Life History
The obliquebanded leafroller (OBLR) is a pest of sweet cherries throughout North America. The larvae feed primarily on foliage but can infest fruit and contaminate bins, causing fruit to be rejected by the packing house.
OBLR overwinter as small larvae and begin emerging with the first bud swell in late March. These larvae are known as the overwintering generation. Most larvae in the orchard have emerged by bud stage 4 (tight cluster). These larvae mature to the adult stage and begin the first adult flight in mid-May. Eggs from the first flight hatch during Royal Anne harvest beginning the summer generation. the larvae of the summer generation infest fruit and mature throughout harvest. The second adult flight begins in late summer. The offspring produced by second flight adults hibernate and emerge next spring to repeat the cycle.
Strategies for Controlling OBLR
Diligence prior to and during the growing season is the key to controlling OBLR. By paying close attention to the following points, control is possible.
Proper sprayer calibration is critical. Call your fieldman for help.
Adjust sprayer to give better coverage towards the bottom third of tree. Be sure to cover root suckers.
Spray penetration to the tree center is critical:
Do not spray in wind.
Tractor speeds should be 2 mph or less.
Apply insecticide with a minimum of 200 gallons of water per acre.
Remove suckers for better spray penetration.
- Do not skimp on chemical rates to save money.
- Proper timing of spray is critical. This is especially true for Bacillus thuringiensis (Bt.). Spray Bt. only when daytime temperature equals or exceeds 60°F and rain is not expected for four days.
Delayed Dormant Bloom
(Delayed Dormant to Mid-May)
All Wasco County cherry growers should plan on applying a delayed dormant spray targeting emerging overwintering larvae. Effective control at this time can prevent an outbreak later in the season.
What to do:
- Apply a delayed dormant Lorsban spray at green tip.
- If the summer generation population was above threshold (0.50 larvae/tree) the previous year, either during or after harvest, apply an additional control spray after petal fall.
- Begin scouting orchards at petal fall for OBLR populations.
- Bt. can be applied anytime after petal fall when daytime temperatures are above 60°F to 70°F and no rain is expected for several days.
- The larvae must ingest the Bt. if it is to be effective. Larvae feed more actively in warm weather.
- Rain will easily wash Bt. off the leaf.
- Success is an effective OBLR control product.
- Unlike Bt. the effectiveness of Success is not as affected by temperature or rain. Success can be applied in cooler temperatures. Rain will not wash Success from the leaf.
- Be sure to use spray materials which are approved by your fruit packer.**
Trapping Adult Moths
J. Brunner & E. Beers
- The Wasco County Extension Service will monitor emergence of first flight. Call the office at 541-296-5494 if you want notification. Place traps immediately after first emergence.
- Place one trap per 10 acres
- Locate traps near block centers
- Hang trap on the outside of tree canopy in large trees.
- Place trap at eye level.
- Check trap every 7 days and record numbers of OBLR moths in trap.
- Continue monitoring through the end of the first flight (usually mid-June).
- If at any time accumulated moth counts reach or exceed 20 moths per trap, the block should be scouted for OBLR larvae.*
- Trapping moths should not be considered a substitute for scouting for larvae. Actual larval counts are a much more reliable indicator of populations.
- Remove all insects from the trap each week with a knife.
- Replace trap bottom when necessary.
In order to avoid OBLR larvae in your fruit, it is critical that you know the current leafroller population in your orchard. A good scouting program can give you the information that you need.
Do not assume that a superficial search will reveal the extent of an infestation; "hot spots" are common. Illustrated below is an example of a block that was infested only on the south side. A quick survey of the north end would have missed the infestation altogether with potentially serious consequences.
What to do:
- When scouting for the overwintering generation, select 60 widely spaced trees in a 20 acre block.
- Select 30 trees per 20 acres when scouting for the summer generation.
- Time your search. Spend one minute per tree.
- Look for rolled leaves, skeletonization, or leaves webbed together.
- Check suckers in the tree center first, then check root suckers, then survey tree perimeter.
- Surveying the entire tree is not needed -- just spend one minute per tree.
- Place suspicious leaves in a bag.
- After one minute check bagged leaves for larvae.
- Check bag for leafroller larvae which fell off leaves.
- Record the number of larvae found.
Monitoring Overwintering Larvae
(Post-bloom to mid-May)
What to do:
- Survey 60 trees in a 20 acre block.
- Count larvae and papae.
- Threshold for spray is 0.125 larvae per tree.
- Apply Bt. if more than 7 larvae and/or pupae are found in 60 tree search. *
- Control applications should be timed at 14 to 21 day intervals.
- Larger larvae require higher rates of control product. **
Monitoring Summer Generation Larvae
(Late Royal Ann/Early Bing Harvest)
OBLR Larvae Skeletonizing a Leaf
These larvae hatch during Royal Ann harvest and may enter the cherry at any time. Initial damage is the skeletonizing of the leaf (see picture), where green leaf tissue is eaten but veins remain. Scouting for leaf skeletonization is an effective method for lacating OBLR larvae.
Larvae are very small at Royal Ann harvest time, 1/8 to 1/4 inch in length. Larvae reach a size where they can be easily detected in the fruit and bins, approximately 1/2 inch in length, during freeze and Lapin harvest. Larvae are more likely to be a problem in later harvested fruit (Lapin, Sweethearts, etc.) because the larvae are larger and more easily detected at these harvest times.
What to do:
- Pick "clean"; if leaves go into buckets, so will larvae.
- Survey 30 trees in a 20 acre block.
- Count only larvae. Webbing or damage does not always indicate an OBLR larvae is present.
- Threshold for spraying is an average 0.50 larvae per tree or greater.*
- Apply a control spray if more than 15 larvae are found in 30 tree search.*
* Thresholds and scouting techniques are based on current levels of understanding and should only be used as a guide.
** Use pesticides with care. Apply them only to plants or sites listed on the label. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livesotck. Always check with your fruit packer regarding acceptability of pesticide products before application.