July 28, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 28, 2015, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 28th Call download: Click Here

Managing second generation codling moth and pre-harvest intervals
Wild trees that harbor populations of codling moth (CM) typically see a lower amount of damage in July, between first and second generation, and a higher amount of damage in September. Over the last week John sampled wild apple trees for first generation CM damage and found ten percent injury and in two-thirds of the fruit, the larvae had already matured and exited the fruit, and are likely in pupal stage. One-third had fourth or fifth instar larvae feeding in the fruit. These finding fit with our current degree day (DD) accumulation and development curve. In general, if first generation was managed well, pressure should be less during second generation. In areas with wild hosts, e.g., crabapple, English walnut, hawthorn, pressure may be greater.

Across the region growers are currently 1000-1200 DD from their first generation biofix. Cool temperatures in the late spring/ early summer allowed first generation to extend to five or six weeks. Second generation flights have just begun and will likely continue through the beginning of September. With a higher average temperatures degree-days will be accumulated more rapidly and the flight may not last as long. Lighter flights during first generation may also result in lower trap captures during second generation.

Continue to monitor pheromone traps to time insecticides applications. If traps do not exceed threshold an insecticide application is not necessary. Spot spraying blocks where traps exceed threshold may be an option. If larvae are in fruit following harvest, damage can continue to occur in storage; larvae may emerge from fruit. Continue to monitor and consider treatment for other direct fruit pests, e.g., apple maggot, lesser apple worm, obliquebanded leafroller and oriental fruit moth.

Degree day formula:
((Temperature High+Low)÷2)-Lower Development Threshold=Degree Days

Example:
((85°F+65°F))÷2)-50°F=25 DD

Note: the lower developmental threshold for CM is 50°F, upper limit is 86°F. 500-600 DD need to be accumulated before flight is completed per generation. If an average of 22 DD are accumulated per day, the flight may last three to four weeks.

Pre-harvest intervals

Click image to enlarge
Click image to enlarge

Tips in identifying internal lepidoptera
In addition to codling moth, lesser appleworm (LAW) and oriental fruit moth (OFM) are two additional lepidoptera that can cause internal fruit damage. When monitoring for these two species most growers are likely to catch LAW regardless of use of LAW or OFM pheromone lure; OFM may be caught in select areas along Illinois/ Wisconsin border, in orchards with more stone fruit or that have purchased orchard-run fruit from Michigan or Washington. It is important to look at fresh specimens, check traps frequently (at least once per week). Moths left in traps for two weeks will become desiccated and difficult to identify. Fresh LAW reflect a light copper sheen when hit by sunlight and OFM can show various shades of grey. For photos of adults visit these links:

  • http://www.mda.state.mn.us/Global/MDADocs/pestsplants/applefieldguide/law_ofm.aspx
  • http://entomology.osu.edu/welty/pdf/How%20to%20keep%20apples%20wormfreeJan09r.pdf (see page 2 for illustration and description)
  • Official thresholds have not been established for this region. Larry Gut, Michigan State University, noted his personal threshold for OFM is 100/ trap/ week. John’s threshold for LAW is 10-15/ trap/ week. Our experience has been, 10 to 15 moths in a ten to 14 day time period has generated a several percentage of LAW injury. Larvicide applications targeting LAW can be timed for 250 DD following date trap exceeded threshold.

    It is not recommended to use descriptions in scouting manuals to differentiate larva. These resources indicate:

  • LAW feeds on the surface like a summer leafroller and later instars may feed deeper in to the flesh.
  • OFM will feed in flesh right up to the core, but not in the core.
  • Codling moth will go into the center of the fruit and target the core.
  • These descriptions are generally true, yet there are variations of all of these. Our experience is we see LAW feed deeper into the flesh and may meander right up to core, but will not feed in the core. If damage is in the core, then we can safely presume it is codling moth. Immature larvae that is half way to center is difficult to differentiate without microscope. Under magnification (greater than 15x) the key diagnostic trait is the larvae’s anal comb.

    Notes on imidacloprids

  • Overuse could increase risk of resistance issues with pest with multiple generations per year, e.g., San Jose scale, white apple leafhopper, woolly apple aphid. Apply spot sprays or alternate-row-middle applications, only use as full cover when necessary.
  • Imidacloprids impact insects that have piercing, sucking mouth parts. These materials translocate readily into plant tissue and the cuticle of fruit flesh. Apple maggot larvae are impacted in this manner, may not offer effective control if it is not working on adults.
  • Surface v. systemic washoff rates vary: susceptible to washoff following one inch of rain, systemic residue may remain within the plant tissue.
  • The neonicotinoids have limited lethal action on adult apple maggots, but provide strong curative activity on eggs and larvae. It is recommended to apply neonicotinoids as full cover spray to blocks that exceed threshold. Alternate-row-middle applications will not provide adequate control. For more information visit: http://msue.anr.msu.edu/news/managing_apple_maggots_with_insecticides

    Current observations of beneficial insects
    Populations of syrphid fly larvae have varied across the region, with lower numbers being observed in the southern part of the region. Other beneficials observed include black hunter thrips, gall midge larvae, minute pirate bugs and parasitic wasps. For information on the toxicities of insecticides and miticides to natural enemies and honey bees visit: http://www.ipm.ucdavis.edu/PMG/r4900211.html