Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

Client's Request (via phone message)  Last year my apple tree was seriously impacted by codling moths. I understand that there are routines timed to the hatching of the moth that a home gardener can follow to minimize, maybe even eliminate, damage to the apples. Can you advise me on those routines.

MG Help Desk Response:  Thank you for your call to the UC Master Gardener Program Help Desk. Your message indicated you are looking for information on the hatching timing for codling moths in your area.

The easiest way to determine hatching time in a backyard orchard is by monitoring stings. Do this by checking fruit at least twice a week, starting about 3 to 4 weeks after bloom. Look for tiny (about 1/16”) mounds of brown/reddish frass (insect poo). Under the frass you can see the entry hole where the larva has entered the apple. Make sure you check especially where 2 apples touch each other, as this is a common spot for the eggs to be laid. Spray the tree as soon as you find the first sting. Make sure you remove any apples with stings, as sprays do not reach larvae already inside.
 
In cooler areas (e.g., west Contra Costa County), look for first stings in early to mid-May and stings from a second generation mid-July to mid-August. In warmer areas (inland Contra Costa County) start looking for first stings by mid-April. Inland, there may be as many as 3 generations hatching through the summer, all requiring treatment.
 

Frass, a mixture of feces and food fragments, fills tunnels that codling moth larvae have bored into this apple.

A more precise way to determine hatching dates is by using degree-day calculations and pheromone traps. Degree days are a calculation of the accumulated heat over a set period of time. The trap will let you know when the moths are flying, then you can calculate when hatch will occur with a degree-day calculator. The University of California has an “easy-to-use” degree-day calculator that you can use with a variety of tree crops: http://www.ipm.ucdavis.edu/calludt.cgi/DDMODEL?MODEL=CM.

To use the calculator, you will need to know the date of when moths are found in your traps and sunset temperatures have reached 62 degrees. This date is known as the biofix date. When asked to select a UC CIMIS weather station, choose the one of five in Contra Costa County that is closest to you. That will produce a chart with expected degree days for the time period you specified and recommendations for degree-day accumulations for each spraying.
 
For more information on codling moths and their control, see this UC document: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7412.html. For a calendar of gardening operations for apples: http://homeorchard.ucanr.edu/Fruits_&_Nuts/Apple/.
 
Please let us know if you have further questions. 

Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Don't miss our 2017 Great Tomato Plant Sale: 
http://ccmg.ucanr.edu/EdibleGardening/GreatTomatoPlantSale/

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (http://ucanr.edu/blogs/CCMGBlog/).