Management Considerations For Peach Orchards With Edge Damage From Oriental Fruit Moth

 

What growers need to do to manage oriental fruit moth in Michigan peach blocks.

 

Growers in west central Michigan diligently applied mating disruption to most peach orchards in response to heavy oriental fruit moth damage to the crop in 2016. Oriental fruit moth captures in traps at many sites this spring were low at the beginning of this season, leading growers to feel secure in their management from last year, as well as the decision to use mating disruption to help combat this pest.

 

However, this sentiment changed for many growers with the discovery of heavy damage on the edges of orchards across the region in the past several days, despite using mating disruption.

 

 

This article covers three big questions growers have about what is happening in the region right now, covering a quick discussion of mating disruption’s continued efficacy and what growers need to be doing to manage oriental fruit moth in peach blocks at this time.

 

 

Mating disruption lessens egglaying and subsequent damage by stopping male moths from finding female moths to mate with inside of the area where it is deployed. This means that the damage that is happening at the edges of orchards right now is likely the result of egglaying from mating that happened outside of the orchard.

 

Female moths are mating outside of orchards and then flying in to the edges of peach blocks, particularly those along the edges of wood lines, and laying their eggs on peach shoots. The fact this damage is only happening at the edges of blocks is some of the best evidence that mating disruption is effective. If mating disruption was not working, growers would have relatively uniform shoot damage throughout a peach block resulting from moths mating and laying eggs within the orchard.

 

 

Mating disruption not only interferes with male moths finding females, it also greatly inhibits the male moth’s ability to find a scout’s traps, which often leads to low weekly catches. This can be particularly true for traps located at the center of an orchard that has had mating disruption deployed.

 

The trap is imitating a female’s pheromone plume, thus if mating disruption is deployed correctly it becomes very difficult for males to locate the trap, just as it is difficult for them to locate females in the managed orchard. This is why trap counts can be near zero inside a block, particularly at a center, and still see heavy edge infestation from females that are flying in to orchard blocks already mated and ready to lay eggs.

 

A mated female that is already carrying eggs is not deterred in any way by the presence of mating disruption. Remember, she found her mate outside of the orchard, mated and is now just looking for a suitable site to lay the fertilized eggs.

 

 

The existing damage to peach shoots at edges is generally beyond our control, as the larvae inside of shoots are protected from insecticides by the layer of plant stem that surrounds them. Michigan State University Extension recommends focusing on managing these insects as they emerge from shoot strikes as the second summer flight of oriental fruit moth.

 

This second generation will lay eggs on developing peaches, resulting in fruit damage if they go unmanaged. The regional biofix for oriental fruit moth was April 30 for west central Michigan, so growers should consult the closest MSU Enviroweather station to calculate the growing degree-days since biofix that have accumulated when considering management timings.

 

Preliminary data from MSU Entomology professors Larry Gut and David Mota-Sanchez indicate that several of the pyrethroids are no longer effective options for managing oriental fruit moth. Although the current “Michigan Fruit Pest Management Guide” currently labels pyrethroid products such as Asana as “excellent,” this rating is likely to changes as resistance data is collected. Below is a table of current labelled products for oriental fruit moth that excludes the pyrethroids.

 

Growers that have edge infestations are advised to select the product for their next application from the list of “excellent” products provided below, and consider a timely application to supplement their pheromone treatment and prevent fruit damage. Control measures should be timed for the beginning of second generation egg hatch, which occurs around 1,100 growing degree- days (base 45) after biofix.