Shoot tips are killed when oriental fruit moth and peach twig borer larvae bore inside them and feed, resulting in "shoot strikes." Monitoring shoot strikes helps to distinguish damage caused by these pests from similar appearing damage and to determine if the oriental fruit moth or peach twig borer populations require treatment. In orchards where mating disruption is used against oriental fruit moths, it gives an indication of whether it is working.
THE COUNT METHOD – When and How to Sample
1. When to monitor depends on which species has been more prevalent in the past:
- Oriental fruit moth – monitor between 600-900 degree-days (DD) after the first trap catch for the 2nd through 4th generations.
- Peach twig borer – monitor between 500-900 DD after the first trap catch during 1st through 3rd generations.
2. Inspect a minimum of five trees per block (usually 5-10 acres of trees of the same variety).
3. Randomly select trees to inspect by starting with an outside tree and moving towards the middle of the block to get a good cross-section of the block.
4. Pick a starting point and circle the tree looking up, down, and inside the tree, counting all shoot strikes.
5. Record the total number of shoot strikes on the form below before moving on to next tree. Do not distinguish between old and new shoot strikes, but be careful not to confuse shoot damage from breakage or pests such the plant bug Calocoris, which will not leave a tunnel whereas oriental fruit moth and peach twig borer will.
6. Once five or more trees have been inspected, calculate the average strikes per tree using the form below. If you are approaching the treatment threshold (an average of three strikes per tree), sample a few more trees.
|Date||Flight||Tree 1||Tree 2||Tree 3||Tree 4||Tree 5||Total # Strikes||Average strikes/tree*|
|* Total number of strikes divided by number of trees inspected.|
7. When larvae are present in the shoots, verify the predominant species causing the shoot strikes by examining several strikes. When oriental fruit moth (OFM) is present, fresh strikes may have excrement (frass) on the outside of the hole, whereas this is not the case with peach twig borer (PTB). Pull the shoot apart to find the larva. Use the description of the pests in the individual pest sections and the photos in the online version of this guideline to correctly identify the species. Generally, peach twig borer first appears before the leaves are 2 inches long. Oriental fruit moth strikes first appear when leaves are about 5 to 8 inches long. After the first generation, the flights tend to overlap and larvae of both species can be present. Knowing for sure which species is predominant is important in spray timing and in the selection of the most effective insecticide. It may be helpful to record your observations on a form like the one below for future reference.
|Date||Flight||No. of OFM larvae||No. of PTB larvae||No. with no larvae|