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This weekend the weather couldn’t have been more perfect.  Now that all the poultry projects are complete we turned our attention back toward the orchard.  We still have a lot of work to do.  The most important task is wrapping up our never-ending irrigation project, so that was our primary goal this weekend.  As we were setting up our clog-resistant Netafim™ drip irrigation lines around our Stella Cherry tree, we noticed lots of small irregular holes on some of the leaves.  Closer inspection revealed the culprit, the Pear Sawfly larvae (Caliroa cerasi).

The larval stage of the Pear Sawfly (Caliroa cerasi)

No, it’s not a slug, although it is sometimes referred to as the ‘pear slug’ or ‘cherry slug’ due to its slimy appearance. There are many different sawfly species, but this particular one has a predilection for the leaves of cherries and pears.  In orchards, this pest may also affect plums, apples, and quince.

The Pear Sawfly is a new pest to us, so it warranted a little research. As we manage the orchard organically, the first thing we needed to do was understand this particular pest’s life-cycle.

The Pear Sawfly larva pupate and overwinter in the soil.  Come spring, the adult flies emerge, and the females lay their eggs on the upper surface of the leaves toward the top of the canopy (where short people like me may not readily see them).

Adult Sawfly (Photo: Cheryl Moorehead (Bugwood.org) - Image licenced under CCA 3.0)

The eggs hatch within two weeks, and the larvae feed on the leaves, skeletonizing them by removing all of the leaf tissue except for the fine mesh network of veins.  When mature these larvae measure approximately 1 cm in length, and lose their slimy coating, making them more caterpillar than slug-like.  The larvae drop to the soil to pupate, and the cycle begins again.  Typically with this species, there are two generations per year.  The first emerging between June to July, the second between August and September.

Most of the leaves on the Stella cherry tree are healthy

A few leaves show evidence of sawfly larva damage

Severe infestations can cause extensive defoliation of affected trees, which in turn can decrease bloom, and subsequent fruit-set the following spring.

The good news is that most often this pest is under effective biological control, as the Pear Sawfly has many natural enemies.  Overall our orchard, thus far, is minimally effected.  The Stella cherry, and three of the four varieties of pears in the orchard show some leaf damage, but the total number of affected leaves is relatively small.

 

This pear leaf is the most severely affected of the few damaged leaves found

For control within the orchard, the trees will need repeated surveillance throughout the growing season, and any larvae that are seen can be washed from the leaves with a strong jet of water, or if the infestation becomes more severe, spot treatment with an insecticidal soap is reportedly effective, providing larvae are present on the leaves.  Once the mature larvae fall to the ground, controls are ineffective.

In time, as we continue to encourage more beneficial creatures to take up residence in the orchard and gardens, we hope this problem will be self-limiting, but in the meantime we’ll continue to monitor our fruit trees for signs of additional damage.