Filbertworm eggs in the orchard

Nik Wiman

July 23, 2022

Orchards in the Willamette Valley have now received enough heat units to have filbertworm eggs (>815 degree-days since April 1) and most have now achieved first egg hatch (955 degree-days). Some orchards will already have a few larvae entering nuts (1022 degree-days). You should have first cover sprays on by now if you are treating based on moth captures in pheromone traps or a history of pressure. We put out our trial on Monday just ahead of egg hatch for our location.

Note that moth counts have yet to peak and by the time they do peak at 1188 degree-days, nut infestation has already occurred from the reproductive efforts of the first moths that emerged. Many of us have concerns about the phenology model for filbertworm (developed in 1983 by M.T. AliNiazee) and its performance in our more variable climate these days.

This week OSU graduate student Erica Rudolph was out looking for signs of eggs that the model predicted should be out there. On Tuesday the 19th she found a fresh filbertworm egg. This is not an easy task as the eggs are laid singly on leaves or clusters and they are very small. She is examining a lot of plant material.

Today, July 22, Erica found two more eggs. One is intermediate in development and has darkened compared to the fresh egg. Some traces of the developing gut of the larvae are apparent. On the second egg found today, the black head capsule of the first instar larva is fully formed and showing, indicating that it is just about finished with embryonic development and is about to hatch! So far so good for model predictions.

A very fresh filbertworm egg has a shiny chorion (shell) and creamy interior. Photo: Erica Rudolph

A developing filbertworm egg. Photo: Erica Rudolph

Fully developed filbertworm egg with neonate larva ready to hatch. Photo: Erica Rudolph