Strawberry Root Weevils are a very common pest in a variety of areas and on a variety of crops. These weevils overwinter as larvae in the soil, and emerge in spring, (or in late winter in warmer climates.) Soon after the larvae emerge, pupation begins, and then adults emerge and females begin to lay eggs. There is only generation per year. Researchers have developed a growing degree day model to help predict when life stages will occur based on that year’s weather.

Calculating the Growing Degree Day Units

There are two distinct Strawberry Root Weevil models, which have developed on different host crops (peppermint and strawberry). The Strawberry Root Weevil growing degree day model uses a lower threshold of 48F on peppermint, and 40F on strawberry, with an upper temperature threshold of 103F for both models. These units can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

For growing degree day models, there needs to be a “biofix”, a set date after which growing degree day units will accumulate. For the Northern Hemisphere, January 1st is the recommended biofix date for the Peppermint model, and February 15th for the Strawberry model.

This can be used to track larvae emergence, pupal development, adult emergence and egg-laying for the season. For best results the in the Pest Prophet app, the biofix date can be reset once each development stage is observed, in order to more precisely predict the next stage.

Sources:

Cacka J. F. 1982. Biology, distribution and economic threshold of the strawberry root weevil, Oriorhynchus ovatus (L.), in peppermint. M. S. Thesis, Dept. Entomology, Oregon State University. J. R. Umble and J. R. Fisher 2000. Temperature-Dependent Development of Otiorhynchus ovatus (Coleoptera: Curculionidae) Pupae Environmental Entomology: 29:758-765.