Modeling Botrytis Risk

We all know we get more botrytis in wet, cloudy conditions.  Researchers from Florida have worked to put numbers to the observations so we can predict just how important a botrytis fungicide application might be to prevent disease….or when we can save that fungicide application for a better time.

The model works with the understanding that to start an infection from a botrytis spore, the spore needs a tiny bit of leaf (or flower) wetness.  Spores also have a favourite temperature (20°C), but they can actually infect in quite a wide temperature range, given enough time with leaf wetness.

The Florida model classifies risk periods for botrytis infection of strawberries by both leaf wetness and temperature.  At the most optimal 20°C, spores take the shortest time to infect.  Hotter or colder and infection will still happen given leaf wetness, it just takes longer.  According to the model:

Remember that spores are also killed by UV radiation, including UV in sunlight.  The model doesn’t use sunshine in the calculations, but often when there’s sunshine the leaves dry quickly.  There’s no fungicide like sunshine!

The Florida model has actually worked reasonably well to pinpoint botrytis infection periods in other US states, so Tau Research, with support from Horticentre Charitable Trust, is trying it out in strawberries in NZ.  Below is the modeled risk for the past 3 weeks in the NZBP variety trial in Auckland, with above the top line indicating high risk for infection.

Not surprisingly, the highest risk periods coincide with rain.

We already know that leaves are wet when it rains and botrytis is bad when it’s rainy, so there’s not a lot of new news here.  However, I’m interested to see the leaf wetness sensor and the model run in a covered system, where theoretically we should be able to avoid leaf wetness, but in cool autumn weather conditions we still struggle with botrytis.  Perhaps a better understanding of leaf wetness and botrytis risk in a tunnel will help us to hone in our watering and venting to more successfully prevent infection periods.