Climate Change: Does it affect professional horticulture growers?

When should I start my spray programme?

Does climate change affect pest and disease activity?

Climate Change: Horticulture growers should plan for flexibility in crop protection programmes

According to the Met Office’s weather review, the winter we’ve just had was both drier and milder than the long-term average. Five of the 10 mildest winters on record have occurred since 2010.

There have been numerous studies, too, on the impact of climate change on nature. One of the most recent, published in January, received a lot of publicity for its findings that flowering dates for many plant species in the wild have shifted forward by up to a month.

Most scientists now agree climate change is happening, which has clear implications for everything from water availability to how you plan crop protection programmes.

Plant pests and diseases don’t follow the human calendar so it has never been a good idea to base when you introduce your biocontrols or schedule preventive sprays on the same date year after year. But climate change makes it more important than ever to take decisions led by on-nursery monitoring and with an eye on recent weather and the forecast.

Last year’s insecticide application in the last week of March, for example, may have kept spider mites well under control but there is no guarantee an application on the same day this year will be as effective. The warmer the start to the spring, the earlier spider mites will get going and the faster they will multiply.

While you need to start the season with an outline plan, you also need to make room for some flexibility. Early signs of a build-up of pest or disease pressure during your routine monitoring will throw your plans ‘off piste’. So too will fluctuations in conditions that might either favour certain pests or diseases, and bring your treatment schedule forward, or slow their development meaning you can wait a little longer before taking action.

For many insect pest species, temperature is the main factor determining when they start to become active and how quickly they might spread – and obviously that’s amplified under glass or in polytunnels. Humidity will be important for some as well.

For fungal plant pathogens, it’s the combination of temperature, humidity – and, with some species, condensation on leaves – that determines when and how quickly spores germinate to kick off an infection.

Various forecasting models can aid spraying decisions based on weather data and actual trap catches of insect pests or even fungal spores. They are mainly designed for pests and diseases of edible crops but might be worth investigating as they may help you pinpoint when you need to be particularly vigilant.

Your crop protection programme should aim for prevention rather than cure – you have a better chance of controlling 1,000 individual insects or fungal spores than 10,000. Adding flexibility to your programme doesn’t mean waiting until an issue gets out of hand, but balancing the odds that you can get the most out of a spray, whether that’s two weeks earlier or one week later than the same time last year.

Given the mild winter we’ve just had, we could be seeing several of our key pests and diseases on the move earlier, and in larger numbers, than you would normally expect.