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Controlling Botrytis on protected ornamental crops

Botrytis is a fungal pathogen that can cause widespread damage to many different crop species in commercial horticulture. Whilst there are many different species of fungus in the Botrytis genus, by far and away the most common and most economically important species is Botrytis cinerea (common name = Grey Mould). This one species can infect multiple crop species and thrives in humid glasshouses and polytunnels. Botrytis is a nectrotrophic pathogen, which means that it kills the plant cells first, then feeds off them. This gives rise to the classic grey-black dead tissue on leaves, fruits, and flowers.

Botrytis is a particular problem for crops that are short in stature, with the foliage close to, or touching the growing media. This includes herbaceous perennial crops, whether they be edible crops like strawberries, or ornamentals like cyclamen.

Unfortunately, the situation is even worse for cyclamen growers because their crops are ready for harvest in the autumn, with lower temperatures, lower light levels, and shortening days all leading to the cool humid conditions in which the Botrytis fungus thrives. And if this wasn’t enough, we are now facing unprecedented rises in gas prices. These gas prices are unsustainable for many growers who would usually heat their glasshouses, so many growers are telling us that they will severely reduce their heating to a bare minimum and closing vents to raise the temperature. This will undoubtedly lead to increased humidity and reduced transpiration rates in the crop. This in turn will lead to far more incidents of fungal diseases that thrive in humid conditions.

Rowlands of Evesham are cyclamen growers who were one of the first commercial glasshouses to trial Eutrema’s Chitosan bio-fungicide. Owner Tony Rowland said ‘my starting point when trialling any new product is always that of skepticism. However, after applying the chitosan I can honestly say I was flabbergasted! The infected plant material dried up within a day of application.”

Rowlands of Evesham do not have a backpack sprayer or fogger on site, so they decided to apply the chitosan through the overhead irrigation in the glasshouse. The product was first diluted into a holding tank, and then dosed into the system via a dosatron. This gave good coverage of the crop even down to the lower leaves, which may have been missed if a backpack sprayer was used.

Botrytis produces a large amount of spores on the leaves it kills. Chitosan helps counter this as it is also a powerful flocculant. This ensures that the spores are conglomerated into particles that are no longer able to float into the air or flow out of the drainage holes and infect other plants. This is a major bonus in potted Cyclamen irrigated by overhead irrigation as it prevents ‘Running Botrytis’. This is where a Botrytis infection spreads through the crop quickly in the irrigation stream and can devastate swathes of a crop. This means, simply ‘managing the crop’ as many cucumber or tomato growers would do with mildew, simply isn’t an option for growers where Botrytis is an issue. Botrytis needs specific intervention or the majority of the crop can be lost, and the pathogen can get established in the nursery beds.

Tony Rowland, Nursery owner, is now so convinced of the effects of chitosan on his nursery he has already planned its use into his growing schedule, with an application every three weeks to activate plant defences and flocculate the spores on any lesions that may appear to prevent their spread.

If you would like to know more on how to apply Eutrema Chitosan Bio-Fungicide on your nursery please get in touch!

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