BOX BLIGHT: The research so far…
Box Blight is a fungal disease that affect all 13 species of box plant (buxus sempervirens) typically used in hedging and topiary. It spreads quickly and kills the plant – leaf by leaf and branch by branch until it is either totally stripped of foliage or is pulled up and burnt. The box variety ‘Suffruticosa’ seems to be the most susceptible to infection.
The disease is spread by microscopic spores and typically gets worse in warm, damp conditions. Early spring or late summer are key times when the weather is warm, which encourages fungal growth, plus seasonal rain showers (or hand watering) cause water droplet splashes – which is how the disease spreads from plant to plant. Dead leaf matter is a prime collection area of the disease with some leaf litter harbouring fungal pathogens for upto 5 years.
Although a ‘cure’ for box blight is not definitive – a number of studies into the fungal disease has agreed there are two phases behind Box Blight infection:
(1) the initial infection or growth of the spore (conidia) and then
(2) the spread of the pathogen (mycelium) which kills the leaf. It is important to understand these two phases as products for treatment will be better at one stage than the other.
Protectant fungicides worked better on stage (1) to stop the spore establishing and growing – these included the chemicals: pyraclostrobin, trifloxystrobin, and kresoxim-methyl as well as fludioxonil, mancozeb, chlorothalonil, and boscalid. Stage 2 or spread and maturity of the pathogen was controlled best by: prochloraz, kresoxim-methyl, carbendazim, and epoxiconazole + pyraclostrobin + kresoximmethyl, also mancozeb and chlorothanolil*
*Several professional fungicide brands include these active ingredients but its important to note they do not specify or approve their use on box plant for treatment of box blight - research has concentrated on chemistry not on specific product. (There are no amateur products on the market which have proven effective against blight).
Where people have managed to rescue box hedging, they have told us that a two pronged approach worked best. Spray with protectant and systemic fungicides while clearing all leaf litter and detritus around the plants. Remove dead branches by cutting and burning while also disinfecting secateurs after each use. Mulching annually, with a good depth of quality leaf mould or compost can also help to improve the nutrient balance in the soil which will prompt healthy growth and infection resistance.
As with all fungicides - a regime of alternate use between 2-3 products is best practice as resistance build-up can occur if only using one ....