Plant Care

Box Blight: Common Causes and Treatments

Box blight in plants

We independently research, review, and recommend the best products. If you buy something through our links, we may earn a commission. Learn more.

If there are two words that can make a gardener’s blood run cold, it’s box blight. Anyone who’s had the misfortune of coming across it knows full well that this devastating fungal disease is something that needs to be dealt with quickly and decisively. As someone who’s had more than my fair share of encounters with box blight (once is enough, believe me), I thought it was time I took you through my tried-and-tested approach to treating and preventing this menace.

What causes box blight?

Box blight is caused by a fast-spreading fungus called Calonectria pseudonaviculata which thrives in warm, damp environments. The leading cause of this type of fungus is poor soil conditions. Overwatering or waterlogged soil creates a perfect environment for the fungus to thrive, making box plants particularly susceptible to the disease.

Box blight can also be brought on by environmental stressors like abrupt changes in temperature, excessive exposure to light, or a lack of proper ventilation. Prevention is always preferable to cure, so make sure that your box plants are growing in a favourable environment and protected against harsh conditions.

How to tell if your plant has box blight

Infected plants don’t always display obvious signs of box blight, so it can sometimes be tricky to know whether you have a case on your hands. The symptoms can sometimes be mild, or even replicate signs of environmental stress or other plant diseases, making detection all the more difficult.

That said, there are a handful of signs to watch out for if you suspect a plant has become infected. The first thing I always look out for is spots on leaves which, if left untreated, often grow larger over time and eventually cover the entire leaf. Wilting or shriveled foliage is another telltale sign that a plant has become infected with box blight. And lastly, watch out for black or brown streaks on stems which are often accompanied by wilting and yellowing of the foliage.

How to treat box blight

If you’ve spotted box blight, it’s essential to take swift action in order to save your plants. Once the infection has taken hold, it can become difficult to treat – so time is of the essence.

One treatment method is to cut out the site of the infection, as well as some of the surrounding areas. Make sure you do this on a dry day, as wet conditions can spread the disease. When pruning, be sure to use sharp tools and disinfect them between uses, and avoid using any power tools that can crush leaves and make them more prone to infection. Once you’ve finished pruning, make sure you dispose of the infected material straight away in order to stop the disease from spreading further.

If the infection persists despite your pruning, you might have to cut the height and width of your plants back by a third, or even half. This approach might sound drastic, but it’s a way of ensuring that all of the infected areas have been removed.

You can also use a fungicide to treat and control box blight. I always recommend Provanto Fungus Fighter Plus to anyone grappling with box blight. It’s become my go-to fungicide, and you can count on it to control box blight as well as most plant diseases. Apply to the site of the infection as soon as you noticed any symptoms, and within a day you should start to notice an improvement in the health of your plant.

Don’t lose hope

If you’re currently dealing with box blight, don’t lose hope! Taking swift action to spot and treat the infection is the key to preventing further damage. Cutting out infected areas, using fungicides, and implementing biological controls are all effective treatments for box blight, and they really can save your plants.

Going forward, make sure you’re providing your box plants with optimal growing conditions – including proper spacing, sufficient drainage, and aeration – to create an environment where plants will be more resistant to disease. By following these steps, and resolving box blight as soon as possible, gardeners can save their beloved plants and gardens.

To Top