Act Quickly to Beat Box Blight

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In one of the larger gardens where I work, we’ve been having a lot more success with controlling box blight.

Weather conditions have been very similar to last year when blight was really bad – a warm, wet autumn. But the difference this year is our speed of action. As soon as I or one of the gardening team see some tell-tale signs of a box blight outbreak starting, such as blackening of the leaves, we apply a fungicide to that area.

box blight

What does a fungicide do?

The application of fungicide slows down the spread of the blight and allows the Buxus to recover. I should add this will only happen if the plant is in good health. Weak or damaged Buxus may struggle to fight off blight infections, even with the help of a fungicide.

How do I keep my Buxus healthy?

The basics of regular watering, feeding and trimming at the right time all contribute to healthy Buxus. I will write about this in more detail in another post. But here’s a few tips;

  • Try not to let the soil dry out. Established Buxus planted in open ground can be drought tolerant but much prefer their roots to have access to some moisture. Watering little and often around the base of the plant works the best.
  • Feed regularly during the growing season. Buxus are hungry plants that require a good balance of nutrients to be healthy. I like to use seaweed extract, ideally organic and from a sustainable source. Organic Shropshire Seaweed is an excellent product. Dilute with water and apply as a foliar feed every 4 weeks during the growing season.
  • There are many factors involved in deciding when best to trim Buxus. Again I will cover this in a future blog post. One key consideration is not to clip in hot sun. This can scorch the leaves and weakens the plant by putting it under stress. The Buxus will recover in time but may be susceptible to blight outbreaks until the plant regains its strength.

How to spot a blight outbreak starting?

The most obvious symptom to look out for is the discolouration of the leaves. Brown or blackening of a leaf often starts at the tip and works its way down. Usually the outbreak will be on a small group of leaves and near the top of the plant, or in the joins where two Buxus plants meet in a cloud design.

box blight

What happens if I ignore the box blight?

When the weather conditions are right, box blight can spread through Buxus remarkably fast. If left untreated the blight gets into the stems of the plant and causes rapid defoliation. Small black streaks on the stems are a sign the blight is starting to take hold and treatment with a fungicide is far less effective.

Which fungicides work best?

If you are a professional gardener with the correct spraying certification then I recommend contacting Agrigem or Progreen to discuss commercial strength fungicides that work.

A widely available fungicide that anyone can buy and use is Provanto Fungus Fighter Plus.

Provanto Fungus Fighter Plus

This fungicide is weaker in strength than the commercial fungicides but I have found it to be effective at slowing the spread of a box blight outbreak- if applied quickly before the infection takes hold. Probably will need two or three applications to get the blight under control and allow the Buxus to recover. I always carry this fungicide in my van- just in case.

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By James Todman

Topiary Specialist based in The Cotswolds, UK.

9 replies on “Act Quickly to Beat Box Blight”

Thanks for great advice. In when best to prune– I think I read somewhere that trimming after a rain is good. Is there anything to that? Maybe the moist leaves heal the cut better.

In my experience, it’s the opposite. Blight fungal spores can be most active in damp conditions. And also be knocked and dispersed by water droplets. So best to avoid trimming in wet conditions. The most ideal weather conditions to clip are dry and cloudy.

Great article. For box with existing box blight, how often in a year would you use the fungus fighter and can you use it on the winter months?

I would apply a fungicide in Spring and Autumn. Would be good to find someone who can apply a commercial strength fungicide like Signum. If the blight is really established in the plants then you may have to consider hard cutting them right back… or worse case scenario – removing.

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