What is blossom wilt? How do I get rid of blossom wilt? Normally we don’t see a lot of blossom wilt in the eastern counties of the UK. However this year there is a lot of it about. Where does blossom wilt come from?

Blossom wilt is a fungal disease that affects apples, pears, plums, cherries, nectarines, peaches, apricots and some ornamental varieties. It is called blossom wilt because you see the first signs on blossom and new leaves on fruiting spurs, which start to shrivel and go brown. This is a sorry sight, particularly on trees that have been planted for their ornamental value. But infection can spread to other parts of the tree, turning the whole of the exterior part of the tree’s canopy brown. As well as marring its appearance, the possibility of the fruit tree producing a reasonable crop has gone out of the window. In fact shoots and spurs also begin to die. Beige spots may appear on dead wood, particularly in very wet conditions. And if it is not dealt with, the infection can affect fruit, causing brown rot.

Monilinia laxa blossom wilt on prunus triloba
Monilinia laxa blossom wilt on Prunus triloba, photo by I. Sáček, senior, CC0 Wikimedia

What causes blossom wilt?

Blossom wilt is caused by two fungi, Monilinia laxa and Monilinia fructigena. The latter is also the fungus that causes brown rot. The severity of infection varies greatly, because blossom wilt is strongly connected to local weather conditions during blossom – such as a very wet spring – and therefore to the location of the tree or trees. Only rarely it is found at the top of a hill or a well-exposed slope, where there is always some wind around. In short, it can develop very quickly in valleys or in situations of stagnant air, such as in a corner protected by surrounding buildings. Areas with poor air movement and a damp environment encourage colonization by the fungus.

Monilinia laxa blossom wilt infection
Monilinia laxa blossom wilt infection, photo by I. Sáček, senior, CC0 Wikimedia

How to deal with blossom wilt

So what can we do about blossom wilt? In the past we could use Bordeaux mixture, which did not cure the problem but made the situation more manageable. Sulphur, if applied at the pink bud stage, helps a little. But the best way of controlling the development of blossom wilt requires actions on a longer timescale. Firstly, if your location is susceptible to blossom wilt, choose resistant varieties, such as the plum varieties Marjorie’s Seedling or President, the apricot Moorpark, and, in apples, avoid James Grieve and Lord Derby which are particularly prone to blossom wilt. Secondly, whatever the variety, make sure that the tree canopy is very open, vase-shape or open bush. This will help to keep the trunk and branches dry, enabling it to dry more quickly when compared to other fruit tree shapes. Thirdly, the tree will build up a degree of resistance to blossom wilt if liquid seaweed is applied at weekly intervals  from bud burst stage onwards. Make sure the tree is well covered and wetted to the point of run off. The reason for this is that blossom wilt also affects the wood spurs.

Fourth and very important is orchard hygiene. Infected blossoms and spurs are a source of fungal spores that can infect fruit. So affected blossoms and spurs have to be cut out and removed from the tree, and eliminated in the non-recycling bin or definitively destroyed. Try to prevent bird damage to ripening fruit on the tree, because fungal spores enter wounds on fruit. Remove and destroy any fruit showing brown rot. It is essential not to leave affected shoots, spurs and fruits on the ground. In autumn, rake up leaves and remove them from the garden. Fungal spores remaining on affected tissues will overwinter and germinate the following spring. It will take time to do these jobs. Currently there is no alternative available.

Monilinia laxa on cherry
Monilinia laxa on cherry, photo by Agronom, CC BY-SA 4.0,