Blossom blight is one of those pesky fungal diseases of fruit trees, particularly apricots (though it can also occur in peaches, nectarines and even plums and cherries) that can make the difference between getting a crop of fruit or not. The trouble is, many people don’t even know they’ve got it!
Caused by various strains of the Monilinia fungus, it’s the same fungus that causes brown rot in fruit (particularly peaches and nectarines) later in the season.
Blossom blight infects and kills the flowers on your fruit trees, and can occur anytime while the trees are in flower, from budburst to after full bloom.
Lots of home fruit growers don’t realise their tree is infected, but there’s an easy way to tell if you have it. Healthy flowers will gradually lose their petals once past full bloom, so you’ll see whole petals on the ground under your fruit tree. In an infected tree, the flowers will shrivel, rot and turn brown on the tree.
Blossom blight can also lead to dieback of new shoots, and where there’s an infection you’ll usually see a sunken area of dead bark. These cankers often ooze honey-coloured gum, which is the tree’s very effective method of containing the infection and preventing it spreading further. The tree will often put out a healthy shoot very close to where it’s contained the infection with gum.
Once your trees are infected—and many trees are, because the fungal spores are everywhere—you can expect some infection every year if the weather conditions are right (or wrong, depending on how you look at it!). The danger period is when flowers stay wet from rain or dew for more than 5 hours at a time, at temps greater than 20°C.
Luckily, there are lots of things you can do to prevent the disease:
- Apply a Bordeaux spray (an organic fungicide made from copper and lime) at budswell and again 7–10 days later to prevent blossom blight taking hold.
- In wet conditions (for example if you’ve had more than about 25mm of rain in one go), or if you see signs of blossom blight developing in the flowers, apply another half-strength copper spray at mid- to full-bloom to stop the disease spreading further.
- Because blossom blight is caused by the same fungus as brown rot, it’s very important to clean up and remove any ‘mummies’ or dried up rotten fruit that were left in or under the tree after last season—in fact this is the single most important thing you can do to prevent the disease!
- Netting can create slightly more humid conditions, and can favour the disease, so don’t put drape netting over the trees until after flowering.
- Remove any infected twigs when pruning your apricots, as spores from old fruit or infected twigs can infect next year’s blossoms.
- It’s very important that trees dry quickly after rainfall in spring, so prune them to an open shape to allow good air flow.
- Check your fruit trees at least once a week, and if you notice some infected flowers, prune them out of the tree, to help prevent the disease spreading to healthy flowers.
- Towards the end of flowering, also remove and burn any diseased shoots.
If you have an apricot tree that flowers but you don’t get fruit, blossom blight is one of the most likely culprits (frost is the other), but once you know what to look for, it’s relatively easy to prevent!
Adapted from an article by Katie Finlay that appeared in the Grow Great Fruit Program, © Mt Alexander Fruit Gardens, September 2014. Find out more at www.mafg.com.au – the One Stop Shop for Home Fruit Growers.