Gadenin日本語Get the appPeach leaf curl: an almond catches it just like a peach
The leaves come out thick, puckered and blistered, flushed red or purple, then turn a dusty white and fall. It is the same fungus that disfigures peaches and nectarines, and an almond, being a close relative, gets it in exactly the same way and to exactly the same degree. Most people meet it in their first spring, reach for a spray, and find that nothing happens.
Nothing happens because the fight was over weeks before the symptoms appeared. The fungus overwinters in the bark and in the bud scales. Its spores move only in water, and they can only enter a bud while that bud is wet and the temperature is between about 45F and 60F (7C and 16C). Cool wet weather in late winter and very early spring is precisely the condition it needs. Once the leaves are open, the tree cannot be infected again that year, and nothing applied to a curled leaf will straighten it.
So the entire strategy is to keep rain off the buds through late winter and early spring. That is not a spray. It is a physical cover, and it is the reason a flat-trained almond against a wall is so much easier to keep clean than a free-standing one.
How to keep the winter rain off
The cover goes up before midwinter, ahead of the first spore splash, and comes down when the tree is in full leaf and the weather has settled. The sides stay open throughout. You are shedding rain, not building a greenhouse, and closing the sides both overheats the tree and shuts out the few insects that will pollinate the early flowers.
- On a fan-trained tree, build a lean-to Fix battens to the wall above the tree and run clear polythene from them out and down to a frame standing 18 inches (45 cm) clear of the branches at the bottom. Leave both ends wide open. A flat tree against a flat surface is the easiest thing in the garden to cover.
- On a free-standing tree, build a tent Four posts and a clear sheet tied over the top, sloping so water runs off one side, will do. It must stand well clear of every branch, because a bud touching wet plastic is infected through the plastic just as if it were in the rain.
- On a potted tree, move it instead The simplest answer of all. A dwarf almond in a large pot spends late winter in an unheated porch, a carport or under a deep overhang, and comes back out once the leaves are open.
- Hand-pollinate while it is covered A covered almond flowers early, in still air, and few insects find it. Go over the open flowers every other day with a soft brush. Since almonds usually need pollen from a second variety, carry the brush between the two trees deliberately rather than working one tree at a time.
- Take the cover down at the right moment Once the leaves are fully out and settled weather has arrived, the cover has done its work. Leaving it up longer draws the tree up soft and brings the aphids.
If curl has already appeared, pick off and bin the affected leaves as soon as you see them, before they whiten and shed spores. Then feed with a balanced fertilizer and keep the tree watered so it can push a clean second flush of leaves. A tree that has to refoliate is exhausted, so expect a light crop that year and plan the cover for the coming winter.
Hull rot and the other summer troubles
Hull rot is the almond-specific problem and it is largely self-inflicted. Around hull split, the inside of an opening hull is soft, sugary and damp, and if the tree is still being watered heavily or the weather is wet, fungi colonise the hull. The damage is not to the nut but to the tree: a toxin moves back into the shoot and the whole shoot dies back, taking its spurs with it. A tree with brown dead shoot tips scattered through the canopy in late summer has had hull rot.
The prevention is to let the tree run dry from the start of hull split, and to avoid pushing it with nitrogen in the second half of summer. An over-fed, over-watered almond going into hull split with a canopy of soft growth is the classic case. Cut out the dead shoots after harvest, back into clean wood.
The rest of the summer troubles are the familiar stone-fruit list, and none of them is beaten by reacting late. Sanitation does most of the work: clear every nut off the tree and off the ground at the end of the season, because nuts left hanging over winter are where the worst of the boring insects survive.
| Problem | What you see | When it starts | What actually works |
|---|---|---|---|
| Peach leaf curl | Thick red puckered leaves that whiten and fall | Cool wet spells before the buds open | A rain cover from midwinter to late spring; remove affected leaves; feed the tree so it refoliates |
| Hull rot | Dead shoot tips in late summer, decayed hulls at the split | From hull split onwards in wet or over-watered conditions | Dry the tree off at hull split; avoid late nitrogen; cut dead shoots back to clean wood after harvest |
| Nut-boring caterpillars | Webbing and sawdust-like frass in a split hull, hollow kernels | Eggs laid into hulls once they split | Remove every nut from the tree and ground at season end; harvest promptly once hulls open |
| Bacterial canker | Sunken dark bark patches oozing amber gum, limbs dying back | Wet autumn and winter, entering through wounds | Prune only in the growing season; cut affected limbs back into clean wood well below the damage |
| Shot hole | Small purple leaf spots that drop out leaving round holes | Prolonged wet weather in spring | Open the canopy so it dries quickly; clear fallen leaves; avoid overhead watering |
| Frost on the blossom | Flowers browning and dropping within days of a cold night, no set | Any frost while flowers are open | Site the tree out of frost pockets; row cover over the tree on marginal nights and off again by morning |
Bacterial canker, and why pruning season is a disease decision
Canker is the reason an almond is never pruned in the dormant season. It shows as sunken dark patches on the bark, often with amber gum weeping from them, and the limb above the patch makes small yellow leaves and then dies. Once the patch has gone right round a limb, that limb is finished.
The bacteria are already present on the tree and are moved by rain. They enter through wounds and are most active in the cool wet months, which is exactly when a winter-pruned tree is standing full of open cuts that cannot callus. Prune in spring and summer instead and the same cuts seal within days.
If you find canker, cut the limb out well below the visible damage and into clean white wood, in dry summer weather. Sterilize the blade between every cut and burn or bin what you remove rather than composting it or leaving it lying by the tree.
One qualification about gum: almonds ooze gum for many reasons, including simple injury, and a bead of gum on its own is not proof of disease. Gum coming out of a sunken discolored patch of bark is a different matter and should be treated as canker.
The record that saves you a season
Write down the date you first see each problem, every year: first curled leaf, first dead shoot tip, first stained or holed nut, first gum on the bark. On its own each note looks like trivia. Over three seasons it becomes the only accurate calendar you will ever have for your own garden.
It matters most for leaf curl, because the whole defense has to happen before any symptom appears. Once you know the date curl usually shows on your tree, you know the cover has to be in place at least eight weeks earlier, and you stop guessing. Record the dates the cover went up and came down as well, and whether curl appeared anyway, because that tells you whether the cover was late, too small, or touching the branches.
Note which limb each problem appeared on. Canker and boring insects return to the same parts of a tree year after year, and a note saying which side was affected last season is worth far more than a general memory that the tree was not doing well.