Gadenin日本語Get the appWhat actually goes wrong, in order of how much it costs you
Radicchio is a tough crop and the list of things that attack it is short. What makes it feel fragile is that its two real problems, crown rot and slugs, both work out of sight inside the plant and only become visible when the head is already spoiled. Catching them means deliberately looking under the outer leaves rather than judging the row from standing height.
Almost everything else, including the leaf spots and the frost scorch on outer leaves that alarm people every autumn, is cosmetic. The outer wrapper leaves are meant to be stripped off and thrown away. Damage on them is not damage to the crop.
| Problem | First sign | When it strikes | What to do |
|---|---|---|---|
| Crown and heart rot | Soft brown base, sour smell, spongy head top | Cool wet autumn weather | Strip lower leaves, clear mulch from the crown, cut affected plants out |
| Slugs and snails | Ragged holes and slime trails inside the wrapper leaves | Damp nights from late summer on | Clear shelter, trap and hand-pick after dark |
| Aphids | Colonies in the growing point, sticky leaves | Warm spells, worse on well-fed plants | Wash off with water, stop nitrogen feeding |
| Leaf miner | Pale winding tunnels inside the leaf blade | Mid to late season | Remove tunneled leaves, no other action needed |
| Tipburn | Brown dry edges on inner leaves | Fast growth after a dry spell | Even watering, less nitrogen |
| Root aphid | Whole plant wilts in mild weather, white powder on roots | Dry late summer | Lift and destroy, rotate the bed |
Crown rot: the one that takes whole heads
This is the main autumn loss. The plant's own shape funnels rain into the center, and once the head starts closing that water has nowhere to go. Add old lower leaves lying against the base, fine mulch packed up to the crown, or a weedy row, and the base of the plant stays wet for days. The rot starts there, runs upwards into the heart, and the first outward sign is a head that feels spongy when squeezed.
The prevention is entirely mechanical and takes minutes. Keep a ring of clear soil around each crown, strip off lower leaves as soon as they yellow or lie flat, weed under the canopy, and grow on a slightly raised bed if your ground lies wet. Space plants properly so air moves between them; crowded rows rot and well-spaced ones usually do not.
Once a plant is affected, cut it out and take it off the bed. There is no treatment, and a rotting plant left in the row wets and infects its neighbors. Cut the head and check inside; if only the outer wrapper is affected, the heart is often still perfectly good to eat.
If you lose several plants in the same corner of the bed each year, the problem is drainage rather than the crop. Note where the losses are on your plan and raise or drain that patch before next season.
Slugs, snails and the things that eat at night
Slugs do two quite different sorts of damage. On young plants they can strip a whole station of seedlings overnight, which is why sowing several seeds a station and thinning later is good insurance. On a firming head they crawl inside between the wrapper leaves, feed in the dark and damp there, and foul the leaves as they go. A head that looks flawless from outside can be ruined two layers in.
The effective work is removing shelter rather than applying anything. Take away the boards, pots, weedy edges and heaps of old leaves within a few feet of the row. Water in the morning so the surface is dry by dusk. Then hand-pick after dark with a torch on two or three mild damp nights in a row, which will remove most of the population that matters.
Check the inside of a few heads every fortnight by pulling back the outer leaves. If you find damage inside a firming head, cut that head now rather than leaving it, because the damage only ever gets worse and never heals.
- Clear the shelter Remove boards, pots, dense weeds and leaf heaps within a few feet of the row. This does more than any treatment applied to the plants themselves.
- Water in the morning A surface that is dry by dusk cuts slug movement sharply. Evening watering at the base of a firming head is close to an invitation.
- Hand-pick after dark Two or three mild damp nights with a torch, working along the row and lifting the outer leaves of each plant, removes the individuals that are actually feeding on your crop.
- Inspect inside the wrappers Every fortnight, pull back the outer leaves on a few heads and look at the base and the inner surfaces for holes and slime.
Aphids, tipburn and the problems you cause by feeding
Aphids settle in the growing point, where they are hardest to reach and where they distort the leaves that will become the heart. A strong jet of water into the crown on a bright morning removes most of them, and repeating it three days running usually settles the matter. Look for ants running up the plants, which is a reliable early tell.
Tipburn shows as dry brown margins on the inner leaves and is not a disease. It happens when the plant grows faster than it can move calcium to the newest leaves, which is what a sudden flood of water and nitrogen after a dry spell produces. Even watering and restraint with feed prevent it entirely.
Both problems trace back to overfeeding. A plant pushed with nitrogen in late season is soft, attractive to aphids, prone to tipburn, slow to color and slow to close. Once the nights start cooling, the best thing you can do for a radicchio is leave it alone.
Keep a short record each season of what appeared, roughly when, and on which plants. Pest timing is remarkably consistent from year to year in one garden, and two seasons of notes let you act a week before the damage instead of a week after.