Managing Autumn Pests and Diseases: Stay Vigilant as the Season Turns

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You’d think that as the weather turns colder, pests and diseases would pack up and leave you alone. And while it’s true that a lot of the summer nuisances do slow down or disappear in autumn, there’s a whole different crew that takes over. Slugs go absolutely mental in the damp autumn weather. Fungal diseases love the moist, still conditions. And some pests are trying to find warm places to overwinter — including in your stored crops. So no, you can’t put your feet up just because summer’s over. The battle continues. But it’s a different kind of battle, and knowing what to look for is half the fight.

I had a year where I basically ignored pest and disease management from October onwards because I thought “winter’ll sort it out.” It did not sort it out. I went up in the spring to find my stored onions had rotted, my overwintering broad beans had been decimated by mice, and every slug in the county had apparently set up home under my leek bed. The devastation was quite something. JB surveyed the scene and said “Looks like nobody was minding the shop.” He wasn’t wrong. Now I stay vigilant right through to the end of the season. And you should too.

Slugs — The Autumn Menace

If slugs are bad in summer, they’re absolutely diabolical in autumn. The damp, mild conditions are literally slug paradise. They come out in force, munching through late-season crops with the enthusiasm of someone who’s just discovered an all-you-can-eat buffet. Lettuce, young brassica plants, autumn-sown seedlings — nothing is safe.

All the usual methods apply — organic slug pellets (ferric phosphate), beer traps, evening patrols with a torch. But in autumn, I add another tactic: clearing their hiding places. Slugs shelter under pots, boards, stones, and debris during the day. Removing or cleaning up these hiding spots reduces the local population. I do a thorough slug-habitat audit every autumn — lift everything, check underneath, relocate any slugs I find to… well, far away. Very far away. The compost heap is a popular relocation destination. What happens to them there is between them and the worms.

Also, copper tape around raised beds or pots can help — slugs supposedly don’t like crossing copper because it gives them a mild electric shock. I’ve had mixed results with this, to be honest. But some people swear by it. Maybe my slugs are just tougher than average. Wouldn’t surprise me. Sunderland slugs. Hard as nails.

Fungal Diseases — The Damp Season Specialists

Damp, still autumn air is a breeding ground for fungal diseases. Here are the main ones to watch for:

Blight — if you had blight on your tomatoes or potatoes in late summer, the spores are still around and can overwinter in the soil and on plant debris. Remove and destroy (don’t compost) all affected foliage. This won’t eliminate blight entirely but it reduces the spore load for next year.

Powdery mildew — that white, powdery coating on leaves. Common on courgettes, peas, and apples in autumn. Affected leaves should be removed and binned (not composted). Good air circulation helps prevent it — another reason not to plant things too close together.

Botrytis (grey mould) — a fuzzy grey mould that attacks dead and dying plant material, then spreads to live tissue. Very common in cold, damp conditions. Remove any affected material immediately. Good garden hygiene is the best prevention — don’t leave rotting leaves and fruit lying about.

Club root — if your brassicas have been looking sickly, with wilting leaves and swollen, distorted roots, you might have club root. This is a soil-borne disease that’s incredibly persistent — it can survive in the soil for twenty years. Prevention is better than cure: keep your soil pH high (add lime), practice crop rotation, and don’t plant brassicas in the same bed year after year. Ronny’s been dealing with club root on one of his beds for years. It’s a nightmare. He’s basically written that bed off for brassicas forever.

Mice and Rats

As the weather gets cold, mice and rats come looking for food and shelter. And guess where they find both? On your allotment. Your stored crops, your compost bin, your shed — it’s all attractive to rodents. Mice will eat sown peas and beans (they can smell them underground, the little blighters), stored fruit, and seeds. Rats are bolder and will tackle potatoes, squash, and pretty much anything they can reach.

Prevention: don’t leave food sources accessible. Store harvested crops in rodent-proof containers. Don’t leave fallen fruit on the ground. Compost bins with solid bases and lids deter rats better than open heaps. Keep the area around your shed tidy — long grass and debris provides cover for rodents.

For pea and bean sowings, I start them in pots and plant out as seedlings rather than sowing direct. The mice can’t find them if they’re not in the ground. If you must direct sow, covering the row with mesh or wire netting helps. I learned this after losing three successive sowings of broad beans to mice. Three times. Before I finally worked out what was happening. Not my finest detective work.

Autumn Garden Hygiene

The single most effective thing you can do against pests and diseases in autumn is clean up. Seriously. A thorough autumn tidy makes a massive difference to the health of your garden next year.

Remove all spent crops. Don’t leave dead tomato plants, bean haulms, or cabbage stumps sitting in the beds over winter. They harbour diseases and pests that will kick off again in spring. Compost the healthy stuff, bin or burn anything that was diseased.

Clear fallen fruit from under trees. Rotting fruit on the ground attracts wasps, harbours brown rot, and provides food for rodents. Either compost it or remove it from the site. I collect all the windfalls in a bucket, keep the decent ones for cooking, and compost the rest.

Clean your greenhouse or polytunnel. Wash the glass or plastic inside and out to maximise winter light, and clean all surfaces with a mild disinfectant to kill any lurking pathogens. I do this once a year in late October and it takes about an hour. Worth every minute. A clean greenhouse is a healthy greenhouse.

Clean and oil your tools. Dirty tools can spread disease between beds and plants. A quick scrub with soapy water, dry them properly, and rub metal parts with an oily rag. They’ll last longer and work better. Plus there’s something deeply satisfying about a clean tool hanging neatly in the shed. Small pleasures, man. Small pleasures.

Look after yourselves. Take good care. 🌱