Globe Artichoke Pests and Diseases: Aphids, Slugs and Crown Rot

Where the damage actually happens

Artichokes are tough plants and most of the leaf damage you see does not matter. The problems worth acting on are concentrated in three places: inside the developing bud, on the emerging spring shoots, and at the crown below soil level. Everything else is cosmetic.

Knowing that saves a lot of effort. Ragged holes in a big silver leaf in midsummer are not worth treating on a plant this size. Aphids packed between the scales of a bud you are about to cut, on the other hand, are a real loss, because you cannot wash them out of a closed head easily.

The one that ends the plant rather than spoiling a crop is crown rot, and it cannot be treated once it takes hold. That one is entirely a matter of prevention through drainage and airflow.

Check the buds every time you walk past once they start forming. Almost every pest problem on this crop is cheap to fix at the start and impossible to fix once the bud is packed.

Aphids in the buds are the main crop loss

Blackfly colonise the flowering stems and then work their way in between the scales of the developing bud. Once they are inside a tightly closed head there is no realistic way to get them out, and you end up trimming the head down to the heart or discarding it. They also foul the head with honeydew, which goes black with sooty mold.

Because the window is short, the answer is inspection rather than reaction. Look at the stem just below each bud, which is where colonies start, and deal with them before they migrate upward into the scales.

1. Inspect the stem below each bud twice a week Colonies start on the soft stem and the bracts at the base of the head. Catching them there is the difference between wiping off a patch and losing the bud.
2. Wipe or wash colonies off by hand A gloved hand or a strong jet of water knocks them off the stem. Do this at the first sign rather than waiting to see whether it spreads, because it always spreads.
3. Do not spray into an open bud Anything you spray into a developing head stays in it, and you are going to eat that head. Deal with aphids on the stem and outer bracts only.
4. Encourage the predators Ladybird larvae and hoverflies clear artichoke blackfly quickly if they are present. Leave some flowering weeds nearby and avoid broad-spectrum sprays that remove them.
5. Cut affected buds early rather than late If a bud is infested and close to size, cut it now and trim it down. Waiting only lets the colony work deeper between the scales.

Ants running up and down the flowering stems mean aphids above, even if you cannot see them yet. Follow the ants and you will find the colony.

Slugs on the spring shoots

The emerging shoots in early spring are soft, sweet and the only green thing on an otherwise bare crown. Slugs and snails find them immediately, and a young plant can have every shoot eaten out before it gets going. On a mature crown the damage is survivable but sets the plant back.

The mulch you put on for winter is exactly where they shelter, which is why clearing it back promptly in early spring matters as much as any control you apply.

1. Pull the winter mulch back early As soon as growth is about to restart, move the mulch away from the crown. Leaving it in place gives slugs cover right next to the emerging shoots.
2. Clear boards, pots and debris nearby Anything lying flat within a few feet of the plants is a daytime shelter. Removing it reduces the population far more than trapping does.
3. Check by torchlight on damp evenings Hand collection on two or three mild damp nights in early spring removes most of the slugs that would otherwise strip the new shoots.
4. Protect first-year plants specifically A young plant with three shoots can lose all of them. Ring new plants with a barrier or check them nightly until the shoots are a hand's length tall.

Ragged, chewed shoots with slime trails are slug damage. Shoots that emerge and then blacken and collapse without being chewed are frost damage or crown rot, and the treatment is completely different.

Crown rot cannot be cured, only prevented

Crown rot is the failure that kills artichokes. Fungal organisms in cold, saturated soil attack the fleshy crown, and the first symptom is usually a plant that simply does not reshoot in spring, or one that wilts in summer despite adequate water. Cut into the crown and it is brown, soft and sour instead of firm and pale.

There is no treatment once a crown has gone. Dig the plant out, take the surrounding soil with it, and do not replant an artichoke in the same spot. Everything useful happens before the fact, in how you site and manage the plant.

If a plant is lost to crown rot, take offsets for replacements from a different healthy plant and put them in fresh ground. Replanting into the same hole loses the new plant too.

The problems you can safely ignore

Powdery mildew appears as a gray-white bloom on the upper leaf surfaces in late summer, usually after the crop is finished. On a mature artichoke it is largely cosmetic. Remove the worst leaves, improve airflow next season by respecting the spacing, and do not spend money treating it.

Gray mold and petal blight show up as brown patches on buds during long wet spells. Cut affected buds off and get rid of them, and cut the stem down so the plant is not carrying rotting tissue. Leaf miners, leaf spots and general insect nibbling on those large leaves are not worth acting on at all.

Keep a short note of what appeared, on which plant, and roughly when. A plant that gets blackfly badly two years running is usually in the wrong position, and the record is what makes that visible.