Brussels sprouts (Brassica oleracea var. gemmifera) is a plant belonging to the Brassicaceae family, cultivated for its sprouts, which have a pleasant taste and a high food value. They contain lipids, sodium, potassium, dietary fiber, protein, vitamins (A, D, C, B-12, B6), magnesium, iron, and calcium. Being a related species to white cabbage, Brussels sprouts share with it several diseases and pests. The Brussels sprouts crop can be affected by pests and diseases, against which it’s important to apply the right treatments.

THE MAIN DISEASES OF BRUSSELS SPROUTS

Bacteriosis

Black rot (Xanthomonas campestris)

Large, irregular, yellow spots appear on the leaves, along which the veins become brownish and blackened. The tissues around the spots become parchment-like, thinned, and eventually dry out. The disease develops rapidly in conditions of high humidity. By cross-section in the stem, you can see the browned vessels. The disease is transmitted by infected seed and bacterial exudate, which is carried by water droplets and slugs.

Prevention and control measures:

• disinfecting the seeds and seedling substrate before sowing;
• growing resistant varieties;
• correct rotation (Brussels sprouts should not return to the same land for 4 years);
• collecting and destroying plant debris after harvest.

Bacterial leaf spot (Pseudomonas syringae pv. maculicola)

The infection manifests as small, dark, moist spots on both sides of the leaves. These spots usually remain small but can spread if conditions are favorable. In older spots, a purple border may appear. Severe infections can lead to premature leaf drop.

Prevention and control measures:

• avoiding sprinkler watering;
• using healthy seeds and seedlings;
• Brussels sprouts treatments with specific fungicides.

Soft rot (Erwinia carotovora pv. carotovora)

The attack occurs in rainy years on compacted soils. Moist, yellowish spots appear in the leaf attachment area. In conditions of high atmospheric humidity, the rot covers all the sprouts and transforms them into a mucilaginous, smelly mass. The bacterium lives on plant debris on the soil surface and infected seeds. The attack can also occur in storage if temperatures are maintained around 20-25℃.

Prevention and control measures:

• gathering and destroying plant debris after harvesting;
• disinfecting seeds and seedling substrate;
• correct rotation (Brussels sprouts should not return to the same land for 4 years);
• sorting the sprouts before storage;
• Brussels sprouts treatments with specific fungicides.

Mycosis

Downy mildew (Peronospora brassicae)

The disease frequently occurs in plants grown at higher densities and is favored by high humidity conditions. The first symptoms are represented by irregular yellow spots on the leaves, which later turn brown. On the underside, opposite these spots, a greyish-white fuzz appears. Under high humidity conditions, the infection spreads rapidly, the leaves rot or dry out, and plant growth is stopped.

Prevention and control measures:

• using resistant varieties;
• removing attacked plants from the crop;
• fungicide treatments during the growing season.

Clubroot (Plasmodiophora brassicae)

It is an easily recognizable disease because of the symptoms that appear on the leaves and roots. Aerial symptoms are represented by plant dwarfing, leaf yellowing, and wilting. On the roots the disease manifests by the appearance of swellings or strangulations, indicating a dysfunctional root system. The disease can appear from the seedling stage.

Prevention and control measures:

• checking the seedlings before planting;
• choosing soils with a slightly basic pH when planting;
• removing diseased plants from the crop;
• correct rotation (Brussels sprouts can return to the same field after 3-4 years).

White rust of crucifers (Albugo candida)

The disease can appear in the early stages of vegetation. Yellowish discoloration spots of various shapes appear on the plant’s parts and white-milky, ring-shaped crusts form on both sides of the leaves. As the disease progresses, the skin cracks, and the spots become powdery. The spots merge and the leaves dry out. Symptoms may also appear on the stem. After the attack, the stem thickens, bends and twists, and finally withers.

Prevention and control measures:

• weed control;
• correct rotation (Brussels sprouts can return to the same field after 3-4 years);
• gathering and destroying plant debris after harvest.

Blackleg disease (Phoma lingam)

The disease attacks the aerial parts of the plant. The first symptoms are discolored spots, on which small black dots appear, representing the fungus’ fructifications. In case of a severe attack, the plant may be defoliated or destroyed. The fungus survives on plant debris and is transmitted by several vectors (water, wind, animals, humans).

Prevention and control measures:

• gathering and destroying plant debris after harvesting;
• planting healthy seedlings;
• growing resistant Brussels sprouts varieties.

Dark spot of crucifers (Alternaria brassicae)

The disease manifests as circular, brown spots on leaves and petioles. The spots evolve, enlarge, and then become surrounded by a yellow border. Affected tissues dry out and fall off. The disease favors the appearance of fungal or bacterial rots.

Prevention and control measures:

• correct crop rotation (Brussels sprouts can return to the same land after 3-4 years);
• disinfection of seeds and seedling substrate;
• avoiding sprinkler irrigation;
• Brussels sprouts treatments with specific fungicides.

Fusarium wilt (Fusarium spp.)

Initial symptoms are wilting of the lower leaves, often on one side of the plant. Attacked leaves turn brown and fall off, and over time the whole plant may wilt. Attacked plants also develop a bitter taste.

Prevention and control measures:

• using healthy planting material;
• removing attacked plants from the crop;
• Brussels sprouts treatments with specific fungicides.

THE MAIN PESTS OF BRUSSELS SPROUTS

Cabbage aphid (Brevicoryne brassicae)

This species attacks all plants belonging to the Brassicaceae family. It develops several generations per year and overwinters as an egg on plant debris on the soil surface. In early spring, colonies appear on wild crucifers, and in June winged forms migrate to cultivated crucifers. Adults and larvae sting the plant parts and feed on their sap. As a result, the leaves become shriveled and in case of a strong attack, they dry up and fall off.

Control measures:

• weed control;
• using sticky traps;
• Brussels sprouts treatments with specific insecticides.

Diamondback moth (Plutella xylostella) 

It has several generations per year and overwinters in the pupa stage in the soil or on various plant debris. Adults lay their eggs on the underside of the leaves. The larvae gnaw the epidermis and parenchyma, giving the leaves a leaden appearance.

Control measures:

• balanced fertilization;
• weed control;
• removing plant debris after harvest;
• chemical treatments with specific insecticides;

Cabbage moth (Mamestra brassicae)

The cabbage moth is a polyphagous pest, attacking cabbage, cauliflower, kohlrabi, and other cultivated and spontaneous crucifers. The caterpillars are located at the underside of the leaves, which they gnaw. The larvae gnaw holes in the leaves and dig galleries inside sprouts. Phytopathogenic agents can settle on the wounds and lead to rot.

Control measures:

• Brussels sprouts treatments with specific insecticides.

Cabbage white butterfly (Pieris brassicae)

Larvae of the cabbage white butterfly attack cabbage, kohlrabi, radish, and other cultivated and wild crucifers. Early larvae feed in groups and gnaw the lower epidermis and parenchyma. Later, they become solitary and skeletonize the leaves.

Control measures:

• Brussels sprouts treatments with specific insecticides.

Cabbage bug (Eurydema ornata)

It has 1-2 generations per year and overwinters as an adult under the leaves of trees. Adults appear early in spring, feed on spontaneous crucifers, then lay their clustered eggs on the underside of the leaves of cauliflower, cabbage, brussels sprouts, etc. Adults and larvae sting and suck sap from tissues, causing necrosis.

Control measures:

• balanced fertilization;
• weed control;
• chemical treatments with specific insecticides.

Flea beetles (Phyllotreta spp.)

Adults appear in early spring, and after additional feeding, they lay their eggs in the soil near cabbage plants, cauliflower, kohlrabi, etc. Adults attack the leaves, and gnaw the tissues, giving the leaf a pitted appearance.

Control measures:

• deep autumn plowing and repeated hoeings;
• specific insecticide treatments.