Alternaria Leaf Spot

Small to large black spots appear on leaves. They may lead to discoloration and decay of cauliflower and cabbage heads and spotting on Brussels sprouts under very wet conditions.

Control

1. Incorporate diseased crop refuse promptly at end of season or rotate fields to avoid carryover.
2. A single application of Rovral WP (see Table 3, Cole Crops (Broccoli, Brussels Sprouts, Cabbage, Cauliflower) Disease Control) is registered for storage cabbage. Bravo is recommended for Brussels sprouts and for late cabbage being grown for winter storage. Do not apply either Bravo or Rovral on cabbage within 7 days of harvest.
3. Hot-water seed treatment is recommended to reduce seed-borne disease.

Bacterial Leaf Spot

(Pseudomonas)

Tiny, brown to purplish spots appear on the outer leaves of Brussels sprouts, broccoli and cauliflower. Yellow halos appear around the spots and they eventually grow together to form light brown papery areas.

Control

1. Use hot-water-treated seed.
2. Avoid sprinkler irrigation.
3. Shred and turn under diseased crop refuse promptly after harvest.
4. Do not replant cole crops in the same field the following year.
5. Tri-basic copper sulphate used for control of downy mildew will also give some control of bacterial leaf-spot.

Bacterial Soft Rot

(Erwinia, Pseudomonas)

This bacterium causes small, water-soaked areas on broccoli florets and on cabbage in storage. As these areas rapidly increase in size, the tissue becomes soft and mushy with an offensive odour. Boron and calcium deficiencies and frost damage may be contributing factors.

Control

1. Keep injuries to plant parts to a minimum.
2. Over-fertilization with nitrogen may result in heavy growth and more rot.
3. Overhead irrigation may encourage infection.
4. Broccoli varieties such as Arcadia which form tall, dome shaped heads are usually less susceptible.
5. Avoid using wetting agents on broccoli late in the season as the water-repellent bloom may be damaged.
6. Application of copper through the heading period as for downy mildew may provide some control.
7. For cabbage, clean and disinfect storage walls and floors (see the Planting section of this guide). Keep storage house dry and the temperature below 4°C.
8. Eliminate crop residues and cull piles by discing deep or burning.

Boron Deficiency

Boron deficiency causes browning of stem pith, excess leaf-curling and, sometimes, a failure to head. Cauliflower shows brown curd and broccoli shows corky scars on stalks.

Control

Soil should be tested for boron and if necessary it should be added to the main fertilizer mix.

If symptoms of boron deficiency appear in the planted crop, spray the foliage with Solubor at 500 to 1,000 g/ha (200 to 400 g/acre) in at least 1,000 L/ha (400 L/acre) of water. One or two foliar applications of boron are good insurance in case the soil boron is not available to the crop.

Note: In the Interior, fields to which boron has been applied should not normally be planted to beans or cucumbers the following year, as both these crops are extremely sensitive to boron. See also “Boron”, Nutrient Management section of this guide.

Clubroot

Clubroot is a soil-borne fungus which causes large, irregular swellings on roots and yellow and stunted plants. The fungus can survive in soil for years following an infected crop and may be spread by infected seedlings, contaminated manure, drainage water, farm implements, wind-borne soil and on the feet of animals and people.

Control

1. Plant in soil known to be free of clubroot.
2. For transplant production, ensure that the seed-bed is free of clubroot or thoroughly fumigated before seeding. The seed-bed may be treated with Basamid or Vapam prior to seeding, but clubroot infested land should still be avoided as the fumigants may not be 100% effective. See Planting section of this guide for method of application. Lime (as discussed in point 5) should not be used in the seed-bed for clubroot control as it will only mask symptoms and result in clubroot spread to the field.
3. In the field, plant in well-drained soils.
4. Where clubroot is known to occur, rotate with crops other than cole crops at least three out of every four years.
5. At least 6 weeks prior to planting in light, sandy soils, thoroughly disc in enough lime to increase the soil pH to 7.0. An application of at least 11 tonnes/ha (4.5 tonnes/acre) of ground limestone is required to raise the pH of an “Abbotsford Airport” soil type from pH 6.0 to 7.0. Hydrated lime may be used but high rates may “burn out” the organic matter in the soil. Finely ground limestone is preferred. Lime is not as effective on muck soils or soils with a high clay content. A high pH may also cause scab problems in following crops such as beets and potatoes.
6. On organic (muck) soils, a side-dressing of calcium nitrate at 90 kg N/ha, 3 weeks after transplanting has reduced clubroot significantly in preliminary research trials.

Note: Application of additional boron and other minor elements (Zn, Mn) may be necessary on heavily limed soils. Soil applied boron may damage following crops of beans and cucumbers particularly in dry interior regions.

Downy Mildew

(Hyaloperonospora)

Shows as a white, fuzzy fungus in patches on leaves, stems, and heads. It may cause browning and black streaking in stems, and black spotting on heads of broccoli and cauliflower. Moderate temperatures of 15°C and high humidity or wet conditions favour this disease.

Control

1. Avoid thick or heavy seedings, excessive nitrogen fertilizer and over-watering.
2. Use tolerant varieties such as Emerald City broccoli when available.
3. In the seed-bed, spray seedlings at germination and repeat twice weekly until transplanted, with one of the products in Table 3, Cole Crop (Broccoli, Brussels Sprouts, Cabbage, Cauliflower) Disease Control.
4. In the field, when wet weather conditions favor disease development, apply one of the products in Table 3.
5. Plow in crop remains as soon as harvest is complete. Obtain good soil coverage of plowed refuse to ensure early breakdown of crop remains.

White Mould

(Sclerotinia)

This fungus disease can cause losses to Brussels sprouts, particularly when wet conditions occur in August. First symptoms are a water-soaking of the leaf tips followed by the appearance of a white, cottony mould. The fungus grows down the leaf petioles and attacks the sprouts causing rot. In severe situations the stalk may be affected causing the plant to collapse.

Control

1. Rotate with corn, cereals, forages, onions or potatoes. Avoid fields with a history of the disease.
2. Varieties differ in susceptibility. Lunet and Vancouver have some tolerance.

Wirestem

Seedling stems are discoloured and constricted, finally becoming hard and brittle. Plants are stunted and may fall over and die.

Control

1. Measures used to avoid downy mildew in the seed-bed will help to prevent wirestem.
2. When transplanting from a seed-bed, discard all seedlings exhibiting a dark, constricted area near the base of the stem.

Root Rot

RootShield WP (Trichoderma harzianum Rifai strain KRL-AG2) is a biological fungicide for the suppression of Root Rot in greenhouse vegetable transplants.  When applied to transplants, greenhouse planting mix or soil, the product grows into plant roots as they develop to protect roots  against Pythium, Rhizoctonia and Fusarium. 

Suppression

1. Suspend RootShield WP using a spray volume of 30 to 45 g/100 L and apply at the rate of 55 to 110 g per cubic metre (loose) of greenhouse potting mix, soil or planting beds. 
2. Apply using hand-held backpack or ground spray equipment. 
3. Becomes active when soil temperatures are above 10 degrees C and is not effective while soils remain cold.
4. More effective at suppression of root rot in neutral or acidic soils.  
5. Should be used within 12 months of the date of manufacture.  
6. Contains the allergens wheat and sulfites.