Plant protection
Many pest and disease problems can be avoided through Integrated Pest Management (IPM) procedures.
The following will help to ensure any pests and diseases in your cabbage crop remain below the economic threshold and swift action is taken should they become a problem.
Use of pest resistant varieties - This ensures your crop has natural resistance to pests and diseases, minimizing the need for expensive chemical control.
Row covering of seedlings with nets - These should be put up immediately after transplanting and left up for 10 – 15 days. They protect your crop from numerous insect pests, such as caterpillars, aphids, leafhoppers, leaf miners, beetles and white-flies.
Crop rotation - Do not plant cabbages more than once every 3 – 4 years in the same field. This will minimize the risk of fungal and bacterial diseases such as bacterial black rot and fungal diseases such as downy mildew, powdery mildew, white rot and damping off.
Soil solarization - This involves preparing land to a fine tilth so as to expose soil to the sun for one month during the hot season. This helps to control soil borne pathogens, soil insects, weeds and root-knot nematodes.
Companion crops - Planting corn and squash as a trap crop around the borders of your cabbage crop keeps aphids away, reducing the incidence of turnip mosaic virus.
Traps - Placing yellow and blue sticky traps and pheromone traps around your cabbage crop will help control whitefly, leaf miners and caterpillars.
Removing and destroying all crop residues immediately after harvest - All crop residues should be removed and destroyed by burning or burying in deep pits. This helps prevent last season’s pests including caterpillars, aphids and beetles re-infesting your new crop and also control fungal and bacterial diseases.
Good weed management - Irrigate the beds to stimulate germination of weed seeds and remove all weeds prior to transplanting. Following planting, the field should be monitored regularly and kept free of weeds. Remove weeds by hand at early growth stages of cabbage and before the canopy covers over.
Crop monitoring - Cabbage crops should be monitored for pests and diseases every week. This is especially important during the early stages of growth when cabbages are susceptible to pests and diseases. Consistent monitoring enables a swift and effective response should an outbreak occur, which will minimize crop damage and expense. Thorough composting of all organic matter. All manure put on the crop should be thoroughly composted to prevent pest and disease outbreaks.
Weeds
Weeds are the unwanted plants found in your fields and gardens. They compete with your crops for nutrients, moisture, and sunlight which can decrease the crop quality. They increase production costs due to increased cultivation and hand weeding, and considerably reduce the crop yields. They also serve as alternate hosts of insect/mite pests and diseases.
Preventative methods
• Thorough land preparation
• During the seed bed preparation, make sure that the seed bed is free of weeds.
• Place the fertilizer where the crop has access to it but the weeds do not. This allows the crop to be more competitive with weeds.
• Maintain cleanliness on the drainage canals.
• Keep the surroundings of your farm free of weeds, unless they are maintained and intended as habitat for natural enemies.
• Mulching: Use rice straw/plastic mulch as mulch to partially control weed. Apply straw perpendicularly to the rows at a rate of 5 t/ha. Apply mulch within a few days after transplanting.
• Crop rotation. Do not continuously plant crucifers in the same field.
• Regularly monitor the status of your crops.
Mechanical and physical preventive practices include;
• Hand weeding. The weeds are easier to control in their earlier growing period. Do not let the weeds flower. Remove them from the field before they start to flower. Weeds bearing seeds should not be placed in compost since seeds may not be killed in the process of decomposition. Otherwise, compost might be a source of reintroduction of weeds into your fields.
• Hoeing, mowing, and cutting
Pests
Pest damage causes a reduction in quality and quantity of produce
The following are the major pests of Cabbage in Kenya:
Diamondback Moth (Plutella xylostella): One of the most common and destructive pests in cabbage farming, this small moth's larvae feed on the leaves, causing extensive damage. The eggs are laid on the upper surface of leaves.
Damage
They feed on the underside of leaves making huge holes.
Infestations are normally serious in drier months
If infestation occurs at an early stage, it affects the formation of cabbage heads.
Control:
Intercropping with other crops which act as repellants. Commonly used repellants crops are tomato & India Mustard plants.
Use of parasitic wasps (Diadegma spp.)
Application of neem products
Use of pesticides
Use of bio-insecticides
Cabbage Aphids (Brevicoryne brassicae): These small, gray-green aphids suck sap from cabbage plants, stunting growth and causing curled leaves. They also transmit plant diseases.
They are pale green in color and usually covered with a powder-like matter. They suck plant sap from the central part of the plant and near the base of leaves
Damage:
They attack the leaves resulting in curled and distorted leaves leading to poor heads and low quality yields.
Control:
Use of biopesticides
Use of certified insecticides
Use of repellant crops
Use of parasitic wasps
Removal and destruction of previous crop residues.
Cutworms (Agrotis spp.): These nocturnal pests cut down young cabbage seedlings at the soil level. They are grayish black larvae that partially or completely destroy the plant's stem.
Damage:
If left unnoticed and unmanaged during the early stages of infestation, they bite through the stem, causing the plant to collapse. Early intervention is crucial to prevent significant damage and potential crop loss.
Control:
Proper and timely weeding to destroy egg laid
Proper land preparation to destroy the pest and the eggs, to expose them to predators.
Use of appropriate and certified insecticides
Hand removal of the pests from the infested crops
Slugs - they usually locate themselves under the leaves.
Damage: They reduce cabbage quality and also reduce marketability
Control:
Use of cultural control methods to remove the slugs for instance drowning them in water. Bury tins at ground level and fill with water and add yeast to attract the slugs. The yeast acts as an attractant for slugs, the slugs are then drawn into the water-filled tin where they drown. This method helps reduce slug populations without the use of chemicals, making the method eco-friendly and safe for crops.
It is advisable to place these tins strategically around the cabbage field, especially near areas where slugs are more active, ensuring better control over the pest population. Regularly emptying and refilling the tins ensures continued effectiveness.
Use slug pellets
Diseases
Disease infection leads to reduction in quality and quantity of produce.
The following are the major diseases of Cabbage in Kenya:
Damping-off - Damping-off disease in cabbage production is a serious issue caused primarily by soil-borne fungi, such as Pythium, Rhizoctonia, and Fusarium species. This disease typically affects cabbage seedlings, leading to poor germination and crop death.
Seeds rot in the soil before they germinate, resulting in poor or uneven seedling emergence or after the seedlings emerge, the stems become water-soaked and soft, especially near the soil line. This weakens the plant and causes it to collapse and die. This results in poor distribution of seedlings in the field, consequently leading to low yields.
This condition often results from poor practices in seedling production. Seedling production is very key in determining crop health in the production chain. Poor practices include overwatering and poor soil drainage, high humidity and cool, damp conditions, planting seeds too densely, which limits airflow.
Prevention strategies:
Use sterilized soil or well-drained soil to reduce fungal presence.
Ensure proper spacing of seedlings to allow good air circulation.
Avoid overwatering, especially in the early growth stages.
Apply certified and the recommended fungicide treatments if necessary, particularly in high-risk areas.
Best practices in the nursery seed bed is key in disease prevention.
Bacterial Black Rot -Bacterial black rot is a serious disease in cabbage production caused by the bacterium Xanthomonas campestris pv. campestris. The disease can be spread through infected water, infected plant debris, and contaminated seeds, causing significant yield losses if not controlled during early stages. It results in formation of yellowish V-shaped lesions at the leaves, darkening of veins, leaf drops, wilting of leaves affecting the growth of the crops and eventually crop death if left unmanaged. Crop heads are later affected, the head becomes soft, rot and usually produces an offensive odor.
Humid and high temperature weather increases the spread and severity of the diseases, overhead irrigation facilitates bacteria movement from upper leaves to lower leaves.
Prevention and Management:
Use certified disease-free seeds and transplants.
Crop rotation with non-brassica crops to prevent the buildup of the bacteria in the soil.
Avoid overhead irrigation to reduce the spread of bacteria on leaves.
Remove and destroy infected plant debris, remove previous crop residues
Use of certified and recommended fungicides.
Ring Spot
Ring spot in cabbage is a fungal disease caused by Mycosphaerella brassicicola (formerly known as Cercospora). It primarily affects brassica crops, including cabbage, kale, and cauliflower. The disease is characterized by small, dark, ring-like spots that form on the leaves. Small, dark spots with concentric rings appear on the leaves. These spots can enlarge and turn brown or gray, eventually causing leaf tissue to die. Severe infections can cause leaves to wither, die, and drop off. Cool and moist conditions, especially in soil with poor drainage, encourage the development and spread of the condition. Overhead irrigation and rainy weather increases the spread of the fungal spores from leaf to leaf and plant to plant.
Control:
Crop rotation ro reduce build up of the bacteria in the soil.
Remove and destroy infected plant debris to prevent infestation of healthy crops.
Use of certified and recommended fungicide especially in areas with a history of ring spot conditions.
Proper spacing of plants should be adopted to improve air circulation, which helps to keep foliage dry and reduces the risk of infection.
Use disease free transplants.
Other conditions include club root, Black leg & Alternaria leaf spot
