Peculiar to broad beans, this disease tends to affect autumn-sown plants grown in poorly drained soil. Brown spots can affect the leaves, stems and even the flowers, and the whole plant may subsequently die. Plants grown through the winter are most vulnerable, and those that are affected need to be sprayed or pulled out.
Previously classified as plants, fungi are now recognised as a distinct group of organisms. They do not contain chlorophyll and are therefore unable to manufacture their own food. The result is a lifestyle built on being saprophytic, when they are dependent on dead tissue, or parasitic, when they survive off the kindness of others.
Most fungal diseases will leave garden plants struggling to survive, and may even cause their death. In their weakened state, affected plants also become susceptible to bacterial and viral diseases.
Fungi are encouraged by humid weather and spread via spores, which are usually carried in water or by wind. The spores may also be transferred from plant to plant by insects, so eradicating an insect pest may also eradicate the fungal disease.
All infected leaves, stalks and plant material should be disposed of by burning or throwing it out in the rubbish. Don't throw the material in the compost as the fungi will thrive in the warm conditions.
Clubroot attacks brassicas, especially if the soil is poorly drained and too acidic. Watch out for plants that have small leaves, bad colour and swellings on the roots, which will eventually decay. This disease persists in the soil and, ideally, you should not replant brassicas in an infected patch of land for another four or five growing seasons. If you have concerns, raise seedlings in sterile seed mix and dip the roots in a fungicide before planting out.
This disease will cut a plant down early in life. The stems turn black and shrivel at soil level, then the plant starts to suffer because its basic water and nutrient flow is being strangled at the very base of the stem. Avoiding overwatering is rule number one. Second, use good-quality sterile soil and keep up a good airflow. A copper-based spray can be applied, but it may be overkill for this problem.
Potato blight is what wiped out a legion of potatoes in Ireland in the mid-1800s. It appears on tomatoes and potatoes, especially when the weather is hotter and more humid than normal.
Large, dark brown spots appear on the leaves of infected potatoes, which then become distorted and yellowy, and the plant begins to fail. In tomatoes, it leaves the fruit hard, spotty and unusable. Blight is a serious disease and needs to be dealt with quickly.
Pick off any dead and dying leaves before treating the plant with spray. Blight can be treated with copper-based sprays or a really strong fungicide. Alternatively, try a garlic spray and repeat the doses every seven days.
Mulch your plants really well with pea straw or well-rotted seaweed and try sprinkling Tui Lime under each plant. Remember to rotate your crops: don’t plant tomatoes, potatoes or beans in the same spot each year.
Powdery mildew gets its name because it looks like a dusting powder on your plants and flakes when touched. It attacks when the soil is dry and the air humid. The whole plant can be coated in the powdery residue. The leaves and skins of plants like cucumbers, courgettes, melons, pumpkins and silver beet can all be affected.
Use Tui Disease Control for Fruit & Veges to stop further spread. Space plants so that the air can move freely, rotate crops properly so the mildew is not spread further, and keep the soil moist during dry periods. Spraying with a weak vinegar solution also helps.
This disease is caused either by Fusarium or Verticilium fungi, and causes leaves to turn yellow and wilt. It is prevalent in warm climates and can be spread by beetles from plant to plant.
Wilt is best destroyed by burning the plants.
Crop rotation is not effective and the only solution is to grow disease-resistant varieties.