A permaculture plot that is designed and maintained in harmony with nature should remain fairly disease-free. With the right sort of companion planting, use of native species suited to the soil and climatic conditions, soil improvement and irrigation techniques, the plants on the site should generally be free from the worst ravages of pest insects, nematodes and vegetative diseases. Indeed, there is a school of thought that if a disease does strike a plant on the permaculture plot then it is an opportunity for learning, to analyze the soil conditions, plant companions or climatic events that may have contributed to the occurrence. One of the ways of learning from plant diseases is to know the signs to look for, so that wherever possible remedial action can be taken to tackle the problem.
Cankers are an abnormal development of tissue that affects stone fruit trees. There are strains that infect certain species, such as apple rot, but cankers can grow on many types of stone fruit tree. It takes the form of sunken or raised areas or growth that looks different to the surrounding wood, discolored and sometimes turned black. Left untended, cankers will girdle branches, preventing nutrients and water being dispersed by the tree to those branches and so causing them to rot and die off. Diseased branches should be cut off the main tree to prevent the disease spreading. When pruning stone fruit trees, avoid making more pruning cuts than are needed, as cankers can attack weak points like wounds in bark.
This disease targets legumes primarily, such as peas and beans. Leaves and seedpods can develop spots on them that seem saturated with water. These areas can end up dropping from the leaf or pod. The disease also exhibits itself by causing dark lesions to the stems of the plants. Infected plants should be removed to stop the infection spreading. Preventative measures include using vegetable bed rotation over at least three years to prevent the build up of the disease, and avoiding touching the plants with wet hands, as this can be a contributory factor.
This bacterial disease primarily affects Brassicas, like cabbage and cauliflower. It cause parts of the stems of the plant to be discolored; if you cut open an infected stem it will look like veins of black are running through it. It can be difficult to pinpoint a source of black rot, as it has been known to be spread by wind, water, infected seed and insects. Thus preventative measures should be used, such as crop rotation and, if it has previously been a problem on the permaculture plot, soaking seeds in hot water before planting. If black rot does strike, remove the infected plants as soon as possible to prevent spread.
Powdery mildew is a fungal disease that tends to attack older leaves on plants such as pumpkins, cucumbers and peas, as well as fruit trees and strawberries. It is visible as powdery white circular spots on the leaves and the attached stems. While young growth often has enough vitality to prevent infection, the mildew on the older leaves will reduce the cropping potential of the plant. If you spot powdery mildew, remove the affected leaves immediately. The fungus can reproduce its spores at an incredibly rapid rate and because the disease is spread by wind, it can rapidly transfer to other plant specimens. One of the potential causes of powdery mildew is excessive moisture on the leaves. Avoid applying irrigation overhead onto the plants; target ground level instead, and mulch to preserve soil moisture, and so requiring fewer direct applications of water. A seaweed spray can also help as a preventative measure when applied to the leaves of vulnerable plants.
Just like the rust that affects metal, vegetative rust takes the form of orangey brown pustules underneath leaves. These pustules contain the spores of the disease and if they burst they can coat the foliage in a fine reddish dust. This prevents the normal functioning of the leaves such as photosynthesis and transpiration, causing the leaves to yellow and fall off the plant. Rust can affect a wide variety of vegetable species, including asparagus, spinach, silverbeet and beetroot. As with mildew, avoid overhead watering to minimize risk, and mulch to preserve soil moisture.
This mold takes the form of grey fungal growth that can spread over leaves and fruits. Those plants most at risk include strawberries and grapes, particularly those located in humid conditions. To avoid having to water too often and add to the level of moisture in the air, keep the plants well mulched. Furthermore, ensure that the plants are well ventilated; this will also help reduce humidity.
This fungus infects plants from the soil and is particularly damaging to potatoes and tomatoes. The fungus invades the plant’s roots and inhibits take up of moisture and nutrients. This causes leaves to yellow, wilt and eventually die. The disease is more active in dry, warm conditions and can be spread by water or on garden tools. Use good soil practices such as adding lots of organic matter and utilizing crop rotation to prevent the disease. (It can remain in the soil for a long time, so if you have had an area afflicted with Verticillium rot, it is recommended that you don’t replant the affected species of vegetable in that location for at least eight years.) If plants do get infected they should be removed at once.
Mosaic is a viral disease that can affect a variety of vegetable species, such as cucumbers, potatoes and turnips. It severely stunts the growth of the specimen and may cause leaves to curl, become yellowed or mottled with brown spots. Aphids primarily spread it, so companion planting species that attract beneficial insects that will keep aphid populations under control – such as dill and fennel to attract ladybugs – is an ideal preventative measure. Already infected plants should be removed to prevent the virus spreading.