How to control diseases in a vegetable garden
There are many parasitic and non-parasitic agents that cause diseases in plants. Parasitic agents generally are viruses, bacteria, fungi, algae, and higher plants and animals. Non parasitic agents are external physical attributes like sunlight, low light intensity, lack of water, excess of water, mineral deficiencies, etc.
This guide presents the control measures that may be adopted for some of the plant diseases. Common plant diseases that affect a wide range of plants are lesions, cankers, blights, rots, wilt, necrosis, scabs, damping-off, mildews, spots, rust, & moulds.
Grow disease resistant varieties
Many plants, though more expensive to buy at the garden stores and nurseries, may be disease resistant varieties which are able to battle diseases better than their non-resistant varieties. At times, climatic conditions are such that the onset of a particular disease is inevitable; season to season. In this case, the best option would be to grow a disease resistant version of that plant.
Indulge in crop rotation
Many plant diseases build up in garden soil over a period of time, even over years. Crop rotation is a means of breaking this cycle so that the habit of the disease agents is disturbed and affects the disease agent population. When a different crop is grown in an area, at times, these disease agents are unable to thrive as the plant may be unfavourable or repelling.
Suggested crop rotation for diseases seen in common vegetables:
Asparagus — susceptible to fusarium wilt and root rot.
Beans — susceptible to rots, moulds and bacterial blight
Cabbage — club foot, fusarium yellows, blights, blackleg, blackrot
Carrot — leaf blight
Celery — leaf blight
Lettuce — bottom rot and drop
Parsley — damping-off
Radish, Turnip — club-foot
Note: In these cases, do not replant same plant or similar disease prone plants in the same area for a few years.
Resort to soil inoculation
Soil inoculation is a method of adding ‘good’ agents to the soil that fight against the ‘bad diseases causing agents’. It is simply adding good microbes that fight against or feed on the disease microbes. It acts as a defence mechanism for the soil where natural and organic methods are adopted without the use of harmful chemicals.
Use pesticides / fungicides
Most plant diseases are caused by fungi. Chemicals which are organic in nature and do not cause drastic damage to soil nutrient levels may be sprayed on plants and in the soil. Some sulphur based mixtures may be used, as sulphur is a naturally obtainable pesticide from the earth and is good in pesticide combinations. The most common are Bordeaux Mixture and Lime-sulphur Mixture. They can be prepared at home and have to be used immediately after preparation.
Ingredients: 1 kg Copper sulphate + 1 kg Calcium hydroxide (Lime) + 10 litres of water
Preparation: Mix Copper sulphate in 5 litres of water and calcium hydroxide in 5 litres of water each. Mixing is done in two plastic or copper vessels. After the two chemicals have been diluted with water, mix them together; the copper sulphate into the lime — pouring slowly while mixing vigorously. Use immediately. used to treat downy mildews in grapes, abnormal leaf fall of rubber, leaf spot of coconut, rusts and blights
Ingredients: 8 pounds sulphur powder + 8 pounds burned lime + 50 pounds (23.7 litres) of water.
Preparation: Slake the lime in a little water. When it is dissolved, add the sulphur, mix well and boil. Dilute with remaining water and use immediately. Boiled version is most ideal for vegetables. Used especially in the treatment of scabs and lesions.
Frequently clean the garden, add mulch and compost
Some of the diseases in plants are caused due to deficiencies in nutrient levels. This can be combated by
a. cleaning the garden off weeds that drain the soil of nutrients for the plant
Mulch and compost are rich in nutrients and nutrient releasing micro-organisms, that when they are added to the soil, they enrich the soil and make sick plants healthy.