Crop rotation
Some important soil-borne pests and diseases attack specific crops, such as potato cyst nematode on potato and club root on cruciferous plants. As they are soil-borne, they are slow in their dispersal, but are difficult to control. By the simple method of planting a given crop in a different plot each season, such pests or diseases are excluded from their preferred host crop for a number of years, during which their numbers will slowly decline. A gardener often creates five or six plots (sometimes bounded by wooden planking) to achieve successful rotation. Plants belonging to the same plant families fit into the rotation system. They have the same sensitivity to particular pests and diseases. Potatoes, tomatoes, peppers and aubergines are all members of the Solanaceae. Melons, marrows, courgettes and cucumbers all belong to the Cucurbitaceae. When considering a rotation plan, it is advisable to confine members of the same family to the same plot in the same growing season. Rotation does not work well against unspecific problems, such as grey mould, which may attack a wide range of plant families. Rotation is also not likely to be effective against rapidly spreading organisms such as aphids.
The sclerotium stage of white rot disease (Sclerotum cepivorum) on onion and related crops, such as leeks, garlic, chives and shallots, is able to survive in the soil for 15 years or more. It can be seen that a very long rotation period would be necessary to remove this serious disease. A six year rotation is not normally sufficient.
Post a comment