Dec. 5, 2020
Nov. 27, 2020
Soil-borne pests and diseases are harder to detect than those on the aerial parts of a plant. Visible symptoms in leaves and stem appear only in the final stages of the attacks. If plants are treated at this point, it may be difficult to avoid plant injury, as plants could already have been severely impacted. Early detection and identification are key to prevent crop loss. There are, however, only a few instruments available which can help in monitoring crops on the field to prevent or arrest soil pests and pathogen growth.
It is common to have pests and pathogens attacking plants. However, monocultures, which are the prevailing means of growing crops, increase the intensity of attacks by enabling easy spread of the causal organisms. A recent study covering sixty seven countries investigated loss of crops. They found that, on a global scale, five main food crops suffered losses ranging from ten to forty percent due to pests and diseases. The loss in different crops was as follows:
Experts identified 137 pathogens and pests affecting these five crops, including bacteria, fungi, viruses, oomcyetes, nematodes, arthropods, vertebrates, molluscs, and parasitic plants.
The soil is a special ecosystem dictated by soil conditions—like pH, moisture content, and organic matter availability—where the different soil organisms interact with the plants through its roots. Normally, all the organisms, even those that cause diseases or behave as pests, live in a balance with other species.
When any of the soil conditions are changed unfavourably, it can encourage the growth of one particular set of microflora or microfauna at the expense of others. If these are pests or pathogens, the attack on plants’ roots can be severe enough to affect its performance and yield. Good soil management is, therefore, one of the best ways to deal with soil diseases and pests.
Figure 1: “Potato plant infected with potato mop-top virus.” FAO ( Image credits: http://www.fao.org/agriculture/crops/thematic-sitemap/theme/spi/soil-biodiversity/soil-organisms/the-function-of-the-soil-community/pests-diseases/en/
In the soil, disease-causing pathogens include bacteria, fungi, viruses, actinomycetes, phytoplasma, and protozoa.
Some of the common soil pests are nematodes, ants, aphids, snails, slugs, and rodents. For example, nematodes can cause gall-like lesions, while snails, slugs, and rodents feed on parts or whole roots.
The effects of the pests and pathogens are not restricted to the roots and can be seen as symptoms on leaves, a reduction in the rate of development and growth of plants, and in extreme cases can also affect plant survival (Figure 1).
The losses that soil pathogens and pests cause are partly because the causal organisms are working underground, out of sight, and are difficult to detect. By the time the symptoms appear in the above-ground aerial parts, the damage to the plant is substantial. There is also the danger that if the pathogens and pests are not contained they can spread and establish themselves in/on neighbouring plants and increase crop loss.
It is, therefore, crucial to detect incidence of pest and disease attacks as soon as possible. Many methods are currently available. Some of the more important ones are mentioned below.
Many of the methods involve destructive sampling and are not suitable for repeat testing, as they involve loss of crops. Most of them are expensive, time-consuming, and require laboratory and skilled personnel.
There are also some non-destructive modern methods to detect and identify pest and disease incidences, which are now available.
Since pests and disease development is an indication of the soil ecosystem that is off balance, one of the best ways to prevent infections would be to ensure ideal growing conditions. The soil should neither be water-logged or dry. Provide the right amounts of fertilizers, as too much can kill beneficial microbes that maintain soil health. Crop rotation and intercropping will reduce build-up of populations of any single species in the soil. With the help of simple tools, like the root imagers, a grower can also easily keep track of the health of the crops and detect any problems caused by pests and disease attacks in the soil.
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture
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