Crop protection the healthy wayCrop protection the healthy way
Watch the nutrient balance - says PDA
How much of the world’s attainable crop production is lost as a result of damage inflicted by pests and diseases? A precise answer is hard to ascertain but what is certain is that, just as healthy, balanced nutrition is known to give humans good defence against diseases, the same is true for plants. Strong, vigorously-growing crops resist attack from pests and pathogens and they also compete more successfully against weeds.
According to data collected from a number of sources, and presented in Discussion Paper 25 of the International Food Policy Research Institute, Washington DC, USA, losses in global production are huge. Estimates by Oerke et al. (1995), who studied eight major crops (wheat, corn, rice, barley, soybean, cotton, potatoes and coffee), suggest that losses from pathogens alone are equivalent in value to US$76.9 billion. For the same crops, pest damage accounts for losses of $90.8 billion (Figure 18). If the yield loss caused by weeds is also taken into account, the value of actual production represents only 58% of that attainable with full potential yield, with the highest losses occur-ring in rice grown in Asia.
actual production $335b
loss through pathogens $76.9b
loss through weeds $75.9b
loss through pests $90.8bIn an attempt to reduce these losses, farmers have increased their use of pesticides. In the fifteen years between 1983 and 1998, global consumption of pesticides increased from $20.5 billion to $34.1 billion. These are facts which clearly illustrate how pests and diseases damage farmers’ incomes twice; with lower yields and higher input costs. And yet balanced nutrition, which would help crops resist such damage at much lower cost to the farmer and the environment, is often neglected.
The importance of balanced nutrition, and the biotic stress that occurs as a result of imbalance, was presented in a paper by A. Krauss for the 7 th International Congress of Soil Science in Faisalabad, Pakistan. The ratio of N to K is critical but, equally important, are the lesions, necroses and other injuries that occur if plants are suffering from deficiency of potassium, calcium or boron, for they open the tissue to invasion by pests and diseases. Plants that are suffering from K or Mg deficiency become yellowish in colour and prone to wilting. Such plants attract aphids which compete for assimilates and transmit viruses at the same time. Plants excessively supplied with N have soft tissue with little resistance to penetration by fungal attack or sucking and chewing insects. Excessive growth, due to an unbalanced N supply, can also create microclimatic conditions favourable for fungal diseases.
| Figure 19: Potash helps to make soybean more resistant to pests as seen in the IPI-PRII-OILFED on farm program in Amiaha in India |
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Micronutrients also have a critical role to play in disease prevention. Manganese, for example, acts as a catalyst to form phenolic compounds in tissues. These act as a repellent and interfere with the enzymatic reactions that are triggered by pathogens. When balanced nutrition can contribute so much to crop protection, why neglect it? Helping the plant to defend itself against attack should surely be the first line of defence.
Oerke, E.C., Dehne, F., Schohnbeck, F. and Weber, A. (1995): Crop production and crop protection: estimated losses in major food and cash crops. Elsevier, Amsterdam (quoted in IFPRI Discussion Paper 25, 1998).