To spray or not to spray – the economics of fungicide use

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By Kari Burnett Regional Farm Business Management Specialist, and

Shannon Chant Regional Crops Specialist

Saskatchewan Ministry of Agriculture, Swift Current

With all the moisture that has been received since seeding, there have been many questions surrounding the application of fungicides. Three reasons for using a fungicide are to control disease during crop establishment, to maintain yield by protecting photosynthetic potential, and to maintain market value by reducing blemishes and improving kernel characteristics. It can also improve the storage life and quality of the grain, harvested plants, or produce.

At what point does it make economic sense to use a fungicide? Determining if disease is present at levels capable of reducing yield is important. In some situations, disease may be present in a field, but not at levels that will impact yield. Fungicide should be applied only if the timing is correct to control the disease in question and an economic gain is likely. It may be possible to apply the fungicide to part of the field or as a buffer strip.

If expected reduction in income due to yield loss per acre is higher than the cost of a fungicide application, then the crop should be sprayed – the expected net return would be positive. To calculate estimated yield (bushels/acre), use prior years experience and evaluation of the crop. To calculate the expected yield savings (per cent) for cereal crops for example, use the following guidelines:

- under favourable environmental conditions for disease and when a susceptible variety was planted, up to 20 to 30 per cent yield savings for cereals can be expected when applying a fungicide compared to no fungicide application;

- for less favourable environmental conditions for disease and when a disease-resistant variety was seeded, expect up to five to 10 percent yield savings for cereals compared to no fungicide use.

For example, assume under normal conditions the estimated yield of a cereal crop is 35 bushels/acre. Under favourable environmental conditions for disease, assume a 20 per cent to 30 per cent yield savings. Therefore: 35 bushels/acre multiplied by 20 per cent equals 7.0 bushels/acre savings; 35 bushels/acre multiplied by 30 per cent equals a 10.5 bushels/acre savings. So under favourable environmental conditions for disease, use of fungicide can make a difference of between 7.0 bushels/acre and 10.5 bushels/acre – or if growing a crop worth $6.50/bushel, $45.50 to $68.25/acre expected gross return.

Under less favourable conditions, this increase could be limited to a five to 10 per cent yield increase. Or, using the same 35 bushels/acre estimated yield and assuming a five per cent savings (35 bushels/acre multiplied by five per cent) equals a 1.75 bushels/acre savings; 35 bushels/acre multiplied by 10 per cent equals 3.5 bushels/acre. So under less favourable conditions for disease, use of a fungicide can make a difference of between 1.75 bushels/acre and 3.5 bushels/acre – or if growing a crop worth $6.50/bushel, $11.38 to $22.75/acre expected gross return.

Expected Gross Return ($/acre) is calculated by taking the estimated yield multiplied by estimated yield savings multiplied by selling price. To calculate the expected net return, take the expected gross return minus the fungicide application costs, which could vary from $10-24/acre depending on the type of chemical, application rate, crop being sprayed, and disease being treated. The cost of the fungicide application compared to the expected gross return will play a large part in determining if it makes economic sense to spray.

The Ministry of Agriculture has a fact sheet: Plant Disease Control: To Spray or Not to Spray.  For more agronomic information stop by the Swift Current Regional Office or contact Shannon Chant, at 306-778-8291 or by email at shannon.chant@gov.sk.ca; for assistance calculating economic thresholds of fungicide use, contact Kari Burnett at 306-778-8216 or by email at kari.burnett@gov.sk.ca; or call the Swift Current Regional Office at 306-778-8285 or contact the Agriculture Knowledge Centre at 1-866-457-2377.

Organizations: Agriculture Knowledge Centre, Saskatchewan Ministry of Agriculture

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