In the process of growing crops, pests and diseases follow like a shadow. Fungal damage in particular produces a great variety of symptoms, commonly including downy mildew, powdery mildew, smut, leaf spot, rust, fusarium wilt and rot. Faced with these diseases, using fungicides is an essential measure.
Different fungicides act mainly on different targets. There are so many diseases that we group the common ones by shared characteristics and identify the products normally used against them.
Group 1
Diseases that tend to break out in the damp spring and autumn seasons: damping-off, root rot, downy mildew, late blight, white rust and so on.
Commonly used products: oxadixyl + mancozeb, metalaxyl + mancozeb, fosetyl-aluminium and so on.
Group 2
Damage with a clear margin, forming lesions of a definite shape: powdery mildew, anthracnose, leaf spot, black spot and so on. Commonly used products: difenoconazole, triadimefon, tebuconazole, diniconazole, carbendazim, thiophanate-methyl, procymidone and so on.
Group 3
Generally only locally invasive, producing spot-type symptoms: smut, rust, sheath blight, damping-off and so on.
Commonly used products are many, for example chlorothalonil, carbendazim, mancozeb, triadimefon, difenoconazole, azoxystrobin and mancozeb + zinc. Among them chlorothalonil and mancozeb are protectants.
So do you know what to watch out for when using fungicides?
When using fungicides, you should at least know the basic common sense, otherwise the spray will be useless and may sometimes even cause crop injury:
Common sense 1: dilute as directed, use an appropriate dose, and spray carefully.
When spraying with a liquid formulation, the product usually has to be made up or diluted to an appropriate concentration with water; too high a concentration causes crop injury and waste, while too low a concentration is ineffective.
For example, the dosage in the figure is a 1,000-fold dilution and the product weighs 500 g (that is 1 jin); the conversion is 1 jin multiplied by the 1,000-fold dosage. Different fungicides each have their own specific concentration requirements, and when preparing the concentration you must strictly follow the instructions and must not arbitrarily increase or decrease it.
The quantity used must be appropriate: too much increases cost and very easily causes crop injury, while too little fails to achieve the purpose.
The quality of application must be attended to: spraying requires fine droplets and even coverage, covering the stems and both sides of the leaves, and striving to leave no gap. Cost should be considered and product used economically.
Common sense 2: timing must be right.
Generally, fungicide application should be timed before disease onset (protectant use) or at the very early stage of disease (nipping it in the bud). Too early or too late both affect the result.
Product should be applied in good time before or just as the disease appears, based on the pattern of occurrence, the prevailing conditions or a short-term forecast. Weather conditions also matter: the effects of temperature and sunshine are usually the most obvious, and high temperatures, strong sunshine, heavy fog or high humidity all readily cause crop injury.
Common sense 3: number of sprays.
The number of sprays is determined mainly by the length of the product's residual life and by weather conditions: generally once every 10–15 days, for a total of 2–3 sprays; where disease is more serious, once every 7 days, with an extra spray after rain.
Common sense 4: resistance problems
Long-term use of a single product (mainly systemic fungicides) will lead to the pathogen developing resistance and the product becoming ineffective. To avoid this, products of different types can be used in rotation, or systemic and conventional fungicides mixed.
These four points of common sense apply not only to fungicides but generally also to other products. Next comes the question of tank-mixing fungicides, where certain prohibitions must be known to avoid crop injury and loss of efficacy.
Mixing prohibitions:
First: pesticides that readily decompose and lose effectiveness on contact with alkaline substances must not be mixed with alkaline substances; for example, alkaline fungicides such as Bordeaux mixture and lime sulphur must not be mixed with parathion (1605), dimethoate or dichlorvos.
Second: products that produce a chemical reaction causing crop injury when mixed must not be applied together; for example, mixing lime sulphur with parathion (1605) not only reduces efficacy but worsens crop injury.
Third: pesticides that after mixing show breakdown of the emulsion or produce a large amount of sediment must not be mixed.
Fourth: copper formulations kill both fungi and bacteria and have a long residual life with little risk of resistance. But inorganic copper has poor mixing compatibility and easily causes crop injury when mixed with other products, so it should be used alone as far as possible. Organic copper has very good mixing compatibility and can be mixed with many products to broaden the control spectrum, though it too has prohibitions.
Source: 191 Agri-inputs People