Features of application of contact fungicides - General phytopathology

Peculiarities of application of contact fungicides

Here are the main ways of using fungicides and their effect on the parameters of epiphytoty.

Method

Decrease

Seed dressing

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Entering into the soil

Ground application for resting plants

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Ground application for vegetating plants

g

Presowing treatment (dressing) of seeds . This technique is technically very convenient, since processing several kilograms of seeds is much easier than processing a hectare of plants grown from them. Calculations show that for the treatment with pesticides of one hectare of corn , 13.50 g of the drug are consumed by spraying the leaves,

by applying to the soil - 600 g, and with the help of seed dressing only 50 grams. However, in order not to waste useless reagents, labor, etc. and, most importantly, do not pollute the environment with xenobiotics, you must first obtain information about which pathogens and to what extent the seed lot is infected. How is this done, described in a number of manuals, in Russian popular book known phytopathologist NA Naumova.

Spores of many fungi remain on the surface of seeds, so they can be destroyed by contact fungicides. Earlier, mercury-containing preparations were widely used for these purposes, but now they are banned due to high toxicity for workers and environmental hazards (for example, treated seeds that crumbled during transportation to the field were pinched by birds that died from mercury poisoning). Now many contact organic compounds are used for this purpose. If the infection is inside the seeds (eg, mycelium pathogen of a dusty wheat germ), then systemic fungicides are required, for example, the drug Vitavax & quot; from the group of oxatines.

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Making fungicides in the soil - is a laborious and expensive exercise, therefore it is used limitedly, mainly to protect especially valuable products. For example, chemical disinfection of soil is carried out in greenhouses when growing vegetable, flower or fruit and berry crops.

Treatment of dormant plants. This method is used in fruit growing for the eradication of wintering in the cortex and in the kidneys of spores and mycelium. Early spring processing of trees in a non-impoverished state allows the use of highly toxic compounds for fungi, for example copper and iron sulfates, which can not be applied in the summer, as they cause leaf burns.

Processing of vegetative plants. This is the most common and energy-intensive way to protect plants. It can be carried out by means of dusting or spraying plants. For dusting, the preparation is mixed with finely ground neutral clay (talc or kaolin), and this mixture is sprayed over the plants with special equipment. Pollination gives a uniform good coating of plants with a pesticide, but is currently used very rarely due to a number of shortcomings:

- the preparation is highly wind-blown when sprayed, therefore, work can be carried out only in absolutely windless weather and only with ground-based mechanisms (when dusting from an airplane the drug can be carried far from the field);

- the drug after falling on the leaves is quickly blown off with them by the wind or washed away by rain, therefore frequent repeated treatments are needed.

Much more common is plant spraying, in which the concentrated preparation is diluted to the required concentration with water. Since many fungicides are insoluble in water, they are released with additives of wetting agents - surfactants, in the presence of which chemicals are diluted in water and form stable suspensions. In addition, the preparation is added with & quot; adhesives & quot; - substances that fix a fungicide on the surface of plants and reduce possible washouts by rain.

When spraying plants, especially with contact fungicides, a number of problems arise that need to be solved:

1) the problem of covering the plant surface. Since the contact fungicide kills the fungal structures only after direct contact with them, it is necessary to cover the surface of the plant as completely as possible; the presence of leaf areas that are not covered with a fungicide solution may be the reason for the low processing efficiency. Old designs of tractor sprayers with acorn tips gave large-droplet treatment (droplet size more than 300 microns), at which to satisfactorily cover the leaves with a film of the fungicide solution, it was required to pour out hundreds of liters of the drug per hectare. This led to very low labor productivity, increased cost of work due to additional fuel costs, etc. In addition, krupinoopapelnoe spraying is inevitably accompanied by losses of a significant part of the solution falling to the ground, bypassing plants.

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Later, mechanisms were developed that reduced the required volume of liquid by reducing the size of droplets, for medium-drop, small-drop and ultra-small-drop spraying. In the latter case, the size of the droplets was reduced by an order of magnitude - up to 30 μl, and the volume of liquid for processing 1 hectare was reduced to several liters. With small-drip treatments on the sheet is formed not a film of the drug, but a dense mesh of its droplets. Blown from small spray drills, the preparation forms an aerosol cloud around the plants, evenly covers the upper and, most importantly, the lower sides of the leaves, so that losses due to falling to the ground are reduced. However, very fine drops dries quickly, after which the preparation turns into a powder used for dusting with all its drawbacks, therefore, additives of adhesives that help to retain dry residue on the leaves are absolutely necessary;

2) the problem of choosing the timing of the first and subsequent sprayings. This is a very important issue, especially when treating contact fungicides. Most fungi of parasites are introduced into plant tissues and form an endophytic (interstitial) mycelium that is inaccessible to contact fungicides, therefore, pre-treatment of plants is necessary before most sprouts sprout inside. But we do not know whether chemical treatment of plants will be necessary at all, since neither the stock of infection nor the weather conditions that are necessary for the development of the disease are known. Perhaps the weather conditions of the season will contribute to the depressive development of the disease, and, therefore, under such conditions, chemical treatments will lead to unjustified financial costs and environmental impacts. To avoid this, a variety of methods for predicting the development of diseases specific to different parasites have been developed, but have some general principles.

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