Why is wheat smut dangerous and how to deal with it?
When growing wheat, it is not always possible to obtain the maximum yield, since it is demanding on climatic conditions and soil, as well as susceptible to many diseases.
One of the most common is smut. We'll tell you why it's dangerous and how to deal with it.
Wheat smut: nature of the disease
Wheat smut is a type of fungal disease that affects cereal crops of spring and winter varieties.. The causative agents of the disease are smut fungi, which belong to the class of basidiomycetes. Their contact with seeds or soil leads to plant disease.
Smut is difficult to treat. Basidial fungi have very strong and viable mycelium.
This disease causes significant harm to agriculture, leading to partial or complete loss of crops. wheat. The quality of the resulting grain decreases. Ears infected with mycelium develop poorly, weaken, and cannot resist other diseases. They become less winter-hardy and drought-resistant.
Many infected plants do not have time to emerge by harvest time. Smut causes particular harm to winter crops.
Causes
The risk of infection increases during autumn droughts and non-compliance with planting technology wheat, deep immersion of seeds into the soil.
Reference. Planting winter wheat too late or spring wheat too early creates a favorable environment for the development of the disease.
Most often, healthy plants become infected from diseased ones.. The infected cereal breaks down into pieces, and the released spores are carried by the wind to other plants.
Infection is also possible when spores are in the soil. In the spring they begin to germinate and form a mycelium. The optimal temperature for spore activation is +2…+5°C. The developing mycelium infects the sprouts of cereal crops and spreads inside their stems. During the flowering period of cereals, the mycelium reaches the panicle and accelerates its development. As a result, the ear turns black, and the grains are replaced by parasite spores. An infected plant produces an unusable spore mass instead of grain.
Undisinfected containers and agricultural equipment can also become a source spread of the disease. The pathogen is carried by animals, birds and insects.
Symptoms
Symptoms of infection appear on the panicle and ear of wheat. At a certain stage of development, the mycelium of smut fungi breaks down into individual cells, which are covered with a thickened membrane and turn into spores.
A dusty or dark-colored mass forms in modified grains, stems or even on leaves. Clusters of spores give affected parts of the plant a charred appearance, as if the plant is covered in soot. That’s why the disease is called smut (photo below).
Kinds
There are several types of smut, which attacks wheat. Each of them has its own characteristics.
Solid
When a crop is infected with smut, the inside of the grain is destroyed., the outer shell does not change. The causative agent of the disease is Tilletia caries. The teliospore of this type of smut enters the external environment during harvesting or during the initial processing of grains. Healthy grain and soil are infected.
Reference. Bunt represents the greatest danger to soft wheat varieties. It appears at the stage of milky ripeness of the cereal.
The main signs of smut:
small, flattened ears;- spread scales;
- swollen elongated grains;
- the plant acquires a blue-green color and an unpleasant herring odor;
- in place of the grains, a black spore mass is formed;
- the ears of affected wheat lose weight and do not fall down during the ripening period.
Disease faster develops in dry and cold weather.
Dusty
When affected by loose smut, the shell and interior of the grain are destroyed.. The causative agent of the disease is Ustilago tritici. The infection affects ears of winter and spring wheat. It begins during the growing season from the bottom of the ear. From infected grains of one plant, the disease is transferred to another by the wind.
Signs of the disease:
heading of the crop is accelerated;- the infected plant is taller than healthy ones;
- the plant bushes weakly;
- the ear has a scorched appearance;
- the infected grain is covered with a gray shell.
Disease accelerates development at low air and soil temperatures, non-compliance with sowing dates, in case of autumn droughts. Loose smut can destroy an entire crop.
It can be useful:
Indian
This type of disease was first reported in India in 1930. Currently distributed in Afghanistan, Pakistan, Iraq, Nepal, USA and Mexico. The causative agent is Tilletia indica. From 1 to 5 spikelets are affected in an ear.
Symptoms of the disease:
instead of grains - seed shells with a black mass of spores inside and the smell of rotting fish;- the affected grains are swollen;
- the infected plant is dwarf;
- when wheat ripens, the spikelet scales of the affected plants diverge;
- teliospores are ovoid or oblong, 1-3 mm in diameter, and when ripe form a brown-black dusty mass.
Infection and development of the disease occurs with sharp temperature fluctuations from +7°C to +22°C and high air humidity (more than 65%). Spores are carried by the wind from diseased plants to healthy ones by insects, animals and birds. The source of spread may be undisinfected agricultural equipment, containers, and storage areas.
Spores remain viable in grain for up to 18 years, in soil - up to 6 years.
Dwarf
It mainly affects winter wheat. The causative agent is Tilletia controversa Kuhn. More harmful than smut. Initially, the seedling of the crop is affected.
Distinctive features appear during the heading period:
plants bushy strongly, forming up to 50 stems;- low growth culture;
- the ears are dense, do not emerge from the axils of the upper leaves;
- the number of ovaries in a spikelet increases to 4-7;
- Instead of caryopses, smut sacs of spherical shape with teliospores are formed in the ear.
Spores are highly viable (up to 10 years in soil).
Stem
Stem smut caused by the fungus Urocystis tritici Koern. Convex light stripes form on the leaves and stems of the plant, which become lead-gray as they develop.
The stripes reach a length from several millimeters to several centimeters. The epidermis on the strips dries and cracks, revealing a dark mass of spores. Wheat becomes infected during germination, then the entire plant is affected.
Features:
- growth retardation;
- the ear is missing or deformed;
- there are no grains in a developed ear;
- leaves and stems are curled.
The source of the disease is infected seeds. Spore viability is 1 year.
How to deal with disease in plantings
If wheat is infected with smut, it is destroyed. On average this is 15-20% of the harvest. If a lesion is noticed during the ripening period, it is better to let it die.
Teliospores cannot be treated with pesticides. This will harm the quality of not only diseased, but also healthy plants more than smut.
The fight against the disease consists of preventing possible infection. Control measures:
- compliance with agricultural technology and crop rotation;
- testing of seeds to identify contaminated grain;
- disinfection of agricultural implements and machines;
- use of wheat varieties resistant to the disease;
- disinfection of seed material.
Chemical dressing of seed material is effective in the case of hard and dusty smut. There are several etching methods:
Dry. It is carried out using machines using powder pesticides: “Merkuran”, “TMTD”, “Granozan”. Since the chemicals are poorly retained on the grain, the method is considered ineffective.- With humidification. The grain is treated with special machines using a suspension of pesticides: “Merkuran”, “Granozan”, “Hexachlorobenzene”. This method is effective - the number of infected cereals is reduced, and good germination of seeds is observed.
- Wet. Seed material is treated with formaldehyde solution 5 days before sowing. The method consists of three stages: wetting, simmering, drying. The process is very labor-intensive, so it is rarely used, either with a small amount of grain, or in case of severe damage to the seed material.
- Semi-dry. The principle is the same as in the wet method, but without drying the grain.
On mown wheat
If the wheat is mowed, they begin to fight the spores that remain in the ground. Manure and minerals are added to moist and well-warmed soil. This creates conditions conducive to the death of the fungus.
The soil is also enriched with manganese and boron. They increase plant resistance to diseases.
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Use of contaminated grain
It is undesirable to use wheat grains infected with smut for food.. The spores contaminate the flour, it acquires the smell of spoiled herring and a dirty color. Bread made from such flour does not bake well, smells unpleasant and has a sweet taste.
To get rid of smut, wheat is washed in a washing machine and processed three times brush apparatus. The grain purified in this way is mixed with clean grain. According to quality standards, the amount of smut grain in wheat should be no more than 5%
Geographical distribution of the disease
Smut is widespread. The causative agents of this disease have the same range as the plants that feed them.
Head smut is ubiquitous. Loose smut - in the European part of Russia, in some areas of Western Siberia, in small pockets in the Samara and Orenburg regions, in the North Caucasus and Transcaucasia.
Stem and dwarf smut are observed in the Stavropol Territory and Crimea.
Indian smut is not registered in Russia.
Preventive measures
For preventive purposes, to combat smut, you should:
use only healthy material;- do not allow sowing of wheat seeds collected from fields affected by smut by more than 0.5%;
- treat seed material in a timely manner;
- use varieties resistant to this disease;
- sow wheat on time.
Conclusion
Smut is a fungal disease that affects wheat, widespread and difficult to treat. Fungal spores have high viability. The disease leads to partial or complete loss of wheat yield, so it must be combated. Since affected plantings cannot be treated with pesticides, special attention is paid to preventive measures.