White mold of sunflower: everything you need to know and how to fight it
One of the most destructive diseases of agricultural crops is Sclerotinia disease or white mold, which affects more than 500 species of cultivated and wild plants. The name “white mold” was given to the disease because the affected parts of the plant are covered with white cottony strands. The pathogen of the disease is the polyphagous fungus Sclerotinia sclerotiorum (Lib.) de Bary. In the development cycle, this fungus forms sclerotia - dark solid formations of various shapes and sizes that are formed inside stalks and on the surface of the affected plant organs.
Where can you find white mold? White mold is everywhere. The greatest harm is caused in areas with humid climate and cold, prolonged springs. The disease has gained a special significance in recent years due to violations of crop rotations and inclusion of crops that are affected by Sclerotinia wilt - sunflower, soy, rapeseed, corn, etc. to them. Very often the outbreaks of Sclerotinia wilt are observed in wet weather, heavy rainfalls and high air humidity.
When can white mold infect a plant? White mold affects plants throughout the growing season that makes it very difficult to protect crops against it. All parts of sunflowers are affected. The following forms of disease are distinguished: root, base, stalk and head rots.
The root form affects the root system; the roots become soft and wet, in moist soil they are covered with white cottony strands - mycelium of the pathogen. Due to deep tillage, the seeds of the plant die without coming to the surface.
The stalk form is observed both on the germinating and adult plants. Seedlings, cotyledons, leaves and stalks turn brown at the base part, rot and become covered with white strands. The upper part of stalks droop, the leaves wilt and the plant dies. On the older plants, brownish-brown spots appear, the tissue in the affected areas is destroyed, the main bundles become exposed, the core of the stalk shrinks and numerous sclerotia are formed in the cavity. The stalks in the affected areas breaks, dry up and die.
The head form is the most destructive. It begins to appear from the flowering stage to the end of maturation. Symptoms of infection appear as a wet rotting brown spot on the back of the head. The spot covers most of the head and spreads down the stalk. As a result, the head partially or completely rots. The damaged tissue gets wet and is easy to push through. The lesion passes to the front side of the head and forms white cottony strands on it that penetrate the seeds. Mycelium destroys the germ. Often, black sclerotia are formed between the seeds and in the seeds.
Why is white mold dangerous? The harmfulness of the disease is manifested in the loss of affected young plants and the thinning of the crop stand, early maturation of diseased plants resulting in formation of underdeveloped seeds with reduced seeding and technological properties. When epiphytotic manifestations of white mold occur, sunflower crop losses exceed 60%. The most harmful is the head form of the disease, the biological threshold of which is 5% of the destroyed heads.
What is the source of Sclerotinia wilt? The source of infection is the fungus sclerotia on the affected plant residues, in soil or in the form of impurities in seeds; mycelium on plant residues and seeds. In soil, they do not lose their viability for 5-10 years or more.
How does the disease develop? Sclerotia during harvesting of the affected crop fall into soil or remain on the affected crop residues. In the presence of winter thaws, the fungus continues to develop on plant residues forming new sclerotia. In spring, sclerotia in soil at moisture content of 50-60% and temperature of 18-24° C germinate hyphae, which quickly form white cottony mycelium and penetrate the plant (underground type of lesion). Due to sufficient soil moisture, sclerotia germinate during the entire growing season of plants. With early infection of plants, as well as sowing infected seeds, seedlings can die. Due to damage to the roots, the basal form of white mold is later observed (see the photo).
But the disease can be still harmful. The risk of infection of plants exists throughout the growing season. Sclerotia located in the upper layers of soil or on its surface form ascomycetous sporulation in the form of open fruit bodies - apothecia with ascospores. During the growing season, the fungus is spread by ascospores, which are released from the maturing apothecia at high humidity and are carried by the wind for considerable distances. Getting on the plant, ascospores germinate and penetrate the plant. Favorable conditions for development of the pathogen are high relative humidity - about 80 % and air temperature +18-25 °C.
How to protect plants from white mold? As you know, the disease is easier to prevent than to treat. Therefore, all measures that reduce the amount of infection in soil, on plant residues and seeds are effective for controlling white mold – fall plowing, compliance with crop rotation, isolation of crops in time and space, thorough cleaning of seeds from sclerotia, seed treatment, and so on.
But the economy dictates its rules and therefore the main preventive measures (crop rotation, plowing, spatial isolation) are not observed by farmers. And this, of course, leads to new outbreaks of the disease and significant losses of the yield and its quality.
Protection of the crops from white mold is complicated by the fact that the source of infection of the disease is soil, where no crop protection chemicals can be used for treatment. Therefore, sclerotia will germinate and infect plants throughout the growing season.
Are there any modern biological methods of protection? Yes, there are. BTU-CENTER recommends using the biological fungicide SCLEROCID to suppress the development of causal agents of white mold (Sclerotinia diseases) Sclerotinia sclerotiorum and Sclerotinia minor.
What is SCLEROCID® action? The biofungicide includes the microscopic fungus Coniothyrium minitans predatory to Sclerotinia sclerotiorum. This fungus has enzymes chitinase and glucanase that hydrolyze the polysaccharide of sclerotia - sclerotan. Coniothyrium minitans causes degradation of mycelium and sclerotia walls using the organic host as a source of nutrients for its development and inhibits development of the pathogen. This fungus blocks germination of sclerotia and leads to its destruction. Coniothyrium minitans affects exclusively Sclerotinia pathogen and is not harmful to other micro- and macroorganisms. It infects the pathogen at all stages of sclerotia and mycelium growth at soil temperature of 5-28°C.
Coniothyrium minitans fungus has a unique selectivity towards sclerotia of fungi of the genus Sclerotinia that makes it impossible to develop sclerotic rot in case of its presence in soil.
Coniothyrium minitans fungus has a long-lasting effect, eliminating sclerotia and mycelium from soil and harvested crops during storage. Introduced into soil, it provides a significant reduction in the infectious potential of Sclerotinia during the growing season, as well as reduces the risk of infection of next crops in the crop rotation.
Highly effective protection against the pathogen of white mold is also provided by other biological agents of the preparation SCLEROCID, namely the fungus-hyperparasite Trichoderma harzianum, bacteria Bacillus licheniformis and Bacillus subtilis. They are able to synthesize natural antibiotics that suppress not only development of white mold, but also pathogens of other fungal diseases (Alternaria, Septoria, Phomopsis, Fusarium diseases and gray mold).
In addition, the preparation SCLEROCID improves soil fertility and contributes to its improvement.
How to apply Sclerocid? The preparation SCLEROCID can be used in several ways.
1. Treatment of soil and crop residues at the application rates of 1-5 l / ha
Treatment of soil and crop residues is an extremely important measure, because it helps to destroy the infection of white mold in soil and on plant residues, preventing infection of plants. Treatment is carried out with a working solution of the biological preparation after harvesting the preceding crop and 15 to 40 days before sowing or planting crops. The preparation is applied on soil surface by spraying and should be immediately incorporated into soil into depth of 10-25 cm using tillage equipment, so that the microorganisms are not exposed to sunlight for a long time. A prerequisite is the presence of moisture in soil – at least 25-35 % of the total soil moisture content at temperature of 5-28°C.
To improve efficiency, it is advisable to combine the biopreparation SCLEROCID in a tank mixture with the biodestructor ECOSTERN. In this case, its effectiveness increases by 20-30%.
2. Pre-sowing treatment of seeds of soybean, corn, rapeseed, sunflower and other crops at the application rates of 1-5 l / t
Pre-sowing treatment of seeds destroys white mold seed infection and protects seedlings from soil infection, increases seed germination energy by 19-20% and germination capacity by 15-17%. The seeds are sprayed with the working solution of SCLEROCID or soaked in it for 1-2 hours on the day of sowing. Seed treatment is carried out manually, using a sprayer or seed treater. The treated seeds are sown immediately or dried in shade to a loose state.
3. Fertigation (band application) during the growing season: through a drip irrigation system (0.5-2.5 l / ha)
The application of SCLEROCID through a drip irrigation system allows you to destroy soil infection of white mold and protect vegetable and berry crops not only from white mold, but also from Alternaria, Fusarium diseases, gray mold, etc.
4. Other application methods
The biofungicide SCLEROCID can be used in the pre-sowing treatment together with GROUNDFIX, as well as applied in a row at sowing together with liquid complex fertilizers.
Scientific adviser on plant protection,
PhD in Biology, Tamara Serhiivna VINNICHUK