Integrated control of the Humid Rottenness

Source: INTA - Edition: Cálamo, contents for internet

The Humid Rottenness of the Chapter (Rottenness) it is one of the most important illnesses in the sunflower cultivation. It is presented practically in all the productive areas of the sunflower of the country, causing bigger losses in the southeast area and south of the county of Buenos Aires.

A characteristic that makes more dramatic to this illness is that the conditions that favor its installation and development in the sunflower cultivations are similar to those conditions that they favor high yields of the cultivation. It determines it that he/she goes in a few days from the hope of high yields to the desperation by the loss of the cultivation. To that height of the events, they are already few the available tools to face the problem.

It is known that the infection of the cultivation takes place when they coincide periods of three or but cloudy or fresh days and of high humidity, with the floración of the plants.

The presence of the illness is manifested by stains of color tea with milk in the holder. These stains are very soft, of about 3 to 7 diameter cm and in them a finger can be introduced easily. If the illness advances, the rottenness can embrace the whole chapter and to cause its fall, leaving in the superior part of the shaft, only fibers isolated in broom form.

In advanced states of the rottenness and as the mushroom goes degrading the fabrics of the vegetable, the micelio goes concentrating on certain points and forming the esclerotos that are the bodies that the mushroom takes place for its perpetuation. These at the beginning are white, then gray and finally black with similar sizes to a sunflower fruit or bigger.

The Rottenness produces direct losses on the yield and envelope the quality of the crop product. The yield loss is given by pudrición of the fabrics and the fall of grains, as well as for the loss of quality. The esclerotos presence in the harvested product, increases the proportion of heavy strange bodies and the acidity of the oil, both causing of important discounts in the final price of the given grain.

In the last years, the due losses to the illness have diminished considerably, because they have improved the knowledge on the behavior of the cultivares and the handling of the cultivation, what allows to face the problem better. The main tools that are included in the current package of integrated control of the illness are:

Resistance behavior in cultivares

Due to the high dependence of the meteorological conditions and their coincidence or not with the susceptible period of the hospedante for the development of the illness, it is difficult to establish the behavior of varieties or hybrid of sunflower under natural conditions.

However, in the Agricultural Experimental Station of the Inta of Balcarce it is used successfully for some years a method of reproduction of the illness, based on the inoculation of sunflower plants in floración, with spores of the mushroom obtained under laboratory conditions. This method detects differences of behavior of the cultivares before the illness. The results obtained with this method have been confronted under natural conditions of infection and it was demonstrated that it is a good predictor of the behavior of the cultivares before the illness.

Siembra date

The siembra date together with the election of cultivating is the two fundamental pillars to combat the illness. It has been determined that in the south area of the region girasolera, the siembras of October has less percentage of sick plants than the siembras of ends of November or December. This is since related with the environmental conditions that he/she will have the cultivation in floración, a cultivation field in October it will flourish, independently of the cycle of the hybrid one, at the beginning of January, when the probability of cloudy days and cool airs are low.

Cycle of the hybrid one

The ability of a to cultivate of sunflower of escaping to the most favorable period for the development of the illness to possess an early floración is another quality to keep in mind to the moment to buy the seed. This is due to the escape for a premature floración to the most favorable time for the infection of the mushroom that is given from now on from ends of January in the area of Balcarce. For that reason, in the siembras of ends of November, the materials of shorter cycle, get sick less than the cultivares of intermediate cycle or I release.

Biological control

In the Inta Balcarce the use of microorganisms non patógenos is proving for the control of the illness, mainly mushrooms of the I generate Trichoderma. Also, the formulation of these way microorganisms is studied of favoring its effect biocontrolador, and that it is also a simple and economic practice for the producer. Another aspect that is studied is the form of application of the biocontroladores. An important advance has been the confirmation that the bee can be an effective transportadora of the one formulated toward the chapters and that the antagonists retard the infection and they reduce the sick area of the chapters. This technology is not still available still for its commercial use.

I use premature of desecantes

The desecantes application between 7 and 10 days before the physiologic maturity can avoid the advance of the illness and to avoid the esclerotos formation, improving the action from the product when having bigger number of green leaves. When they have not been kept in mind the previous recommendations or in atmospheres very predisponentes, the illness can be presented. In this case he/she seeks advice the desecantes use to brake the pudrición of the chapters and the esclerotos formation.

With relationship to what happened 10 years ago, the situation has improved considerably, diminishing the risk of falling in situations of big losses in yield and quality.

The use of materials of high yield potential and good resistance to the illness, together with the election of a date of early siembra and the premature application of desecantes to brake the development of the illness have facilitated an important control of the humid rottenness of the I surrender of sunflower. These basic tools together with the biocontroladores use will facilitate to maintain the controlled illness, diminishing the risk of falling in situations of big losses in the yield and the quality.

The results of the works of evaluation of the cultivares behavior in front of the attacks of Sclerotinia and the selection of new materials, allow to recommend for the siembra to hybrid sunflowers of more crop security that possess indexes of moderate resistance to the illness.