We have before us a crop with double use. One would be the sunflower oil that we all know and use according to what things in our kitchen, and another, to take advantage of the pipes as nuts.
However, like all known plants, it is subject to the presence of numerous pests and diseases.
In what happens to this article, we are going to see the main diseases of sunflower crops.
WET ROT ( SCLEROTINIA SCLEROTIORUM )
This disease lives in humid conditions and progresses through the sunflower crop generating basal rot in the lower part of the stem.
It destroys the conductive tissues (where the sap circulates) and causes the death of the plant. Nutrients and photoassimilates cannot reach the aerial part of the sunflower and it ends up drying out.
Sunflower wet rot can occur in any phenological stage of the crop.
CONDITIONS FOR THE APPEARANCE OF WET ROT IN SUNFLOWER
The appropriate conditions for its development are based on temperature (from 5 ºC) and sufficient humidity in the soil, where there is presence of sclerotia, which germinate and infect the crop.
VERTICILOSIS (VERTICILLIUM DAHLIAE KLEB)
Verticillosis or Verticillium is a very important disease in sunflower cultivation. As in the case of soft rot caused by S clerotinia , it affects the conducting vessels, preventing the circulation of sap and slowing the advance of the aerial part.
Verticillium dahliae Kleb
The disease progresses from the basal part (the lower part of the sunflower stem) to the upper part, affecting the stems (where some necrosis is observed in the vessels) and leaves.
Therefore, when observing the disease, we will see the first physical samples in the leaves of the lower part and, little by little, they will advance towards the upper leaves.
In an advanced stage of the disease, it is possible to observe how the seeds rot in the aerial part, rendering them useless for their commercialization.
CONDITIONS FOR THE APPEARANCE OF VERTICILLOSIS IN SUNFLOWER
The appropriate conditions for this common sunflower disease to appear are warm temperatures and good availability of soil moisture.
Often times, excess irrigation caused by rain is the breeding ground for a general weakening of the crop and the germination of this type of spores.
Increasing the pH of the substrate is an important factor in controlling the advance of the disease from the soil.
Disinfection or solarization will also help eliminate any type of fungus spore, if done well and for long enough.
CHANCRO DEL TALLO (PHOMOPSIS HELIANTHI MUNT)
This disease makes an appearance in the reproductive conditions of the sunflower (in full pipe production).
The first effects of the disease are observed on the leaves, where necrotic spots are seen in the shape of an inverted V. That is, the vertex of the spot begins in the basal part of the leaf and increases as it approaches the tip of the leaf.
A necrotic spot is also observed on the stem, a sign of disease progression and collapse of the sap-conducting vessels.
If we look with a magnifying glass, we can see small dark spots of very small diameter in these spots on the stem.
EVALUATION OF DAMAGE IN ROOT AND STEM DISEASES
Presence of few lesions on stems healthy capitula
Up to 1/3 infected stem and / or up to 5% infected capitula
Up to 2/3 infected stem and / or up to 10% infected capitula
More than 2/3 infected stem and / or more than 10% infected chapters
CONDITIONS OF ONSET OF THE DISEASE
Sunflower stem canker usually appears when, in the presence of the disease, excessive fertilization tends to be abused or early plantings are carried out out of date.
SUNFLOWER MILDEW ( PASMOPARA HALSTEDII (FARL) BERL. & TONI)
Mildew is one of the most widely known diseases in crops. In sunflower, it is also important, since it reduces or eliminates the emergence of the seeds.
The sunflower affected when young tends to a slow growth and causes dwarfism. The veins of the leaves become chlorotic and the leaf area becomes discolored.
As the disease progresses, a kind of cottony mass appears, indicating a growth of mildew spores.
CONDITIONS FOR THE APPEARANCE OF MILDEW IN SUNFLOWER
Moderate temperatures (between 15 and 25 ºC) together with high humidity (above 90%) are the conditions for the maximum development of the mildew.
Sunflower dwarfism caused by mildew
STEM BLIGHT ( SCLEROTIUM ROLFSII)
The blight disease in sunflower causes the death of the sunflower whatever the phenological state it is.
However, despite the severity once the plant is infected, the infection conditions are not so simple and only isolated cases occur depending on the geographical area.
On the base of the stem, the advance of the blight occurs, which necrotic the area and inhibits the conduction of sap through the xylem channels.
In addition, a kind of cottony and soft spot forms that the sclerotia of the blight form, as a kind of soft rot.
CONDITIONS FOR BLIGHT TO APPEAR
As in other cases of soft rot, blight appears in times of warm temperatures (above 25 ºC) and high humidity conditions.
ALTERNARIA (ALTERNARIA HELIANTHI (HANSF.))
Alternaria is a well-known disease in many types of crops when there are high humidity conditions.
It affects the leaves, reducing their photosynthesis capacity and causing their premature fall.
Necrotic spots form on the foliar mass, which also reproduce on the sunflower stem. Around this black spot, a chlorotic halo of yellow color is formed, very characteristic in this disease.
ROYA (PUCCINIA HELIANTHI SCHW)
Rust is also a typical disease in cereals whose visual symptoms are reflected in the leaves.
Necrotic spots appear on these, reddish or black, which progress from the lower to the upper leaves.
The conditions for the development of rust in sunflower are warm temperatures (between 18ºC and 25ºC) and high relative humidity.
Puccinia helianthi en girasol
SEPTORIA (SEPTORIA HELIANTHI)
Septoria helianthi leaf spots on sunflower
This disease is not standardized in sunflower cultivation and only rare cases occur. The septoria is located on the basal leaves, causing brownish spots with a yellowish halo (similar to anthracnose).
The disease evolves from the lower to the upper leaves and only in exceptional cases does it spread to the sunflower stem.
High relative humidity and warm temperatures are the ideal conditions for the development of the disease.
BACTERIAL ROT ( ERWINIA CAROTOVORA )
Of all the sunflower diseases that we have treated, this is the only one mentioned of bacterial origin. Although there are others within the compendium of diseases of bacterial origin, Erwinia carotovora is one of the most famous.
A watery-looking rot appears on the stem . It is formed on the inside and only from cracks is it visible on the outside.
With the advance of the disease , the affected stem breaks and totally affects the development of the plant.
The disease transport agent is the Melanagromiza cunctanoides insect , so the control of the disease involves eliminating the vector.