Fomoz Of A Stem Of A Sunflower

2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38

Sunflower stem phoma is most often manifested on young plants. The fungus-pathogen that infects sunflower is first localized in the form of spots on the leaf blades, and after some time it passes to the stems. This attack develops throughout the growing season. The tissues of stems infected with a dangerous disease often die off, the grains are of low quality, and, alas, there is no need to talk about a good harvest in this situation

A few words about the disease

Manifestations of phomosis on a sunflower can be detected as soon as three to four pairs of true leaves are formed on it. On the leaf blades, the formation of dark brown spots framed with yellow edges begins. Gradually expanding, they cover the affected leaves entirely, including leaf petioles. And then the defeat spreads to the sunflower stalks.

The causative fungus strongly affects the inner tissues of the stems, significantly reducing their strength. When the formation of baskets begins, you will notice vague brownish specks on their lower sides. As they grow, they can easily cover the entire basket, including its wrapper. This happens especially often when the stage of active development of the disease coincides with the flowering of the sunflower. It is noteworthy that, despite the softening of nearby tissues, rot on the sunflower does not develop at the same time. And on the obverse of the sunflower baskets, there is a slight browning of the tubular flowers.

Along the stalks, the infection moves to the root collars, on which you can see ellipsoidal black specks of quite impressive size, sharply demarcated from the juicy green tissues.

Achenes in infected baskets form rather puny, staining brownish as they ripen. They are often half empty. And with early and very severe lesions, seeds are not formed at all.

In the case of late development of a harmful misfortune, small specks form on the stems, gradually merging into rather long stripes. And on the leaves, at the same time, you can notice specks limited by veins, which differ in an irregular shape. Sometimes they can orient themselves along the central leaf veins, provoking tissue decay, and a huge number of pycnidia arranged in concentric circles are formed on infected tissues.

The causative agent of phomosis of sunflower stems is a harmful fungus from the genus Leptosphaeria, which remains in the form of mycelium on plant remains, as well as in seeds affected by the disease. In the tissues of the growing sunflower, this fungus forms a dark gray or whitish mycelium. And black pycnidia of the pathogen in huge quantities are formed not only on the surfaces of the stems, but also in their cores or in the lignified parenchyma. As for the massive spread of infection, it occurs with conidia.

Most often, the development of phomosis can be observed at the stage of sunflower budding, and its especially strong development usually occurs before harvesting. To a large extent, this is favored by the presence of moisture, which is necessary for the release of spores and their subsequent spread and germination. By the way, phomosis is capable of developing at a fairly wide temperature range - from five to thirty-five degrees.

How to fight

The main preventive measure against phomosis of sunflower stems is a competent crop rotation. As for sunflower varieties, at the moment there are no varieties completely resistant to phomosis, however, if you wish, you can pick up some hybrids for planting with an average tolerance to this dangerous infection.

Before planting, the seeds are recommended to be treated with fungicides, and with the onset of autumn, all post-harvest residues should be removed from the plots.