Pea Ascochitis

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

Ascochitosis causes serious damage to pea crops. It attacks growing crops especially violently during wet seasons. There are three types of pea ascochitis - pale, dark and confluent, differing not only in the nature of the lesions, but also in their pathogens. However, these varieties of ailment have common features - they all develop with particular force when the humidity rises, as well as at temperatures from twenty to twenty-five degrees. A delay in the development of peas and the maturation of their seeds, along with a noticeable thinning of seedlings, lead to a significant reduction in the yield

Pallid ascochitis

On the beans of growing peas attacked by pale ascochitosis, unpleasant light chestnut spots, framed by dark brownish edges, gradually appear. Slightly less often, similar spots can be observed on stems with leaves. At the same time, on petioles with stalks, the spots are slightly elongated, and on leaves with beans, they are rounded and often reach nine millimeters in diameter. In the very center of the specks, a lot of pycnidia are quickly formed, which have a dark brown color. Sometimes, when ripening peas are affected, closer to the end of the growing season, spots on the stalks with beans are not formed at all, nevertheless, their surfaces are still dotted with an impressive amount of pycnidia. Infected seeds acquire a wrinkled appearance and are characterized by barely noticeable light yellow specks.

The causative agent of the destructive pale ascochitosis is a pathogenic fungus called Ascochyta pisi Libert. This mushroom is affected exclusively by peas, on which asexual pathogenic sporulation occurs (a huge number of pycnidia with pathogenic pycnospores). All pycnidia are slightly flattened, differ in spherical shape and reach a diameter of about 200 to 212 microns. And oblong small pycnospores are equipped with rounded tips and have one septum (much less often - two or three). Their germination is noted mainly in dripping moisture, and the most suitable temperature for this is the range from eighteen to twenty degrees.

Dark ascochitis

The manifestations of an extremely unpleasant dark ascochitosis are observed on stalks and leaves with beans, on which the formation of irregularly shaped dark brown spots of various sizes is noted. In this case, their size can vary from 0.5 to 7 mm. Large spots are usually zonal. As for the pycnidia scattered over the entire surface, they are just formed on larger specks. On the stems attacked by dark ascochitosis, ulcer-like depressions often appear, and on tiny seedlings, blackening of the root collar is noted with its subsequent decay, which sometimes leads to the loss of plants. Clearly visible dark spots can be observed on seeds affected by the harmful disease.

The causative agent of the ill-fated dark ascochitosis is considered Ascochyta pinodes Jones - a harmful fungus, in addition to attacking peas and other legumes, but still to a much lesser extent. This fungus is characterized by both sexual and asexual sporulation. The first is formed most often on the drying parts of growing crops in the form of small dots of dark brown, almost black, color - pseudothecia, including bags and tiny ascospores. And the asexual is characterized by the formation of pycnidia with pathogenic dark pycnospores.

To a large extent, the development of rampant dark ascochitis is favored by a temperature of sixteen to twenty degrees and a relative humidity of more than 90%.

Confluent ascochitis

This type of ascochitosis manifests itself on stalks with leaves in the form of light-colored slightly rounded specks with dark edges. Often such spots merge. And in their middle you can see little black pycnidia, the diameter of which is about 100 - 210 microns.

The causative agent of this form of ascochitosis is the harmful fungus Ascochyta pisicola Sacc. The pathogenic colorless pycnidia found in its pycnospores are both unicellular and bicellular.

How to fight

Treatment of seeds with phosphorobacterin and application of phosphorus-potassium fertilizers and molybdenum will help to reduce the susceptibility of peas to ascochitosis. Growing resistant varieties is another way to avoid an unpleasant ailment.

Also, the seeds are treated with TMTD before planting. Good results can be achieved when using "Fentiuram" - it is either dusted with seeds slightly moistened with water, or the seeds are treated with a suspension of this drug immediately before sowing. In addition to the above methods, the seeds can also be treated with a lime-sulfuric broth, Bordeaux liquid, or exposed to high temperatures.

Seed crops of peas in case of severe damage by ascochitosis during the growing season are sprayed with permitted fungicides.