2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Downy mildew of peas, also called downy mildew, occurs quite often on pea plantings. To a large extent, its development is favored by cool and rather humid weather with an average daily temperature ranging from fifteen to seventeen degrees. Abundant dew and cold nights also create excellent conditions for the development of the ill-fated disease. If downy mildew attacks the peas hard enough, yield losses can be as high as 25% to 75%
A few words about the disease
Downy mildew of peas is characterized by its manifestation in two forms: local and diffuse. On pea leaves, as well as on sepals with stipules, a huge number of specks of brownish or yellowish shades begin to form. And on the lower sides of such spots, a very unpleasant bloom of grayish-purple color is formed - this is how conidial fungal sporulation looks like.
On the beans, the infected tissues gradually lose their color and discolor, and after a while they begin to darken and become dark brown.
The diffuse form of peronosporosis is characterized by dwarfism of plants in combination with a gradual change in their color. Most often, they dry out before they have time to form beans. And the leaves and tops of the stalks are so close to each other that the affected peas begin to remotely resemble the heads of cauliflower.
The early development of an ill-fated disease often leads to a significant underdevelopment of beans, leaf blades and internodes.
The causative agent of pea peronosporosis is a pathogenic lower fungus called Peronospora pisi Sydow, which actively spreads with post-harvest residues and, a little less often, with seeds. This fungus is characterized by the presence of an intercellular mycelium. In this case, pathogenic conidial sporulation, which looks like a plaque, forms on the surface of cultures attacked by peronosporosis, and the formation of oospores occurs exclusively in infected tissues. The conidiophores of this fungus are dichotomously branched and colored in brownish-purple shades. They are usually released from the stomata in an amount of 1 to 11 pieces, often forming sods. And spherical yellowish-brown oospores reach 40 to 50 microns in diameter and are endowed with folded and rather thick shells.
The primary source of infection is considered to be infected plant remains - oospores overwinter in them.
Most often, downy mildew begins to appear at the stage of budding. In this case, all aboveground organs of the pea are affected. Plants attacked by the ill-fated misfortune begin to lag behind in growth and form rather puny grains. They often differ from healthy crops and dwarf species.
This ailment is especially widespread in areas characterized by sufficient moisture.
How to fight
Among the main protective measures against pea downy mildew, early sowing dates, adherence to the rules of crop rotation, timely weeding, elimination of post-harvest residues and seed dressing can be noted. In this case, only healthy seeds should be taken, and the areas should be thoroughly blown by the wind. It is also advisable to try to avoid shaded areas. These events are good because they are completely harmless from the ecological point of view.
The selection of varieties tolerant to downy mildew will also do a good job. And although there are no varieties completely resistant to this scourge, there are varieties that are affected to a much lesser extent. These are such varieties as Yubileiny 15/12 (vegetable peas), as well as Pauli, Orlik and Victoria Heine (grain peas).
Before sowing, it is useful to pickle seeds with Fentiuram or TMTD. And as soon as the first signs of peronosporosis are noticed on the plants, they are sprayed with one percent Bordeaux liquid or a suspension of "Tsineba" (0.5 - 0.75).
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