Pea rust is commonly observed in years with increased spring rainfall. To prevent the occurrence of this disease, it's essential to understand and apply effective control techniques, including the use of appropriate **pesticides**.
Symptoms of pea rust typically affect the leaves and stems. Infected leaves show small, round, red-brown spots on either the upper or lower surface. When these spots rupture, they release dark brown spores. As the infection progresses, raised, dark brown lesions form, covered with a black powdery substance. The stems may exhibit similar symptoms.
The pathogen responsible for pea rust is *Uromyces pisi* (Pers.) Schrot, a basidiomycete fungus. It primarily infects peas and other legumes. Summer spores and teliospores are produced on peas or related plants, while rust spores and reproductive structures can also be found on ornamental plants like those in the *Euphorbia* genus. There are multiple physiological races of the fungus that affect peas. Another related species, *Uromyces ervi* (Wallr.) Westnd., known as wild pea rust, is also a threat. This fungus infects peas and produces rust spores on the underside of leaves, petioles, stems, or pods. These spores are cup-shaped, often white or yellow, with a raised margin. They are spherical to elliptical, dense, and light yellow, measuring 16–25 × 14–21 microns. Summer spores are found on both sides of the leaves, stems, or petioles, appearing cinnamon-colored. They are spherical to elliptical, with a rough surface and yellowish-brown color, ranging from 18–33 × 18–27 microns. Teliospores are similar in appearance to summer spore clusters, dark brown, subglobose, and measure 23–38 × 15–24 microns.
The transmission of the disease occurs through spores that remain on infected plant residues during winter. When conditions are favorable, these spores germinate, produce new spores, and spread via wind to healthy plants. Upon germination, the spores form germ tubes that directly penetrate the host, leading to the formation of sexual structures and new spores. Uredospores then develop, causing secondary infections. In northern regions, the cycle involves overwintering spores, while in southern areas, the infection cycle is completed through urediospores. The development of pea rust is influenced by temperature, humidity, variety selection, and sowing time. The fungus thrives in warm and humid conditions, with optimal spore germination between 14–24°C. At temperatures of 20–25°C, summer spores multiply rapidly, making the disease more prevalent. Therefore, pea-growing areas often experience outbreaks after temperature increases, especially in years with heavy spring rain. In Yunnan, where winter and spring temperatures are relatively high, the disease begins early, even before the first planting, forming disease centers. By the second year, increased rainfall heightens the risk. Soil type and topography also play a role—low-lying, waterlogged, or compacted soils with poor drainage promote disease development. Plants with dense foliage and poor air circulation are more susceptible. Early maturing varieties, which have a shorter growth period, can avoid peak rust periods.
To effectively manage pea rust, the **Pesticide Network** offers the following practical measures:
(1) Plant at the right time to avoid pre-winter infections and reduce pathogen load, ensuring the crop avoids the rust period during late growth.
(2) Use early-maturing varieties to harvest before the disease becomes active.
(3) Implement proper spacing, ensure good drainage, and prune regularly to reduce field humidity.
(4) Avoid planting summer or early peas, which can serve as sources of infection for winter peas. Washing seeds thoroughly during winter planting can also help reduce disease incidence.
(5) At the first sign of infection, apply fungicides such as 15% triazole wettable powder diluted 1000–1500 times, 50% rust emulsifiable concentrate diluted 800 times, 50% sulfur suspension diluted 200 times, or 25% mancozeb emulsifiable concentrate diluted 3000 times, or a mixture of 25% mancozeb emulsifiable concentrate (4000 times) and 15% triazole wettable powder (2000 times). Apply every 15 days for 2–3 treatments.
In regions where resistance to these fungicides has developed, the **China Pesticide Network** recommends switching to alternatives such as 10% Supreme emulsifiable concentrate diluted 3000 times or 40% Nova emulsifiable concentrate diluted 7000–8000 times. Ensure no application is made within 7 days of harvest.
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