What is rust?
Rust is a type of plant disease caused by the parasitism of rust fungi. It harms the leaves, stems and fruits of plants. Rust fungi generally only cause local infection. The affected parts may produce small blisters or blister-like, cup-shaped, and hair-like objects of different colors due to the accumulation of spores. Some may also cause tumors, rough bark, clumps, and bent branches on branches, or cause leaf fall, scorched tips, and poor growth. In severe cases, the spores are densely piled into pieces, and the plants quickly die due to the evaporation of a large amount of water in the body.
Pathogens of rust
Rust is a disease of thousands of important economic plants and weeds caused by more than 4,000 species of fungi. Different plants have different pathogens. For example, the rust pathogens of flowers include rose polycystic rust, rose short-pointed polycystic rust, rose polycystic rust, mountain polycystic rust, thorny rose polycystic rust, chrysanthemum rust, and daylily rust.
Symptoms and characteristics of rust disease
The lesions mainly appear on leaves, leaf sheaths or stems, and yellow to rust-colored summer spores and black winter spores are generated at the diseased parts. The lawn infected by rust fungi looks yellow from a distance. Different rusts can be distinguished according to the shape, color, size and attachment characteristics of their summer spores and winter spores. The summer spores of stem rust grow on stems, leaf sheaths and leaves.
The summer spores are large, scattered, dark brown, oblong to rectangular, with strong penetration ability. Summer spores can be formed on both sides of the leaves, and the back is larger. The epidermis at the lesion site is torn in large pieces and rolled to both sides in the shape of a window.
The summer spores of leaf rust grow on leaves, medium-sized, round, scattered, orange-red, and the leaf epidermis is cracked. The summer spores of stripe rust mainly grow on leaves, but also on stems and leaf sheaths. The summer spores are small, bright yellow, arranged in rows, dotted, and the leaf epidermis is not obviously cracked. Crown rust is similar to leaf rust.
What is the law of rust transmission?
The summer spores of some rust fungi can be spread over long distances by air currents, which plays an important role in the rust cycle. Usually, rust fungi overwinter as winter spores. The source of the first infection is basidiospores or summer spores, and then the rust spores or summer spores continue to cause damage during the growth of crops by air currents. In subtropical and tropical areas, many rust fungi do not produce winter spores, but overwinter with summer spores or directly on self-sprouting seedlings or winter crops. In some areas, the host transfer does not play a role in the disease cycle.
For example, the climate during the leaf development period of Amur barberry in Northeast China is not suitable for the germination of winter spores of wheat stem rust fungi. Although summer spores cannot overwinter locally, they can be blown from the southeast coastal areas from south to north by air currents over long distances to become the source of the first infection. In addition, the main problem in the infection cycle of some rust fungi is not overwintering but oversummering. For example, wheat stripe rust fungi are not resistant to high temperatures and must oversummer on self-growing wheat seedlings and wheat plants in different growth periods in high-cold areas.
Harmfulness of rust
Rust is widely distributed and highly harmful, and is often found in cereal crops, legumes, and pears. Rusts of many crops are worldwide, and some are characterized by regional epidemics, with yield losses often measured in tens of thousands of tons. Therefore, it is necessary to strengthen the prevention and control of rust.
What are the prevention and control methods for rust?
1. Plant disease-resistant varieties: Since there are obvious differences in resistance to rust between grass species and varieties, disease-resistant grass species and varieties should be selected first when building lawns, and mixed planting of different grass species or varieties is recommended, such as mixed sowing of meadow bluegrass, perennial ryegrass and tall fescue in a ratio of 7:2:1, or mixed sowing of meadow bluegrass with different varieties.
2. Scientific maintenance and management: Increase the application of phosphorus and potassium fertilizers, and apply nitrogen fertilizers in appropriate amounts. Rationally irrigate, reduce field humidity, mow the grass in time after the disease occurs, and reduce the number of fungal sources.
3. Chemical control: Triazole fungicides are an ideal class of agents with good control effects on rust, long-lasting effects, and both protective and therapeutic effects. Common varieties include triadimefon, hydroxyadimefon, terproazole, and licoxone. When sowing, 0.002% to 0.003% of pure triazole drugs can be used for seed mixing per 100 kg of seeds, or sprayed during the growth period.
Generally, in the early stage of the disease (with the focus on blocking the center of the disease), 25% triadimefon wettable powder 1000 to 2000 times liquid, 12.5% terproazole wettable powder 1500 times liquid, etc. are often used for spraying with water. Usually after pruning, 25% triadimefon emulsion 1500 times spray, and spray again after an interval of 20 days, the control rate can reach more than 85%.
