Why Autumn Yardlong Beans Are Prone to Rust Disease and the Main Control Methods

Yardlong beans, also known as long-pod beans, band beans, or ribbon beans, are nutritious and high in protein, rich in crude fiber, carbohydrates, vitamins, and elements such as iron, phosphorus, and calcium, with strong adaptability and a wide cultivation range, making them one of the main vegetables in summer and autumn in China. China is a secondary center of origin for yardlong beans, with a long cultivation history and rich variety resources, possessing nearly a thousand germplasm accessions, and great progress has also been made in breeding. Due to the continuous promotion of excellent new varieties and the widespread application of techniques such as seedling transplanting, plastic film mulching, and greenhouse cultivation, the quality and yield of yardlong beans have been greatly improved. When planting yardlong beans in autumn, improper management can easily lead to the occurrence of yardlong bean rust disease, so why are autumn yardlong beans prone to rust disease? What are the main control methods?

I. Causes of Autumn Yardlong Bean Rust Disease

Autumn-planted yardlong beans grow in an environment with high temperatures and relatively high rainfall, and in addition, the amount of inoculum (urediniospores) left in the field from spring-planted yardlong beans is large. Therefore, autumn-planted yardlong beans are prone to rust disease, and integrated control should be carried out early.

The pathogen belongs to the subdivision Basidiomycotina and the genus Uromyces. The source of infection is the diseased residues of spring-planted yardlong beans or the uredinial pustules left in the field; the urediniospores germinate to produce germ tubes, which invade the host through stomata. At 18°C to 25°C, when air humidity is high or fog and dew are heavy, and when there are water droplets or a water film on the host surface, the urediniospores are most likely to germinate and invade the host; the diseased plants then spread the urediniospores through airflow, insects, and humans and livestock among plants in the field, causing frequent reinfection, and the resulting telial pustules become the primary infection source for leguminous crops planted the following spring.

II. Symptoms of Autumn Yardlong Bean Rust Disease

Autumn yardlong beans can be infected by the pathogen throughout the entire growth period, but resistance weakens and susceptibility increases from the beginning of flowering to the fruiting stage. The disease mainly attacks the leaves; in the early stage of the disease, chlorotic yellow-white spots appear on the leaves, and the spots gradually increase until they densely cover the entire leaf. The plants become stunted, with few and small pods, the growth period is shortened, and eventually the plants wither and die.

III. Control Methods for Autumn Yardlong Bean Rust Disease

The control methods are integrated control measures based on strengthening the management of soil, seed, fertilizer, and water, supplemented by timely spraying for control.

1. Thoroughly remove the diseased residues of the previous crop, deep-plow the land, expose it to the sun for 2-3 days, and spray the entire garden with a disinfectant to effectively reduce the sources of pathogen infection.

2. Select disease-free varieties with good disease resistance, and before sowing, treat the seeds with a new high-fat film, which can repel underground pests and diseases, isolate virus infection, and increase the seed germination rate.

3. Apply fertilizer, water, loosen the soil, and weed in a timely manner according to the growth needs of yardlong beans. Apply sufficient base fertilizer and increase the application of phosphorus and potassium fertilizers, etc., so as to enhance root nodule activity, make the plants grow robustly, and strengthen disease resistance. Spray Caiguo Zhuangdiling before flowering, at the young pod stage, and at the pod expansion stage of yardlong beans to improve the water and fertilizer uptake capacity of yardlong beans and promote high and excellent yields.

4. Chemical control: spray pesticides in a timely manner to control yardlong bean rust disease. In the early stage of the disease, spray targeted pesticides plus a new high-fat film to form a protective film, greatly improving the utilization rate of the effective ingredients of the pesticide.