Control Methods for Leaf Spot Disease in Balloon Flower Cultivation

Balloon flower (Platycodon grandiflorus) is a perennial herbaceous medicinal plant, with its roots used as medicine. The control methods for leaf spot disease in balloon flower are as follows:

1. Symptom identification: This type of disease mainly damages the leaves of balloon flower. (1) When infected by the septoria leaf spot pathogen, white circular or nearly circular lesions appear on both sides of the leaves, with a diameter of 2—5 mm, appearing grayish-white. In the later stage, the expansion of the lesions is restricted by the leaf veins, becoming polygonal in shape, and numerous small black spots develop on the lesions. When there are many lesions, they merge with each other, causing the leaves to wither and die. (2) When infected by the alternaria leaf spot pathogen, the leaf lesions are relatively large and circular. With a diameter of 5—10 mm, brown in color, with concentric rings, and numerous small black spots developing on them. (3) When infected by the anthracnose pathogen, discolored spots appear on the leaf surface in the early stage of the disease, gradually expanding and spreading to the stems and branches, with the epidermis becoming rough and dark brown, and in the later stage the lesions shrink and become depressed. Under rainy and high-temperature conditions, the lesions appear water-soaked; in the later stage, the stems and leaves of the plant wither.

2. Disease occurrence pattern: During the growing period of balloon flower, the lesions produce large numbers of new conidia that spread through wind and rain, continuously causing multiple re-infections, leading to disease epidemics in the field. Damage is generally severe in July—August. High temperature, rainy and heavy dew or fog weather conditions, extensive management, and poor growth are conducive to disease occurrence and epidemics. If control is inadequate, it often leads to massive leaf withering.

3. Control techniques: (1) Improve plant disease resistance, strengthen field management, maintain reasonable planting density, and pay attention to timely drainage after rain to reduce humidity. (2) Chemical control: Before disease onset, spray 1:1:100 Bordeaux mixture or 600 times diluted Keshade 2000 for disease prevention; after disease onset, the following chemicals can be selected for spraying according to the type of disease: 80% Daconil 600 times dilution, 50% mancozeb 500 times dilution, 50% thiophanate-methyl 600 times dilution, 50% carbendazim 600 times dilution. If anthracnose occurs severely, 25% prochloraz 800 times dilution can be used for spraying. When spraying, pay attention to being thorough and meticulous, and spray 2—3 times consecutively depending on disease progression and weather conditions, with an interval of 7—15 days between sprays.