Identification and Control Methods for Common Pests and Diseases of Azaleas

Azaleas are mainly grown for ornamental purposes, and they are highly vigorous and easy to plant. Azaleas have a habit of four loves and five fears: they love partial shade, love coolness, love moisture, and love acidic soil; they fear blazing sun, fear intense heat, fear heavy fertilizer, fear coal smoke, and fear poor air circulation. Here is an introduction to common pests and diseases and their control methods;

(1) Azalea diseases. During the growth process of azaleas, the diseases manifested on the leaves fall into two types: physiological diseases and pathological diseases.

(1) Physiological diseases. During the growth process of azaleas, if the trace element iron is deficient, iron-deficiency chlorosis often occurs. In the early stage of the disease, the mesophyll of new leaves fades from green to yellow, while the veins remain green, thus forming leaves with a green net-like pattern. As the condition worsens, the entire leaf turns yellow-white, the leaf tips and leaf margins become scorched, and finally leaf drop results. To control azalea chlorosis, iron can be supplemented regularly, that is, spraying 0.2%-0.3% ferrous sulfate on the leaves in the early stage of the disease, mixed with a small amount of sticker, once every 25 days, with quite good results.

(2) Pathological diseases. Because of invasion by pathogens and the like, azalea leaves often develop diseases such as brown spot, sooty mold, and gray mold. In practice, it has been found that brown spot and sooty mold have a relatively high incidence, accounting for more than 75% of pathological diseases, and the closer to urban areas, the higher the proportion.

Brown spot: The lesions on the leaves are reddish-brown or brown, later gradually turning yellow-white or gray-white, with dark brown leaf margins. The lesion shape is often round or polygonal, and when moist, the surface has gray-black mold spots. The control method is to strengthen cultivation management, cut off diseased and dead leaves, and promptly spray 50% thiophanate-methyl wettable powder at 800 times dilution, once every 15 days, until the end of August.

Sooty mold: There is a layer of soot-like material on the leaves. When the outbreak is severe, the entire plant is contaminated, the branches and leaves wither, and the plant dies. In control, it is necessary to focus on eliminating the insect vectors such as scale insects and aphids, and maintain ventilation and light transmission. Spraying 25% carbendazim wettable powder at 1000 times dilution gives relatively good results.

(2) Azalea pests. The most common pests of azaleas are red spiders and lace bugs.

(1) Red spider damage: In the high-temperature season from June to August, red spider damage is severe, often causing azalea leaves to turn yellow and fall off. The control method is to spray with 1/1000 dicofol, once a week for 4 consecutive times.

(2) Lace bug damage: From May to July each year, azaleas often suffer from lace bug damage, and it spreads faster when the climate is dry. The commonly used control method is to spray with 1/1500 dimethoate or dichlorvos.