How to prevent and control common pests and diseases of clivia?

I. Leaf blight

Symptoms: The disease occurs on the upper surface of the leaves of variegated clivia, starting first at the leaf tip and leaf margin. In the early stage, it appears as small brown spots, which later expand into semicircular dry patches. The lesions are shrunken, grayish-brown in the center, with a water-soaked dark brown ring at the margin, on which small dark brown dots (pseudothecia) are arranged in concentric circles. The pathogen belongs to the genus Leptosphaeria. Disease characteristics: It occurs throughout the year, and is especially common in greenhouse cultivation, but the severity of the disease is milder than that of anthracnose.

Control methods

① Strengthen greenhouse management, provide timely ventilation to control greenhouse humidity, apply fully decomposed fertilizer, use nitrogen fertilizer rationally, and increase the application of phosphorus and potassium fertilizers.

② Cultivate disease-free seedlings.

③ Remove diseased plant debris promptly.

④ At the early stage of the disease, begin spraying 64% oxadixyl-mancozeb wettable powder at 500 times dilution; 50% mixed sulfur suspension, or thiophanate-methyl wettable powder at 500 times dilution, or Bordeaux mixture at 1:1:200. Choose one of these and apply once every 10-15 days, spraying 2-3 times in succession. The control effect is over 90%.

II. Brown spot

Symptoms: The disease occurs on the leaves of variegated clivia. In the early stage, it appears as dark green water-soaked small spots, which later expand into round or irregular lesions. The center of the lesion is sunken, reddish-brown to grayish-brown, and firmer in texture than anthracnose lesions. The lesions can penetrate both sides of the leaf but do not perforate it. On the upper surface of the leaf, reddish-brown small dots are produced, which are its pycnidia. Occasionally, anthracnose pathogens are found mixed on diseased leaves.

Control methods:

① High temperature and high humidity, and dripping from the greenhouse roof, are conditions that trigger the disease. Therefore, during the high-temperature seasons of summer and autumn, attention should be paid to shading, ventilation, cooling, and dehumidification, and disease prevention measures should be taken early.

② At the early stage of the disease, you can use 40% metalaxyl-copper wettable powder at 600-700 times dilution; 64% oxadixyl-mancozeb wettable powder at 500 times dilution; 36% thiophanate-methyl suspension at 400-500 times dilution. Choose one of these and apply once about every 10 days, with 1-2 consecutive applications.

III. Anthracnose

Symptoms: The disease occurs on the leaves of variegated clivia. The lesions are round or nearly round, grayish-white and sunken in the center, with dark brown margins, penetrating both sides of the leaf, appearing film-like, and even perforating it. On the lesions on both sides of the leaf, there are occasionally small black dots, which are the acervuli of the pathogen, mostly pink sticky spore masses, especially obvious under humid conditions. The pathogen belongs to the genus Colletotrichum, hence the name anthracnose.

Control methods

① First, in cultivation, select and breed excellent varieties with strong disease resistance, and avoid cultivating varieties with poor leaf quality and high purity.

② Use disease-free nutrient soil, or disinfect the soil, to reduce the primary infection source; increase the application of phosphorus and potassium fertilizers to improve the disease resistance of the plants.

③ Strengthen greenhouse management and carry out ecological control, that is, provide ventilation and dehumidification to keep the greenhouse humidity at around 60%, and reduce water spraying on the leaves.