Common diseases of dragon blood tree and their prevention and control methods

Common diseases of dragon blood tree: Alternaria black spot

Symptoms

The black spot disease of Alternaria officinalis mainly harms the leaves of Dracaena. The leaves of Dracaena develop irregular or nearly circular spots, with brown circles around the leaves and grayish white in the center. The diseased parts are covered with densely packed small black mold spots, which are the conidiophores and conidia of the pathogen.

The disease is more likely to occur and become more severe during the rainy season or when the air humidity is high or there is a lack of fertilizer.

Pathogen analysis

The pathogen Alternaria sp. is a type of chain spore, belonging to the class of Ascomycetes. Conidiophores are usually unbranched, have obvious spore scars, are septate, and are 14-48×6-13 (μm) in size.

Conidia are obclamped, with 3-18 septa, the transverse septa are constricted inward, and there are 0-15 mediastinum. The pathogen overwinters in the form of mycelium on diseased parts or diseased fallen leaves, and produces conidia in the following spring that are spread by wind and rain.

Alternaria black spot disease on dragon blood tree: prevention and control methods

Smoked

After closing the doors and windows at the turn of spring and summer every year, use 200g of 45% Benomyl smoke agent for fumigation overnight for every 667㎡, which can kill most of the pathogens and reduce the incidence of disease. It is recommended to use "Fu Teng" brand temperature-controlled electric sulfur evaporator, which uses electric heat to make sulfur or other bactericides enter the protected area in a vapor state and diffuse evenly to completely sterilize.

Chemical control

After the disease occurs, in addition to the above-mentioned smoke method for prevention and control, you can also spray 400-500 times diluted 40% Benomyl suspension or 1000 times diluted 50% Promethazine wettable powder, 500 times diluted 70% Mancozeb wettable powder, 500 times diluted 80% Penke wettable powder, once every 10 days or so, for 3-4 times of prevention and control.

Prevent problems before they happen

Carefully maintained. Dracaena prefers high temperature, humidity and semi-shady environment. The suitable temperature for growth is 20-25℃. The winter temperature should be higher than 5℃. The potting soil must be well drained. Direct sunlight is too strong in summer and the leaf tips will be burned. Sufficient water should be supplied during the growth period. Water should be sprayed frequently on the leaves or around the plants to increase the air humidity. Fertilize once a month to enhance disease resistance.