How to prevent and control pests and diseases on desert rose? Ventilation and dryness are the key to prevention
The desert rose, also called Adenium obesum, is a succulent plant of the genus Adenium in the family Apocynaceae, and it naturally loves high temperatures, dry conditions and plenty of sunlight. It rarely suffers from pests and diseases, but once it is affected, the consequences range from slow growth and a long delay in flowering to the death of the whole plant, so it is well worth learning the prevention and control methods in advance. Practice has shown that keeping the environment ventilated and the air dry is the key to preventing pests and diseases on the desert rose.
Two major pests: scale insects and leaf-rolling caterpillars
Scale insects are the main pest of the desert rose, attacking leaves and branches, causing yellowing leaves, withered shoot tips and declining vigour, and they also easily trigger sooty mould. For prevention, turn the soil and repot regularly, fertilise and water sensibly to improve the plant's resistance, and prune promptly. For treatment, while the nymphs are not yet fully formed, use 40% omethoate at 1000 times dilution, spraying once every 7 days for 2-3 consecutive sprays; in severe infestations, switch to a 1:1 mixture of 40% omethoate emulsifiable concentrate and 80% dichlorvos emulsifiable concentrate and spray 2-3 times.
The larvae of the leaf-rolling caterpillar feed on the leaf mesophyll, leaving behind the veins and upper epidermis so that the leaf develops a greyish-brown membranous patch; the adults are mostly brown or yellowish-brown and do great damage to the leaves. Prevention focuses on ventilation and avoiding excessive humidity, draining well during the rainy season, and moving the plant to a ventilated spot indoors when necessary. When larvae are found, promptly spray 60% double-effect phosphorus emulsifiable concentrate at 1500 times dilution, or 50% phoxim emulsifiable concentrate at 1000 times dilution.
Two major diseases: soft rot and leaf spot
In the early stages of soft rot, the outer leaves wilt and droop, then recover on cloudy days; afterwards large areas of the leaves dry up and pale greyish-yellow water-soaked lesions appear at the base of the stem. The pathogen overwinters in soil and compost, enters through wounds carried by wind and rain, and can infect and multiply from spring to autumn. Prevention first requires healthy, clean soil; in the early stages of the disease, spray dexon technical powder at 1000 times dilution, or 38% oxadixyl-cymoxanil-kresoxim-methyl at 800 times dilution.
Leaf spot shows up as dark brown spots on the leaves first, which then expand into irregular patches with slightly raised edges, and on both sides of the leaf there are small black dots arranged irregularly. The pathogen overwinters in diseased plant debris or on the soil surface, spreads by wind and rain the following year, and is severe in the high temperatures of summer; it is closely linked to overly dense planting, poor ventilation and excessive humidity. The key points of control are good ventilation and humidity that is not too high, since dry air suits its growth better; when the disease occurs, spray 80% mancozeb at 400-600 times dilution, or 50% captan at 500 times dilution.
Good care means fewer pests and diseases
The desert rose prefers a temperature of 25-30°C. Container plants at home should be placed in a spot with plenty of sun or bright indirect light, and because it tolerates cold poorly in winter it should be moved indoors in good time. When watering, err on the side of dryness rather than moisture and water only once the potting soil has dried out completely; standing water and dampness are normally taboo, otherwise pests are easily attracted and the plant withers. Apply plenty of fertiliser during the summer growing season, choosing a slow-release fertiliser or well-rotted compost, and stop fertilising after it goes dormant in autumn. After flowering is the best time to prune, promptly dealing with leggy shoots to keep the plant's shape attractive and to reduce places where pests and diseases can hide. In addition, leaf spot can also be controlled with thiophanate, and scale insects and leaf-rolling caterpillars can be sprayed with fenitrothion. Finally, a reminder: the whole desert rose plant is toxic, and accidentally eating the stems, leaves or sap can cause a racing heartbeat, irregular heart rhythm and other problems, so households with young children and pets must place it properly.