Diseases of Succulents, Cactus & Desert Roses

Adeniums, if grown well, are remarkably free of problems. Many of the commonest problems can be prevented by proper culture in the first place. Spider mites and mealybugs are the worst problems but are readily treated with normal remedies. Be careful with pesticide use, though, since desert rose is sensitive to many sprays, especially those containing oils. Inspect plants after any cold weather for damage to branches, since this renders them more prone to subsequent rot that can then spread to healthy parts of the plant. Any cold damaged branches (look for burnt leaves and a loss of turgor) should be removed. The commonest cause of Disease problems are due to over watering. Pest problems tend to be concentrated on soft new growth and early in the growing season one needs to keep an eye out for pest build up.  

Fungal leaf Spotting Diseases  

These are occasional problems, more so during extended periods of wet weather. Cover your plants so that the leaves are allowed to dry out, and if possible, water directly in the soil. 

Caudex Rot - A Death Sentence

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Cactus Diseases
Varieties of Cactus

Cactus Diseases
Varieties of Cactus
Desert Roses

Cactus Diseases
Varieties of Cactus

Mealy Bugs: 

These are very common pests, usually concentrating on the soft new growth. They distort new growth and flowers. The leaf distortion is similar to boron deficiency and since the mealy bug causing this may be extremely small, it is often difficult to distinguish between the two. The mealy bugs, however, usually cause a reddish discoloration where the stylets have sucked the juices. This can be seen even on the colored flowers as deeper colored spots. 

Once established, it is difficult to totally clear off this pest. They are very resistant to most pesticides. Prune as many affected branches as you can and dispose of them without contacting with any other plants. Then brush on a mixture of 50% isopropyl alcohol to kill the rest. Make sure you get to the dormant egg cases as well. There are formulations such as Imidacloprid that may work as well. 

 One sign of mealy bug presence is the presence of lots of ants. Follow their trails and they may lead you some pest, usually mealy bugs or aphids, both of which secrete sugar. Follow the trail backwards and try to find the nest and destroy it- mealy bug numbers decrease rapidly if ants are controlled. 

Root Mealy Bugs 

These are often seen on neglected or stressed plants. Again, the presence of ants going into the pots will often alert one about their presence. Check for them when repotting and in case of plants that seem to be doing badly for no obvious reason. 

Examine the roots, paying close attention to any white cotton like threads. Use a magnifying glass if you need to, which may reveal slow moving, flat white insects about 2mm long.  

Adeniums tolerate bare rooting and washing of the roots. For more widespread problems, a granular insecticide like Thimet or Marathon ( active ingredient: Imidocloprid) will usually do the trick. 

Spider Mites: 

Another important pest is the spider mite. Usually a problem during the drier winter months, it first starts on the susceptible Adenium species and hybrids, such as A. swazicum and A. bohemianum. If left unchecked it will then spill over onto the other Adeniums. 

Examine the leaves for flecking, particularly the underside of the leaf, which will show a web formation and slow moving reddish yellow spider mites. 

Part of the solution is to keep the susceptible types separate so that the problem can be identified as soon as possible and spraying started. The first change is loss of the usual healthy look and luster of the leaves. Look out for typical flecking and discoloration of the older leaves. Rotate miticides, using Metasystox, Kelthane, Mavrik, Vertimec etc., one after another. Removing the most affected lower leaves with heavy mite populations is a good idea but often the best solution, especially late in winter, is to prune all the green growth off the plants and wait for healthy fresh growth in spring. 


Aphids are small, soft-bodied, slow-moving insects that suck fluids from plants. Aphids come in many colors, ranging from green to brown to black, and they may have wings. They attack a wide range of plant species causing stunting, deformed leaves and buds. They can transmit harmful plant viruses with their piercing/sucking mouthparts. Aphids, generally, are merely a nuisance, since it takes many of them to cause serious plant damage. However aphids do produce a sweet substance called honeydew (coveted by ants) which can lead to an unattractive black surface growth called sooty mold. 

Aphids can increase quickly in numbers and each female can produce up to 250 live nymphs in the course of a month without mating. Aphids often appear when the environment changes - spring & fall. They're often massed at the tips of branches feeding on succulent tissue. Aphids are attracted to the color yellow and will often hitchhike on yellow clothing. 

Use a water spray or soap solution to keep it clean of pests. If that does not work, try using Sevin or Marathon. 

Keep weeds to an absolute minimum, especially around desirable plants. Lady bugs and lacewings will feed on aphids in the garden. 

Soft Scale on Adeniums 

Check the underside of the lower leaves, where most pests tend to concentrate. They do not spread rampantly on Adeniums, and are easily controlled by pruning off affected branches and treating with a good insecticide. 

Lapidopterous Larvae (horn worm): 

Watch for an infestation, especially in spring when there are a lot of new shoots. At other times it is just an occasional worm, best picked by hand. A good spray of any decent insecticide when caterpillars are first seen will prevent large scale build up. Try and get them early as big worms can eat a lot of the soft shoot and will eat most of a newly grafted top. 

Stink Bugs: 

These usually show up at the end of the rainy season and land on the Adeniums en masse.  
They create a lot of problems by sucking the juices from seed pods, killing the young ones and forcing the larger ones to open prematurely. They lay eggs on the open pods and feed off the seeds and other organic debris. The tiny nymphs get carried around on the pappus and may infect other plants. Even if the pods hold and seeds ripen, germination is affected and one can see seedlings with kinks and other damage where the sucking stylus has pierced the embryo. Fortunately, they are easy to control. In small numbers, simply catch them by hand and crush them. A good organophosphate or pyrethroid insecticide will kill them. Scrupulous cleaning measures and ensuring that all aborted seed pods are picked and disposed off will help. Prevention is by using a mesh around the seed bearing plants. 


Anthracnose is the result of a plant infection, caused by a fungus, and may cause severe defoliation. Sunken patches may appear on on stems, fruit, leaves, or twigs. They may look grayish brown, watery, or have pinkish-tan spore masses that appear slime-like.  

Try not to over water. If your climate is naturally rainy, grow resistant varieties. In the vegetable garden, stake and trellis plants to provide good air circulation so that plants may dry. Increase sunlight to plants by trimming limbs. Prune, remove, or destroy infected plants and remove all leaf debris. Select a fungicide that is labeled for anthracnose. 

Adenium Leaf Diseases 

Continuously wet foliage will eventually start turning brown and rotting. White fungal hyphae can be seen after some time and the mass of leaves will stick together. The rot soon spreads down to the soft stems and can be seen as a dark discoloration externally and when cut. The solution is to prevent wet foliage in the first place. If this is inevitable and plastic cover cannot be provided, spray foliage with a general contact fungicide like Captan at 3gms per litre water on a regular basis. The aim is to cover the foliage with a protective layer of fungicide. If some rotting is seen, pick off the affected leaves and cut back any rotting stems. Always remove any dry leaves or flowers at the beginning of the rainy period and keep plants totally free of any dead material. 

Flower Rot: 

If your Adenium are too closely spaced, the flowers will point upwards and fill with water, which can cause it to decay due to stagnant water inside. The decay may pass onto the pedicel and moves into the stem, which may decay and collapse. The infected portion remains mushy. It is best to cut off the stem as soon as you see signs of stem rot.  

Water early in the morning, so that the flowers can dry out by nightfall.  

Stem Diseases 

Apart from the stem rotting due to downward movement of leaf rotting pathogens, often the stem will start to decay away from the leaves. This decay will usually be dry but may also be wet. Blocking of the vascular tissue leads to rapid yellowing of the leaves above the rotten portion- usually it is this yellowing that is seen first. 

Dry stem rot indicates that the decay has stopped progressing. The dead stem portion has formed a natural abscission zone and can be snapped or cut off, leaving a clean white ended stub which will give branches soon.  

Old dry rot at the junction of several branches needs to be cleaned up for aesthetic as well as sanitary reasons: such areas will often hide mealy bugs or their egg cases. Gently remove the dead stubs, leaving clean, healthy white tissue. 

Moist stem rot is more dangerous. You can help to dry the stem by pulling off the thick epidermis. Either that or cut the stem back to a healthy white zone to remove the rotten portions. 

Caudex Rot: 

This affects the main stem or caudex and leads to all the leaves suddenly drooping and turning yellow. The leaves tend to stay on the stem, but yellow from the midrib outwards. 

Almost the entire caudex is discolored and soft while most of the roots have rotted away.  
This rot is often fatal, though larger plants will often heal themselves and carry on with a hollow trunk after the rotten core has decayed off. If this is the case, simply scrape off the infected portion. 

If the rot has not healed, and is deep into the caudex, you may consider drying the entire plant, removing the rotting area with a sharp, sterilized blade, and allowing it to dry for a week or so. Pot the plant, making sure the infected portion is above the soil lever, provide minimal water, and hope for the best. 

Root Rot 

This rot starts below soil level. If it affects the main tap root it will manifest itself with the same symptoms as caudex rot but often only a side root is affected and it is seen only when the plant is being repotted or bare rooted for export. 

Massive root rot will be seen immediately as yellowing of most or all the leaves followed by leaf shedding. If the main root of small plants is affected it will usually kill them. Big plants will often loose a large tuberous side root without any problem. Remove any infected roots, allow to scar for a day or two, and repot in a fresh soil mixture. 

Seedling Damp Off: 

This is primarily a problem of very young seedlings. Seedlings will rot and shrink just above ground level; the tops remain green and topples over. This is typical Rhizoctonia damping off. Careful watering during the early stages will ensure healthy, vigorous seedlings with hard, disease resistant roots and caudexes. 

Viral Problems: 
Viral problems may cause patterned mottling on leaves, color break on flowers and split or deformed flowers. It normally occurs because poor sanitary measures were taken during grafting. It does not cause any fatal problems, but reduces vigor and flowering. This is an area that is currently being researched. 

Caudex Sunburn: Adeniums that have been pruned or raised from the soil need to remain in the shade for a couple of days to avoid sunburn. Some addeniums may be sensitive to full sun, which can sunburn the leaves. Move into a more shaded environment. 

Fluid Exudation: The plants take up water but are unable to release it by transpiration, literally causing the vessels to burst. It's a minor problem, but stains the leaves. 

Phytotoxicity: Leaf burn due to use of insecticide in too high a concentration in full sun.  

Cactus, Succulents & Desert Roses