Anyone who has ventured into the cultivation of aloes will know that the plants are attacked by a variety of insects, mites, and fungi. The important role aloes play in a successful water-wise succulent garden or succulent collection makes it imperative to take the treatment of these pests seriously.
In this article, we would like to give information on the most serious aloe pests and propose effective ways of treatment of the problems.
One must, of course, remember that those we call pests are part of nature, we concentrate large numbers of plants (and aloes) in a small area, creating a very friendly environment for the predators, therefore we have no choice but to take over and control. It is also worthwhile to remember that we must be as eco-friendly as possible. Always be aware of your own safety as well as that of visitors, which includes friends like birds and bees.
We would welcome any input and advice from our readers. If you have photos of pests, please send those to us.
The article is divided into three sections, the first part deals with the various pests found on aloes as well as possible treatments, the second part gives a proposed treatment programme. Part three gives a list of recommended pesticides.
Part one: The Enemy
To control insects (including snout beetles, scale, and others) we currently use a systemic insecticide, marketed under the names Bandit or Aphicide Plus (active ingredient Imadacloprid), very successfully. Every Spring and Autumn every aloe in the garden is treated with 2 to 5 litre (depending on the size of the plant) mixture of Imadacloprid and water, this is poured at the base of the plant. The systemic pesticide is absorbed by the roots and is effective for months. One could of course use any of the insecticides proposed below for treatment. In many cases an eco-friendly solution would be the use of a soapy mixture.
This is a photo of the larger snout beetle (photo by Cornelia Hanekom). This snoutbeetle can be up to 25mm long and normally found on the underside of leaves. It is mostly found on stemless aloes and as in the case of the smaller snoutbeetle the larvae eventually destroy the plant stem.
These are the tell-tale markings of the smaller snout beetle, if you look carefully you will detect two dead beetles after treatment with Imadacloprid. They are much smaller than their bigger cousins, up to about 8mm long. Both lay their eggs in the stem of the aloe, the larvae eat away at the stem, leading to the whole plant falling over and dying. Other insecticides can be used as well. The powder insecticide with active ingredient Carbaryl works well if the problem is spotted early enough.
Scale on aloes is caused by an insect which protects itself with a hard and tough “shell”. It makes the plant unattractive and eventually kills it. The problem here is that the shell protects the insect from treatment. As mentioned above, a systemic insecticide like Imadacloprid works well in this case as well. Taken up by the roots the insects on the leaves are killed by the treatment. Any other insecticide can also be used, but is advisable to add some dishwashing liquid, this breaks down the protective shell. If the problem is spotted early, the insects can be removed with a toothbrush and dishwashing liquid.
Woolly aphids and aphids
Woolly aphids as well as common aphids usually occur in the crown of the aloe. They can destroy the crown of the aloe as well as the whole plant. The crown rot in this photo was probably caused by aphids (photo by Daan Labuschagne).
Aphids can be treated with a powdery insecticide containing Carbaryl. Again, this should never be a problem if plants are regularly treated with a systemic insecticide.
Sometimes small insects are spotted, moving very quickly on the surface of the leaves. If left without treatment the leaf starts showing the effects of the insects sucking on it, small white spots give it an unhealthy appearance. As in the case of other insects, the systemic pesticide Imadacloprid should eliminate the problem.The pest can also be treated by using a pesticide containing Carbaryl.
Flower damaging insects
A problem which occurs only in summer (pests are, of course, more active during the warmer months) is that the flower buds suddenly abort and fall off. This is caused by a small fly laying its eggs in the developing bud. One can treat the problem by spraying the developing inflorescence with a systemic pesticide. The plant in the picture is the rare Aloe porphyrostachys from Arabia, which flowers in summer like many other Arabian aloes
Aloe Mites/Aloe cancer
Aloe mite is one of the most serious problems for anyone growing aloes. The mites are microscopically small, causing aloe cancer. In these two photos the initial stage as well as the advanced stage of aloe cancer is shown. Mites are relatives of ticks and spiders (please remember that spiders are friends and not enemies). The cancer usually starts on the edges of leaves or on the flower buds.
Unfortunately most insecticides will not control the mites (they are not insects). Our strategy at the moment is to cut away all cancerous gowth, treating the wound with Formalin (available at chemists). Formalin must be handled with great care, it should not be inhaled or get in contact with the skin. Less drastic measures will be a paste of Carbaryl on the wound. If one experience problems with the mite it is a good idea to spray from time to time with a mitecide like Abamectin, alternating with other products registered for mites.
Fungi or Rust
A number of fungi attack aloes. The most common fungus is one which causes yellow circular areas with black dots from where spores are released. Infected leaves should be removed and put in the dustbin. Plants should be treated with a suitable fungicide as well.
Another rust problem we have experienced over the last year or two, is aloe leaves turning black (or brown), this is also caused by a fungus. It seems as if the problem is most common during wet periods.
A fungicide should be used when any fungus is spotted. We have found Imidazole very effective, one could alternate with other products.
Snails can be a problem when leaf surfaces are eaten. This can be treated with a product registered for snails and slugs.
Part two: Treatment
Insects: Soaking of soil with Imidacloprid once in spring and once in late summer should effectively control insects like snout beetles, scale and others. Additional treatment for specific pests can be handled as discussed above. Fungi: Spray with one of the recommended fungicides like Imidazole when a rust problem is spotted. Spray with Imidazole if the leaves turn black.
Treatment of aloe cancer: Whenever aloe cancer is spotted, immediate action should be taken. Please see the notes on aloe cancer above. As a preventative, spray bi-monthly with a product which is registered for mites (as well as insects if possible), alternating with a different product the next time (mites and insects might become resistant to certain products).
Part three: List of Recommended Products
In this list we give the active ingredient with some of the commercial products containing the ingredient. Product names change all the time, which can be a bit confusing. We do have some of these products available in our shop, please come and have a look or phone Rudolph at 066-273-2938 for information.
Insecticides Mercaptothion (Malasol or Malathion) Imidacloprid (Bandit, Aphicide Plus or Kohinor) Carbaryl (Karba 50DP or Karbadust) (effective for mites as well)
Dimethoate (Aphicide) (effective for mites as well)
Mitecides Abamectin (Agromectin or Biomectin)
Amitraz (Parsec) (effective for insects as well) Bifenthrin (Seizer) (effective for insects as well)
Fungicides Mancozeb (Metazeb or Dithane) Copper Oxychloride (Virikop) Imidazole (Chronos)
Remember that it is always advisable to add a wetter/sticker (you may use dishwashing liquid) when spraying. Take care to read the label for each product carefully.
Copy right: Gariep Plants