How to prevent aloe plant disease
With aloe disease, an ounce of prevention is worth a pound of cure.
It’s not cancer, but looks and acts like it. For a very long time, it was dubbed aloe blight because it spread from plant to plant. Blight is a common turn for the disfiguring viral, bacterial and fungal diseases. But it’s not blight, either!
Heavy rain in the southwest and California after extended drought brings the flourishing of microscopic Eriophyid mites. Among aloes it’s Aceria aloinis, a mite named for its host plants. Wherever they feed upon aloe skin, tumorlike growths occur.
Recent heavy and sustained rains have created an ideal environment for aloe blight this year. While other problems tend to attack weaker plants, mites go to healthy hydrated aloes first. During drought, when many aloes were dehydrated over the long term, these mites were not as apparent. Now that the plants are fully turgid, there’s no question aloe mites will flourish.
Growers today are still trying to control mites because they can wreck havoc among aloe collections. They are serious problems in hot houses, and even in the field aloes grown too close together. Three types of chemical insecticide are needed to keep their crops clean. This is because these mites actually airborne driven by wind until they land on the next suitable aloe to colonize it. Gardeners learned early on that aloes that touch an infected plant will often be the next victim. Those downwind outdoors from the host plant will also experience more pests.
By the time you see the galls forming, the mites have already infested the plant and those around it. Remove all afflicted aloes in ground and in pots, then throw them away to avoid further spread.
The typical approach is to surgically remove the galls themselves, but recent discoveries prove the mites are actually not present there. They’re moving on to greener pastures at the edges, so these will be the most active areas for these pests and should be removed or treated.
South African aloe growers slice off the galls with margins using a razor sharp blade. Then they wash the wound with a Clorox solution to kill any residual bugs on the adjacent leaf surfaces. The wound is then allowed to dry out and callus over two weeks time.
More unorthodox but sworn to by foreign growers involves the caustic chemical formalin. They avoid watering to dehydrate the plants, then use a small brush to paint the straight formalin onto the galls. Repeat three days later. Dehydration helps formalin soaks in and perhaps makes the whole leaf so toxic the mites that survive exit entirely. Formalin will burn all parts of the plant so this is a very precise treatment.
However, it’s widely accepted that one plant is all it takes to infect a large number of surrounding individuals. Like human cancer it can be controlled when first discovered, but once established it metastasizes over large areas, eventually killing the host. Therefore many succulent gardeners are vigilant to spot these early signs and take steps to eradicate the problem plant entirely.
This is also why it’s so important to inspect all aloes large and small coming into your garden carefully. This involves retail plants, gifts, cuttings and roots of all aloe species. Look for small galls or distorted growth on leaves, nooks and crannies. Dumpster aloes are often afflicted, so beware of any salvaged plants that have been disposed of.
New aloe gardeners have been spared much aloe mite damage due to the drought, but after this year’s heavy rain they’ll be back with a vengeance. If you’ve recently installed aloes or have a lot of established species, particularly expensive ones, look closely for these signs. If you find anything weird, get help immediately to stop the spread before it gets to the rest of your plants.
Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at www.MoPlants.com.