What to Do When Aloe Vera Develops Black Spots? A Detailed Guide to Prevention and Treatment
Aloe is a perennial evergreen herbaceous plant of the genus Aloe in the family Liliaceae (Asphodelaceae), native to the tropical arid regions of Africa and now distributed almost throughout the world. It combines edible, medicinal, cosmetic and ornamental uses, and its exudates have been widely applied in medicine and daily chemicals. In Chinese folk tradition it has long been used as a natural remedy for beauty care, hair care and the treatment of skin diseases. Let us take a look below at what to do when aloe develops black spots!
Symptoms of Aloe Black Spot
Aloe black spot disease is a bacterial disease that seriously affects the growth and quality of aloe and can lead to total crop failure in aloe cultivation. In the early stage of the disease, water-soaked lesions appear on the leaves, which later develop into nearly round blackish-brown spots; some spots have radiating edges and are surrounded by a yellow or yellowish-black halo. In the late stage of the disease, many dark brown granules appear on the spots, the leaf surface becomes sunken, and the usable portion of the leaf mesophyll is completely lost.
Patterns of Aloe Black Spot Development
The severity of aloe black spot disease varies with the resistance of different aloe varieties. When the temperature stays below 20°C for two hours, the metabolism of most aloe varieties is impaired and resistance begins to decline, and localized spots appear on leaves carrying the pathogen. When the temperature stays below 15°C for more than two consecutive days, spots occur on about half of the leaves. When the temperature drops below 12°C, the disease incidence on leaves reaches 2/3. When the temperature falls to 8 to 10°C, the leaves are basically covered with spots within a week, and the incidence is even higher in open-field cultivation areas where frost damage occurs. In addition, typhoons, foggy weather, hail, concentrated rainfall, and weather with a day-night temperature difference above 10°C can also trigger this disease and lead to widespread outbreaks.
What to Do When Aloe Develops Black Spots?
1. Choose disease-resistant varieties. The variety most susceptible to spots is Aloe vera (Chinese aloe), followed in order by Yuanjiang aloe, Aloe arborescens, Aloe vera (Curaçao aloe), and soap aloe. Therefore, the best choice for planting is the disease-resistant and highly usable Curaçao aloe and Yuanjiang aloe.
2. Newly introduced seedlings must be disinfected, generally by soaking them in a 1000-fold dilution of 50% carbendazim wettable powder for 5 to 10 minutes, then drying them before planting. For severely diseased plants, the whole plant should be buried deep, and the soil in the affected area should be disinfected with a 1000-fold dilution of 50% carbendazim wettable powder + an 800-fold dilution of 70% thiophanate-methyl wettable powder.
3. During the growing period, ensure that the minimum temperature for aloe growth stays above 8°C, while reducing and controlling sources of the disease. Adopt single-ridge planting to improve ventilation and light penetration. On the premise of applying sufficient base fertilizer, additionally apply 0.1% potassium dihydrogen phosphate and 0.1% zineb, etc., to enhance the disease resistance of the plants. At the same time, do a good job of field drainage to prevent waterlogging in the plots. During frost periods, use the smoke method to raise the temperature and carry out comprehensive control.
4. In the early stage of aloe black spot disease, you can use an 800-fold dilution of 75% thiophanate-methyl wettable powder, or a 1000-fold dilution of 50% carbendazim wettable powder, or an 800-fold dilution of 70% thiophanate-methyl wettable powder for control.