What to Do When a Cactus Gets Spots? Causes and Solutions
Cactus plants are everyone's favorite succulent pets; although they are covered in spines, that does not stop people from loving them. They are also among the easiest succulents to grow, but during cultivation people often find spots on their cacti, and many do not know what to do when a cactus gets spots. Let's take a look together below!
Causes of Spots on Cacti
The cause of spots on cacti is generally that the cactus has contracted cactus rust (cactus yellow spot disease), mainly caused by improper cultivation and management in daily care, such as potting soil that is too poor, insufficient or incomplete nutrients, or excessive use of nitrogen, which makes plant tissues tender and soft, or potting soil that is too sticky and heavy, drains poorly, and has excessive moisture, or seedlings and pots kept in shade for a long time with poor ventilation, or sudden cold and heat in winter and spring and other unsuitable environmental factors that trigger rust fungus infection. In addition, when watering, water droplets touching the cactus body can also cause bacteria to breed and form spots, and excessive sun exposure can also cause sunburn spots.
What to Do When a Cactus Gets Spots
1. If it is caused by rust, you can take the plant out, disinfect the soil with potassium permanganate (or steam it in a pot or heat it in a microwave), and disinfect the cactus body with a diluted solution of carbendazim, chlorothalonil, or thiophanate-methyl.
2. In normal times, pay attention to controlling watering, do not water too much, maintain a well-ventilated environment, and do not place it in direct sunlight for prolonged exposure. When repotting the plant, remove weeds from the pot, shake off the infected old soil, and repot with freshly prepared growing soil. If conditions permit, add a small amount of carbendazim or thiophanate-methyl powder to the growing soil for sterilization. In daily cultivation and management, apply a certain proportion of phosphorus and potassium fertilizer to improve the plant's disease resistance.
3. In the early stage of rust occurrence, you can spray with 75% chlorothalonil wettable powder at 500 times dilution, or 20% triadimefon emulsifiable concentrate at 2500-4000 times dilution, which has preventive and killing effects on rust. You can also choose 80% zineb wettable powder at 600-800 times dilution, or 12.5% diniconazole wettable powder at 6000 times dilution, spraying once every 7-10 days, with obvious preventive effects.
How to Grow Cacti
1. Preparation of growing soil: Cacti are desert plants and are relatively suited to acidic and weakly acidic soil environments. Because the root system of cacti is not well developed, the soil must be rich in organic matter and loose and breathable. Generally, the growing soil is made by using humus soil exposed to the sun for 2-3 days plus phosphorus and potassium fertilizer; usually, for every 50 kg of potting soil, mix in 1 kg of superphosphate and 0.5 kg of potassium phosphate as base fertilizer.
2. Reasonable water management: The principle of watering is “do not water if not dry, better dry than wet.” Do not water the center of the cactus. Generally, water once every half month in spring, once a week in summer, and in autumn and winter when growth slows, watering once every 20-odd days is enough. Note that it is best to water flowers with rainwater; if using tap water, it is best to expose it to the sun for two days before use.
3. Reasonable fertilizer management: You can put rice-washing water in a sealed container for half a month, then use it for watering. This rice-washing water is rich in nutrients and weakly acidic, very suitable for watering cacti. When necessary, apply additional fertilizer; generally, in spring and summer each year, apply 1% potassium dihydrogen phosphate along with watering, 2 to 3 times a year is enough.
4. Control light and placement: Cacti are plants that greatly enjoy sunlight, but if the temperature exceeds 36°C, shading treatment is also necessary. Cacti are not suitable for long-term placement indoors, as this easily causes the cactus to turn black. Generally, about once a month, place it outdoors in the sunlight for 2 to 3 days, then move it back indoors, and be sure to place it in a sunny spot indoors.
5. Timely repotting and soil changing: Generally, after a cactus grows in a pot for 2 to 3 years, the nutrients in the soil will indeed be depleted, and the growing soil will also become compacted; at this time it must be repotted. Be careful to take the cactus out of its original flower pot, place some pieces at the bottom of the new flower pot to facilitate drainage and ventilation, then fill in the growing soil prepared in step one, filling to 1/3. Press down with your hand, gently place the dug-out cactus (be sure to cut off rotten, old, and diseased roots) inside, fill growing soil around it, lift the cactus gently to help the roots spread, and finally fill in the remaining growing soil and press it firm.
6. Prevent pests and diseases: The main pests and diseases of cacti are anthracnose, canker, scale insects, and whiteflies. Mainly control moisture, ventilate in time, and focus on prevention. Carbendazim has a certain effect on anthracnose, and streptomycin is relatively effective against canker, but the main thing is still prevention.