Okay, rust spots and curling leaves on the lower part of your cannabis plant could be a sign of a few things. It might be a nutrient deficiency, like magnesium or calcium. Those older leaves need those nutrients to stay healthy. It could also be a pH problem, making it hard for the plant to absorb what it needs. Or, and this is less likely, it could be a fungal disease.
To figure out what's going on, you might want to check the pH of your water and soil. You could also try giving your plant a balanced nutrient solution to see if that helps. If the problem gets worse, then you might be dealing with a disease.
let's dig a little deeper into those rust spots and curling leaves. Nutrient deficiencies usually show up on older leaves first because the plant pulls nutrients from them to support new growth. Magnesium deficiency often causes yellowing between the veins of the leaves, while calcium deficiency can lead to brown spots and stunted growth.
pH imbalances can lock out nutrients, even if they're present in the soil. Cannabis prefers a slightly acidic pH, usually between 6.0 and 7.0. If the pH is too high or low, the plant can't absorb certain nutrients, leading to deficiencies.
If you've ruled out nutrient problems and pH issues, then you might be dealing with a fungal disease like Septoria leaf spot. This usually starts with small, round, yellow spots that eventually turn brown and develop a dark border. Good airflow and avoiding overwatering can help prevent fungal problems.
