This is a rare but possible condition that can affect weed plants if they receive too much calcium or magnesium. This can happen if the soil is already rich in these nutrients, or if the grower overfeeds the plants with Cal Mag supplements. The toxicity of Cal-Mag can cause a nutrient lockout, which means that the plants cannot absorb other essential nutrients from the soil. This can lead to symptoms such as leaf burn, brown spots, wilting, or reduced yield and quality.