Marigolds are common companion plants, which appear to repel many pest insects. They are fairly resistant to insect issues, but diseases in marigold plants are an occasional problem. The most prevalent diseases are fungal and affect stems, leaves and roots. Marigold plant diseases are relatively easy to diagnose and treat, however. In fact, most can be cured by using different cultural methods.
Common Marigold Diseases
Among the most common marigold diseases are blights, rots and mildews. Usually, these types of diseases show up when conditions are wet and warm, and fungal spores are rampant. In most cases, simply discontinuing overhead watering can stop the formation and spread of spores.
As mentioned, fungal marigold plant diseases occur most often. These might be Aster yellows, wilt and stem rot, collar rot, flower bud rot and damping off when in the seedling phase. Fungicide applications can help in controlling diseases of marigold caused by fungus along with avoiding overhead irrigation.
Powdery mildew is another fungal disease that affects all kinds of plants. It is recognized by a powdery white film on leaves and other surfaces. Spraying a mixture of baking soda, water and a touch of dish soap is an effective weapon. Correct timing when watering plants will allow the moisture to dry on foliage, and is another effective strategy to avoid fungal diseases like this. Additionally, ensure that you have correct drainage in your containers and beds.
Other Diseases in Marigold Plants
While many issues can be caused by inadequate nutrients, nutrient excesses in soil can also lead to many plant ailments. Leaf burn, where the tips of leaves and new growth yellow and die, is the result of surplus boron, manganese or molybdenum.
When using a fertilizer, be certain your soil needs the amount of nutrients it contains. Soil levels for boron should be 55 parts per million, manganese 24 ppm and molybdenum just 3 ppm. It may be necessary to perform a soil test to determine what nutrients are already in the soil.
Marigolds are not tolerant of low pH soils. This causes manganese or iron toxicity, which will cause leaves to brown and speckle. If pH is too low, you will need to amend soil with lime for the next year’s plants.
Bacterial leaf spot is another disease in marigold plants. Unfortunately, the entire plant must be destroyed to prevent spreading the disease.
Controlling Diseases of Marigold
Hindsight is 20/20, but prevention is a crucial part of the strategy.
- Most marigold plant diseases will be due to fungal spores, so correct watering is key.
- Removing infected plant material can also help limit spread of disease.
- Amend soil with well-rotted compost. If you have heavy clay soil, add sand or other grit to loosen the soil.
- Use containers that drain well and avoid using saucers, which can catch water and cause root rot.
- Use pathogen free potting mixes or sterilize your soil before planting marigolds. If you had an infected plant in the past, use bleach to clean containers before installing any new plant species.
- Choose French and dwarf varieties of marigold, rather than the African species.
Fortunately, problems with marigolds are rare and easily fixed, leaving you with happy plants and a season of golden blooms.