Problems with Marigolds

Marigolds are hardy flowers susceptible to a few pests and diseases.

Marigolds are a Mexico native that produce flowers with a distinctive yellow, orange or combination color. They are moderately easy to grow and require very little care once established. The primary types of marigold cultivated today are of French and African origin. These plants produce lush green foliage and will grow to be between half a foot and 3 feet in height. Though generally hardy, they are susceptible to a few problems. Does this Spark an idea?

Insects

Marigolds are generally a hardy species and are often placed in gardens as insect deterrents. They are especially useful when it comes to preventing parasitic nematodes in vegetable gardens. Spider mites, however, are a major concern for the marigold and may cause serious damage and death to the plant. These arachnid insects are active during warm and cool weather. They are visible with the naked eye, but their size makes them difficult to spot. Their coloring varies and may include black, brown, red and yellow. These pests remove much-needed nutrients from the plants cells, which leads to a yellow or bronze appearance and overall decline in health. Once the insects take over, foliage will begin to drop and the plant may die.

Disease

Growers should be especially vigilant about fungal diseases with marigolds. These plants may fall victim to botrytis blight and powdery mildew. Both are forms of fungi that will cause discoloration of the plant and may lead to plant death if left untreated. Botrytis blight presents with a gray fungal growth on leaves and blooms of the marigold. It favors cool, rainy weather and is most common in spring and summer. Growers should clean away any dead or dying organic material to prevent infestation and remove any infected leaves, blooms or branches as needed. Powdery mildew is a gray fungus that coats leaves and other parts of the plants. It is easily confused with dust, but should be wiped or washed away as soon as possible.

Water

Overwatering may be detrimental to the health of the marigold, and a high quality, well-draining soil is essential. Growers need to keep soil moist, but not wet. This balance is especially important for the first few weeks after planting. Once established, growers should only water occasionally during the warmest parts of the summer, again keeping soil moist, but not leaving any standing water. Standing water will reduce oxygenation of the roots, ultimately suffocating them and the plant. Overwatering may also promote root rot, a bacterial infection that turns root material into an unusable grey mush. This condition interrupts nutrition and water transport, which is ultimately lethal.

Environment

Marigolds have a few environmental needs that must be met to inspire healthy growth and flower production. Primarily, they should be planted in a nutrient-rich, well-draining soil. Approximately 16 elements are required for healthy growth, and if even one is lacking, leaves will often turn yellow, growth may be stunted and flower production reduced. The cure for a deficiency is usually the addition of well-decomposed organic matter. Additionally, the flowers require an area with several hours of sun exposure per day. If this need is not met, the plant may not grow as well as expected. Some protection from high winds or storms may be necessary, particularly for tall varieties.

References

• Ohio State University Extension; Spider Mites and Their Control; David J. Shetlar
• Cornell University Plant Clinic: Marigold Disease Factsheets
• University of Minnesota Extension; Root Rot of Houseplants; Jill Pokorny; 2000

Resources

• Read this Article in UK English
• University of Arizona; Marigolds and Nematode Management; Jeff Schalau; 2004
• Iowa State University; Marigolds; Richard Jauron; 1996
• Marigold Lane: About Marigolds