Lantana is a tender shrubby perennial that is most often grown as a warm season annual for gardeners in USDA zones 7 and lower. Although this plant is extremely low maintenance and able to survive periods of high heat and drought, some gardeners may have issues with fungal diseases late in the growing season.
Powdery Mildew and Botrytis are the two most common diseases to infect Lantana. One is active when temperatures are cool at night and warm during the day with low humidity (Powdery Mildew). While the other needs periods of cool temperatures and high humidity or rain to make it active (Botrytis).
Powdery Mildew
Powdery Mildew is most often a problem for plants when they are growing in the wrong conditions. Lantana requires at least 8 hours of full sun exposure and does not tolerate soils that are slow to drain. When nighttime temperatures are dramatically cooler than the daytime hours powdery mildew may make an appearance on a wide range of ornamental and edible plants in the garden.
Low humidity allows the spores to easily be carried on the wind to infect parts of the plant and its neighbors. Spring and late summer or early fall are the two most common periods of Powdery Mildew outbreaks. Most infections will not result in anything other than cosmetic damage. The overall growing vigor or blooming ability of Lantana is rarely affected.
Identifying Powdery Mildew
Small white specks on the top of leaves eventually grow into large masses that cover both sides of the foliage. Stems and flowers can also be covered in the spore growths. Powdery Mildew is mostly a species-specific disease, although any plants in the Verbena family will be susceptible to the same strains.
Treating Powdery Mildew On Lantana
Removing the affected foliage as soon as possible is the best way to control an outbreak of Powdery Mildew. Since the spores can move easily in the air, watering the plant down carefully before removing affected foliage will help to contain the spores better. Powdery Mildew needs dry air, not humidity. Do not remove more than ⅓ -½ of the leaves at a time.
If a plant is very badly infected consider removing it entirely from the garden and disposing in the trash or community composting bin. Home composting generally does not maintain a high enough temperature for long enough to completely kill fungal disease spores.
Botrytis
Botrytis is also commonly known as Grey Mold. This fungal disease is common in most garden soils and becomes very active during periods of cool temperatures and high humidity. Broken stems, rotten leaves, and spent flower heads that are allowed to lay on the soil and not removed are the ways in which Botrytis take hold of a plant. Lantana may slow down flowering or stop altogether. Overall growth will be slowed or stopped altogether until the disease is treated.
Most often Botrytis is a disease found in cramped growing conditions of a greenhouse or hoop house tunnel. The fungal spores overwinter in the soil and will become active the following season. Botrytis is not a species-specific disease and needs to be treated so that it does not spread.
Identifying Botrytis
Specks of brown or bronze appear on foliage and flowers, typically after a period of wet and cold weather. Flowers may die off faster than normal. The spores will spread covering plant parts in a fuzzy greyish mold that rots away stems and flowers. The fungal spores overwinter in dead plant material and can reinfect plants at any point during the growing season.
Treating Botrytis On Lantana
Proper air circulation and good watering techniques are crucial to keep Botrytis from overtaking large plantings in a greenhouse or other enclosed growing space. Overhead watering should only be done early in the day in warm weather to prevent the foliage from remaining wet during the night. Remove damaged plant materials as soon as possible.
Disinfect or sterilize cutting tools between cuts when cleaning up damaged material. Over-fertilizing with a high nitrogen feed encourages dense growth on plants that us generally weak and more susceptible to pests and diseases. Only fertilize when absolutely necessary.
Common Lantana Disease Chart
| Disease | Identifying | Treating |
|---|---|---|
| Powdery Mildew | White or gray spots on the leaves which spread to cover both top and bottom | Prune out affected foliage or flowers, overhead watering will help to slow the spread, provide at least 8 hours of direct sun. |
| Botrytis | Wet or mushy stems and foliage, fuzzy gray or black fungal growth that spreads to other parts of the plant | Remove damaged plant material as soon as possible with clean cuts, avoid overhead watering, provide plenty of air circulation for container-grown plants. |
Sources:
“Common Problems - Plant Diseases”, Washington State University Hortsense database. www.hortsense.cahnrs.wsu.edu