Extension

Oklahoma landscapes are taking shape, thanks to gardeners’ hard work. The last thing a gardener wants to see is any kind of disease in the garden. Warm, wet weather is the perfect combination for fungal growth, which will cause problems.

What does fungus look like? Some common symptoms are easily identified… round black spots, irregular brown spots or a downy, white dusting on leaves. Plants such as hydrangeas, roses, columbine, dogwood trees and zinnias are some of the susceptible species, but any plant can get a fungus if the conditions are right, fungus spores are present and the plant is a susceptible host.

One way to help prevent fungus is to encourage good air flow between plants. To do this, plant the plants based on mature size. While it is tempting to plant young plants close together, this decreases air flow, increases pruning needs and can make disease control harder.

While plants need plenty of irrigation to grow and develop strong root systems, how plants are watered is just as important as when they are watered. Ideally, plants should be watered early in the morning so that the foliage can dry quickly in the sun and breeze. When watered in the evening, the water sits on the foliage in a dark environment, which encourages fungal growth. Also, watering plants at the soil level reduces the risk of fungal outbreaks.

Gardeners face the decision of whether to treat the fungus. This decision will depend on how the plants look rather than their overall plant health. Treatment options include a fungicide, sometimes combined with fertilizer and insect control products. Aggressive control includes a systemic fungicide and a non-systemic fungicide. Copper fungicide is a good option for food crops and is approved for organic gardening. Always read and follow all label instructions.

Fungicides need to be applied when the foliage is dry, and weather conditions will remain dry for about 24 hours. This will help the fungicide absorb. Additional sprays may be necessary if hot, moist conditions continue. When the air is warm and humid, controlling fungus can be difficult. However, once the full heat of summer hits, fungal growth typically stops spreading. Be sure to remove and dispose of infected leaves.

Fungus isn’t limited to landscape plants. Lawn fungus symptoms include large circular, thinning brown spots that grow in size each year. Some control measures can be put in place before the fungus starts, helping reduce the risk of infection and shorten recovery time. Fertilize with a slow-release fertilizer. Water the lawn deeply but less frequently to encourage deeper root growth. Good drainage is key in a landscape, for both plants and grass.

It’s best to treat the entire lawn area to help control the spread of the fungus. This needs to be done while the conditions for fungal growth are present.

The best tool to control diseases is disease resistance. Many species known to be susceptible to fungal problems have disease-resistant cultivars available. Planting disease-resistant cultivars can go a long way in keeping fungi under control in the garden and landscape.