Growing and eating collards, turnips and other greens are a Southern tradition. But home gardeners often complain of spots on the leaves of homegrown greens.
This is a very common question University of Georgia Cooperative Extension agents get this time of year concerning turnips and other greens such as mustard, collards, radish, spinach and kale. There are actually several common leaf spot diseases caused by different fungal pathogens that infect leafy greens. These include Cercospora leaf spot, anthracnose, powdery mildew, and Alternaria leaf spot.
These plant diseases do not pose a health concern to gardeners, but can be a major problem for growing greens in the home garden.
Work to prevent conditions
All of these leaf spot diseases are basically managed the exact same way. Prevention is the key to avoiding these disease problems.
Moisture and humidity are the main reasons these types of leaf spot diseases form. Fungi thrive wherever moisture is present. Any cultural tactic that reduces leaf moisture will help reduce the severity of these types of plant diseases.
Take a look at what time of day you water your garden. Watering in the late afternoon or in the evening can leave plant leaves wet for an extended period throughout the cool, nighttime hours. This creates perfect conditions for diseases to spread.
However, watering your garden early in the morning isn’t likely to add moisture to the leaves for an extended period. As the sun rises in the morning, plant leaves will quickly dry out.
You can’t control when it rains, unless you have a greenhouse, but you can control when you add water. The analogy to remember is to not add salt to the wound. If rainfall provides irrigation, you don’t need to add more water. The less moisture on plant leaves, the less severe these leaf spot diseases will spread.
Look at how you water
Along these same lines, consider the method of watering you use. Overhead irrigation or sprinkler type watering is more likely to soak the leaves of garden greens as well as splash potential fungal pathogens from the soil onto the leaves. If this is your only option, then watering in the morning can help.
Using a soaker hose or drip irrigation system will target water only on the roots rather than the leaves. Hand watering with a water breaker or watering wand can direct water at the soil rather than the leaves. Also consider adding mulch to garden rows to minimize the amount of splashing soil on leaves and keep weeds down.
Ultimately, when it comes to leafy greens there aren’t many fungicides you can safely use since you will eventually eat the leaves. Also, the few fungicides which are labeled for leafy greens are better at preventing diseases rather than actually controlling diseases.
Options are limited to natural, safe methods
The only options available to home gardeners for garden greens are copper- and sulfur-based fungicides. These are actually considered natural or organic fungicides and are safe enough that there no time limits or restrictions on harvest after application.
These fungicides are readily available at most garden centers and local farm supply stores. They should be applied as soon as the first symptoms of disease are present. Preventive applications are a good practice if you have a history of these leaf spot diseases in your garden.
If leaves or entire plants are severely diseased, the best option is to cut out the worst leaves or remove the entire plant to minimize spreading to adjacent plants. As with any fungicide, read and follow all labeled application rates and safety precautions.