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Issue link: http://read.dmtmag.com/i/282929
Y our turf has a disease! What do you do? Reach for a fungicide? What kind? And what's the best way to use it? What exactly do fungicides do? How can I maximize my chance of getting a good result from a fungicide? There are several ways in which fungicides are classified: By when they are used, by how they move (or don't move) inside a plant, by their chemical structure, and by their mode of action (how they kill a fungus, or prevent it from growing). Time of use Fungicides can be used both preventively — before any disease symptoms are present — and curatively — after disease occurs. This distinction is important, because some fungicides are much better suited for one of these uses than others. For example, fungicides that work by activating a plant's natural defense responses to infection must be used preventively. By the time a disease is ravaging a plant, its de- fenses are already being overcome. Although a fungicide application made after disease symptoms ap- pear is called curative, it's important to remember that fungicides don't actually bring dead plants back to life. If a lawn or field is suffering from a disease, a curative fungicide application can stop the dead patches from getting bigger. But for the turf to recover takes either good growing conditions for the grass to fill back in if it can spread vegetatively, or to re-establish via new seed if it can't spread vegetatively. This is why turf managers should be much more aggressive about treat- ing — and preventing — diseases at the end of the growing season. Movement in a plant Some fungicides are able to be absorbed into plant tissue and moved in a plant's vascular system, while others are not. In general, fungicides that do not move inside a plant are called contact fungicides. These fungicides work by coating the leaf with a protective fungicide barrier that will prevent any spore or piece of fungal mycelium that lands on a leaf from growing and being able to infect the plant. Since contact fungicides can only protect plant parts that the spray lands on, they are useless for treating root diseases like spring dead spot, summer patch, Pythium root rot or anything else that infects below ground. Because the contact fungicides work outside the plant, they must coat the entire leaf on both sides. Getting even spray coverage can be tricky in turfgrass, which has many small leaves that overlap each other. This is why fungicide labels specify using large volumes of water, often as much as 5 gallons per 1,000 square feet (more than 217 gallons per acre). This is much more water than is used for spraying herbicides, but it is needed to ensure there is enough fungicide solution to cover every 26 Landscape and Irrigation April 2014 www.landscapeirrigation.com Landscape and Turf Maintenance What Fungicides Do... and What they Don't By Dr. Dave Han Photos provided by Dr. Dave Han Left: Fungicide trial in foul territory. Right: Bermudagrass football field with spring dead spot.