Large patch disease

Large patch disease, previously known as brown spot, can be controlled with a fungicide. 

CONTRIBUTED PHOTO FROM LEE ROUSE

The cooler weather we have been hoping for is finally, here and let's hope it stays for a while.

Autumn lawn and garden issues are much easier to tackle when the temperatures are so pleasant and welcoming. Unfortunately, the cooler temps also encourage specific lawn diseases and weeds.

One of the most prevalent diseases gardeners could see this time of year is large patch, previously know as brown patch, which loves cooler nights and warmer days. Optimal conditions for disease development are when nighttime temperatures range from 60-75 degrees and daytime temperatures do not climb above 85-90 degrees.

Large patch, which is caused by the soil-borne fungus Rhizoctonia solani, is a very fitting name for the disease because, when conditions are favorable, it will spread rapidly into large circular or irregularly-shaped patches of brown turf.

Although the grass is usually not killed, the fungus does attack and rot the bases of the leaf sheaths, killing the leaf blades. This results in areas of sparse grass that are readily invaded by weeds, which creates another problem requiring additional management. St. Augustine grass is by far the most susceptible, but centipede grass and zoysia grass also have issues with large patch.

Though the disease is soil borne, it does need water on the leaf blade to begin developing. When scouting for this disease in your lawn, check areas near trees and shrubs. These areas will typically be shadier or will block adequate air flow through that area of the lawn. Both the shade and lack of air flow will allow water to sit on the leaf blade slightly longer than in open areas and could start the disease progression.

To treat large patch, administer at least two fungicide applications one month apart in the fall. However, if conditions remain favorable for disease development into November and December, additional fungicide applications may be necessary. In areas where large patch is known to have occurred previously, an application of a fungicide in mid-March at “green-up” is also advisable.

While chemical controls do exist and will help manage the disease, there are cultural controls that can be employed, such as cutting back on irrigation. A lawn needs about one inch of irrigation per week, whether it’s by sprinklers or rainfall, during the spring and summer growing seasons. Check your irrigation system and be sure you are not exceeding the recommended amount. In fall and winter seasons, turf grass demands much less water. In fact, you may not even need to use your irrigation at all during most average winter seasons with established turf grass.

If the disease is originating in shady areas due to a tree canopy, consider options other than growing grass in those particular areas. Creating a shade garden or simply mulching in these shady spots are two great alternatives.

Got a question?

Email gardennews@agcenter.lsu.edu.