Rhizoctonia (Brown Patch) diseases of turfgrass

The Perfect Storm

Due to the recent weather conditions including excessive rainfall, night time temperatures above 70, daytime temperatures in the 80’s -90’s, with high humidity and poor air movement, the St. Louis region has been set up for the perfect storm. Starting late, the week of June 15, 2015, you probably have noticed some irregular brown patches developing in your lawns.

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The primary fungus activity is known as:

Common Name: Brown Patch
Scientific Name: Rhizoctonia Solani

The symptoms of brown patch vary according to mowing height. In landscape situations, turf mowed at 3” or more, brown patch appears as rough circular patches that are brown, tan, or yellow in color and range from 6” to several feet in diameter. The affected leaves typically remain upright, and lesions are evident on the leaves that are tan in color and irregular in shape with a dark brown border. When the leaves are wet or humidity is high, small amounts of gray cottony growth, called mycelium, may be seen growing amongst affected leaves. The disease can appear in Bluegrass, Fescue, Ryegrass and Bentgrass.

Short term infection from Brown Patch will normally not kill the turf that is affected. It will damage the leaves but if the conditions change it may not kill the entire plant. When the soil dries out, temperatures drop below 70 degrees at night, the humidity drops and air movement improves the disease will normally become inactive and not cause further damage. The turf will grow out of the condition. A prolonged infection due to the conditions above can cause more serious damage.

CULTURAL CONTROLS

Don’t overwater, let the soil begin to dry out, mow the lawn on a regular schedule. It is better to let the turf get a little lean right now by not fertilizing. If you are doing grub control you can go ahead and apply the grub control because you are normally applying 1/2# nitrogen slow release fertilizer with your grub control products. Do not fertilize right now unless you have to. The long range weather forecast beginning Saturday 6/27/15 – Wednesday 7/1/15 with temperatures in the 60’s at night may help slow the disease activity somewhat. Remember the turf will have to grow out of the condition. It normally takes 20-30 days for grass plants to produce new leaves. If weather conditions return so will the disease activity.

LAWN TREATMENTS

You can apply a fungicide application to the lawn, it will take at least 3 applications on 10 day intervals to help control the disease. If the environmental conditions continue you will need to re-apply the fungicide. It will not cause the browning in the lawn to change immediately. The damage to the leaves will need to grow out for the turf to recover.
Applying fungicide is not a 100% guarantee you will not get the disease in your lawn. I would recommend that you discuss with your customers or if you are taking care of your lawn yourself then consider the costs vs benefits of a fungicide application. We normally only apply fungicide to high-value turf such as Athletic fields, golf courses and high end properties. If you need help with your cultural, lawn program or fungicides, don’t hesitate to give us a call at (314) 423-9244.

There are other disease active right now due to our environmental conditions.

Dollar spot is active and will normally stop and recover after the environmental conditions have changed and we can apply fertilizer to the turf. The same fungicides would be used for Dollar Spot as Brown Patch.

Pythium is prevalent primarily on Ryegrass and Bentgrass and will normally stop and turf will recover after the environmental conditions have changed. A special fungicide would be needed to help control Pythium.

(This information is courtesy of Scott’s Power Equipment newsletter.)

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