You Are Here: Management Updates 2002 Archive July 19, 2002

Date: July 19, 2002
Category: Diseases
Subject: Why is it So Difficult to Control Anthracnose?

Anthracnose used to be predominantly a summer stress disease affecting mostly the foliage. It would respond well to most fungicides when accompanied by cultural management. This is no longer the case. Why?

Turf management has changed dramatically even in just the time that I have been working as a turf pathologist. Putting greens are no longer mowed at ¼" and there are many more rounds of play each year. Golfers are demanding faster greens, so superintendents, against their better judgment, are keeping them on very low nitrogen fertilizer, minimal water, and with repeated sand topdressing to keep them hard and fast.

Anthracnose is a stress disease. It is caused by a fungus that infects weakened plants. One aspect that makes this disease difficult to control is that the fungus produces abundant sticky spores that can be easily tracked to new areas by machinery and feet. The increased stress in turfgrass has also resulted in the common occurrence of the basal rot or crown rot stage of the disease. Once the fungus has infected the growing point of the plant, recovery will be much slower, if it occurs at all. Anthracnose is now commonly seen throughout the growing season- even in cool weather.

Factors that reduce the ability of the turfgrass plant to "outgrow" the pathogenic fungus:

• low mowing height
• compaction of soil
• low N conditions
• traffic
• poor drainage

Anthracnose commonly appears in the following situations:

1. Right after a tournament. The turf has typically been double-cut repeatedly groomed excessively, and received more traffic than usual.

2. In greens that are:

• too small
• poorly drained
• compacted
• have poor air movement
• receive sand topdressing brushed in during disease outbreaks

Most superintendents use the following cultural practices to help mitigate anthracnose:

• temporarily increase mowing height during disease outbreaks and going into heat stress periods with or without disease (prevention!)
• skip the clean-up pass during disease outbreaks and during heat stress periods
• regular aeration- core aeration in spring and fall, spiking or hydroject during heat improve drainage where needed
• improve air movement through pruning of trees and landscaping
• minimize leaf wetness by early mowing or whipping of dew
• syringe turf in the heat of the day with care to continue into the late afternoon when needed
• wash mowers when moving from affected areas
• traffic pattern modification
• move the cup more frequently
• skip sand top-dressing during disease outbreaks- sand wounds plants
• maintain sufficient N and water for good turf growth

Clearly, green speed may suffer during these practices, but they may keep the turf alive. Small greens with limited air movement and poor drainage should be rebuilt. Once anthracnose develops on the "bad" greens, it can often spread to less stressed greens.

When cultural practices are not sufficient and chemical control is required, it is best to combine chlorothalonil with a systemic/penetrant fungicide. Early applications while the disease is still in the foliar (leaf) stage are most effective. Applications for the foliar stage should be a combination of a DMI fungicide (e.g. myclobutanil-Eagle, propiconazole-Banner or triadimenol-Bayleton) plus chlorothalonil. When the disease has progressed to the crown/basal rot stage, it is recommended that a systemic fungicide be applied and watered in while still wet on the leaves to deliver it to the crown area. Choices include thiophanate-methyl (e.g. Cleary's 3336 or Fungo), a DMI fungicide, or a strobilurin/QoI fungicide (azoxystrobin or trifloxystrobin). This should be followed by a separate application of chlorothalonil that is not watered-in because it is a contact that needs to coat the leaves to make a protective layer.

Anthracnose is not always easy to diagnose. If you are unsure about the presence of this disease, please use the UMass Turf Disease Diagnostic Lab for confirmation.

- Submitted by: Dr. Gail Schumann