You Are Here: Management Updates 1998 Archive July 22, 1998

Date: July 22, 1998
Category: Diseases
Subject: Summer Stress, Summer Patch, Anthracnose, Patch Diseases

Last week's heat and stress resulted in a number of turf problems. Some Pythium blight was observed, but it is generally in localized low spots or where turf leaf blades are somewhat longer and hold dew longer. Spot treatment with fungicides and/or care not to track through the fungus to spread it are usually sufficient for control. Free "fungicide" was delivered via the weather front that produced cooler, dry weather over the weekend. We are in a similar situation this week except that the cool front may take longer to arrive, especially in eastern areas.

Summer patch has been confirmed in many golf courses. Many samples were from compacted fairways where curative chemical control may not be very effective- to save the plants or as far as budget constraints. You might consider this part of your "Poa conversion plan" and try to establish more bentgrass in these areas later in the season.

A number of samples still show no active fungal pathogen and seem to be primarily suffering from physical stress. Unfortunately, many areas could use some fertilizer, but adding it now will probably cause more problems than it solves until the weather is less stressful.

Anthracnose has been found in several samples this week. Luckily, many of the plants are diseased mostly in the leaves where fungicide treatment may improve their condition. When the disease has moved into the crown (charcoal black in the basal tissues), plants are less likely to recover. Note that the spores of this fungus are very sticky and can spread easily by mowers, etc. There are 3 approaches to control and all are important:

1) reduce stress (avoid low N, compaction, excess thatch, not enough water, low mowing heights)

2) reduce chances for the fungus to infect the plants- minimize the time water is on the leaves, dew removal on nonmowing days, avoid brushing in sand topdressing when plants are stressed, improve air circulation where areas tend to stay wet.

3) chemical control- a combination of a systemic (esp. DMI fungicides such as propiconazole, triadimefon) + chlorothalonil (Daconil etc.)

Many lawns also show patch disease activity although laboratory analysis generally proves this to be necrotic ring spot. Many lawns started to show drought dormancy because homeowners do not appreciate how much irrigation is really necessary in the absence of natural rainfall. Brown patch and Pythium blight are more common on ryegrass lawns, but there has not been enough prolonged moisture in most areas. Where spring leaf spot was common, Kentucky bluegrass and fine fescues may be declining because of crown rot caused by the continuing stressful weather. Although gray leaf spot has not yet been documented this far north on perennial ryegrass, be on the lookout for any unusual leaf spot disease as we enter the second week of heat stress.

- Submitted by: Dr. Gail Schumann