|  |
Managing Pythium Blight in Overseeded Turf1
Lawrence Datnoff, Carol Stiles, and John Cisar2From September through November in Florida, the growth of bermudagrass tends to slow down and many superintendents and sports turf professionals consider overseeding their greens or sports turf. Understandably, many of them are concerned about establishment of the overseeded turfgrass. One reason is pythium blight. This fast moving disease can destroy an established grass stand within 24 hours after the first symptoms become visible, especially in a warm, humid environment. Typical initial symptoms include irregularly purplish to dark shaped areas, with a dark water-soaked appearance on the leaf blades. These leaves will become soft and slimy, mat together and eventually turn necrotic (brown), and die ( Figure 1 ). Early in the morning or when the humidity is high, the leaves may be covered with white, cobwebby mycelium of the pathogen, Pythium aphanidermatum ( Figure 2 ).
CREDITS: Lawrence E. Datnoff
Figure 1. Initial symptoms of pythium blight on overseeded turf include whitish (A) to brown (B) irregular shaped areas.
CREDITS: Lawrence E. Datnoff
Figure 2. Close-up of Poa trivalis leaves covered with white cobwebby mycelium of Pythium aphanidermatum. Superintendents and sports turf professionals often ask how to manage this disease in the overseed with fungicides. Some superintendents have even suggested applying fungicides to the bermudagrass before overseeding. Others have asked how effective would a curative application vs. a preventative application be in suppressing this disease. We tried to answer these questions. In the first experiment, eight treatments plus a control were arranged in a randomized complete block design with four replications. Fungicides (Banol, Subdue MAXX, Heritage 50WG and Signature) were applied either before seeding, after seeding or at emergence (Table 1). (Emergence is defined as stand establishment 14 days after seed germination in this study. This allows for establishment of a full canopy of grass for inducing a Pythium blight epidemic). In the second experiment, Heritage 50WG and Subdue MAXX were applied after seeding and emergence, and when approximately 1 to 3% visible symptoms of Pythium blight were apparent (Table 2). Fungicide treatments were arranged in a randomized complete block design with four replications. Fungicide sprays were applied at 30 psi using a CO2 backpack sprayer equipped with a single flat fan nozzle tip on a hand-held boom. All treatments were delivered in 3 gal. water/1000 sq. ft. Poa trivialis, Dark Horse, was used in both experiments. Pythium aphanidermatum was grown in a cornmeal-sand medium for about 10 to 14 days and incorporated into the plots. Inverted plastic boxes were placed directly within each plot to increase the temperature and relative humidity, and potentially enhance infection. The plots were rated for Pythium blight development throughout a four-day period.
Pythium blight development was relatively uniform and high throughout both experiments since the controls reached disease severities of 80%. In the first experiment to evaluate when to apply the fungicides, all fungicides significantly reduced Pythium blight development in comparison to the control (Table 1). Applying Subdue MAXX to the soil and bermudagrass before overseeding did reduce Pythium blight development in comparison to the control, 37.5% vs 80.2 %. However, at this level of disease development, a superintendent or sports turf manager would have to re-seed these infected areas. Applying fungicides either at seeding, emergence or the combination of the two were the most effective treatments for significantly reducing Pythium blight development. In the second experiment to evaluate preventative vs. curative application of fungicides, again, all treatments significantly reduced Pythium blight development in comparison to the control (Table 2). Curative treatments applied to infected overseed reduced Pythium blight development between 54.4 and 60.2 % compared to the control. However, as mentioned earlier, a superintendent or sports turf manager would have to re-seed these infected areas. The fungicides were best applied on a preventative basis. Pythium blight has a short incubation period (the time period between infection and visible symptoms). Fungicides need to be applied preventively for optimum disease control and they need to be applied directly to the seed or foliage. If superintendents and sports turf managers follow these simple guidelines for fungicide disease management as well as appropriate cultural control methods (including appropriate levels of nitrogen fertilizer), they should have no trouble in establishing and maintaining an overseed. Remember, always read and follow the fungicide label recommendations.
Tables
Table 1. Effect of fungicides applied before overseeding and after overseeding Poa trivialis into a bermudagrass green on Pythium blight development at the UF/IFAS Ft. Lauderdale Research and Education Center.
Treatment and rate per 1000 sq ft
Disease Severity1 (%)
Control 80.2 a2
Subdue MAXX 1 fl oz before overseeding
37.5 b
Banol 2 fl oz @ seeding + emergence3
8.8 cd
Signature 8 oz @ seeding 8.8 cd
Signature 8 oz @ emergence 3.2 cd
Heritage 50WG 0.2 oz @ emergence 1.5 cd
Subdue MAXX 1 fl oz @ seeding + emergence 0.8 d
Signature 4 oz @ seeding + emergence
0.5 d
Signature 4 oz @ emergence 0.5 d
1Disease Severity = percent area of overseed with symptoms of Pythium blight, where 0 = no infection and 100 = total area infected. 2Means followed by the same letter are not significantly different based on Fishers Protected LSD (P=0.05). 3Emergence is defined as stand establishment 14 days after seed germination in this study. The data reported herein do not imply endorsement of the products listed nor criticism of similar products not mentioned.
Table 2. Table 2. Effect of fungicides applied preventatively and curatively on pythium blight development on Poa trivialis overseeded into a bermudagrass green at the UF/IFAS Ft. Lauderdale Research and Education Center.
Treatment and rate per 1000 sq ft
Disease Severity1(%)
Control
80.2 a2
Heritage 50WG 0.2 oz after visible disease3
25.8 bcd
Subdue MAXX 1 fl oz after visible disease 20.0 bcd
Heritage 50WG 0.2 oz @ emergence4
1.5 cd
Subdue MAXX 1 fl oz @ seeding and emergence 0.8 d
1Disease Severity = percent area of overseed with symptoms of Pythium blight, where 0 = no infection and 100 = total area infected. 2Means followed by the same letter are not significantly different based on Fishers Protected LSD (P=0.05). 3Fungicides were applied when approximately 1 to 3% visible watersoaking symptoms of Pythium blight on leave blades were apparent. 4Emergence is defined as stand establishment 14 days after seed germination in this study. The data reported herein do not imply endorsement of the products listed nor criticism of similar products not mentioned.
Footnotes
1. This document is PP-66, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: July, 2003. Please visit the EDIS Web site at http:/edis.ifas.ufl.edu2. Lawrence Datnoff, Professor, Department of Plant Pathology, University of Florida-IFAS, Everglades Research and Education Center, Belle Glade, FL 33430, Carol Stiles, Assistant Professor, Department of Plant Pathology, University of Florida-IFAS, Gainesville, FL 32611, and John Cisar, Professor, Department of Environmental Horticulture, Ft. Lauderdale Research and Education Center, Ft. Lauderdale, FL 33314.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.