Feature
Fungicide Application Methods and Timing to Optimize Spring Dead Spot Suppression
TABLE 1. List of isofetamid1 applications for studies conducted in Blacksburg, VA and Chesterfield, VA.
By Wendell Hutchens and David McCall, Ph.D.
It
is the middle of summer, the weather is warm, bermudagrass is thriving, and spring dead spot (SDS) (Ophiosphaerella spp.) is the last thing on any turfgrass manager’s mind. However, in short time thoughts of fungicide applications for the disease will be on the forefront of many turfgrass managers growing warm-season grasses in the transition zone as these applications are typically made in the fall for suppressing SDS. But when exactly in the fall is the optimal time to apply fungicides to suppress SDS and reduce the symptoms that appear the following spring? Moreover, what are some best management practices one can implement to optimize fungicide applications for SDS? These two questions have intrigued the Virginia Tech Turfgrass Pathology lab over the past couple of years as many turfgrass managers throughout Virginia and the surrounding states have asked us these exact questions about managing SDS with fungicides. “When do I need to apply?” And “how do I get the most out of my fungicide application?” These are excellent questions that have not been fully answered even though years of research between our lab and other labs around the country have been devoted to solving these challenging problems. Fortunately, the past year of research in our lab has given us some insight on how to mitigate these issues in regard to fungicide management of SDS.
FUNGICIDE APPLICATION TIMING STUDY A study was conducted at two bermudagrass locations in Virginia to determine the optimal time to apply fungicides for SDS suppression based on soil temperature and time of year. Isofetamid [Kabuto, PBI Gordon] was applied once at the highest labeled rate (3.2 fl.oz./1000ft2) for SDS at specific soil temperatures throughout the year (Table 1). The bermudagrass at the Chesterfield location
12 | VIRGINIA TURFGRASS JOURNAL July/August 2021 www.vaturf.org
1
Location
Treatment
Application Date
5-day Soil Temperature Average (°F)
Blacksburg
Early spring (60)
19 May 2020
60.2
Blacksburg
Spring (65)
4 Jun 2020
64.8
Blacksburg
Late spring (70)
11 Jun 2020
69.6
Blacksburg
Early fall (75)
20 Jul 2020
75.6
Blacksburg
Fall (70)
14 Sep 2020
70.4
Blacksburg
Fall (65)
21 Sep 2020
62.0
Blacksburg
Late fall (55)
8 Oct 2020
55.8
Blacksburg
Late fall (45)
23 Nov 2020
44.0
Blacksburg
Early winter (40)
14 Dec 2020
42.0
Blacksburg
Late winter (40)
1 Mar 2021
42.6
Chesterfield
Early spring (60)
8 Apr 2020
58.8
Chesterfield
Spring (65)
14 May 2020
55.6
Chesterfield
Late spring (70)
3 Jun 2020
70.4
Chesterfield
Early summer (75)
11 Jun 2020
76.4
Chesterfield
Summer (80)
7 Jul 2020
79.4
Chesterfield
Early fall (75)
28 Aug 2020
79.6
Chesterfield
Fall (70)
21 Sep 2020
66.4
Chesterfield
Fall (65)
28 Sep 2020
65.0
Chesterfield
Late fall (55)
17 Nov 2020
58.6
Chesterfield
Early winter (40)
8 Jan 2021
41.4
Chesterfield
Late winter (40)
16 Mar 2021
54.2
Kabuto [PBI Gordon, Kansas City, MO]
