April 30, 2008

1. Dollar Spot – Home lawns

A video about Dollar Spot is available at: http://www.aragriculture.org/diseases/audio/dollar_spot_video_hires.htm

Dollar spot is a foliar fungal disease that can affect all species of warm- and cool-season turfgrasses. This disease is perhaps the most widespread turf disease in the home lawn. In Arkansas, bentgrass, hybrid bermudagrass and zoysiagrass are the most susceptible turfgrasses. The disease is caused by the fungus Sclerotinia homoeocarpa. This disease can occur in the spring, but it is most common in late summer and fall when temperatures are mild and conditions are moist. Dollar spot is usually more of a problem on drought-stressed grass. Low cutting heights and low nitrogen fertility can also increase disease severity.

Symptoms and Identification. Small, circular, straw-colored spots in the lawn which are 1 to 3 inches in diameter are the most common symptoms of dollar spot. These spots are most obvious on closely cut hybrid bermudagrass and zoysiagrass. The randomly occurring spots may grow together, forming larger dead areas of turf. The fungus produces white “cottony” growth or threads on the dead grass that are visible during the early morning hours when dew is heavy. These fungal threads quickly disappear once the dew has dried. Fungal threads may resemble “cob webs” in the affected turf areas. On individual infected leaves, yellow to brown lesions with a distinctive dark brown border develop which eventually girdle the leaf blade. Lesions have a distinctive dark brown border that surrounds this area. This distinctive symptom is readily visible with the eye and is useful for diagnosis. Most of the damage to the plants is restricted to the foliage, but the fungus may occasionally cause some problems with the crown.
Disease Cycle. The disease is favored by temperatures between 59 and 86 degrees F. and high humidity over extended periods. Dollar spot is particularly favored by hot days with cool nights. Heavy dews encourage disease development. The disease also tends to be more severe on dry soils and in sites that are nitrogen deficient. The fungus survives as mycelium in the diseased grass. Infected clippings left by the lawnmower contribute to future disease outbreaks. Dollar spot usually spreads by the movement of infected grass clippings by lawn-mowers and other lawn maintenance equipment.

Management. Since the severity of dollar spot is closely related to how well the lawn grass is maintained, adequate nitrogen fertility and soil moisture are effective in controlling the disease. Fertilizer applications should be based on a recent soil test, and turf should be irrigated deeply but infrequently to minimize moisture stress. Early morning irrigation is best to help reduce the time the leaves remain wet. Always cut the grass at the recommended height using a sharp lawnmower blade. Temporarily raising the height the lawn is cut to minimize stress on the plants can be helpful in managing the disease. Soil aeration and excess thatch removal may also be beneficial. If this disease causes severe damage for several successive years, fungicide applications, in conjunction with cultural practices, may be necessary to prevent disease or reduce its severity. Fungicide choices for the home lawn include those that contain myclobutanil, triadimefon, thiophanate-methyl or propiconazole. For best results, applications should begin in the spring before the disease appears. Always read and follow label instructions for proper application rates and intervals.

Early recognition and identification of dollar spot as well as other diseases is essential to the maintenance of a beautiful lawn. A regular inspection of the lawn can easily help identify and correct a potentially serious problem. Laboratory evaluation by the Plant Health Clinic may be necessary to diagnose dollar spot in the lawn. If you need additional information about this and other turfgrass diseases, contact your local county Extension office.

More information about Dollar Spot is available at:
http://turf.uark.edu/publications/factsheets/Dollar Spot of Turfgrass in the Homelawn FSA-7541.pdf

More information about fungicides available for the control of dollar spot in Arkansas lawns:  
http://www.uaex.edu/Other_Areas/publications/PDF/MP154/LawnDisHome.pdf

Dollar Spot

A video about Dollar Spot is available at: http://www.aragriculture.org/diseases/audio/dollar_spot_video_hires.htm
Steve Vann

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2. Dollar Spot on bentgrass - Professionals

Dollar spot is beginning to rear its head on bentgrass putting greens in Arkansas. Golf course superintendents are easily recognize this disease with hour glass lesions on the leaf blades (A, Kentucky bluegrass) and silver dollar sized blighted areas (B) on the creeping bentgrass putting greens. Golf Course superintendents are also used to managing this perennial disease, but a few tips are offered here that may help with your preventative or curative dollar spot management program.

Dollar Spot

Tip #1. Choose a cultivar with a low susceptibility.  Creeping bentgrass continues to be the prevailing turfgrass species used for golf course putting greens throughout northern and central Arkansas.  Identifying cultivars that are well-adapted to the region remains a central focus of the University of Arkansas turfgrass research program. The National Turfgrass Evaluation Program is the predominant means by which cultivars are tested throughout North America. A bentgrass cultivar trial, including selections of creeping and velvet bentgrass was planted in the fall of 2003 at the University of Arkansas Research and Extension Center (Fayetteville, AR).  The trial was maintained under golf course putting green conditions and data on turfgrass quality, color, density, dollar spot and brown patch incidence, and recovery from core aerification were collected.  A full report is available online and is linked below. When averaged across both dollar spot outbreaks in June and August of 2006, there were significant differences in disease severity among bentgrass varieties (Table 1).  On average, the creeping bentgrass cultivars were more susceptible to dollar spot than the velvet bentgrass cultivars.  The 18 cultivars that ranked highest for dollar spot severity were all creeping bentgrasses.  Among the creeping bentgrass cultivars, the most severely infected with dollar spot were, Bengal, SR 1020, T-1, Independence, Tyee, and Penn G2, whereas the cultivars with the lowest dollar spot severity were Declaration, Memorial, 13-M, Kingpin, Pennlinks II, and Benchmark DSR.


Table 1.  Dollar spot ratings for creeping and velvet bentgrass cultivars in the 2003 NTEP Bentgrass trial.  Cultivars are ranked according to their dollar spot ratings. Two separate outbreaks of dollar spot occurred in June and August 2006.  During each disease outbreak, disease severity was rated on a 1 to 9 scale where 9 represents turf completely infected with disease and 1 represents no disease present. 

Entry

Species

Dollar spot

 

 

- rating value (1 to 9 scale) -

Declaration

Creeping bentgrass

1.3

Memorial

Creeping bentgrass

1.5

13-M z

Creeping bentgrass

1.8

Legendary

Velvet bentgrass

1.8

Venus

Velvet bentgrass

1.8

Kingpin

Creeping bentgrass

2.0

Pennlinks II

Creeping bentgrass

2.0

Villa

Velvet bentgrass

2.0

Vesper

Velvet bentgrass

2.2

Benchmark DSR

Creeping bentgrass

2.3

SR 7200

Velvet bentgrass

2.3

Greenwich

Velvet bentgrass

2.5

IS-AP 9 z

Creeping bentgrass

2.7

007

Creeping bentgrass

2.8

CY-2 z

Creeping bentgrass

2.8

Penncross

Creeping bentgrass

2.8

Authority

Creeping bentgrass

2.9

LS-44

Creeping bentgrass

3.1

Penn A-1

Creeping bentgrass

3.3

Penn A-2y

Creeping bentgrass

3.3

L-93 y

Creeping bentgrass

3.7

MacKenzie

Creeping bentgrass

4.0

Shark

Creeping bentgrass

4.3

Alpha

Creeping bentgrass

4.5

Penn G-2 y

Creeping bentgrass

4.8

Tyee

Creeping bentgrass

4.8

Independence

Creeping bentgrass

5.3

T-1

Creeping bentgrass

5.3

Bengal

Creeping bentgrass

5.8

SR 1020 y

Creeping bentgrass

5.8

 

LSD(0.05)

1.15

z Entry is experimental and at this time not commercially available.
y Not an official entry of the 2003 NTEP bentgrass trial and was included as an Arkansas standard.

Read more selecting a bentgrass cultivar for Arkansas:
http://turf.uark.edu/research/research%20series/557/Summary of the 2003 NTEP Bentgrass Trial.pdf

Tip #2. Choose an effective fungicide. Many products are labeled for the control of dollar spot, but not all are equally effective. Drs. Paul Vincelli and A.J. Powell, plant pathologist and extension turfgrass specialist at the University of Kentucky, has developed a comprehensive guide for choosing fungicides for the control of various turfgrass diseases. Below some fungicides labeled for the control of dollar spot are ranked by Drs. Vincelli and Powell (Table 2).

Table 2. Fungicides for the control of dollar spot, some common product names, their efficacy, and their application internal. This table is adapted from Vencelli, P., and A.J. Powell. 2008. Chemical control of turf diseases 2008. University of Kentucky Cooperative Extension Service, Publication no. PPA1. Original version available at: http://www.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf.

Fungicide

Trade name

Mode of action

Efficacy z

Application interval (d)

boscalid

Emerald

Carboximide

4

14-28

myclobutanil

Eagle

DMI

4

14-28

propiconazole

Banner MAXX, Spectator

DMI

4

7-28

thiophanate-methyl

Cleary’s 3336, Fungo, Proturf Systemic Fungicide, Systec 1998, Cavalier, T-Storm

MBC

4

10-21

triadimefon

Bayleton, Proturf Fungicide VII

DMI

4

14-30

triticonazole

Trinity

DMI

4

14-28

vinclozolin

Curalan, Touché, Vorlan

Dicarboximide

4

14-28

iprodione

Chipco 26GT, Raven, Lesco 18 Plus, Iprodione Pro

Dicarboximide

3+

14-28

chlorothalonil

Daconil Ultrex, Manicure, Concorde SST, Chlorostar, Echo, Pegasus L

Chloronitrile

3

7-14

fenarimol

Rubigan

DMI

3

10-30

Bacillus licheniformis

EcoGuard

Biological

2

3-14

pyraclostrobin

Insignia

QoI

2

14

hydrogen dioxide

Zerotol

Oxidizing agent

1

7

mancozeb

Fore, Protect T/O, Dithane,Mancozeb

EBDC

1

7-14

thiram

Spotrete, Thiram, Defiant

Dithiocarbamate

1

7-10

Trichoderma harzianum

Bio-trek

Biological

1

7-14

Bacillus subtilis, strain QST 713

Rhapsody

Biological

L

7-10

copper hydroxide +mancozeb

Junction

EBDC

L

7-14

PCNB

Cleary’s PCNB, Penstar,Terraclor, Turfcide, Revere

Aromatic

L

21-28

z Rating system for fungicide efficacy: 4 = consistently good to excellent control in published experiments; 3 = good to excellent control in most experiments; 2 = fair to good control in most experiments; 1 = control is inconsistent between experiments but performs well in some instances;
N = no efficacy; L = limited published data on effectiveness; + = intermediate between two efficacy categories.

Rankings on the effectiveness of fungicides for the control of dollar spot and other diseases is available at:  
http://www.ca.uky.edu/agc/pubs/ppa/ppa1/ppa1.pdf

More information about professional fungicides available for the control of dollar spot in Arkansas:  
http://www.uaex.edu/Other_Areas/publications/PDF/MP154/TurfDisCom.pdf

Tip #3. Alternate your modes of action. Avoid repeated use of the same mode of action, especially DMI fungicides to avoid building fungicide resistant among dollar spot isolates. Sclerotinia homoeocarpa, the pathogen that causes dollar spot, is resistant to iprodione, thiophanate-methyl, and propiconazole at some locations across the country. Therefore, use caution when treating for dollar spot and make sure to alternate between fungicide modes of action.

Tip #4. Mow putting greens early in the morning when possible. Research in Minnesota has shown that mowing putting greens at 4 am will reduce dollar spot more than if you mow at 10 am. Mowing early reduces the dew period and effectively reduces disease.

Reference:
Ellram, A., B. Horgan, and B. Hulke. 2007. Cultural practices to minimize dollar spot on creeping bentgrass: Daily mowing at the appropriate time can significantly reduce the occurrence of dollar spot. Golf Course Manage. 75(1):150-153.

Tip #5. Choose nozzles that provide good coverage of the leaf. Since the dollar spot pathogen is active on turfgrass leaves, fungicide applications with better spray droplet coverage provide better control. A study in Connecticut and Pennsylvania by Kaminski et al. (2006) found the following “Dollar spot suppression generally was improved when fungicides were applied with XR11004, XR11003, and AI11004 nozzles. Moderate and poor dollar spot suppression was achieved with TJ11003 and TTJ11004 nozzles, respectively. Results indicate that the efficacy of fungicides applied in low water volumes can be improved through the selection of proper nozzles.” Nozzles used in this particular experiment were selected to produce droplet sizes that are extremely coarse (TTJ11004), very coarse (AI11004; air induction), coarse (TJ11003), medium (XR11004), and fine (XR11003).

Reference:
Kaminski, J. E., M. A. Fidanza, M. Agnew, and J. Gregos. 2006. Impact of nozzle type on dollar spot control. Phytopathology. 96(6):p. S58.

 

Aaron Patton and Doug Karcher


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