Review of Basal Rot Anthracnose

With temperatures warming up, and plant samples beginning to appear in the plant diagnostic laboratory showing anthracnose samples, it is a good time to take a look at basal rot anthracnose. Basal rot anthracnose (Colletotrichum graminicola), the new proposed pathogen name is C. cereale, may be a serious problem on Poa annua (annual bluegrass) putting green, and at times on creeping bentgrass greens. Basal rot is very difficult to control once the turfgrass shows signs of thinning. This is especially true when Poa annua develops the disease in March, April or May. To alleviate basal rot, increase the height of cut and use walk-behind greens mowers. Divert traffic away from affected areas by moving cups frequently. Apply light rates of soluble fertilizers to improve plant health. A moderate application of nitrogen from ammonium sulfate or urea (0.1 to 0.125 lb. per 1,000 sq. ft.) is suggested every 7-14 days. When the disease is active, avoid topdressing, double cutting, core cultivation, brushing, vertical mowing and other abrasive practices. This is because the pathogen enters plants more easily through wounds. Furthermore, avoid mowing when greens are excessively wet and spongy. This will increase mechanical damage which can intensify the disease. Switch from grooved to solid rollers.

In the autumn, after symptoms have dissipated, coring and overseed to increase the amount of bentgrass in the greens. Avoid excessive irrigation at any time and water only as-needed to prevent wilt. Poor surface and internal soil profile drainage seems to aggravate the disease problem. The winter and spring symptoms of basal rot anthracnose may be different from anthracnose foliar blight symptoms that are traditionally experienced in the summer. In most cases the Poa annua or the creeping bentgrass is affected, but not both grasses at the same time.

Thus, where concern exists about this disease, preventive applications of fungicides are suggested, beginning two to four weeks prior to the expected onset of the disease. Since disease outbreaks can occur at different times of the season, even within a small geographical area, keep records of when and under what conditions the disease occurs, then use this information as a guide for application timing the following year.

Placement of the fungicides is very important to manage this disease once the stems and crowns of plants are infected. Since the pathogen is located in the crown, lower stem and base of the plant and since most fungicides are local penetrants or only move upward in the turfgrass plant the fungicides most be placed in this area. To accomplish this 4 - 5 gallons of water per 1000 sq ft is recommended. If a sprayer is calibrated for 2 gals/1000 sq ft often the superintendent will only add one half the recommended amount of fungicide and then spray the area two times so that 4 gals/1000 sq ft are delivered and a full rate of fungicide. By using the high volume of water the fungicide(s) are placed in the crown area and have optimal placement to protect uninfected plants and have the best placement to reduce damage on infected plants. Remember most of todays fungicides do not eradicate the pathogen and successful fungicide programs must be made prior to significant infection by the pathogen.

Thiophanate-methyl (Cleary 3336® or Fungo 50®), azoxystrobin (Heritage®), pyraclostrobin (Insignia®), trifloxystrobin (Compass®), propiconazole (Banner MAXX®), triadimefon (Bayleton®), myclobutanil (Eagle®), fenarimol (Rubigan®), triticonazole (Trinity®), polyoxin D (Endorse®), or fosetyl-Aluminum (Signature®) are products that can be considered for the management of this disease. It may be necessary to schedule numerous fungicide applications on 7-10 day intervals to arrest basal rot, particularly in annual bluegrass. Not all of these or equal have the same impact on the disease and none will eradicate basal rot anthracnose after the disease is active. These fungicides work best preventively. Check label instructions for timing intervals and details for the most effective use of the product. Also refer to the Fungicides: Products, Rates, Families & Mobility chart on the last page for more information. It is also recommended to include foliar nitrogen fertilizer applications, stop the use of plant growth regulators, and avoid any mechanical stress.

In curative situations always include an application of the high labeled rate of chlorothalonil. Since chlorothalonil is a contact fungicide a volume of 2 gallons of water per 1000 sq ft should not be exceed. High volumes (4 -5 gallons of water per 1000 sq ft ) used to place the other produces at the crown and base of the plants will greatly dilute contact fungicides and seriously reduce efficacy. A separate application is recommended for the contact fungicides.

In some chronically infected annual bluegrass greens, especially when managed at mowing heights of less than 1/8 (0.125 inches) of an inch for maximum green speeds, basal rot may NOT be controlled with fungicides. In these extreme cases, chronically infected greens that consist mostly of annual bluegrass may have to be renovated and regrassed to the latest generation of low-growing creeping bentgrasses. There are several options including resodding, fumigation and reseeding, and complete reconstruction of the diseased greens.

Another common denominator seen on greens with this disease in the spring is that these courses experienced significant loss of Poa annua the previous year. Basal rot anthracnose may be less of a problem on greens that have not experienced a significant loss of grass in recent history. In addition, low mowing heights of 1/8 of an inch or less, along with the associated mowing stress, contribute to the initiation and difficulty in controlling this disease.

BASAL ROT ANTHRACNOSE MANAGEMENT

Cultural Practices:

Mowing

* Avoid scalping and mowing stress in any way possible.

* Do not mow when greens are excessively wet (spongy).

* Using solid rollers.

* Use walk-behind mowers and reduce mowing frequency (floating head mowers preferred).

* Raising mowing heights, mow at 5/32" (0.156 in) this may be easier said than done.

Water Management

*Install drainage systems or rebuild greens to correct poor drainage or design problems.

* Avoid excessive irrigation. Syringe to prevent wilt.

*Address soil compaction problems

Fertility, wound management, limit stresses and other pest problems

* Apply 0.1 to 0.125-lb. N/M sq. ft. from ammonium sulfate or urea every 7-14 days. Tank-mix with fungicide applications.

* Avoid PGRs when anthracnose is active.

* Avoid grooming operations (topdressing, dethatching, verticutting, brushing, aeration) when anthracnose is active.

* When grooming operations cannot be avoided, apply fungicides tank-mixed with soluble fertilizers prior to grooming, even if anthracnose is not active. Syringe after grooming.

* Attempt to suppress or control Poa annua seedheads in the spring.

* Monitor parasitic nematode activity in the spring and early summer as nematode activity may be another predisposition factor to the development of anthracnose during the summer and fall.

Fungicides:

If the disease is active, rotate penetrant fungicides from the classes shown: Thiophanate (CL 3336 or Fungo 50) in the first 7-10 days; followed by a strobilurin (Compass, Heritage or Insignia in the second 7-10 days; followed by a sterol-inhibitor (Banner, Bayleton, Eagle, or Rubigan in the third 7-10 days period. Consider including Signature in this rotation at least once per month. Endorse is an additional penetrant to consider however works best as a preventative fungicide. Normally do not use a fungicide from the same chemical class in succession, rotate whenever possible. As temperatures increase keep in mind the growth regulating side effects of sterol-inhibiting fungicides.

NOTE: Spray volume recommendations: for systemics (most are upward moving only) 4 - 5 gal water / 1000 sq ft, for contacts and local penetrants 1 - 2 gal water/ 1000 sq ft.

Strobilurin and thiophanate-methyl resistant biotypes of anthracnose have been reported.

Fungicides: Products, Rates, Families & Mobility

PRODUCT, RATE(oz/1000 sq.ft.),FAMILY,MOBILITY:

Daconil Ultrex, 3.25 - 5.0 oz, Nitrile,Contact

Medallion, 0.25 - 0.5 oz, Phenylpyrolle,Contact

CL 3336, 4.0 - 6.0 oz, Benzimidazole, Systemic (upward)

Endorse, 4.0 oz, Polyoxin, Local Penetrant

Heritage, 0.2 - 0.4 oz, Strobilurin, Systemic (upward)

Compass, 0.25 oz, Strobilurin, Local Penetrant

Insignia, 0.5 - 0.9 oz, Strobilurin, Local Penetrant

Banner MAXX, 1.0 - 2.0 oz, SI / DMI, Systemic (upward)

Bayleton 50W, 0.5 - 1.0 oz, SI / DMI, Systemic (upward)

Rubigan 1AS, 1.0 - 1.5 oz, SI / DMI, Systemic (upward)

Eagle, 0.6 - 1.2 oz, SI / DMI, Systemic (upward)

Trinity, 0.5 - 1.0 oz, SI /DMI, Systemic (upward)

Signature, 4.0 oz, Phosphonate, Systemic(upward & down)

Finally, the best long-term control strategy for chronic basal rot anthracnose is to encourage bentgrass, which is much more tolerant of this disease. Reducing thatch, soil compaction by core aeration, topdressing, verticutting, etc., when anthracnose is not active and maintaining healthy turfgrass remain Best Management Practices (BMP's) and Integrated Turfgrass Health Management (ITHM).

For the 2007 Families of Fungicides for Turfgrass click here

Authors: Joseph Rimelspach & Michael Boehm