Anthracnose

Anthracnose symptoms on a Poa annua green. Notice that the bentgrass plugs are not infected.

Anthracnose is a serious disease of Annual bluegrass (Poa annua L.)and Creeping bentgrass (Agrostis stolonifera).  The pathogen now known as Colletotrichum cereale, was formerly known as Colletotrichum graminicola.  Although related to some degree anthracnose is associated as either a foliar blight or a basal rot.

 

Foliar Blight

 

The foliar blight occurs during summer stress periods when nighttime temperatures remain above 68 F.  During infection extended wetting periods favor disease development.  Symptom expression is enhanced with intermittent periods of moisture stress.  Poa annua fairways are most susceptible to the foliar blighting. 

 

Initial symptoms appear as an irregular yellowing of the turf.  The initial yellowing is shown where the arrow is pointing.  Symptoms progress to an irregular shaped yellow orangish-red areas.  If conditions remain favorable blighting of large areas can occur.  Symptoms are often confused with heat and drought stress. 

 

The leaf symptoms appear as yellowish-orange lesions.  A sign of the pathogen is the presence of black fruiting structures within the lesion. These black fruiting structures are called acervuli. Small spines called setae often protrude from the acervuli.

 

Basal Rot 

Acervuli present on the sheath of creeping bentgrass plants.
Acervuli present on the sheath of creeping bentgrass plants.

 

Basal rot anthracnose is considered  more widespread and devastating than the foliar blight.  Basal Rot, which can occur from early spring through late fall into winter.  During the spring, basal rot initially appears as yellow or orange speckles or spots on Poa annua greens.  Rarely if ever occurs in the spring on creeping bentgrass.    

 

In some cases Poa annua greens coming out of winter or early spring may exhibit the characteristic yellow to bright orange to red color symptoms you may expect later in the summer.  As the symptoms progress or as summer stress conditions arrive, the turf can start to thin and irregular shaped patches become more evident.  The turfgrass plants often progress from a yellowish to a bright orange or red color prior to dying. 

 

Although Poa annua is primary turfgrass attacked, creeping bentgrass may be infected during summer stress months.  Interestingly, I have not observed anthracnose on both Poa annua and creeping bentgrass on the same green.  It is either on one or the other species.  Symptoms are similar on creeping bentgrass as those on Poa annua.  Besides the overall symptomology, signs of this disease include water-soaking and rotting and blackened areas along the lower portion of the sheath. 

 

Upon closer examination of the crown may reveal the presence of the fruiting structure called acervuli, sometimes devoid of the characteristic spines or setae.  Acervuli may also be present along the sheath of the plant in this case these plants are creeping bentgrass.  For some reason, most likely pathogen host specificity, anthracnose tends to attack either Poa annua or creeping bentgrass but not both on in the same area or on the same green. 

 

Cultural controls should center or relieving stress to the Poa annua or creeping bentgrass green.  This may include reducing the intensity of management such as raising the height of cut, reducing the frequency of double cutting, and maintaining adequate fertility levels.  Promoting air movement and increasing light through the removal of trees has reduced the severity of basal rot anthracnose.