Anthracnose

Anthracnose is a fungal disease that especially attacks Poa annua and creeping bentgrass in turf, but it also attacks other crops. It was believed that the pathogen causing disease in turf species was the same pathogen that caused disease in other crop, such as corn. However research by J.A Crouch, B.B. Clarke and B.I. Hillman in 2006, showed the pathogen causing the disease in cool-season turf was a different species. Research using DNA analysis showed that even the species attacking bentgrass and Poa annua are different from each other, which could mean that if you have an attack of anthracnose in plants other than turf, those are will not cause problems on the turf (1).

Symptoms

On Poa annua dying or senescing leaves will show yellow or orange spots that will coalesce and eventually turn the entire leaf yellow or orange. Acervuli, the reproductive structure, can be seen through a microscope and is a distinct feature to identify the pathogen as anthracnose.

As the disease progresses from the foliar stage to infect the stem (basal rot), it means the end for the infected plant. Once the disease reaches the crown the plant dies.

Managing Anthracnose

As with most diseases there is no miracle drug, no “octopus saliva”, that gives total control at all times. Therefore o a combination of approaches must be used to get the best results. These approaches include

• Chemical control

• Cultural practices

Chemical control

In chemical control there are two ways of going about it: preventive and curative control. According to Murphy etal. preventive control has proven more effective than curative. When to apply the preventive spray of fungicides is not yet known, but Murphy etal. recommends to start the preventive program a month before a potential outbreak of the disease. Making predictions is a tricky thing, especially about the future, which is why good records of previous year’s conditions on the golf course are crucial.

Using chemicals comes with its downsides. One of them is the possibility that the strand of pathogen will develop resistance to the fungicide. To avoid that, or at least keep the resistance off for as long as possible, it’s recommended that you use different fungicides and fungicides with different modes of action.

Fungicide resistance develops when using a single fungicide that does not kill off all the fungi. The surviving organisms, that for some reason had a genetic mutation that protected them from the fungicides, will reproduce and pass down the genetic mutation. Using the same fungicide over and over increases the percentage of the resistant organisms and there by result in less and less control with the fungicide. When the resistant strand has finally taken over the population you have no control with the fungicide and you have a resistant population.

Cultural Practices:

The members expect fast rolling greens, so the superintendent does all he can to produce that. This is accomplished by, keeping the fertility low to keep the grass from growing and by mowing the greens at very low heights and therefore the turf gets stressed. Stressed or weakened plants that are using all there photosynthates to just keep alive are susceptible to attack from pathogens. Poa annuais particularly affected because it produces seedheads under extremely low mowing heights. The seedhead production takes up a lot of the photosynthates produced by the leaf tissue.

Mowing

Research in New Jersey showed that a slight increase of mowing height by 0.015 inches reduced the severity of the attack (1). A double cut produced the same green speed as the lower mowing height. Alternating with rolling and double cutting showed the same results; less disease.

Topdressing

Diluting the thatch with topdressing creates better growth environment for the plant and the topdressing helps protect the crown. All this helps strengthen the plant and thereby make it healthier and better equipped to fight off the invading pathogen. Light and frequent (14 days apart) topdressing showed better results than heavier topdressing put out less frequently.



(1) Murphy, James; Wong, Frank; Tredway, Lane; Crouch, Jo Anne; Inguagiato, John; Clarke, Bruce; Hsiang, Tom; Rossi, Frank. 2008. Golf Course Management. August. 76(8): p. 93-104.