Bacterial Disease

The summer of 2010 has taken its toll on turf, budgets, and superintendents. This summer we seen areas with 25 or more consecutive days of 90 degree heat, high humidity, extended drought in some areas, and heavy rains in other areas, the turf has been pushed to the very edge.

We have received some very disturbing emails about bacterial disease hitting creeping bents this summer. After emailing and visiting with several university experts, they all tend to agree that there is not a widespread outbreak of bacterial disease. Most would agree that the creeping bent grass has already been compromised by other contributing factors, and that has resulted in the onset of bacterial wilt as a secondary infection. Contributing factors were weather with extended high heat and humidity, low mowing height, wear from mowers and foot traffic, rainfall, and onset of other diseases due to the extreme weather. They have also stated that ALL bents are susceptible to this infection, not just certain cultivars. The ones being maintained at a very high level seem to be the ones most likely to be affected.

The golf courses that are maintaining their bents at these extreme levels during these high-stress times are the ones that seem to be more vulnerable. Private, semi-private, and upper scale public courses are always under pressure to keep their turf at so-called standards at all times. These standards put superintendents at a disadvantage from the start. As most superintendents know, they need to take measures to protect their greens, but their hands are forced by the clientele they serve. One superintendent stated to his members, “ We can have green speed now and run a risk of losing greens, or we can raise the height for a couple of weeks and have perfect greens this fall.” His greens are some of the best I have seen this summer.

Below you will find information sent to me from one of the university turf pathologists.

Bacterial Disease on Turf
There is a great deal of concern in the northeastern quadrant of the U.S. over a bacterial disease on creeping bentgrass. Most diseases on turf are caused by fungal pathogens, therefore most research and knowledge has been generated on diseases caused by fungi. With the current bacterial disease outbreak, pathologists are trying to learn more about the disease and causal agent(s).The information below summarizes what we know about the nature of the bacterial disease.

Disease Observations--
The disease seems to be limited to creeping bentgrass putting greens. Initially it appears as a normal summer decline, but damage gets progressively worse. On individual plants, leaves turn yellow or a blotchy yellow green. They often appear weak and wilty. If symptomatic leaves are examined microscopically and a bacterial streaming is observed, then it is reasonable to conclude that bacteria have entered and are multiplying within-- turf leaves.
The bacteria are most likely normal saprophytes within the turf environment, and that unusual conditions have predisposed plants to invasion by normally inconsequential bacteria. That is, they have not been introduced with storms or with seed of a certain type of grass.

The warm, wet summer of 2010 seems to favor bacterial invasion. No cases were brought to our attention during the cool summer of 2009. Bacteria thrive in wet environments. Nitrogen fertility does not appear to be a factor in the levels of disease development.

To date, most reports seem to involve a all cultivars that are more intensively managed. The likelihood that these varieties have a genetic susceptibility to infection or invasion by these bacteria is very low. Bacteria enter plant tissues through natural openings (stomates and hydathodes) and through wounds (think mowing and top-dress dragging). Until the weather changes (I think turf will begin to recover with the arrival of cool nights and dry days), a variety of marginally effective treatments may be considered. Since we have no real research results, the only control information is anecdotal. No magic bullet has been found in fact, no treatment has been shown to slow the invasion and promote recovery.



Below are my opinions on the following treatments.
1. Conventional fungicides. They will not be effective. Not chlorothalonil, not DMIs, not QoIs--none.
2. Phosphites. These fungicides reportedly trigger a plant's own defense mechanisms. They can't hurt-- and they may be effective against fungi, but only when disease pressure is fairly light. I am not convinced phosphites will reduce severity of these bacterial outbreaks. Furthermore, on some courses where outbreaks occurred--a regular phosphite application program was already in place.
3. Zerotol. This hydrogen dioxide "biorational" can be effective against surface bacteria, but may also eliminate natural antagonistic "good" bacteria. In our research trials, plots treated with Zerotol often suffered greater levels of dollar spot than untreated check plots. There are no reports where bacterial outbreaks were quelled after Zerotol application.
4. Mycoshield. This is an antibiotic (oxytetracycline) used against true bacterial pathogens of tree fruit. There is no turf label and no research indicating the tetracycline will be effective against bacterial outbreaks on turf.
5. Copper hydroxide. Copper formulations may be effective against bacteria. We know that high rates can be phytotoxic (yellow leaf margins), especially during periods of hot humid weather. If you give it a try, use the low label rate. The Junction product includes copper hydroxide and a mancozeb (remember Fore?) fungicide. The combination has reduced bacterial disease severity in vegetable crops. The phytotoxicity issue is a concern.
6. Rhapsody. Rhapsody is labeled for control of some fungal diseases on turf. The "active ingredient" is bacterial. The bacteria colonize plant surfaces and release certain metabolites that may be toxic to fungi. Our research shows that it is not effective against dollar spot. However, if the bacteria do increase on plant surfaces, then they may out-compete the bacteria that cause the issue on creeping bentgrass. There is no evidence here--just a reasonable theory. It smells awful, so be prepared.

Special Thanks to Dr. Rick Latin Purdue Univeristy