The Magic Of Rain

By John H. Foy, director, Florida Region
July 14, 2011

The magic of rain!  Kyle Sweet, Golf Course Superintendent at the Sanctuary Golf Club on Sanibel Island provided these dramatic before and after pictures of the 13thhole.  Once the summer rainy season finally started, it has taken about three weeks for the seashore paspalum fairways and roughs to recover.  A similar and even faster recovery has occurred with bermudagrass on other courses in South Florida.  

Over the past two or three weeks, summertime thunderstorm activity has ramped up and brought very much-needed rain to South Florida.  Unfortunately however, there are areas in the central and northern part of the state that are still experiencing record-setting drought conditions.  The short range forecast from the National Weather Service calls for above-average rainfall for the entire region; and with this, the magic of rain will result in a recovery in turf health and quality.  Although we still need a lot of rain to get back to normal, remember that there are management challenges when summertime thunderstorms result in a pattern of frequent and very heavy rainfall events. 

Even when an adequate quantity of good quality water is available for irrigation, the growth response that occurs with rainfall is still much more significant.  This is especially true after a prolonged period of no rain, and the pronounced growth response is at least in part due to flushing of salts out of the rootzone.  However, one of the subsequent challenges of frequent and heavy rainfall is maintaining sufficient levels of available nutrients in the soil to support sustained, balanced and healthy turf growth.  Both potassium and magnesium are extremely mobile in the sandy soils that are found throughout Florida.  Thus, these key nutrients are quickly leached out of the rootzone by typical summertime thunderstorms that can dump ½-inch or more of rain in a very short amount of time.  Over the next three or four months, frequent but light spoon feeding with potassium on putting greens, tees and fairways is advised to maintain adequate availability and in turn support photosynthesis, carbohydrate production and storage in preparation for the fall and winter months.

During the summer rainy season, a saturated rootzone can persist for extended periods of time, and with this soil oxygen content is depleted and the root system of the turf literally begins to suffocate and decline.  The rapid onset of drought stress can then be a problem with very shallow rooted putting greens when there is no rain for just a couple of days.  Thus it is still a good idea to closely monitor rootzone moisture content and be prepared to begin irrigating again to prevent the onset of drought stress.  This always tends to raise questions from golfers about why the maintenance staff is running water after it has rained almost everyday for a week or more. 

Another challenge with bermudagrass during the summer rainy season in Florida is significantly reduced sunlight.  From June through September, Florida honestly cannot claim to be the Sunshine State because there are only three to four days each month when totally clear skies prevail.  The normal buildup of afternoon thunderstorms and the resulting moderate-to-heavy cloud cover significantly reduces sunlight/total solar radiation, which in turn has a negative impact on bermudagrass growth and turf quality.  To compensate for a lack of sunlight, maintaining slightly higher heights of cut is necessary, especially on putting greens.  Along with having adequate leaf surface area to support photosynthesis, carbohydrate production and storage, maintaining a slightly higher height of cut is favorable to increased root system development.

Last, but certainly not least, constant high temperatures, humidity, and abundant moisture are the ideal conditions for fungal disease development.  University research over the past two or three years has determined that the greatest risk period for infection for Rhizoctonia zeae leaf and sheath spot is when canopy temperatures (which tend to be hotter than air temperatures) are in the low-80’s to mid-90’s.  The University of Florida Rapid Turfgrass Diagnostic Service has also reported that Rhizoctonia zeae is often identified in samples submitted to the lab between May and September, and yet disease symptoms and problems do not occur until the fall to early winter when the growth rate of the turf naturally slows down.  Given this scenario, many turf pathologists are now recommending that preventative fungicide treatment programs be employed during the summer and early fall.  Besides being more effective in controlling outbreaks of leaf and sheath spot, lower rate preventative fungicide treatment programs are actually more economical. 

Should the challenges mentioned in this update become a concern, give us a call.  We stand ready to work with you in any way we can.  If your course has not yet signed up for a Turf Advisory Service visit this year, we look forward to hearing from you.

Source:  John Foy, 


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