Disease Happenings - 2009

Archive of Disease Happenings 2007
Archive of Disease Happenings 2008

May 2009

Yellow Blotches in St. Augustinegrass Lawns

Hundreds of calls, emails, and inquiries have come to the attention of turfgrass faculty at UF this spring.  Many St. Augustinegrass lawns developed chlorosis (yellowing) symptoms with various levels of severity and patterns.  Email and phone conversations between turf faculty, one survey of a small number of affected lawns, and several samples processed at the Florida Extension Plant Disease Clinic have provided some insight as to possible causes.  The yellowing itself is a response of the turf plant indicating the lack (or overabundance) of a vital nutrient.  The underlying cause can be a compromised root system, unfavorable soil chemistry (such as improper pH, or soil nutrient levels), or presence of particular classes of herbicides in some cases. 

Photo credit: George Hochmuth

Primary causes
Winter injury:  St. Augustinegrass can be injured or killed by below-freezing temperatures (-7 C or colder).  The degree of injury is dependent on many factors including the cultivar of grass.  Symptoms can range from yellowing and thinning to death of the turf stand.  The symptoms of winter injury will sometimes occur in patterns that suggest a secondary stress is involved.  Soil compaction, disease, and fertilizer or pesticide application patterns all can show up as variation in the winter injury severity or occurrence in a lawn.  Cultural management of the lawn prior to and during winter can affect the likelihood and severity of winter injury as well.  Follow the fertilizer application rates and timings in UF resources and avoid late-season fertilizer applications in particular as these may contribute to winter injury later.  (see http://edis.ifas.ufl.edu/EP221 http://edis.ifas.ufl.edu/document_lh014 for more fertilizer information)

Take all root rot:  The disease is typically thought-of as a summer disease that kills large areas of turfgrass.  However, the first symptom that often is observed is yellowing of the lawns in areas where the disease will later develop to be most severe.  The pattern of the yellowing will be random, non-uniform, and will tend to occur in low areas with high soil pH in many cases where take all root rot is the cause.  To test if the symptoms are being caused by disease, take samples from the yellowing turfgrass and from nearby healthy grass and send them to the Florida Extension Plant Disease Clinic.  If the pathogen is present, the disease could be contributing to the problem.  A fungicide application now, before the turf dies, (preventative) may help reduce the chance of turf death this summer.
What to do:

If no disease is found, then fungicide isn’t necessary.  Maintain the turf according to University of Florida management recommendations and the symptoms should fade with time.  Dead areas will not recover, so they will need to be sprigged or sodded or will have to grow-in from unaffected areas of the lawn.  Ensure that the proper fertilizer, irrigation, mowing height, herbicide, insecticide, and other recommendations are observed to give the turf the best chance possible for a speedy recovery. See UF resources at: http://edis.ifas.ufl.edu/
Simply type “St. Augustinegrass” or the particular topic of your choice in the search box.

 

Mapping Function for Rapid Turf Service

IFAS DDIS folks (thanks Xin) have developed a mapping website for our turf sample data. It shows what diseases occur on what grasses in what FL counties, during time periods the user specifies. Download the plug-in and try it.

Rapid Diagnostics Map

 

• Rapid Turfgrass Diagnostic Service