Disease Happenings - 2007

September 20, 2007

Several diagnoses of Rhizoctonia leaf and sheath spot, caused by Rhizoctonia zeae have been made this month. The most common symptom is an irregular and diffuse patch of thin and blighted turfgrass. The pathogen can be isoalted most of the year, but periods of stressful weather tend to make symptoms worse and more noticeable. Recent cloud cover, rain, and cooler temperatures will probably result in more samples in the next few days with leaf and sheath spot, Bipolaris leaf spot, and Pythium root rot.

At the research plots, turfgrass quality is suffering due to the recent weather. Plots in fungicide trials that have been treated preventatively with fungicides look significantly better than untreated plots. Fairy ring is active, bipolaris leaf spot, Fusarium blight on paspalum, leaf and sheath spot, etc.

October is going to bring shorter day lengths, cooler temps and the threat of large patch to zoysiagrass, seashore paspalum, and St. Augustinegrass. Preventative apps in our fungicide trials in central Florida, will go down when soil temps fall to 75F at about 2 in.

June 18, 2007

Take all root rot on St. Augustinegrass and Bermudagrass decline have been diagnosed recently from central and south Florida. Both diseases are caused by the same pathogen, Gaeumannomyces graminis var. graminis. Diagnoses are made after association of root rot symptoms with dark hyphae and lobed hyphopodia on roots and stolons (see pic below).

Management of these diseases can be difficult—especially curative management. The most important practice is to minimize stresses that could be caused by improper mowing, fertility, irrigation, or other cultural factors. The pathogen is soil borne and the disease tends to occur in the same places year after year. Fungicide applications made to these perennial problem areas can prevent symptoms when used in combination with cultural practices to reduce turf stress. For more information see: http://edis.ifas.ufl.edu/LH07

Two diseases that we expect to see starting to come into the clinic on bermudagrass are Pythium root rot and Rhizoctonia leaf and sheath spot. Last year these two made up a majority of summer diagnoses. Symptoms are generally not as distinct as something like dollar spot, but generally include thinning declining areas of turfgrass that do not respond well to fertility and have little recuperative potential. UF research has shown that preventative fungicide programs that rotate systemic and contact products with efficacy on Pythium and Rhizoctonia pathogens can greatly increase turfgrass quality in areas such as these.

Image: Lobed hyphopodia of the take all root rot and bermudgrass decline pathogen

May 1, 2007

Drought conditions over much of the state have stressed turfgrasses on golf courses, sports fields, and lawns. An outbreak of dollar spot on seashore paspalum occurred two weeks ago (mid April) at the UF turfgrass research plots in Citra. Large patch on zoysiagrass and paspalum also was active around the same time, but symptoms were mild and the disease didn’t amount to much loss in turf quality.

Yesterday, I noted significant Bipolaris leaf spot and melting out symptoms on the Envirogreen in Gainesville. A handful of bermudagrass samples also have been diagnoses by Oscar and I in the lab recently. Bermudagrass typically recovers from leaf spots quickly when given plenty of sunshine and light, but recovery from the crown rot or melting out symptom can take longer, especially when it occurs in winter or under other envirionmental stresses. Several fungicides are labeled for leaf spot diseases, and several different pathogens have been associated with these symptoms. Remember to follow all product label recommendations, including resistance management strategies such as product rotation.

Image: Two spores of a Bipolaris pathogen and conidiophores (structures that produce the spores)

April 6, 2007

Dry weather has predominated in the previous month bringing on drought condition for most of Florida. However, the most predominant disease being diagnosed on all turfgrass samples (golf course, sod farms, lawns) has been Pythium root rot.

Most turfgrasses are starting to come out of dormancy and are beginning to recover from winter stress, disease, and damage. Turfgrasses affected by root diseases sometimes begin to show severe above ground symptoms when drought-stressed. The occurrence of these disease symptoms during dry weather is somewhat counter-intuitive, because root rot development is typically favored by water-logged soils. Although the pathogen is not likely to be actively infecting new turfgrass plants (unless over-irrigation is an issue), we suspect turf with existing root damage is showing symptoms because the less efficient root systems of diseased plants are failing to provide the turf with adequate water.

In cases where roots are damaged, the turf may appear drought stressed, but even over-irrigation will not relieve this physiological stress. In fact, over-irrigation favors continued development of Pythium and other root rot diseases.

To help prevent this disease we should be mindful of irrigation quantity and frequency. Frequent and short irrigation cycles are not ideal. When possible we want to make longer, less frequent irrigation applications to help promote deep root growth and drought tolerance.

February 22, 2007

The colder weather that followed my 25 Jan comments meant a week's slow down in sample numbers at the clinic. Samples now are arriving at the lab with regularity. These are the top diagnoses for the last month in Florida Rapid Turfgrass Samples.

Pythium root rot and blight have been diagnosed in a number of bermudagrass samples. Research conducted by Dr. Stiles has shown Pythium infestation of bermudagrass roots to increase in winter months even though above ground symptoms of root rot may not be visible in some cases. It is not well understood what specific environmental factors trigger disease development.

A handful of samples of cool-season overseed have been diagnosed with Rhizoctonia leaf and sheath spot. These isolates are the subject of a joint research project between Dr. Datnoff and myself and may represent a previously unreported disease in Florida.

Bipolaris melting-out disease was diagnosed on a bermudagrass putting green as well. A group of related pathogens that used to be referred to as "Helminthosporium" causes melting out (crown and shoot rot-like symptoms) in winter and distinct purple leaf spots in summer. Summer leaf spots generally do not result in significant turf losses, but melting-out symptoms can significantly reduce turf quality well into spring and bermudagrass growing conditions.

January 25, 2007

Samples have been pouring into the Rapid Turfgrass Diagnostic Service since the New Year. Much of the state has seen above average temperatures and wetter, more humid conditions than normal. Below are some of the diseases we have seen recently. This is what to look out for in your turf.

In north central and central Florida, several samples have been diagnosed with large patch (brown patch) disease. Hosts and turf sites have included St. Augustinegrass, zoysiagrass, and seashore paspalum on sod farms, home lawns, and golf turf. Preventatively treated plots in fungicide trials did not develop disease, but only if repeated applications were made. Curative fungicide applications do not typically result in turfgrass recovery until turf growing conditions improve in spring. However, disease continues to develop on our research plots in Citra, so protectant applications may still be warranted as long as warm wet conditions persist.

In south Florida, several golf courses have experienced dollar spot and brown patch on seashore paspalum. Several bermudagrass greens have been diagnosed with Pythium blight (unusual diagnosis, but not surprising with recent weather). Some samples also were diagnosed with both Bipolaris melting-out and Pythium blight. Additional disease development is entirely possible if warm humid weather continues. Today’s cooler temperature should relieve some disease pressure.

• Rapid Turfgrass Diagnostic Service