Non-salt tolerant cultivars of rice, lettuce and radish as well as salt tolerant varieties of alfalfa, barley, and wheat were screened in the greenhouse and laboratory to determine if Labyrinthula terrestris, a new turfgrass pathogen, could infect plants other than turfgrasses. Wheat, barley and rice plants were infected, symptomatic and died. Radish and lettuce were infected but nonsymptomatic. Alfalfa was not infected and exhibited no symptoms. Results indicate that L. terrestris is capable of infecting and causing symptoms in plants other than cool season turfgrasses.

Rapid blight is a new disease of cool season turfgrasses that affects several important turfgrasses used for overseeding Bermuda in Arizona such as Poa trivialis and Lolium perenne (perennial rye). It is caused by Labyrinthula terrestris, an unusual organism that causes collapse of susceptible hosts and usually occurs in turfgrasses irrigated with moderate to high salinity irrigation water (EC>2.0). Rapid blight has not been observed in the field in warm season grasses such as Cynodon sp. (Bermudagrass) although laboratory trials have shown that common Bermudagrass and other grasses may be hosts. Because the survival mechanism of Labyrinthula terrestris in the absence of cool season turfgrass hosts was unknown, this study was initiated to determine if L. terrestris "over-summers" in different Bermudagrass systems. Results of assays of several different Bermudagrass systems show that Bermudagrasses are good hosts for L. terrestris and explains why rapid blight is a perpetual threat year after year in the same locations.

Rapid blight is a new disease of cool season turf grasses that has occurred on over a dozen golf courses in Arizona. It is caused by Labyrinthula terrestris, an organism in a group referred to as the marine slime molds. A trial was conducted in fall 2005-winter 2006 to evaluate efficacy of selected fungicides for control of rapid blight at a golf course in central Arizona with a previous history of disease and high salinity irrigation water (about 5 dS/m). Plots were established in late October 2005 on a practice tee on which Bermuda was overseeded with Poa trivialis. Treatments included Insignia and Fore, alone and in combinations; elemental sulfur, potassium sulfate and potassium chloride as pre-plant applications on Bermuda; gypsum, Daconil Zn, Heritage TL, Soil Life and Soil Builder. Disease symptoms appeared immediately after the first mowing. Disease ratings at 3 weeks after first mow showed that applications of the high rate of Insignia at first mow and the pre-overseed application of sulfur gave excellent control. Moderate control was shown in applications with early applications of Fore alternated with the lower rate of Insignia, Fore alone, Soil Life, and of the high rate of Insignia combined with Fore applied as a curative at first disease. Treatments with Daconil Zn, Heritage TL, Soil Builder, and preoverseed treatments with potassium sulfate, potassium chloride and gypsum gave little or no control compared to the untreated control. At 10 weeks after first mow, treatments with Insignia and the high rate of sulfur were still effective but all other treatments were either marginal or not different from the untreated control. Results show that applications of Insignia at first mow are effective for severe early season disease, and extended intervals of Insignia applications give effective long term control. Results also show that treatments of Bermudagrass with elemental sulfur reduced disease dramatically indicating that preventive chemical applications before overseeding may be possible.

Rapid blight is a new disease of cool season turf grasses caused by Labyrinthula terrestris, an organism in a group referred to as the marine slime molds. A trial was conducted in fall 2006-winter 2007 to repeat an evaluation of efficacy of different rates and intervals of Insignia fungicide and elemental sulfur, both of which gave acceptable control in trials in 2005. The trial was conducted at a golf course in central Arizona with a previous history of disease and high salinity irrigation water (about 5 dS/m). Plots were established in August 2006 on a practice tee on which Champion 419 bermudagrass was overseeded with Poa trivialis "Laser". Treatments included pyraclostrobin (Insignia) as a preventive and as a curative, pyraclostrobin (Insignia) combined with Fore as a preventive, and elemental sulfur (DsiperSul) as a preventive. Disease symptoms appeared immediately after the first mowing. Disease ratings 15 days after first mow showed that applications of the high rate of Insignia at first mow gave excellent control. Moderate control was shown in applications with early applications of Fore combined with the lower rate of Insignia. Treatments with Insignia as a curative and with sulfur as a preventive were not acceptable.

Rapid blight is a new disease of cool season turf grasses caused by Labyrinthula terrestris. It is problematic in Arizona and ten other states in cool season turfgrasses at sites with elevated salinity of soil and/or irrigation water. L. terrestris colonizes Tifgreen bermudagrasses in the field, but causes no apparent disease. Laboratory trials have shown that as concentrations of sodium chloride in irrigation water increase, disease severity increases, and when calcium and potassium salts are used to increase salinity, disease is greatly reduced or not observed. In preliminary field assays of cool-season turfgrasses irrigated with effluent, L. terrestris was observed in laboratory cultures from non-symptomatic turfgrass. To further substantiate if L. terrestris and/or other Labyrinthula species were present in non-symptomatic turfgrass in the field and to determine if disease could be induced by increased salinity, a trial was conducted at the Karsten Turfgrass Research Facility of The University of Arizona. In August 2006, field plots were established in bermudagrass "Tifway 419" and overseeded with Poa trivialis "Laser" in October. Plots were treated with potassium chloride, potassium sulfate or sodium chloride salts to increase soil salinity. Other plots treated with fungicides that are ineffective in controlling rapid blight as well as a sulfur treatment also were included in the assays. Poa trivialis was sampled in December 2006 and April 200. In laboratory assays using a semi-selective medium, Labyrinthula was detected in all treatments. Incidence was significantly higher in the untreated control and fungicide treated plots than in the salt treated plots. Results show that increasing soil salinity did not induce disease or result in an increase in detection of Labyrinthula at this site. Results of this study on Poa trivialis and previous studies on Tifgreen bermudagrass suggest that Labyrinthula may be widespread in non-symptomatic turfgrasses.

Rapid blight is a new disease of cool season turf grasses that has occurred on over a dozen golf courses in Arizona. It is now known to be caused by Labyrinthula terrestris, an organism in a group referred to as the marine slime molds. A trial was conducted in fall 2003 and winter 2004 to evaluate efficacy of selected fungicides for control of rapid blight at a golf course in central Arizona with a previous history of disease. Plots were established in late October2003 on a practice green on which Bermuda was overseeded with Poa trivialis. Treatments included Compass, Insignia, Fore, Bordeaux, Kocide 2000, Microthiol Disperss, Ecoguard and Floradox in various combinations and application dates. Disease symptoms appeared about 6 weeks after the first mowing and were evaluated in mid January. Results indicate that applications of Fore, Insignia and tank mixes of Insignia and Compass with Fore gave excellent control. Bordeaux, Compass alone, Compass alternated with Fore, Insignia alone, and Kocide gave good control. Microthiol Disperss, Floradox and Ecoguard gave poor control.

Rove beetles (Osorius planifrons) can and often do cause extensive surface disruption on turf mowed at greens height. Two rates (1x and 2x of product label rate) of Crusade (fonophos), Sevin (carbaryl), DeltaGard (deltamethrin), and Chipco Choice (fipronil), were applied on September 28, 2001 on an SR1020 creeping bentgrass green. Percent rove beetle control was nearly 100% for DeltaGard at 9, 15 and 32 days after treatment, regardless of rate. Crusade had nearly 100% control at either rate at 9 days after treatment, which decreased slightly to 90-93% control by 15 days after treatment. Deltamethrin maintained 95% and 98% control at the 1x and 2x rates respectively, at the close of the test (32 DAT). Crusade maintained 93% and 98% control at the 1x and 2x rates at 32 DAT. Chipco Choice had a maximum control of 24% at 7 DAT when applied at the 1x rate, and a maximum control of 57% at 32 DAT when applied at the 2x rate. Sevin provided low levels of control which peaked at 53% at the 1x rate at 9 DAT, which decreased immediately afterwards. Delta-Gard and Crusade provided excellent control levels of rove beetles on SR1020 bentgrass greens.

Rapid blight is a new disease of cool season turf grasses that has occurred on several golf courses in Arizona over the past five years. It is now known to be caused by a Labyrinthula sp., an organism in a group referred to as the marine slime molds. A trial was conducted in fall 2002 to evaluate efficacy of selected fungicides for control of rapid blight at a golf course in central Arizona with a previous history of disease. Plots were established in October 2002 on a practice green on which Bermuda was overseeded with Poa trivialis. Treatments included Compass, Insignia, Fore, Eagle and Aqueduct in various combinations and application dates. Disease symptoms appeared several days after the first mowing and continued for over three months. Results indicate that both pre- and post-plant applications of Fore and post-plant applications of Insignia and Compass gave good control. The best results were obtained with the treatment of Fore combined with Compass that included a pre-plant application of Fore, or with post-plant application of Insignia.

A number of turfgrasses were screened in the greenhouse and laboratory for susceptibility to Labyrinthula terrestris, a new turfgrass pathogen that causes rapid blight of cool season turfgrasses. Salt tolerant varieties and warm season grasses such as Bermuda grass, tufted hairgrass, inland saltgrass, centipede grass, seashore paspalum and kikuyugrass were not susceptible; cool season grasses such as velvet bentgrass, annual ryegrass, perennial ryegrass, annual bluegrass, Kentucky bluegrass, and rough bluegrass were very susceptible.

Rapid blight disease is a potentially devastating disease on cool season overseed turfs when irrigated with saline water. A two year test was conducted on a closely mowed Tifgreen bermudagrass turf which was infected with visual symptoms of necrotic patches of turf, and various degrees of blighting. The test included a broad representation of turf species for overseeding in an effort to (1) determine selected specie/cultivar susceptibility and disease expression to rapid blight in the field and (2) survey and assess the association of laboratory isolate detection from field sampling, with disease occurrence and severity of expression of field maintained overseed turf. Over a two year period, Rapid blight, caused by Labyrinthula terrestris was capable of infesting most cool season grasses in this test. In year one, Dawson CRF, SRX 555 slender creeping red fescue, and SR 105210 slender creeping red fescue showed no positive lab detection results from field plots. In year two (2003-2004), only SRX 555 SLQ had only 1 plot known to carry Labyrinthula throughout the main infestation season. In year two, essentially all turf plots showed some symptomology of disease expression. This was confirmed by lab identification. Tiller infection rates varied from 2% to 80% infection in the lab from field samples. The relationship between tiller infection rates and field plot disease expression was determined by Pearson’s product and Spearman Rank correlation coefficients. Field plot disease scores were correlated with percent tiller infection rates, R² = -0.56 plot basis, and R² = –0.71 treatment mean basis, respectively. Spearman Rank correlation coefficients were R² =; -0.62 on a plot basis, and R² =–0.78 based on treatment means Agreement between the disease condition (yes/no) vs. lab findings (positive/negative) occurred on 51 of 59 plot cases, and was significant compared to chance alone occurrences. Over two years, entries which had low disease scores included Fult’s alkali grass, Dawson creeping red fescue, SRX 555 SLQ slender creeping red fescue, SR 5210 slender creeping red fescue, and Providence creeping bentgrass. Over two years, entries which produced high field disease rating scores included SR 3100 Hard fescue, TransEze intermediate ryegrass, SR 4400 perennial ryegrass, SR 7200 velvet bentgrass, SR 7100 colonial bentgrass, Sabre and Laser Poa trivialis, and Redtop.