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.