Field Evaluation of Phosphite-Based Products Challenged with Heat Stress and Pythium, 2007.

PERENNIAL RYEGRASS (Lolium perenne)

Pythium blight; Pythium aphanidermatum

Trial ID: PO3-07

 

A.E. Nichols, D.S. McCall, and B.J. Horvath

Department of Plant Pathology, Physiology, and Weed Science

Virginia Tech Blacksburg, VA 24061

Field evaluation of phosphite-based products challenged with heat stress and Pythium, 2007.

Phosphite-based fertilizers and fungicides were evaluated for their efficacy in alleviating summer heat stress, and control of pythium blight in perennial ryegrass when applied preventatively. Plots treated with phosphites were evaluated against untreated plots, fertilizer check plots, and Subdue MAXX for comparison. This study was conducted at two test sites. The first trial (HR) was conducted at the Hampton Roads Agricultural Research and Education Center in Virginia Beach, VA on nine month old stand of ‘Southern Belle Overseeding Blend’ perennial ryegrass (44% Bright Star SLT, 35% Citation Fore, 19% Quicksilver). Mowing was performed once per week at 4 in. with clippings returned. The site was irrigated heavily to increase disease pressure. Fertilization was applied to increase disease pressure as 46-0-0 on 6 Jun, 5 Jul, 24 Jul, 8 Aug, and 23 Aug at the rate of 0.75 lb N/M, 0.5 lb N/M, 0.5 lb N/M, 0.5 lb N/M, 0.5 lb N/M, and 0.5 lb N/M, respectively. Iprodione (18+, 26GT) (8 oz/M) was applied preventatively on a 14 day schedule beginning on 22 Jun for the control of non-Pythium diseases. Prostar 70WP (2.2 oz/M) was tank mixed with the iprodione application on 20 Jul for control of suspected Rhizoctonia zeae. The experimental area was inoculated four times on 8 Jul, 22 Jul, 5 Aug, and 29 Aug with a sand/cornmeal mixture infested with P. aphanidermatum (isolate BG1). The second trial (WF) was conducted at the Waterfront Country Club in Moneta, VA on an established perennial ryegrass fairway. The WF test site was managed by the golf course maintenance staff. Mowing was performed three to four times per week at .75 inches. Plots were irrigated to prevent drought stress. Fungicides were applied preventatively to both sites for control of non-Pythium diseases. Individual plots were 3 ft x 6 ft at HR and 6 ft x 6 ft at WF and were arranged in a randomized complete block design with four replications. All treatments were applied at a spray volume of 2 gal per 1000 ft² with a CO₂ powered backpack sprayer at 46 psi using TeeJet 8004 EVS nozzles (HR) and 37 psi using TeeJet 11003VS nozzles (WF). Treatments were initiated on 6 Jun (HR) and 18 Jun (WF) and were reapplied every 14 days +/- 2 days through 29 Aug and 13 Aug, respectively. Percent Pythium blight severity and turfgrass quality were evaluated periodically and data were subjected to analysis of variance and means were separated by Fisher’s Protected LSD (p=0.05).

At HR, Pythium symptoms remained low until disease developed in August. On 9 Aug, Pythium was highly active, with all treatments except Subdue MAXX controlling the disease. Turfgrass quality was decreased by a severe outbreak of rust (Puccinia spp.). The phosphite formulations evaluated provided acceptable control of Pythium when applied preventatively under moderate conditions, but lost their significant efficacy once the disease became more severe. There were no significant differences disease ratings at WF, due to high variability in disease development from natural infestation. The entire first replication was deleted from the analysis because plots were accidentally oversprayed with a Pythium control product. Though differences were insignificant, there was consistently less Pythium in plots treated with phosphite fertilizers and fungicides than in untreated checks or fertilizer checks. There were no significant differences in overall turf quality on any rating date.

Pythium blight severity at the Hampton Roads AREC, Virginia Beach, VA, 2007.

^z Fertilizer Check rate in lbs N per 1000ft², Aliette and Signature rate in oz product per 1000ft², all other treatment rates in fl oz product per 1000ft²

^y Values are means of four replicates. Means within columns followed by the same letter are not significantly different according to the Least Significant Difference test (P=0.05)

Turfgrass quality at the Hampton Roads AREC, Virginia Beach, VA, 2007.

^z Fertilizer Check rate in lbs N per 1000ft², Aliette and Signature rate in oz product per 1000ft², all other treatment rates in fl oz product per 1000ft²

^y Values are means of four replicates. Means within columns followed by the same letter are not significantly different according to the Least Significant Difference test (P=0.05)

Pythium blight severity and turf quality at the Waterfront Country Club, Moneta, VA, 2007.

^z Overall turf quality on a 1 to 9 scale, where 9 = highest quality and 5 = acceptable.

^y Application rate in fluid oz/1000ft², except for (*) lbs N/1000ft2 or (**) oz/1000ft².

^x Values are means of four replicates. Means within columns followed by the same letter are not significantly different according to LSD (P=.05).