Physiological Effects of Phosphite Formulations on Turfgrass Challenged with Pythium and Heat Stress

Background:
> Estimated in 2003 that over $400 million spent on fungicides for disease control on US golf courses; for all sectors the cost must be close to $1 billion/yr.

> Pythium blight is one the most potentially devastating summer diseases of cool-season grasses.

> Chipco Signature ™ (fosetyl-AI) is a very popular fungicide for pythium blight control on golf courses, costing -$250/A per application. However, its patent expired recently.

> Active ingredient of fosetyl-AI as far as the plant is concerned is phosphite (POi) which can be supplied to plants by applying phosphorous acid or its K or NH4 salts.

> Bottom line: Flood of turf market with phosphite fertilizer formulations costing about $40 to $50/AII

> Phosphite, as an active ingredient, has been shown to have a direct fungicidal mode of action and an indirect one.

o Direct MOA: perturbs P-metabolism in oomycetes (Pythium & Phytophthora), inhibiting enzymes essential for energy production

o Indirect MOA: perturbs P-metabolism in plants, but in a non-lethal way. This P-stress signal appears to tum on defense genes and increase production of defense compounds to fight off pathogen attack and other stresses.

> Chipco Signature™ not only contains phosphite but is formulated with a patented green-blue pigment. Over the last 10 years, numerous turfgrass researchers have reported that this formulation not only controls Pythium

blight, but also results in greater summer stress resistance relative to other Pythium fungicides.

Objectives:

Is formulation important in terms of phosphite source and additives?
Do all formulations provide equivalent fungicidal activity and plant

physiological response (stress resistance)?

Three Field Trial Locations:

USGA L-93 green at TRC in Blacksburg (south location)
USGA L-93 green at TRC in Blacksburg (north location)
Perennial ryegrass fairway in Moneta, VA

Treatments 1-4 and 9-10 are phosphite fertilizer products or experimentals;

Treatments 5-6 are EPA-labeled as phosphite fungicides.

Disclaimer: Commercial products are named in this research summary for informational purposes only. Neither Virginia Tech nor Virginia Cooperative Extension endorses these products and does not intend discrimination against other products which also may be suitable.

Table 2. Percent algae on L-93 creeping bentgrass putting green at the Turfgrass Research Center in Blacksburg, VA when treated every 14-d with Phosphite Products.

Summary:

> At the perennial ryegrass fairway site in Moneta, VA all of the treatments except one experimental provided similar, and adequate, control of Pythium blight.

> On the creeping bentgrass putting green sites in Blacksburg, VA most of the treatments also provided good algae suppression. Do the phosphite applications perturb P-metabolism of algae as well as oomycetes such as pythium?

> Two rounds of pythium inoculation on the putting green trials were unsuccessful in causing pythium blight epidemics. No major differences in overall quality or performance have been noted due to phosphite treatments on these two trials.

> Leaf tissue samples collected for defense chemical analyses have yet to be lab processed; these results will be presented at the Jan 06 winter conference.

Researchers: E.H. Ervin, D. McCall, and X. Zhang

Sponsors: Virginia Turfgrass Foundation, Virginia Agriculture Council, Helena Chemical, Bayer Environmental Science, GRIGG™, LidoChem, and Luxembourg Industries

Treatment List: N, P, and Kare equalized across plots; chlorothalonil was applied to each plot every 14-d to control dollar spot and brown patch.

Fertilizer check = 0.115 lb NIM from Plant Marvel 20-20-20 with micros
P-K Plus® (3-21-18) @ 6 oz/M + Gary’s Green Ultra® (13-2-3) @ 9 oz/M
ExpG (0-28-28) @ 6 oz/M
Nutrol (0-50-32) @ 10 lb/100 gal + Prudent (6-20-6) @ 4 oz/M
Vital Sign @ 6 oz/M
Subdue Maxx @ 1 oz/M
Signature @4 oz/M
Aliette @4 oz/M
HM1 = EleMax Foliar Phosphite (0-28-26) @ 5 oz/M
Experimental 04 @ 3 oz/M + 06 @ 7 oz/M

EXAMPLE DATA TO DATE: SUMMER 05

Table 1. Percent Pythium Blight on Perennial Ryegrass Fairway at Waterfront CC in Moneta, VA when treated every 14-d with Phosphite Products