Use of Salt to Control Annual Bluegrass in Seashore Paspalum.Use of Salt to Control Annual Bluegrass in Seashore Paspalum.Lewayne White, Paul Raymer, and Patrick E. McCullough Lewayne White, Paul Raymer, and Patrick E. McCullough

Introduction

Annual bluegrass (Poa annua) is a problematic winter weed of seashore paspalum (Paspalum vaginatum) turf with limited herbicides for control.

Annual bluegrass reduces the aesthetic quality of turf and is a prolific seed producer that can grow well into early summer.

Salinity tolerance of seashore paspalum may allow practitioners to apply sodium chloride for annual bluegrass control but application timing may influence turf tolerance.

Objective To investigate efficacy of sodium chloride for annual

bluegrass control in seashore paspalum.

Materials and Methods

A field experiment was conducted in the spring 2009 to dormant seashore paspalum infested with annual bluegrass. The experimental design was a randomized complete block with four replications of 0.9 x 1.5 m plots. Sodium chloride rates were 0, 49, 98, and 147 g m-2. A pronamide (Kerb®) herbicide treatment at the maximum labeled rate of 0.18 g a.i. m-2 was included for comparison. All sodium chloride treatments were applied to wet foliage using a drop spreader while the pronamide treatment was applied at a spray volume of 187 L ha-1 using a backpack sprayer fitted with a boom. Annual bluegrass control was rated on a percent scale where 0 equaled no control and 100 equaled complete control. Data were subjected to analysis of variance and means were separated using Fisher’s LSD at the 0.05 probability level.

A growth chamber experiment was conducted in 2009 to evaluate annual bluegrass and seashore paspalum response to sodium chloride at three temperatures, 10, 20, and 30° C. Sodium chloride levels were 0, 24.5, 49, 98, 196, and 392 g m-2. Sod from field grown grass was placed in pots with 1 dm2 surface area and 10 cm depth filled with soil. The experimental design was a randomized split block. Temperatures were the main plots and herbicide rate the subplots. To help reduce chamber effects, pot positions in each chamber were randomized every ten days. Plant quality was visually rated four weeks after treatments on a 0 to 10 scale where 0 was dead and 10 equaled optimum health. Results were then converted to percent of the untreated at each temperature. Data were subjected to regression analysis in growth chamber experiments.

Results and Discussion

Field Study Results

• Seashore paspalum was not injured by sodium chloride or pronamide treatments (data not shown).

• At 21 days after treatment (DAT), sodium chloride treatments were more effective than treatment with pronamide (Table 1).

• At 42 DAT, sodium chloride treatments were as effective in controlling annual bluegrass as the maximum labeled rate of pronamide.

Growth Chamber Results

• Annual bluegrass injury from sodium chloride increased with temperature (Figure 1).

• At 10 and 20° C, annual bluegrass required approximately 49 g m-2 for complete desiccation. All sodium chloride treatments, including 24.5 g m-2, desiccated annual bluegrass at 30° C after four weeks.

• Conversely, seashore paspalum injury from sodium chloride decreased as temperature increased. Rates of rates of 24.5, 196, and >392 g m-2 were required to injure seashore paspalum at 10, 20, and 30°C, respectively.

Conclusions Sodium chloride has potential to control annual bluegrass.

Efficacy and seashore paspalum tolerance may increase with temperature.

Figure 1. Annual bluegrass and seashore paspalum growth chamber response to salt at three different temperatures.

Check

Field plots and growth chamber pots after sodium chloride treatments were applied.

The University of GeorgiaThe University of Georgia

50.0 ab2.5 bc0.18Pronamide

1. Days after treatment.

2. Means within the same column followed by the same letter are not statistically different at the p=0.05 level according to Fisher’s protected L.S.D.

78.8 a57.5 a147

57.5 ab45.0 a98

27.5 bc32.5 ab49 NaCl

0 c0 c20Control

annual bluegrass control (%)g a.i./m2

42 DAT21 DAT1RateTreatment

Table 1. Annual bluegrass control in dormant seashore paspalum field plots in response to NaCl and pronamide applications in 2009.

NaCl

146 g m2 -1

NaCl

49 g m2-1

NaCl

98 g m2-1

0 98 195 390 Kerb24 49

NaCl (g m-2

Seashore paspalum

Seashore paspalum with annual bluegrass

10 C

0

20

40

60

80

100

Annual BluegrassSeashore Paspalum

20 C

In

ju

ry

(%

)

0

20

40

60

80

100

30 C

Salt Rate (g m-2)

0 20 40 60 80

0

20

40

60

80

100

20oC

30oC

10oC

0 98 196 294 392Sodium Chloride (g m-2)