15 ml vials because of the large number of treatments involved, and also 250 ml mason jars for different tests. Yellowing caused by dollar spot was assessed daily for up to two weeks after inoculation.
Results
Objective #1: Replacement of synthetic fungicides by plant defense activators where disease control occurs by inducing (that is “turning on”) natural resistance mechanisms in turfgrass. In tests done in the lab, creeping bentgrass cv. ‘Penncross’ was grown for two weeks in 250 ml mason jars containing 0.5 cm of top-dressing sand. These were then treated with defense activators by spraying 10 ml onto the leaves or exposing roots by adding 10 ml to the soil. Seven days later, the grass was inoculated with the dollar spot pathogen. We tested eight different defense activators in 20 different treatments on foliage, and 11 different defense activators in 31 different treatments on roots at a variety of concentrations based on reports in the literature. Some defense activators showed phytotoxicity (damaged the grass), a few reduced disease, but most showed no effectiveness in reducing dollar spot. For
foliar treatment of creeping bentgrass, the most promising defense activators tested (based on reduced disease at 12 day post inoculation) were humic acid (type 1), Regalia, fulvic acid, humic acid (type 2), Keyplex 350DP and humic acid (type 2). For soil treatments, the most promising ones thus far were para-aminobenzoic acid (PABA), fulvic acid, humic acid (type 1), hexanoic acid and humic acid (type 2). Optimizing the concentrations of defense activator was critical for control. For example, hexanoic acid applied to the soil resulted in less disease than the control at 4 mM but more disease at 0.6 or 1 mM at 12 days post inoculation. Objective #2: Determination of which turfgrass varieties respond best to plant defense activators to induce relatively high and long lasting resistance. As part of this study, we first tested different bentgrass varieties for their natural resistance to dollar spot disease to facilitate further testing with resistance activators. This was done under laboratory conditions using yellowing as a measure of disease. Grass which was not inoculated with the dollar spot fungus showed less than 5% yellowing by 12 dpi (days after inoculation).
TABLE 2. Cultivar
TURFGRASS CULTIVARS WERE SCREENED INSIDE 15 ML GLASS VIALS WITH GRASS GROWN ON A SAND BASE. AT 8 DAYS AFTER INOCULATION WITH SCLEROTINIA HOMOEOCARPA, THE VIALS SHOWED OBVIOUS DIFFERENCES BETWEEN WEAK ACTIVATION (IN SOME CASES, ENHANCED YELLOWING BEYOND FUNGUS ALONE) TO MODERATE ACTIVATION, TO A STRONG ACTIVATION OF RESISTANCE WHERE THE ONLY INDICATION OF FUNGAL ACTIVITY WAS SOME HYPHAL WEBBING ON THE GLASS WALLS OF THE VIALS.
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Percent Disease Compared to the Inoculated Water Control Humic Acid-1
Humic Acid-2
Hyaluron
PABA
Phosphite
Silicilic Spray
Silicilic Soil
111
100
87
89
91
53
80
Alpha
76
68
74
103
65
45
67
Cato
55
65
100
82
103
53
44
Focus
86
49
70
80
64
70
21
Kingpin
72
83
91
99
96
49
40
MacKenzie
61
61
61
75
61
62
14
PennA4
100
127
79
109
123
27
20
Penncross
82
92
76
75
83
64
44
Sandhill
84
97
112
99
103
29
62
SR1150
137
125
87
194
106
31
44
T1
84
84
74
97
81
42
55
Tyee
75
90
79
75
79
59
55
Vesper
79
77
95
72
75
50
46
LSD (p=0.05)
35
29
32
50
34
41
40
007
DOLLAR SPOT CONTROL IN CULTIVARS OF CREEPING BENTGRASS (AGROSTIS STOLONIFERA) OR VESPER VELVET BENTGRASS (A. CANINA) TREATED ONE TIME WITH WATER OR A DEFENCE ACTIVATOR AND INOCULATED 7 DAYS LATER WITH SCLEROTINIA HOMOEOCARPA. TREATMENTS WERE 0.75% HUMIC ACID-1 (HUMIC ACID-1=16% HUMIC ACID), 0.75% HUMIC ACID-2 (HUMIC ACID-2=15% POTASSIUM HUMATE, 12.5% HUMIC ACID), 33.3 MG/L SODIUM HYALURONAN, 28 MM PARA-AMINOBENZOIC ACID (PABA), 25 MM POTASSIUM PHOSPHITE, OR 5 MM SILICILIC ACID. MEANS ARE PER CENT CHANGE IN FOLIAR YELLOWING RELATIVE TO THE WATER CONTROL AT 12 DAYS AFTER INOCULATION. MEANS IN RED SHOW SIGNIFICANTLY LESS DISEASE THAN INOCULATED WATER CONTROL (LOWER VALUES ARE BETTER). JULY/AUGUST 2014 | GreenMaster 17