1997 Ornamentals Research Report - AUrora - Auburn University

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ALABAMA AGRICULTURAL ExPERIMENT STATION
ALABAMA AGRICULTURAL EXPERIMENT STATION
WG, and Pendulum 60 WDG, when compared to that of lodged plants were short, stubby, and enlarged at the distal
control plants.
ends. Lack of development of these roots which normally
Foliar dry weights of plants treated with Surflan provide support for developing shoots probably contributed to
4AS, Rout 3G and Factor 65 WG were less than those of lodging. Pendulum 60 WDG-treated pampas grass generally
plants in all other treatments. Plant mortality was 100% and had less root development than plants treated with the granular
12.5% in Surflan 4AS and Rout 3G treatments, respectively formulations of pendimethalin, Ornamental Weed Grass
(Table 2). Lodging occurred in 100%, 50%, and 12.5% of Control and Pendulum 2G; 50% of the WDG- treated plants
plants treated with Factor 65 WG, Pendulum 60 WDG, and had lodged compared to 6.3% of plants treated with the
Ornamental Weed Grass Control, respectively, at 75 DAT
(Table 2). The authors observed that aerial support roots of
granular pendimethalins.
JI I V
Chemical Control of
Cercospora Leaf Spot of
Crapemyrtle
AUSTIN K. HAGAN AND J. RANDALL AKRIDGE
Cercospora leaf spot, which is caused by the fungus,
Cercospora lythracearum, is a common but often unrecognized
disease of crapemyrtle in field nurseries and landscapes.
Typically, spotting starts on the leaves near the base of the
plant in July or August. The most noticeable symptoms of
Cercospora leaf spot are yellowing and premature loss of
damaged leaves. Although Cercospora leaf spot usually has
little impact on the health of crapemyrtle, the spectacular fall
color of some cultivars may be ruined by the progressive
yellowing of the leaves and defoliation. In an AAES field trial
in southwest Alabama, the experimental fungicide ICIA5504
gave effective control of Cercospora leaf spot on crapemyrtle.
METHODS
In March 1996, bare-root crapemyrtle 'Carolina
Beauty' were planted in a Benndale fine sandy loam at
the Brewton Experiment Field on eight foot centers with
10 feet between rows. Before planting, soil fertility and
pH were adjusted according to the results of a soil
fertility assay. On March 20 and July 3, half pounds of Trea
16-4-8 and 12-6-6 fertilizers were uniformly distributed
around each tree. A trickle irrigation system was Ban
ratings of leaf spot incidence and defoliation were made on
Oct. 10. The rating scales used to access disease is listed at the
bottom of Table 1.
RESULTS
Light to moderate leaf spotting was seen on all the
fungicide-treated crapemyrtle, as well as the unsprayed
control. Leaf spot levels were considerably lower on the
crapemyrtle treated at two-week intervals with all three rates
of the experimental fungicide ICIA5504 or every week with
Banner 1.24 MEC, as compared with the unsprayed control.
On the ICIA5504-treated crape myrtle, spotting and yellowing
of the leaves was confined to the lower 5-10% of the tree
canopy. Typical leaf spot symptoms were seen on 25% or
more of the leaves of crapemyrtle treated at two- to four-week
intervals with Banner 1.24 MEC and the unsprayed control.
Defoliation ratings generally mirrored those for leaf spot. The
least disease-related defoliation was noted on the crapemyrtle
sprayed with ICIA5504. No differences in defoliation were
seen across rates of this fungicide. Defoliation was not
reduced by any treatment of Banner 1.24 MEC as compared
with the unsprayed control.
Table I. Chemical Control of Cercospora
Leaf Spot on Crapemyrtle
Rat per icDisease rating'
tment Rate per Spray interval Disease ratingi
100 gallons Leaf spot Defoliation
installed at planting and trees were watered as needed.
A tank-mix of one pound of Gallery and two quarts of
Surflan per acre was applied to the plot area twice
during the growing season. Hand weeding and directed
applications of Roundup herbicide were also employed
for weed control. Fungicides were applied between June
er 1.24 MEC
Banr er 1.24 MEC
Banr er 1.24 MEC
Banr Eagl er 1.24 MEC
e 40W
ICIA 5504 80W
ICIA 5504 80W
5504 80W
UnsFprayed
control
6 fl. oz.
6 fl. oz.
6 fl. oz.
6 fl. oz.
4 oz.
4 oz.
8 oz.
16 oz.
-
weeks
I
2
3
4
3
2
2
2
5.2
3.8
5.0
4.8
5.3
4.2
3.5
3.3
3.3
4.5
4.0
4.5
4.3
4.7
4.0
3.0
2.7
2.7
7 and Aug. 2 following the schedule found in Table 1 to
run-off using an ATV-mounted electric sprayer set at 45
psi with a single nozzle on a hand-held wand. Visual
I Leaf
spot and defoliation were assessed using the Barratt and Horsfall
Syst em: I = 0% of the leaves diseased or prematurely lost due to Cercospora
leaf,
8 =" spot, 2 = 0-3%, 3 = 3-6%, 4 = 6-12%, 5 = 12-25%, 6 = 25-50%, 7 = 50-75%,
75-87%, 9 = 87-94%, 10 = 94-97%, II = 97-100%, and 12 = 100%.