EVALUATION OF FUNGICIDES FOR CONTROL OF
CERCOSPORA LEAF SPOT OF CARROT, 2007
J.L. Mayfield1 and D.B. Langston, Jr.2Univ. of Georgia Coop. Ext. Ser., Depts. 1Horticulture and 2Plant
Pathology, P.O. Box 748, Tifton, GA 31793.
Introduction
Approximately 1,369 acres of carrots were grown in Georgia in 2007 which were worth $8,294,508 in
farm gate income. Many foliar diseases of carrot occur in Georgia with Cercospora leaf spot (caused by
Cercospora carotae) beginning to emerge as a significant pathogen. While several fungicides are labeled
for suppression of this disease in carrot, many have not been critically evaluated for use in Georgia. This
trial specifically evaluates some of the fungicide options available for carrots and their efficacy on
Cercospora leaf spot.
Materials and Methods
Carrot seed were planted on 21 Nov 07 on 6-ft beds in Lake Park, GA. Seed were planted every 1.5 in.
in twin rows spaced 8 in. apart. Standard practices for management of irrigation, weeds, nematodes and
insects for carrots grown in Georgia were followed throughout the season. The experiment utilized
randomized complete block design with 5 replications. Fungicide plots were 20-ft long with a 5-ft buffer
between replications. Fungicides were applied using a CO2 -pressurized backpack sprayer calibrated to
deliver 40 gal/A at 75 psi through TX-18 hollow cone nozzles. Once disease was observed, microscopic
examination of the lesions indicated the presence of conidia of Cercospora carotae and no Alternaria
dauci was found for either rating date. Plots were harvested by digging and weighing the two center rows
of each plot on 15 May.
Results
Weather conditions during the experiment were very dry with rainfall accumulation almost 15 in.
below the 98 year average for Nov through May. The onset of Cercospora leaf blight occurred late and
symptom development was not severe until after the last application of fungicide. Plots receiving Topsin
M were the only treatments that did not significantly suppress Cercospora leaf spot compared to the check
on either rating date. However, yield was only significantly improved with applications of Endura at 7.8
oz and Omega 500F. The lack of suppression offered by Topsin M in this study indicate that the
pathogen may be resistant to benzimidazole chemistry. No phytotoxicity was observed in the test.
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Efficacy of certain fungicides for suppression of Cercospora leaf blight of carrot.
Treatments, rate/A, and spray dates ()
Cercospora Leaf Blighty
19 Apr
15 May
Yieldx
z
Endura 70EG, 7.8 oz (1-6) ........................................................................ 1.0 dw
1.2 c
60.5 a
Endura 70EG, 4.5 oz (1-6) ........................................................................ 1.0 d
2.0 c
52.0 ab
Omega 500F, 1.0 pt (1-6) .......................................................................... 1.9 bc
5.8 ab
57.7 a
Rovral 4F, 2.0 pt (1-6) .............................................................................. 1.4 cd
4.2 b
49.6 ab
Rovral 4F, 1.0 pt (1-6) .............................................................................. 2.2 b
4.2 b
43.8 b
Topsin M 70WP, 2.0 lb (1-6) .................................................................... 4.4 a
6.6 a
42.6 b
Topsin M 70WP, 1.5 lb (1-6) .................................................................... 4.5 a
7.0 a
42.8 b
Non-treated check ..................................................................................... 4.2 a
6.2 a
44.5 b
z
Spray dates are as follows: 1=8 Feb; 2=22 Feb; 3=8 Mar; 4=22 Mar; 5=5 Apr; 6=18 Apr.
Cercospora leaf spot ratings used a 0-10 scale where 0=no symptoms and 10=total defoliation.
x
Yield was recorded in lbs/plot.
w
Means in columns with letter(s) in common are not significantly different according to Fisher’s
Protected LSD test at P=0.05.
y
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