Everglades Station Mimeo Report EES 68-7 March 1968
Rate and Interval of Fungicide Application on
the Control of Celery Early Blight
R. D. Bergerl/
Purpose: Some celery growers have experienced poor early blight control
on celery by following an apparently sound spray program using a good fungicide
with applications every four to seven days., More frequent applications should
undoubtedly provide better disease control because of the greater opportunity
to furnish the youngest plant growth with an early fungicide coverage and also
. to keep the entire foliage canopy covered with a coating of fresh fungicide.
However, in order to make more frequent applications economically feasible, a
reduction in spray concentration would be necessary. The experiment reported
here was designed to test this hypothesis and to determine the comparative
efficiency of two fungicides, Daconil 2787 (Diamond Alkali Company) and Dithane
M-45 (Rohm and Haas Company). Previous year's data indicated Daconil gave good
commercial control at 0.75 Ibs/A applied twice-a-week and the experiment was
also designed to find the minimum concentration of this material which would
provide effective disease control.
General: Celery transplants of variety Utah 52-70H were set on October 31,
1967. Weed control was obtained by one application of Randox-Vegadex. Insect
control was maintained by periodic applications of Cygon, Dibrome, and Diazinon.
Fungicide application was accomplished by the pathology plot sprayer operating
at approximately 150 psi and about 150 gallons per acre. The experiment was
terminated on January 29, 1968.
Disease situation: Early blight incited by Cercospora apii did not occur
for any significant amount until mid-December even on the unsprayed rows.
Infrequent favorable infection periods during the latter part of the trial
provided only a slow, moderate build-up of disease but the disease was uniformly
severe on the guard and check rows when the trial was terminated.
Results: Disease severity data and treatment comparisons are given in the
Discussion and summary: The results presented here indicated that reduction
in spray concentration can provide effective disease control if the number of
applications are increased. The minimum amount of material necessary that gave
effective control was .75 Ibs/A/three times a week for Dithane M-45 (total 2.25
1/ Assistant Plant Pathologist, Everglades Experiment Station, Belle Glade,
Ibs/A/week), and .75 lbs/A/twice-a-week for Daconil (total 1.5 lbs/A/week).
Daconil was found to give better blight control than Dithane M-45. There
was no significant difference between these two materials under the milder
disease conditions in mid-seasonbut the superiority of Daconil was clearly
expressed when blight became more severe. The difference between the two
fungicides was again less prominent as the disease diminished near termination
(Table II). The difference in control between Daconil and M-45 was not great
but it was consistently expressed between treatments.
Spraying three times-a-week was clearly superior over spraying twice-a-
week at the same rate as should be expected (Table III).
Increasing the number of spray applications would only have merit if a
saving in material cost could be achieved. I believe a 25-30% saving in mater-
ial cost could be realized by reducing the rate and increasing the number of
applications. For example, 0.75 lbs. of Dithane M-45 applied three times-a-
week (total 2.25 Ibs/week) gave equal or better control than 1.5 lbs. of the
same material applied twice-a-week (total 3 lbs/week) in an adjacent, concurrent
test'. 'The disease severity on January 22, 1968, (when the maximum disease
expression occurred) was 3.0 and 3.2 for 0.75 pounds (three times) and 1.5
pounds (two times) respectively.
In this trial, one pound of fungicide per acre per application was slightly
better but never significantly so than 0.75 pounds per acre regardless of which
fungicide or interval tested (Table IV).
Celery growers may be able to make minor savings in their disease control
program by reducing their fungicide rate and maintain a spray interval of two-
three days provided they have the equipment to accomplish this.
Greater savings can undoubtedly be realized by extending spray intervals
and have fungicide omissions during periods of minor disease spread. In this
trial, the spray applications between November 1, 1967, and December 8, 1967,
were of little value in affecting the final disease severity.
This work was supported in part under a grant from the Diamond Alkali
Table I. Cercospora early blight on Celery. Rate atd Interval of two fungicides
and effect on disease control.
Rate_ 3/Disease severity/
Applications/wk. Fungicide Ibs/A 1-11-68 sig-R 1-22-68 sig. 1-26-68 sig.
21 Daconil 0.25 3.5 3.8 2.8 a
2 Daconil 0.5 3.0 3.8 3.0 a
2 Daconil 0.75 3.0 2.8 a 3.0 a
2 Daconil 1.0 2.8 a 2.8 a 3.0 a
2 M-45 0.25 3.2 4.0 3.8
2 M-45 0.5 3.2 4.0 4.0
2 M-45 0.75 2.8 a 3.2 3.2
2 M-45 1.0 3.0 3.2 3.0 a
31 Daconil 0.25 3.0 3.2 3.0 a
3 Daconil 0.5 2.2 a 3.5 3.2
3 Daconil 0.75 2.2 a 2.2 a 2.2 a
3 Daconil 1.0 2.0 a 2.0 a 2.0 a
3 M-45 0.25 3.0 3.2 3.2
3 M-45 0.5 2.8 a 3.5 3.2
3 M-45 0.75 2.0 a 3.0 3.0 a
3 M-45 1.0 2.2 a 2.8 a 2.8 a
-' Twice-a-week for a total of 20 applications and thrice-a-week for a total of
2/ Severity based on Horsfall-Barratt rating scale where 1 = no disease, 12 =
plants dead. Data are the average of four replications.
3/ Duncan's multiple range test. Treatment means followed by the same alphabetical
letter are not significant at the 5% level.
Comparative effectiveness of two fungicides for celery early blight
-' Horsfall-Barratt rating scale. Data are averages of four replications taken
over four fungicide rates and two interval periods.
-/ See Table I for rate and application.
Table III. Effect of spray interval on disease severity.-/
1-22-68 sig.(.001) 1-26-68
3.4 b 3.2
See Table I for fungicide and rate.
- Horsfall-Barratt rating scale. Data are averages of four replications taken
over four fungicide rates and two fungicides.
Table IV. Effect of fungicide rate on disease severity. /
See Table I for fungicide and interval.
/ Horsfall-Barratt rating scale. Data are averages of four replications taken
over two fungicides and two spray intervals.
Duncan's multiple range test. Treatment means followed by the same letter are
not significantly different at the 5% level.
I [ -