NORTH FLORIDA EXPERIMENT STATION
June 18, 1958
NFES Mimeo Rpt. 58-6
PHYTOTOXICITY OF CERTAIN INSECTICIDES AND FUNGICIDES TO SHADE
TOBACCO SEEDLINGS IN THE PLANT BED
By William B. Tappan
This study was undertaken in cooperation with the United States Department of
Agriculture to determine the phytotoxic effect of certain insecticides and fungi-
cides to shade tobacco seedlings in the plant bed.
MATERIALS AND METHODS
Plots, 36 x 52 inches, were sown with Dixie Shade tobacco seeds and were located
in the "bug" plant bed. The bed was enclosed with a cheese cloth covering, which
provided some degree of protection and shade for the young seedlings.
The test consisted of two parts in which 21 dust treatments and an untreated
check were replicated three times in unrandomized blocks. (See Table 1)
In Part One, five applications of two, 6.5 per cent zineb treatments, J-40 and
J-280, were made at two-day intervals beginning March 24, 1958, at the rate of 45
pounds per acre per application. The fifth or last application, April 2, was altered
to the extent that the J-40 treatment was applied to plots which had received four
applications of the J-280 treatment and vice versa.
All plots in Part Two received three applications at one-week intervals. To
simulate the commercial plant bed dusting program, the rate of application was in-
creased gradually each week. The first week, 15 pounds per acre; the second week,
30 pounds per acre; and the third week, 45 pounds per acre of each treatment was
applied to the plots. Rain came immediately following the 45-pound per acre
application, and a second application was made two days later. (See Table 2)
All applications were made with a Model 415 Lowell plunger type hand duster
after the plants had reached a height of approximately 2 inches. The plots were
watered prior to treatment so that the plants were thoroughly wet at the time of
application. A cloth dusting hood, 3 x 5 feet, was used to contain the dust on each
plot during application.
Th .kamnt'sof test material used at the various rates of application were as
S6t e of Application:: Amount Used Per Plot
z~ c / ~ '15 lbs. per acre 2029 mg.
/ 30 lbs. per acre 4058 mg.
,- ~ 45 lbs. per acre 6087 mg.
1Truck Crop Insect Laboratory, Quincy, Florida.
Visual phytotoxicity readings were made in Part One at 24-hour intervals except
on week-ends when no readings were taken. Readings that fell on the same day as the
treatment were made immediately prior to treatment.
Phytotoxicity readings in Part Two were made at 1-, 2-, 5-b 6-, and 7-day inter-
vals. following the 15- and 30-pound per acre applications. Other readings were taker
at 1- and 2-day intervals following the first 45-pound per acre application, and 1-,
3-, 4-, 5-, 6-, and 7-day intervals, following the second 45-pound per acre applica-
All phytotoxicity readings were based on the rating system below:
0 No injury or stunting
1 Slight injury or slight stunting
2 Moderate injury or moderate stunting
3 Heavy injury or heavy stunting
4 Severe injury or severe stunting
RESULTS AND DISCUSSION
All treatments with the exception of 1 per cent parathion plus 10 per cent sevin
and 4 per cent dibrom gave negative results throughout the test. (See Table 2)
One-per cent parathion plus 10 per cent sevin caused slight injury seven days
following the 30-pound per acre application. Slight chlorosis and downward cupping of
the edges and tips of the leaves was observed on all plots. The symptoms prevailed
throughout the remainder of the test with no apparent increase in severity.
It should be noted here that the other formulation containing 1 per cent para-
thion plus 10 per cent sevin plus 3.5 per cent maneb caused no visible injury.
Apparently the stability of the active chemical ingredients in different diluents
may be the determining factor in the phytotoxic difference of the two formulations.
Four per cent dibrom caused no injury at the rates of 15 and 30 pounds per acre.
Slight mottling and crinkling of the leaves followed the second 45-pound per acre
application. Six days following treatment no symptoms of injury were evident. Dibror
caused only a temporary physiological disorder that was later overcome by the plant.
All formulations excluding 1 per cent parathion plus 10 per cent sevin and 4
per cent dibrom are considered safe for application in the plant bed at rates not
exceeding 45 pounds per acre.
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