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Copyright 2005, Board of Trustees, University
J. F. Darby
Professor (Plant Pathologist) and
SEP 27 1977
Ii.F.A.S.- Univ. of.Florida
This is the fourth test in a series designed to control bacterial leaf blight
and shankrot of Gold Cup sweet corn by chemicals proven to have bactericidal
qualities.; In previous tests copper containing bactericides injured the sweet
corn. .None of the treatments in the other tests significantly reduced either
the streaking of the leaves or shankrot phase of the disease. The severity of
the disease in the area used for these tests plus poor drainage severely stunted
the sweet corn plants and prevented the formation of edible ears.
Methods and Materials
Treatment numbers 1, 2, and 9 received one application of spray in a one
foot wide band over the furrow when Gold Cup sweet corn was planted on April
16, 1974. Treatment number one received no foliar sprays. All other treat-
ments received 10 foliar sprays each on the following dates: April 30, May 7.
14, 21, 28,,30, June 4, 6, 11, and 13, 1974. See Table 1 for list of treatments.
The severity of the symptoms (streaking) of bacterial leaf blight,
Psuedomonas alboprecipitans, on the leaves was estimated by rating each plot
on a scale ranging from 0, no foliar streaking to 5. 0, severe foliar streaking.
One rating was made on May 17, 1974, and another was made on June 10, 1974.
The two ratings were averaged and presented in the first column of Table 1.
One-half of each plot was harvested on June 19, 1974. The per cent of
healthy or shankrot free ears were determined by examining each ear. The
corn in this early harvest was slightly immature when compared to commercially
harvested sweet corn, but it was optimum or ideal for eating off the cob. Five
days later, the remaining half of each plot was harvested and the percent shank-
rot free ears were obtained. In order to determine if the sprays reduced the
s ize of the sweet corn, 40 ears from each plot were weighed and recorded in
AGRICULTURAL RESEARCH AND EDUCATION CENTER
Research Pepcrt CF-75-1 July 30, 1974
An Evaluation of Bactericides and Bactericide Combinations for the Control of
Bacterial Leaf Blight and Shankrot, Psueodomonas alboprecipitas,, r nSY
of Gold Cup Hybrid Sweet Corn H \U it L N \I\
Table 1. Summary of results of bacterial leaf blight and shankrot
on sweet corn, Zellwood, April 16-June 24, 1974.
S% Shankrot free ears
Foliar- Early Late Weight of
Treatment and concentration rating harvest harvest 160 ears
per 100 gal/acre averages 6/19/74 6/24/74 (bs. )
1. Isobac 20, 8 fl. oz.
Band, soil, at planting
2. Isobac 20, 8 fl. oz.
Band, Soil, at planting
Nabac 25 EC, 6 fl. oz.
Biofilm, 6 fl. oz.
3. Nabac 25 EC, 6 fl. oz.
Biofilm, 6 fl. oz.
4. Nabac 25 EC, 6 fl. oz.
Manzate 200, 1.0 lb.
5. Agri-mycin 17, 200 ppm
6. Copper Count N, 8%, 0. 75 qt.
Benlate 50 W, 0.25 lb.
7. Agrimycin 17, 200 ppm
Copper Count N, 8%, 0.75 qt.
9. Same as #2, but w/out Biofilm
a-Based on a scale ranging from 0, no streaking to 5,
Results and Discussion
Treatment number 7 with Agrimycin 17 at 200 ppm plus Copper Count N
at 0.75 quart in 100 gallons of water on one acre resulted in 82. 7 per cent
shankrot free ears on the early harvest and 67. 3 per cent shankrot free ears
in the late harvest. This treatment was significantly better than the untreated
with 45.5 per cent shankrot free ears at the early harvest and 38. 3 per cent
healthy ears at the late harvest. Treatment number 7 also had the least
amount of leaf blight or streaking (Table 1).
Treatment number 5 with Streptomycin 17 at 200 ppm was the next best
treatment, but significantly less effective than treatment number 7.
It obviously pays to harvest early (64 days after planting) while the ears
are slightly immature (with 82.7 per cent shankrot free ears) than wait an
additional 5 days when the ears are slightly over mature (with 67. 3 per cent
of the ears shankrot free).
Isobac 20 applied to the soil in a band at planting was of no significant
benefit. Ten spray applications of Nabac 25 EC (Treatment number 3) was
significantly better than the untreated, but not as good as Copper Count N,
0. 75 quart plus Benlate 50 W, 0. 25 pound (Treatment number 6).
There was some nutritional benefit derived from the use of Manzate 200
plus Nabac 25 EC. The plants in these plots were darker green in color,
slightly larger, and the ears were slightly heavier than with Nabac 25 EC
alone. This was probably due to the manganese in the Manzate.
In previous tests on sweet corn combinations of a Copper containing
bactericide and Maneb have shown some bactericidal activity.
Isobac 20, Nabac 25 EC, and Agrimycin are not approved for use on sweet
corn. Some copper containing fungicides are more phytotoxic to sweet corn
than others. At the rates used in this test 0. 75 quart of Copper Count N was
slightly injurious to the leaves of sweet corn and the ears were slightly smaller
than the untreated (compare treatment number 7 and 8 in weight of 160 ears).
The area in which this test was conducted had sweet corn growing on it
last spring and summer (1973) wli ch was so severely infected by the bacterial
blight and shankrot organism that no ears were produced and the sweet corn
plants averaged only 4 1/2 feet at maturity.