'tibiotic tests on 'Schuyler' grapevines: On untreated 'Schuyler'
:;rapevines symptoms of Pierce's disease developed on 40% of the
vines in the second season, and by the fourth year all of the vines
had the disease. Weekly sprays of 500 ppm oxytetracycline delayed
Pierce's disease development until the third year. Symptoms
remained mild in this treatment throughout the four-year test as
only 8% of these vines died. A. monthly 500 ppm drench treatment
delayed symptom development only 6 months. Biweekly sprays of
1000 ppm also only delayed symptoms for 6 months, but when changed
to weekly sprays 1000 ppm oxytetracycline seemed to stop further
disease development completely.

In summary foliar sprays of antibiotics appear to be more effective
than drenches. With foliar sprays, concentrations of at least
500 ppm were needed, and weekly application was best. More work is
needed on rates and timing of antibiotic sprays before any practical
control of Pierce's disease is possible.



Weed Control in Florida Vineyards (J. A. Mortensen)

(ne of the secrets of successful grape growing is an integrated
program of weed control involving mechanical tools, herbicides
.:nd mulches. Weed control between vine rows is much easier to
ccomplish than that under the trellis itself. Herbicides are
-3'rely used for weed control between rows since disking, rotbtilling,
,.r mowing are more practical and less expensive both in young vine-
ya.rds and mature vineyards. The discussion below concerns control
)f *weeds in the vine row where disking and mowing are not possible.

 Young vineyards. Mulching with 2 to 3 inches of oak leaves
ar-ound each newly set grapevine helps control weeds and conserve
soil moisture. Hoeing of weeds in small vineyards is usually
replaced by Paraquat spraying or in-and-out rototilling, or both,
in vineyards one acre or larger. Paraquat kills all the leaf
-urface it covers, including grapevine foliage. A tractor-
mounted boom with a nozzle surrounded by a cone-shaped shield
to prevent drift of spray in windy weather is effective in
directing the material to a band along each side of the row
without getting on the grape plants. Sufficient overlap of spray
bands between vines in the row is essential to avoid leaving a
i-:een strip of weeds under the trellis wire. The in-and-out vine--
yard rototiller (Hester Plow Company, Lake City) is mounted on the
:side of the tractor and operates from the power take-off. It is
very effective in controlling both broadleaf and grassy weeds in
the vine row. Dalapon herbicide controls grassy weeds. Apply in
April or May, or when the grass is green and actively growing.
Avoid spraying the grapevine foliage or on bare ground.

 Mature vineyards (3 years or older). Karmex (Diuron) herbicide
is an effective pre-emergence herbicide if applied once a year,
usually in March. Weed growth occurring in the rows in mid- to
late summer can be burned down with Paraquat herbicide, hoed, or