=FLORIDA COOPERATIVE EXTENSION SERVICE
UNIVERSITY OF F-LORIDA
,. l-.1. IlNS-ITIUTE Or- FOOD AND ,1.GRICLJLTURAL CCIENCP:S
George A. Marlowe, Jr. James Hontelaro
Chairman Vegetable Crops Specialist
Thomas G. Hart James Mi. Stephens
Assistant Vegetable Crops Specialist Assistant Vegetable Crops Specialist
January 5, 1971
TO: COUNTY EXTENSION DIRECTORS AND VEGETABLE AGENTS
IU THIS ISSUE:
I. Anmoniated Superphosphate Use in Vegetable Production
II. Fox on Tomatoes
III. Nlozzle Wear in Spray Equipment
IV. Petite-Sweet A New Small Watermelon
I. Ammoniated Superphosphate Use in Vegetable Production
Vegetable growers need to understand the behavior of ammoniated
superphosphate in the soil in order to avoid unnecessary problems in
the use of this material for fertilization of vegetable crops. As an
example, extension agents encountered a phosphorus deficiency in a
staked tomato crop this fall under conditions not normally expected to
develop such a problem. Upon checking, we found that the fertilizer
was formulated to supply all of the phosphorus from ammoniated super-
phosphate. A quickly-initiated spray program with a soluble phosphate
source corrected the problem for the tomato crop in question, but it
is one that can be easily prevented by the use of common sense in
Ammoniated superphosphate is made by reacting ammonia with
ordinary superphosphate. The degree of anmoniation is the factor that
determines the value of the final product. If not carried to excess,
it actually enhances the value of ordinary superphosphate by neutralizing
some of the free acidity, improves physical condition and granulation,
and incorporates an inexpensive source of nitrogen into the fertilizer.
However, heavy ammoniation reduces the availability of phosphorus. This
is demonstrated in the following table taken from Technical Bulletin 52
published by I.ississippi State University. The authors drew these
conclusions from forty-nine experiments conducted over a five-year period.
COOPE\:RAT-1.lX i NTM)N:r Vi~ RK A GRCULTURE AkND HOME E:PCO OMIC:,. LTATE OF FLORIDA, IFAS. UNIjVEFR;I1'
0F FL.ORI D, IU U Lii RMEiIT F A AGRICULTURE F AD AJ ARf- OS OF COUrNY CO M M 510i INEF R COO PERATING
Table 1. Relationship Between % Superphosphate
Equivalent and Degree of Ammoniation
1 2 3 4 5 6
Degree of Ammoniation
It can be seen from this table that heavy ammoniation severely
reduces the availability of phosphorus. At 1% ammoniation, about 94%
of the phosphate is available, but at 7.2% ammoniation only 28% of
the phosphate is available to the crop. These are average figures and
may vary from crop to crop and soil to soil. Growers should know what
percentage of the phosphate in fertilizer comes from ammoniated super-
phosphate and to what degree it was ammoniated. Tith this information,
a grower can adjust phosphate fertilization accordingly. We suggest
use of ammoniated superphosphate with a meximum of 3 to 4% ammoniation.
In this range from 70 to 80% of the phosphate is available to the crop.
NOTE: Phosphate availability can, also, be greatly reduced by
high pH and cold soils.
II. Pox on Tomatoes
Blemishes on tomato fruit were quite prevalent during the fall
season this year. "Fleck" was rather common, but fortunately it does
not mar the fruit too badly. As the name implies, fleck is characterized
by tiny, gold-like specks on the fruit surface.
"Pox," on the other hand, is much more serious in that the
blemishes often render the fruit unsalable. Pox blemishes are consider-
ably larger than fleck. They vary from 1/16 to 1/32 inch in diameter.
The tissue in the center may appear to be dead and surrounding tissue
C --L II _I I I I r
rox is thouL ht to be a non-parasitic disease which is associated
with genetic make-up of the variety. Foradel variety is considered
to be very susceptible to both pox and fleck. Plant breeders are now
trying to select away from this disorder.
Field diagnosis of the problem can be made by observing fruit-
bearing plants. Susceptible plants will produce many fruits that are
severely affected with pox when conditions are right for its development.
Fruits from plants adjacent to an affected plant may show little or no
pox symptoms. It, also, appears that certain environmental conditions
are necessary for pox development. As yet, we are unable to pinpoint
III. Nozzle Wear in Spray Equipment
Emphasis being placed now on pesticide residues necessitates
accurate calibration of spray equipment. With any given material, the
one factor causing the most significant change in volume of solution
delivered by a sprayer is nozzle wear. Abrasive materials such as
pesticide formulation that are suspended in solution can cause con-
siderably more nozzle wear than a non-abrasive, liquid material.
More important is the type of materials used for the nozzle.
Table II demonstrates relative wear of nozzles made from brass, stainless
steel and chrome-plated brass. Note that chrome-plated brass is very
resistant to wear as contrasted to brass which shows an increase of about
19% in volume after only 18 hours of use.
Table II. Relative Wear Resistance of Different Nozzle Materials
(From A2S 4291, Effects of Diuron on Wear of Spray Nozzles)
S12 A -S BRASS
,----- STAINLESS STEEL
-- CHROME-PLATED BRASS
0 1 8
3 6 9 12 15 18
IV. Petite-Sweet A Hew, Small Watermelon
The breeder who gave us Crimson Sweet has recently released a
small melon which should be of interest to Florida growers. It is
reported to have the same disease resistances and quality characteristics
as Crimson Sweet. However, it only weighs between five and ten pounds.
This type of melon should eventually become an accepted fact for
two reasons. First, it would appear to be more adapted to containeri-
zation, which is a coming thing. Secondly, many of our large melons
are sold by chain stores in slices. This is a practice which is not
conducive to expansion of watermelon demand because of quality loss and
the danger of contamination.
Seed of this variety was released to commercial seedsmen this
year and should be available from them sometime in 1971.
Professor (Vegetable Crops Specialist)