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Copyright 2005, Board of Trustees, University
,J UNIVERSITY OF Gulf Coast Research and
FLORIDA Education Center
5007 60th Street East
Bradenton, FL 34203
Institute of Food and Agricultural Sciences
GCREC Research Report BRA1994-18 (October)
LEAF SURFACE SOLUTION (LSS) AND SPRAY PH VALUES RELATIVE
TO SPRAY EFFICACY AND PHYTOTOXICITY
S.S. Woltz, J.B. Jones, and J.P. Jones'
The pH values (acidity-alkalinity) found in spray solutions and on the surface
of leaves are frequently important to the cultural success in producing the crop,
preventing spray damage and obtaining the maximum benefit from the spray
application (1,2,3). When growers spray a large field in which there is
considerable investment, they are often taking a risk on conditions being
suitable for the action of the spray in terms of crop safety and avoidance of
damage or yield depression. It is possible that some attempts to adjust spray
tank mixes may cause more harm than good. This area has received much attention
from agriculturists the world over (4,5,6,7). Conditions in the environment,
crop, and spray may cause deviations from the expected response to the spray
The most important single chemical factor on the leaf surface and in the leaf
surface solution (LSS) probably is pH (5,6). The concentrations of hydrogen and
hydroxyl ions have a powerful influence on the chemical and biological processes
occurring at the leaf surface. Plant growth and the efficacy and safety of foliar
sprays of nutritional and pesticidal chemicals may depend on the avoidance of any
adverse effects of excess acidity or alkalinity in sprays or pH-related reactions
on the leaf surface. The work reported here was conducted to provide information
on some of the pitfalls that may be found due to a failure to have the desired
pH conditions in the spray and subsequently developing on the surface of the
plant. The research was aimed at identifying changes to be found in the acidity-
alkalinity picture at the plant surface with different spray procedures and
materials and developing methods for following the changes with the passage of
Methods and Materials
Six sulfate compounds were tested for reactions with water from the laboratory
deionizedd), Manatee County Utilities, and Gulf Coast Research Center deep well
(West) (Table 1.). Water for the tests was collected after 5 minutes of tap flow.
Salts and pH, respectively, were 0 and 5.6, 125 and 7.3, and 840 and 7.5.
Chemical compounds were added to the water at the rate of 0.3 g/liter and
reactions permitted for 15 minutes with occasional stirring. pH was then read and
'Visiting Professor, Plant Pathologist, and Plant Pathologist, respectively.
observations made for color change and precipitation of salts. A second addition
of 0.3 g/liter of chemical compounds was made and after an additional 15 minutes
then pH was determined and observations made as to color and precipitation.
Solutions were then discarded.
Plant material for the experiments (Tables 2 and 3.) was cultured in 12 cm pots
holding a mixture (1:1) of Canadian peat and horticultural vermiculite amended
with technical grade CaC03 (powder), 4.5 grams per liter of mix; 14-14-14 slow
release fertilizer, 3 grams per liter; and, 0.7 grams of Micro-Max micronutrient
formulation per liter. Plants were carefully watered in the pots with Manatee
County Utilities water as required, without wetting the foliage. Plants were
grown from repeated plantings and used when 3 to 6 weeks old.
Leaf surface pH values were determined with a combination, single Orion electrode
by applying a few drops of deionized water at the leaf surface and gently moving
the electrode back and forth in the liquid until the reading was stable. Care was
taken not to damage the leaf surface which would alter readings.
Chemical solution pH equilibrations with detached leaves and 17 chemical
solutions (Table 2.) were carried out by placing large leaves in porcelain
evaporating dishes so that the leaf would retain a small puddle of chemical
solution to be tested in the "saucer" made by the leaf when pressed gently into
the evaporating dish. Readings of pH were made on the original solutions and
after 3, 6, 12, and 24 minutes of equilibration. Only the data for 0, 6, and 24
minutes are reported. The puddles were approximately 2.0 ml in volume.
Equilibration of pH was facilitated by gently moving the electrode back and forth
during pH measurement.
Spray water quality comparisons (Table 3) were made using laboratory grade
deionized water, and well water from the Gulf Coast Research center farm. The
well water contained significant amounts of sulfide, sodium, chloride, calcium,
magnesium, and bicarbonates as found in deep wells in coastal Florida. Four crop
species were used in a foliar spray experiment to obtain information on water
source and pH effects. The well and deionized waters were used in making
solutions of calcium chloride, copper sulfate, iron sulfate, and manganese
sulfate. Leaf surface pH was determined at 24 hrs. after spraying. Foliage damage
symptoms were recorded along with ratings for the degree of damage.
The effects of exposure of water samples to aeration (exposure to the atmosphere)
on pH were determined by pouring small samples back and forth for 3 to 5 minutes
using beakers in the laboratory and then reading the pH for detection of changes
due to loss or acquisition of gases. The well water lost hydrogen sulfide and
probably carbon dioxide in the process. The odor of hydrogen sulfide decreased
during the aeration but did not disappear.
Results and Discussion
Table 1 contains data on the relationship of 2 parameters of water quality to
spray quality. Deionized water, comparable to rain water, is not buffered against
pH changes by iron and copper sulfates and has a pH drop to the middle range of
pH 4. This solubilizes these heavy metals and increases the chance of
phytotoxicity from foliar sprays. There was very little precipitation of any of
the compounds, either at 0.3 or 0.6 grams per liter (0.25 qnd 0.5 Ibs. per 100
gallons), with the exception that there was a faint cloudiness with iron sulfate,
probably due to ferric hydroxide present in the laboratory compound.
With Manatee County Utilities water, the beginning pH and buffering capacity
against pH changes were higher, so that the pH was reduced by the iron and copper
compounds but not so drastically. There was a moderate precipitation of iron
sulfate, increasing with the second increment of chemical. Other solutions were
The well water reacted quite strongly with iron and copper sulfates
precipitating heavily, additionally with the second addition of chemical. The
color of the iron compound in well water changed to black with the precipitation.
Copper sulfate produced a green precipitate. The amount of precipitation loss
from solution was not measured. Sprays with the iron and copper sulfates in well
water would likely be less phytotoxic than with the two other water sources.
Well water pH was reduced more by copper than iron, due probably to the unique
chemistry of this water. The opposite was true for Manatee County Utilities
water, with iron reducing pH more than copper. The observed differences in the
three water sources would probably translate to significant spray differences in
the field when using water sources which are chemically similar to those in Table
A perusal of the data in Table 2 for the leaf surface solution (LSS) reactions
between 4 crops on the one hand and 17 chemical solutions on the other indicates
that the chemistry of the leaves in contact with an assortment of solutions is
somewhat specific to the crop and the chemical, as might be expected. Since these
data were nonreplicated and collected as a screening test for the significance
of the LSS concept, they should be used more as a guide to principles than for
definition of specific relationships. Copper sulfate reduced pH more with
cucumber than with other crops when all are compared with the deionized water
control. Chemicals effective in lowering pH were: A1C13.6H20, Peter's 20-20-20,
CuSO4.5H20, and FeSO4.7H20. Those raising pH were: well water, Ca(OH)2, NaHC03,
Kocide K101, and Mancozeb. Acidity values were similar in the case of bean,
pepper, and tomato while cucumber was associated with higher pH values.
Foliar nutritional sprays (Table 3.) applied with well water versus deionized
water demonstrate the effect of water pH and buffering capacity on the leaf
surface pH and phytotoxicity.
Well water was associated with reduced injury. The rates of iron and copper
sulfate selected were on the high side but were selected to study foliar spray
damage in relation to pH and water souce. Calcium chloride is only occasionally
toxic in field use and was included in this test to get information on foliar
spray tolerances because it is one of the spray materials frequently required
when soil applications are ineffective. Bush bean made a good indicator plant for
possible phytotoxicity problems with the chemicals.
Aeration of the well water resulted in an increase in pH from 7.5 to 8.5,
probably due to the loss of acid gases (hydrogen sulfide and carbon dioxide). The
loss of acid gases was incomplete; when samples were taken to dryness and re-
moistened, the pH rose further, to 9.0. This influence will be active on the leaf
surface and depending on plant species and spray, the pH of the LSS will reflect
the alkalinity of the well water.
In summary, the LSS pH is a resultant of the combined influences of plant, spray
components, and the environment. Examples have been given of the nature and
extent of changes that may occur in this critical parameter relating to the
ecology and chemistry of the leaf surface, and methods of evaluating various
influences. More attention should probably be given to tracking the changes of
the LSS pH for guidance in spray and cultural practices to understand what is
happening and how to direct the processes for cultural benefits in crop
production. A word of caution is in order, however; care should be taken to avoid
overcorrecting for perceived problems or in efforts to enhance the efficiency of
foliar spray procedures and materials.
This report relates mainly to methods development in the area of foliar spray
procedures. The data presented indicate that much practical information may be
obtained from the leaf surface chemistry which is of potential significance to
improved crop production methodology.
1. ISK Biotech 1993. (pH stability of Bravo). Manatee County Vegetable
Newsletter pg.4 Mar-Apr, 1993.
2. Jyung, W.H., and S.H.Wittwer. 1964. Foliar absorption an active uptake
process. Amer. J. of Botany. 51:437-444.
3. Leben, C. 1954. Influence of acid buffer sprays on infection of tomato
leaves by Alternaria solani. Phytopath. 44:101-106.
4. Schneider,R.W., and J.B.Sinclair. 1975. Inhibition of conidial germination
and germ tube growth of Cercospora canescens by cowpea leaf diffusates.
5. Skubatz,H., and B. Kessler. 1988. Age-dependent appearance of specific
proteins on cucumber surfaces under normal growth conditions. Plant
6. Oertli,J.J., J.Harr, and R.Guggenheim. 1977. The pH value as an indicator
for the leaf surface micro-environment. J. of Plant Diseases and
7. Woltz,S.S. 1993. Methods for experimental production of edema in some
crucifers. Bradenton GCREC Research Report BRA-1993-24.
Table 1. pH changes and apparent reactions of 6 chemical compounds with water
from 3 sources.
Deionized Manatee Research Center
Compounds Water County Water Well Water
Added Az B A B A B
1 None 5.3 5.6 7.2 7.4 7.4 7.5
2 FeSO4.7H,0 4.6 4.3 5.2y 4.5y 6.5y 6.5y
3 MgSO 10 ,0 5.7 5.8 7.2 7.3 7.4 7.4
4 ZnSO4.6H20 5.6 5.6 6.6 6.7 6.9 6.8
5 CuSO .5H 0 4.8 4.7 5.6 5.8 5.8y 5.5y
6 Na S64.7120 6.1 4.9 7.5 7.9 7.4 7.4
7 MnO4.H20 5.0 4.7 7.1 7.0 7.4 7.4
ZA:added 0.3 g/L, reacted 15 min. B:added additional 0.3 g/L, reacted 15 min.
YPrecipitation of added chemicals.
Table 2. Upper surface solution pH of leaves equilibrated with various solutions.
Initial 'Blue Lake' 'Poinsett' 'Early California
Solution pH bush bean cucumber wonder' pepper 'Walter' tomato
Compound Q/L 0 minx 6 min 24 min 6 min 24 min 6 min 24 min 6 min 24 min
1 Deionized water 5.55 5.92 6.20 6.60 7.22 6.18 6.22 6.10 6.00
2 Well water 7.76 7.98 7.90 7.82 8.03 7.50 7.88 7.91 8.00
3 Deionized water,
pH 5.0z 5.00 5.42 5.82 6.10 6.68 5.30 5.62 5.42 5.72
4 Well water,
pH 5.0z 5.00 5.50 5.62 5.50 5.80 5.22 5.49 5.20 5.38
5 A1C1,.6H20 0.3 4.12 4.12 4.30 4.20 4.30 4.30 4.39 4.12 4.20
6 Ca(O~)2 0.3 10.78 10.50 10.12 10.20 9.90 10.70 10.20 10.45 9.90
7 NaHCO3 0.6 8.53 8.53 8.59 8.60 8.78 8.48 8.60 8.50 8.60
8 NH4NO3 0.3 5.40 5.38 5.25 7.00 7.20 5.88 5.80 5.50 5.60
9 (NH4)2SO4 5.0 5.50 5.50 5.30 6.72 6.88 6.10 6.00 5.67 5.62
20-20-20 3.0 5.18 5.20 5.19 5.90 6.21 5.20 5.29 5.15 5.20
11 CaC1 .2H 0 2.4 5.68 5.65 5.59 6.40 6.70 6.20 6.00 5.50 5.50
12 Ca(N3),2.H20 3.8 5.70 5.61 5.61 6.39 6.78 5.90 6.18 5.70 5.79
13 CuSO .5 20 0.3 5.29 5.46 5.52 5.40 5.60 5.42 5.60 5.50 5.62
14 FeSO .7H 0 0.3 4.68 5.00 5.50 6.38 6.55 5.00 5.70 5.20 5.42
15 Kocide I?01 1.2 6.59 6.60 6.60 6.90 7.40 6.60 6.75 6.69 6.53
16 Bactratey 1.5 5.62 5.88 6.00 6.60 7.00 6.10 6.35 6.22 6.50
17 Mancozeby 0.9 7.20 6.88 6.85 7.00 8.40 6.80 6.80 6.82 6.71
zAdjusted with H3 PO4.
XTime after start of equilibration.
Table 3. Effect of source of water on leaf surface pH and toxicity of some foliar nutritional sprays.
Surface pH Leaf injury rating
'Charleston 'Black 'Charleston 'Black
Foliar Sprays Grey' Bell' 'Blue Lake' 'Senator' Grey' Bell' 'Blue Lake' 'Senator'
Compound q/L watermelon eggplant bush bean zucchini watermelon eqqplant bush bean zucchini
W FeSO4 7H 0
ZD = deionized water in solutions indicated. W =
YO = no visible injury, 10 = maximum injury.
XNumbers in columns followed by different letters
well water in solutions indicated.
are significantly different (LSD) at the 5% level of probability.
The Gulf Coast Research and Education Center
The Gulf Coast Research and Education Center is
a unit of the Institute of Food and Agricultural Sci-
ences, University of Florida. The Research Center
originated in the fall of 1925 as the Tomato
Disease Laboratory with the primary objective of
developing control procedures for an epidemic out-
break of nailhead spot of tomato. Research was ex-
panded in subsequent years to include study of sev-
eral other tomato diseases.
In 1937, new research facilities were established
in the town of Manatee, and the Center scope was
enlarged to include horticultural, entomological, and
soil science studies of several vegetable crops. The
ornamental program was a natural addition to the
Center's responsibilities because of the emerging in-
dustry in the area in the early 1940's.
The Center's current location was established in
1965 where a comprehensive research and extension
program on vegetable crops and ornamental plants is
conducted. Three state extension specialists posi-
tions, 16 state research scientists, and two grant
supported scientists from various disciplines of
training participate in all phases of vegetable and
ornamental horticultural programs. This interdisci-
plinary team approach, combining several research
disciplines and a wide range of industry and faculty
contacts, often is more productive than could be ac-
complished with limited investments in independent
The Center's primary mission is to develop new
and expand existing knowledge and technology, and
to disseminate new scientific knowledge in Florida, so
that agriculture remains efficient and economically
The secondary mission of the Center is to assist
the Cooperative Extension Service, IFAS campus
departments, in which Center faculty hold appropri-
ate liaison appointments, and other research centers
in extension, educational training, and cooperative
research programs for the benefit of Florida's pro-
ducers, students, and citizens.
Program areas of emphasis include: (1) genetics,
breeding, and variety development and evaluation;
(2) biological, chemical, and mechanical pest manage-
ment in entomology, plant pathology, nematology,
bacteriology, virology, and weed science; (3) produc-
tion efficiency, culture, management, and counteract-
ing environmental stress; (4) water management and
natural resource protection; (5) post-harvest physiol-
ogy, harvesting, handling and food quality of horti-
cultural crops; (6) technical support and assistance to
the Florida Cooperative Extension Service; and (7)
advancement of fundamental knowledge ofdisciplines
represented by faculty and (8) directing graduate
student training and teaching special undergraduate
1 The Institute of Food and Agricultural Sciences,
University of Florida.
Q A statewide organization dedicated to teaching,
research and extension.
O Faculty located in Gainesville and at 13 research
and education centers, 67 county extension
offices and four demonstration units throughout
" A partnership in food and agriculture, and natural
and renewable resource research and education,
funded by state, federal and local government,
and by gifts and grants from individuals, founda-
tions, government and industry.
Q An organization whose mission is:
Educating students in the food, agricultural,
and related sciences and natural resources.
Strengthening Florida's diverse food and
agricultural industry and its environment
Enhancing for all Floridians, the application
of research and knowledge to improve the
quality of life statewide through IFAS exten-