Title: Vegetarian
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00087399/00548
 Material Information
Title: Vegetarian
Physical Description: Serial
Language: English
Creator: Horticultural Sciences Department, Institute of Food and Agricultural Sciences
Publisher: Horticultural Sciences Department
Place of Publication: Gainesville, Fla.
Publication Date: June 2010
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Bibliographic ID: UF00087399
Volume ID: VID00548
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.


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Vegetarian Newsletter

A Horticultural Sciences Department Extension Publication on Vegetable and Fruit Crops

Eat your Veggies and Fruits!!!!!

Issue No. 558 June 2010

Elemental Sulfur Use for Increasing Phosphorus Availability to Lettuce in
Everglades Agricultural Area Soil

By: Alan L. Wright, Yigang Luo, Nikol Havranek, David D. Sui, Ronald W. Rice, and
Rongzhong Ye

Everglades Research & Education Center, Belle Glade, FL

The Everglades Agricultural Area (EAA) in south Florida was historically a

seasonally-flooded wetland ecosystem but was converted to agricultural use by

drainage in the early 1900s. Vegetables have been grown on these soils since that

time. Early scientists at the Everglades Research & Education Center in Belle Glade

observed that crops often failed to yield unless supplemented with micronutrients,

especially copper, which was deficient in these soils. Further research optimized

fertilizer use and management for many types of vegetable crops in the region,

including sweet corn, beans, lettuce, and celery. These organic soils are typically

sufficient in nitrogen and while some starter nitrogen is applied, supplemental

fertilization of potassium and phosphorus, as well as manganese, iron, copper, and

zinc, are regularly needed.

Subsidence of the organic soils in the region occurred soon after drainage, which

led to decreases in soil depth to the underlying bedrock limestone. Some of the soils

are becoming very shallow, and interaction with the underlying calcium carbonate has

created conditions where particles of limestone are translocated into surface soils by

tillage and evapotranspiration. The result is that the pH and nutrient retention capacity

of these soils has increased, which tends to tie up nutrients, particularly P and

micronutrients, in forms that are not readily available to crops.

Several options exist to remedy the situation: increase fertilization rates, optimize

fertilizer placement, timing, and application method, and use of soil pH amendments.

Increasing fertilization rates is effective, but adds to grower costs and may pose

potential hazards to aquatic systems due to runoff or leaching of excess nutrients.

Efforts are ongoing to evaluate how fertilizer placement, split application, foliar

application, source material, etc., influence crop growth and yield. Another option

receiving attention is the use of soil amendments to decrease pH, which has the effect

of increasing available nutrient concentrations in soil. Elemental sulfur is a widely used

amendment throughout the world for decreasing soil pH, and its use in the EAA is under


Prior research on these soils has demonstrated that high S rates are needed to

reduce soil pH, but the results were only temporary. Contemporary results also

confirmed that broadcast S application (500 Ib/a) failed to increase nutrient availability

or enhance crop yields (Wright, unpublished data). However, application of elemental S

in narrow bands near crop rows has shown promise in increasing both nutrient

availability and lettuce yield. Elemental S wettablee powder) banded at 200 Ib/a showed

an approximate 20% increase in romaine lettuce yield compared to unamended soil

(Figure 1). Increasing the S rate above 200 Ib/ac did not produce a greater yield

response, although it did increase available P compared to lower S application rates

and unamended soil. Thus, there appears to be some benefit of banded S application

for increasing P availability and lettuce yield. This increase in P availability occurred

within 2 weeks of application and was evident for 2 months. An interesting observation

is that elemental S did not significantly change soil pH, yet it increased P availability.

Sulfur application at 400 Ib/ac decreased soil pH by 5% compared to the unamended

control, but increased P availability by 100%. Thus, P was a much more sensitive

indicator of S effectiveness than soil pH.

Elemental S reduces soil pH through its oxidation by soil microorganisms into

sulfate (SO4-), and this process results in the production of H+ ions responsible for

reducing pH. Since P adsorption in soil is dependent on pH, the temporary reduction in

soil pH releases bound phosphates that are available for crop uptake. Meanwhile, the

natural buffering capacity of the soil, mainly controlled by calcium carbonate, responds

to the lower pH and acts to neutralize the soil acidity caused by elemental S oxidation.

A short time after all elemental S is depleted and oxidized, the pH returns to its

equilibrium point. However, the P released takes much longer to return to its

equilibrium point and it remains in an available state longer until it is taken up by crops

or adsorbed to soil. Thus, the benefits and effectiveness of elemental S use in the EAA

are best evaluated in terms of its ability to maintain available P concentrations in soil

rather than its effect on soil pH. To fully evaluate elemental S efficacy in the calcareous

organic soils of the EAA, perhaps it is best to focus on changes in nutrient availability

rather than on changes in soil pH, especially since soil nutrients rather than soil pH are

responsible for the crop growth and yield response. Replication of this study is needed

to confirm these observations. Other considerations for elemental S use in the EAA

include evaluation of costs of elemental S versus yield benefits, as well as the

environmental costs associated with potential sulfate losses from the EAA into the

Everglades wetlands.









0 200 400 600 800

Elemental S Rate (b/ac)

Figure 1. Response ofromainelettuceto elemental S applicationin Everglades
Agricultural Area soil.

Vegetarian Newsletter

A Horticultural Sciences Department Extension Publication on Vegetable and Fruit Crops

Eat your Veggies and Fruits!!!!!

Issue No. 558 June 2010

Does Shoot Pruning Improve Tomato Yield and Reduces Bacterial Spot Infestation?

By: Bielinski M. Santos and Gary E. Vallad, Vegetable and Small Fruit Horticulturist and
Vegetable Plant Pathologist, respectively.

Gulf Coast Research and Education Center, IFAS, University of Florida, Balm, Florida.


Among the many diseases that affect tomato, bacterial spot is one of the most

troublesome. This disease is caused by Xanthomonas perforans, X. vesicatoria, X. euvesicatoria,

and X. gardneri (formerly referred to asX. campestris pv. vesicatoria) and favored by warm,

humid weather conditions, but often initiated by episodes of wind-driven rain. Infection begins

on the leaves when the bacterium enters the plant through natural openings and wounds

where it multiplies within plant tissues (Figure 1). Within three to four days, the first symptoms,

water-soaked lesions, can be observed on lower leaf surfaces. Lesions can enlarge and coalesce

causing extensive leaf chlorosis and defoliation. All aboveground tissues are susceptible to the

disease. Fruit lesions begin as small raised blisters on the fruit surface that are a lighter green

than the rest of the immature fruit. As the lesions enlarge, they turn brown to black and

develop a layer of scab-like tissue. Fruit lesions are particularly problematic for growers, since

they not only affect fruit appearance but also offer a site for other microbes to enter the fruit.

Control of bacterial spot relies on cultural exclusion of the pathogen from production areas, use

of resistant cultivars, and diligent application of copper-based bactericides. Regardless,

bacterial spot epidemics occur every season in most tomato production regions. The presence

of infected tomato volunteers and weedy hosts are common sources of local inoculum. Infected

seed and transplants are also a mechanism of long distance movement. The use of copper-

based bactericides can offer some level of control, except under the most extreme weather

conditions. However, the reliance on copper in agriculture has led to widespread copper

tolerance among bacterial pathogens on many crops. A dithiocarbamate (either maneb or

mancozeb) is routinely combined with copper-based bactericides to enhance bacterial spot

control, but reduces the fungicidal activity of the dithiocarbamate. The overuse of copper-

based pesticides in vegetable production can adversely affect crop growth and the


Most growers of round tomatoes in Florida perform shoot pruning on their crops during

the early part of the growing season to reduce the number of unwanted lateral branches. This

practice usually occurs between 2 and 4 weeks after transplanting (WAT) and it could be

accomplished once or twice during that period by removing shoots from ground level up to the

primary fork below the first flower cluster. Previous research showed that for some tomato

cultivars, shoot pruning increased early yield, whereas other studies found no response or

reduced growth and yields. Some growers and scientists think that shoot pruning could be a

potential practice to reduce bacterial spot infection because: a) it reduces the amount of foliage

near the soil that could serve as an initial point of entry for the bacterium, and b) it changes

architecture of plant canopies thus changing air and moisture flow through the leaves.

Additionally, shoot pruning costs about $50/acre, which is a significant expense for tomato

production. The objective of this study was to determine the effect of early shoot pruning on

the severity of bacterial spot, and on the growth and yield of different tomato cultivars.

Materials and Methods

Two field trials were conducted in the Spring and Fall 2009 at the Gulf Coast Research

and Education Center of the University of Florida in Balm, Florida, using standard tomato

production practices (e.g. soil fumigation, mulching, drip irrigation). Tomato seedlings in the

four-true-leaf stage (8 inches tall) were transplanted in single rows and 2 inches offset of bed

centers. Planting in-row distance was 18 inches. The study had the combination of two tomato

cultivars, two bacterial spot inoculation regimes, and three shoot pruning programs. The study

had the combination of two tomato cultivars, two bacterial spot inoculation regimes, and three

shoot pruning programs in a split-split plot design with five replications.The tomato cultivars

were 'Tygress' and 'Security-28', which are resistant to the tomato yellow leaf curl virus. Shoot

pruning levels were heavy and light, and a non-pruned treatment was added. Light pruning was

defined as carefully removing by hand only two to three lateral buds ("suckers") from the main

stems from ground level to 6 inches high, whereas heavy pruning was defined as the removal of

all the lateral buds and stems up to 6 inches high. Early shoot pruning occurred between 3 and

4 WAT. Bacterial spot treatments consisted of non-inoculated plots and plots inoculated with a

suspension ofX. perforans strain XT4 (1 x 106 cfu/mL), which was applied to the foliage with a

conventional backpack sprayer at 5 WAT at a volume of approximately 15 mL per plant.

1 Plant heights were determined at 3 and 6 WAT and tomato fruit were harvested twice

2 (10 and 12 WAT) in the mature green stage and graded following current market standards as

3 extra-large and marketable fruit of all categories. Fruit yield from the first harvest (10 WAT)

4 were considered early fruit weight, while the summation of the two harvests (10 and 12 WAT)

5 was the seasonal fruit weight. For bacterial spot, plots were monitored for disease and rated

6 for severity at 7 and 9 WAT in the spring trial, and at 9 and 11 WAT in the fall trial using the

7 Horsfall-Barratt scale, a non-dimensional 12 point scale, to assess the percentage of canopy

8 affected by bacterial leaf spot. Disease severity values were converted to mid-percentages and

9 used to generate area under disease progress curve (AUDPC). Means of significant treatment

10 effects and their interactions were separated with a Fisher's protected least significant

11 difference procedure at the 5% level.

Results and Discussion

Plant height and bacterial spot severity. Shoot pruning did not affect tomato plant

height at 3 and 6 WAT, regardless of cultivars and bacterial spot inoculation (data not shown).

Bacterial spot inoculation increased disease severity based on AUDPC of 1445 (an average

disease severity of 41%) in inoculated versus an AUDPC of 821 (an average disease severity of

29%) in non-inoculated plots averaged across both seasons (data not shown). Disease severity

was greater at the end of the spring trial in comparison to the end of the Fall 2009 trial (65%

and 35%, respectively). Inversely, initial disease severity was much greater in the fall study (24%

disease severity in non-inoculated plots) than the spring trial (1.5% disease severity in non-

inoculated plots). 'Tygress' was more susceptible to bacterial spot than 'Security-28', exhibiting

20.4% more disease on average.

Early tomato fruit weight. Early extra-large fruit weight was affected by tomato cultivars

and the inoculation of bacterial spot, but not by pruning programs or the interaction among

factors. 'Security-28' had the highest early extra-large fruit weight with 5.1 ton/a, which was

more than 2.5 times higher than that obtained with 'Tygress' (Table 1). Tomato plants

inoculated with bacterial spot reduced their extra-large fruit weight by 31% in comparison with

those non-inoculated with the bacterium. Pruning programs resulted in extra-large yields

ranging between 3.4 and 3.6 ton/a. Early marketable fruit weight was influenced by the

interaction between cultivars and pruning programs, and separately by the inoculation of

bacterial spot (Table 1). There were no differences on early marketable fruit weight among the

combinations of 'Security-28' and the three pruning programs, which averaged 6.9 ton/a of

fruit. At the same time, all pruning programs in plots planted with 'Tygress' did not differ

among each other, while having significantly lower marketable fruit weight at 10 WAT than the

'Security-28' and pruning combinations. Tomato plants in plots inoculated with bacterial spot

decreased their marketable fruit weight at 10 WAT by 25% in comparison with the non-

inoculated plants.

Seasonal tomato fruit weight. The cultivar by bacterial spot inoculation interaction

affected the seasonal extra-large fruit weight. However, other main factors and interactions

were not significant. The highest seasonal extra-large fruit weight was obtained in plots non-

inoculated with bacterial spot and planted with 'Security-28' (11.1 ton/a), followed by the

combination of 'Security-28' and bacterial spot inoculation (Table 2). There was no effect of the

bacterial spot inoculation on the seasonal extra-large fruit weight obtained in plots planted

with 'Tygress'. All three factors individually influenced the seasonal marketable fruit weight of

tomato. Non-inoculated plots produced 21% higher seasonal yields (18.1 ton/a) in comparison

with plants inoculated with bacterial spot (15.0 ton/a). When comparing pruning programs,

there was no difference between light pruned plants and the non-pruned control for seasonal

marketable fruit weight, regardless of tomato cultivars (Table 2). However, heavy pruning did

reduce seasonal yields by 10% in comparison with the non-pruned control.

These results indicated that light shoot pruning did not improve tomato yield of total

and extra-large marketable fruit. At the same time, this practice did not reduce bacterial spot

severity on 'Security-28' and 'Tygress' tomato leaves. In contrast, heavy pruning reduced

seasonal marketable yields in comparison with non-pruned plants. It is possible that other

cultivars may benefit from shoot pruning, as the tested cultivars are newer hybrids introduced

to the market for their resistance to tomato yellow leaf curl virus. Data also emphasized the

impact of bacterial spot on fruit production, especially the production of early extra-large fruit,

and the importance of selecting varieties with improved tolerance to bacterial spot when

disease pressure is high. By eliminating light shoot pruning from routine cultural practices,

tomato growers can save up to $50 per acre, which might translate into nearly $2 million per

year in savings for all the planted areas in Florida.

Figure 1. Bacterial spot lesions on the lower surface of tomato leaves and a view of a severely-infected tomato field (Credits: G.E.


Table 1. Effects of early shoot pruning levels, tomato cultivars, and bacterial spot inoculation on early extra-large and total

marketable fruit weight. Spring and Fall 2009, Balm, Florida.

Pruning Pruning x cultivar

ton/acre ton/acre

Non-pruned 3.5 Non-pruned, 'Security-28' 7.4 a

Light 3.6 Light, 'Security-28' 7.1 a

Heavy 3.4 Heavy, 'Security-28' 6.3 a

Significance (P<0.05) NS Heavy, 'Tygress' 4.4 b

Cultivar Light, 'Tygress' 3.7 b

'Security-28' 5.1 a Non-pruned, 'Tygress' 3.4 b

'Tygress' 1.9 b

Significance (P<0.05) Significance (P<0.05) *

Bacterial spot Bacterial spot

Non-inoculated 4.2 a Non-inoculated 6.4 a

Inoculated 2.9 b Inoculated 4.8 b

Significance (P<0.05) Significance (P<0.05) *

ZValues followed by the same letter in the same

significant and significant, respectively.

column do not differ statistically at the 5% significance level. NS and = non-

Table 2. Effects of early shoot pruning levels, tomato cultivars, and bacterial spot inoculation on seasonal extra-large and total

marketable fruit weight. Spring and Fall 2009, Balm, Florida.

Cultivar x bacterial spot Pruning

ton/acre ton/acre

Non-inoculated, 'Security-28' 11.1 a Non-pruned 18.2 a

Inoculated, 'Security-28' 8.1 b Light 17.4 ab

Non-inoculated, 'Tygress' 7.0 c Heavy 16.3 b

Inoculated, 'Tygress' 7.5 c Significance (P<0.05) *

Significance (P<0.05) Cultivar

'Security-28' 18.3 a

'Tygress' 15.0 b

Pruning Significance (P<0.05) *

Non-pruned 8.4 Bacterial spot

Light 8.3 Non-inoculated 18.1 a

Heavy 8.4 Inoculated 15.2 b

Significance (P<0.05) NS Significance (P<0.05) *

ZValues followed by the same letter in the same column do not differ statistically at the 5% significance level. NS and *= non-

significant and significant, respectively.

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