IJE2l A VEGETARIAN NEWSLETTER
A Vegetable Crops Extension Publication University of Florida
Vegetarian 02-11 Institute of Food and Agricultural Sciences
November 2002 Cooperative Extension Service
(Note: Anyone is free to use the information in this newsletter. Whenever possible, please give credit to the authors.
The purpose of trade names in this publication is solely for the purpose of providing information and does not
necessarily constitute a recommendation of the product.)
Vegetarian Archive Vegetarian index
M Print Version
* Understanding Chilling Injury and Recognizing its Symptoms
* Management of Cucurbit Diseases
* Effects of Plant Essential Oils on Bacterial Wilt Incidence in Tomato
* Matrix (rimsulfuron) Herbicide Labeled on Florida Tomato
List of Extension Vegetable Crops Specialists
*** UPCOMING EVENTS CALENDAR *
Florida Drip Irrigation School. GCREC-Dover. November 13, 10:00-4:00. Contact Christine at 813-744-6630. Programs are
offered free of charge but require pre-registration.
Florida Drip Irrigation School. NFREC-Live Oak. December 4, 9:00-4:00. Contact Laurie at 386-362-1725. Programs are offered
free of charge but require pre-registration.
Cucurbitaceae 2002. Naples Beach Hotel and Golf Club; Naples, Fla. December 8-12. Contact Don Maynard at 941-751-7636
x239 or firstname.lastname@example.org
Florida Postharvest Horticulture Industry Tour. Statewide. March 10-13, 2003. Contact Steve Sargent at 352-392-1928 or
email@example.com OR Mark Ritenour at 561-201-5548 or firstname.lastname@example.org
Florida Postharvest Horticulture Institute at FACTS (Florida Agricultural Conference & Trade Show). Lakeland. April 29-30,
2003. Contact Steve Sargent at 352-392-1928 or email@example.com
Vegetable Field Day. GCREC-Bradenton. May 15, 2003. Contact Don Maynard at 941-751-7636 x239 or firstname.lastname@example.org
116th Florida State Horticultural Society. Sheraton World Resort Hotel International Drive Orlando, June 8-10, 2003.
UNDERSTANDING CHILLING INJURY AND RECOGNIZING ITS SYMPTOMS
Plants evolved around the world within relatively narrow temperature ranges and, although the cultivated descendents of wild plants may
nowadays be grown worldwide, they still "remember" their origins. Thus, many cultivated fruits and vegetables that originated in the
tropics and subtropics cannot tolerate low, but nonfreezing temperatures in the range of 32 to 55 F (0 to 12.8 C). The resulting adverse
effects on their growth, development, maturation, or ripening when they are exposed to temperatures in this range are collectively
referred to as "chilling injury." For the postharvest handler, this is an ironic situation because, as we know, low temperature is our best
tool for maintaining the quality of fresh fruits and vegetables.
An important yet simple concept to understand with regard to chilling injury is the "threshold temperature." For each crop species, there
is a unique temperature at or above which chilling injury will not occur. These threshold or lowest safe temperatures are the basis for the
widely circulated "recommended" or "optimum" storage and handling temperatures for various chilling sensitive crops. The lower the
temperature below the threshold temperature and the longer the exposure, the worse the chilling injury will be. Threshold temperatures
for an individual crop can vary substantially among varieties and with differences in maturity less mature or less ripe individuals are
more sensitive to chilling. Chilling injury is also usually cumulative. This means that a number of even brief exposures to chilling
temperatures, including those occurring in the field before harvest, may result in development of injury symptoms.
Examples of crops that are sensitive to chilling injury obviously include the tropical fruits such as bananas, mangoes, papayas, and
pineapples. Less appreciated is the fact that almost all of the vegetables crops that are grown in the northern hemisphere as "warm
season" vegetables are of tropical or subtropical origin and thus subject to chilling injury. These include beans, cucumbers, eggplants
(Fig. 1), most of the melons (cantaloupes are only slightly sensitive), peppers (Fig. 2), all of the squashes (summer and winter types),
sweetpotatoes, and tomatoes. Asparagus and potatoes are cool season vegetables that are also chilling sensitive.
Figure 1. Eggplant chilling injury symptoms. Figure 2. Bell pepper chilling injury symptoms.
The visible symptoms of chilling injury vary widely among these sensitive crops (Table 1), but typically include surface pitting,
watersoaked and discolored flesh, failure to ripen normally, and increased susceptibility to decay.
An extremely important (and insidious) consequence of chilling injury is flavor loss due to inhibition of aroma volatile production. This is
often the first symptom of chilling injury and, in cases of mild chilling exposure, it may be the only symptom. The infamous "tasteless
winter tomatoes" are almost certainly a result of shipping and storage at below the lowest safe temperature! Another ironic aspect of
chilling injury is that chilling symptoms are usually most clearly expressed after the commodity is transferred to a warm, non-chilling
environment. This means that handlers who carelessly expose sensitive vegetables to chilling temperatures may very well never see the
injury that they have caused that will fall to a subsequent handler, perhaps the ultimate consumer, baffled as to why seemingly high
quality vegetables quickly spoiled at home. It also means that vegetables that were chilled in the field due to inclement weather may
develop chilling injury even when they are handled at recommended temperatures!
Table 1. Lowest safe ("threshold') temperatures and chilling injury symptoms for sensitive vegetables.
Vegetable Threshold temperature Visible chilling injury symptoms
Asparagus 35 2 Dull, gray-green and limp tips
Bean (lima) 37 41 3-5 Rusty-brown specks or spots
Bean (snap) 40 45 4-7 Pitting and russetting (rusty-brown streaks)
Cucumber 50 10 Pitting, watersoaked spots, decay
Eggplant 46 8 Surface scald, Alteraria rot, seed darkening
(C-slip) 36 41 2 5 Pitting, surface decay
(full-slip) 32 36 0 2 Pitting, surface decay
Honey Dew 45 50 7 10 Reddish-tan discoloration, pitting, surface decay, failure
Casaba 45 50 7-10 Pitting, surface decay, failure to ripen
Crenshaw 45 50 7 10 Pitting, surface decay, failure to ripen
Watermelon 50 10 Pitting, darkening or watersoaking of flesh
Okra 45 7 Discoloration, watersoaked areas, pitting
Pepper 45 7 Sheet pitting, Alteraria rot, seed darkening
Potato 40 4 Mahogany browning, sweetening
(summer) 41 5 Pitting, watersoaked spots, decay
(winter) 50 10 Decay, especially Altemaria rot
Sweetpotato 55 13 Decay, pitting, internal discoloration, hard- core when
(mature-green) 55 13 Slowed ripening, pitting, poor color, Altemaria rot
(ripe) 45 50 7 10 Watersoaking, softening, decay
Yam 61 16 Tissue discoloration and watersoaking, decay
Adapted from USDA Agriculture Handbook Number 66
Chilling injury is a complicated phenomenon, however it behooves us as postharvest handlers to understand this disorder and be able to
recognize it symptoms. In ongoing research in which we are collaborating with colleagues at University Laval in Quebec, quality curves
are being established for about two dozen fresh fruits and vegetables, including a number that are chilling sensitive. This is being done
by evaluating all measurable quality changes in each commodity every day or every other day (depending on relative shelf life) at 32, 41,
50, 59, 68, and 77 F (0, 5, 10, 15, 20 and 25 C). From these experiments, we are determining both the shelf life and the quality
factors) that limits) the shelf life at each temperature. In the meantime, we recommend that in the absence of specific experience with
a particular chilling sensitive crop or variety, it is best to take a conservative approach and strictly avoid any exposure to temperatures
below the thresholds listed in Table 1.
(Brecht, Ritenour, and Sargent- Vegetarian 02-11)
MANAGEMENT OF CUCURBIT DISEASES
With the South Florida vegetable production season in full swing, and the North Florida Spring season on its way, a review of diseases
for watermelon and other cucurbits is in order. Plant diseases significantly impact yields and quality of cucurbits. Disease pressure is
determined primarily by four factors: abundance of inoculum in surrounding fields, presence of inoculum on seeds and transplants,
climatic conditions, cultural practices during the cropping season, and the choice of variety to plant. Close attention should be paid to all
of these conditions to minimize damage done during the season.
Fungal pathogens such as Gummy Stem Blight (Fig. 1), Powdery Mildew (Fig. 2), and Downy Mildew (Fi. 3) defoliate vines, and
ultimately reduce yields of marketable fruit. With the exception of powdery mildew, these diseases are favored by humid, rainy, and hot
conditions. For effective management, choose a field where cucurbits haven't been grown for at least 4-5 years (practice crop rotation),
choose well-drained fields with good air circulation around them, use pathogen-free transplants or seeds, and eliminate wild (citrons) and
volunteer cucurbits in and around production fields. If possible, use drip irrigation and deep plow plant debris after harvest. Deep plowing
promotes decay of infected debris, reducing survival and sporulation of pathogens. Finally, it is important to follow a protective fungicide
program, i.e. begin applications of chlorothalonil, mancozeb, maneb, or other materials before disease symptoms are present. Quadris
(strobilurin) is both a protective and curative material and may be applied at 15.4 fl oz/trtd Acre, and must be alternated with other
fungicides with different modes of action, with a maximum of 4 applications strobilurin/crop/acre/year.
Figure 1. Symptoms of Gummy Stem Blight
Figure 2. Symptoms of Powdery Mildew
Unlike fungal pathogens, viral diseases
require insect vectors (primarily aphids
and whiteflies) for transmission,
although mechanical transfer of plant
sap may also result in disease spread.
Zucchini Yellow Mosaic Virus (ZYMV)
(Fig. 4), Watermelon Mosaic Virus 2
(WIMV-2), Papaya Ring Spot Virus-W
(PRSV-W), and Cucumber Mosaic
Virus (CMlV) all have been reported in
North Florida. Viral symptoms include
plant and leaf deformation, stunting of
growth, and fruit damage. Planting
virus-resistant varieties is the best
defense against infections, but other
cultural practices, such as destroying
weed hosts and volunteer cucurbits in
and bordering fields, early season
planting of healthy plant material, oil
sprays C'JiS Stylet oil'), and reducing
insect populations all will prove to be
"preventative measures" for growers.
Growers should also beware of "bridge"
weeds left in fields between seasons
that may serve as ways for viruses to
be carried over to the next crop.
__ To be successful at combating
pathogens on cucurbits, producers
Figure 3. Symptoms of Downy Mildew Figure 4. Symptoms of ZYMV must integrate crop rotations,
destruction of weed hosts, use of drip
irrigation and disease-free plant material, proper field monitoring and diagnostics, and a fungicide/insecticide program that is both
protective and curative. Regular scouting and close attention paid to growing crops will keep producers well abreast of disease
developments in fields, thus aiding them in making wise management decisions.
(Josh Mayfield, ext. agt., Gadsden County and Tim Momol, asst. prof., NFREC-Quincy -Vegetarian 02-11)
EFFECTS OF PLANT ESSENTIAL OILS ON BACTERIAL
WILT INCIDENCE IN TOMATO
Bacterial wilt (BW) caused by Ralstonia solanacearum (Rs) is a serious soil-borne disease of many economically important crops, such
as tomato (Fig. 1), potato, tobacco, banana, eggplant and some ornamental plants. This bacterium causes wilt by infecting plants
through roots and colonizing stem vascular tissue. Although diseased plants can be found scattered in the field, bacterial wilt usually
occurs in foci associated with water accumulation in lower areas. Under natural conditions, the initial symptom in mature plants is wilting
of upper leaves in hot days followed by recovery throughout the evening and early hours of the morning. The wilted leaves maintain their
green color as disease progresses. Under hot humid conditions favorable for disease, complete wilting occurs and the plant will die. The
vascular tissues in the lower stem of the wilted plants usually show a brown discoloration.
l yS _...Due to the limited efficacy of the current integrated management strategies, BW
continues to be economically important for field grown fresh market tomato production
in the southeastern United States and many subtropical and tropical areas of the
world. Cultural practices, crop rotation and host resistance could provide a limited
Greenhouse experiments were conducted to determine the effectiveness of plant
essential oils as soil fumigants to manage BW in tomato. Potting mixture infested
-with Rs was treated with the essential oils at 400 mg or il and 700 mg or il per L soil
in greenhouse experiments. Rs population densities were determined just before and
7 days after treatment. Populations declined to undetectable levels in thymol,
palmarosa oil and lemongrass oil treatments at both concentrations, whereas tea tree
oil had no effect. Tomato seedlings transplanted in soil treated with 700 mg/L thymol,
700 ml/L palmarosa oil and 700 ml/L lemongrass oil were free from bacterial wilt and
Figure 1. Affects of bacterial wilt on tomato. 100% of the plants in thymol treatments were free of Rs. Soil amendment with fresh
leaves of essential oil producing plants did not reduce bacterial wilt incidence compare
to untreated inoculated control. Some thyme oil producing plants such as thyme cv. German winter, Creeping thyme, and Greek
oregano were systemically infected by Rs in their roots and therefore identified as hosts of Rs.
(M. T. Momol, asst. professor, Quincy-REC, Olson, P. M. Pradhanang, Plant Pathology Dept, Vegetarian 02-11)
MATRIX (RIMSULFURON) HERBICIDE LABELED ON FLORIDA TOMATO
Dupont has issued a supplemental label for the rise of Matrix on field grown tomatoes. Matrix (rimsulfuron) will control a number of
grasses and many broadleaf weeds applied preemergence and postemergence to the weeds. The label states (at the present time) that
Matrix can be applied preemergence to the seeded crop only.
Matrix may be applied postemergence or posttransplant to the tomatoes at 1-2 oz. product (0.25-0.5 oz. ai). Sequential applications are
labeled. A maximum of 4.0 oz. Product per acre per year can be used. Use a nonionic surfactant of 80% ai or higher with all
applications. Use a surfactant at a rate of 0.25% v/v (2 pts/100 gallons of water). The use of a crop oil concentrate, methylated seed
oils, nitrogen fertilizer solution or nonionic surfactants applied at rates above 0.25% v/v may result in temporary crop chlorosis.
Symptoms usually disappear within 5-15 days.
Matrix must be activated in the soil with sprinkler irrigation or rainfall. Preemergence (weed) use without soil activation do not provide
adequate weed control.
Check the rotational crop guidelines on the label.
(Stall Vegetarian 02-11)
Extension Vegetable Crops Specialists
Daniel J. Cantliffe
Professor and Chairman
Assistant Professor, strawberry
Assistant Professor, vegetable production
Elizabeth M. Lamb
Assistant Professor, production
Assistant Professor, soils
Donald N. Maynard
Stephen M. Olson
Professor, small farms
Mark A. Ritenour
Assistant Professor, postharvest
Ronald W. Rice
Assistant Professor, nutrition
Steven A. Sargent
Assistant Professor and editor, vegetable nutrition
William M. Stall
Professor, weed control
James M. Stephens (retired)
Professor, vegetable gardening
Charles S. Vavrina
James M. White
Associate Professor, organic farming
University of Florida
Institute of Food and Agricultural Sciences
Horticultural Sciences Department
Florida Cooperative Extension Service
North Florida Research and Education Center Suwannee Valley
Gulf Coast Research and Education Center Dover
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