veggies growing.gif (7628 bytes)       Vegetarian Newsletter

A Vegetable Crops Extension Publication
Vegetarian 03-04
April 2003

University of Florida
Institute of Food and Agricultural Sciences
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 Index

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COMMERCIAL VEGETABLES
grnbullet.gif (839 bytes) Integrated Management of Thrips and Tomato Spotted Wilt in Field-Grown Fresh Market Tomatoes
grnbullet.gif (839 bytes) "Graywall" in Tomato Production
grnbullet.gif (839 bytes) Commercial Packaging Options for Beit-Alpha Cucumbers

List of Extension Vegetable Crops Specialists

 * * * * * * * U P C O M I N G  E V E N T S  C A L E N D A R * * * * * * *

Various Extension Events in South Florida - Contact Gene McAvoy at 674-4092
Florida Postharvest Horticulture Institute at FACTS. (Florida Agricultural Conference & Trade Show). Lakeland, Fla. April 29-30, 2003. Contact Steve Sargent at 352-392-1928 or sasa@mail.ifas.ufl.edu
116th Florida State Horticultural Society.  Sheraton World Resort Hotel International Drive - Orlando, Fla. June 8-10, 2003.
CEU Day at Florida State Horticultural Society. - June 9, 2003, 7:30 am - 4:30 pm
49th Conference of the InterAmerican Society for Tropical Horticulture. Fortaleza, Brazil, Aug. 31- Sept. 5, 2003.

ISHS International Symposium on Protected Culture in a Mild-Winter Climate. Renaissance WorldGate Hotel - Kissimmee, Fla. March 23-27, 2004. Contact: Daniel Cantliffe at djc@mail.ifas.ufl.edu


Integrated Management of Thrips and Tomato Spotted
Wilt in Field-Grown Fresh Market Tomatoes

Every Spring, from late April through early June, farmers in North Florida are busy scouting their fields for the #1 threat to tomato yields, Frankliniella occidentalis, or Western Flower thrips. Low numbers of thrips develop slowly on weed hosts throughout the winter. In early spring, they thrive on various weed species along field borders and move into fields as tomato plants begin to set flowers. Thrips reproduce in the flowers and feed on pollen, flower tissue, and developing fruit.

Prior to 1986, thrips feeding damage on tomatoes was largely restricted to premature flower loss, fruit and leaf deformity, and tiny cosmetic holes in the fruit caused by female oviposition and known as "halospotting". Not long after, however, it was discovered that Western Flower thrips were the primary vector of an up-and-coming plant virus known as Tomato Spotted Wilt (TSW), see Figure 1 and Figure 2. During an epidemic year, plant losses from TSW may range from 10% to more than 50% in an infected field. Since thrips acquire the virus as larvae and in most cases infect plants once they are adults, it is a very difficult disease to control. The only option for growers has been to spray organophosphate insecticides on a calendar basis 2 to 3 times per week for a total of 16 - 20 sprays per season.

Figure 1. Tomato Spotted Wilt symptoms
 on tomato foliage.

Figure 2. Tomato Spotted Wilt symptoms
 on young fruit.

Recently, research conducted at the NFREC, Quincy and farm demonstrations in South Georgia and Gadsden County, Florida have demonstrated that IPM measures for managing thrips and TSW are highly successful compared to conventional production methods. These measures include weekly field scouting, planting resistant varieties, alternating organophosphates with Spin Tor ® (spinosad), a "greener" insecticide of a different chemistry, and treatment with Systemic Acquired Resistance Inducers (SAR’s) such as Actigard ® (acibenzolar-S-methyl). Most importantly, however, has been research documenting the value of using UV-reflective (metallized) mulches for repelling thrips (Figure 3). Metallized mulches may reflect up to 75% of UV rays back up into the plant canopy, which has been demonstrated to block the thrips’ ability to find the host plant. This cultural technique has been shown to reduce vector thrips numbers up to 45% and subsequent incidence of TSW up to 50% compared to black plastic mulch, most often used by vegetable growers.

Figure 3. Metallized mulch in staked tomato production.

The Spring 2002 production season proved an epidemic year for TSW incidence. Although production was high, losses were significant. A survey was conducted in Gadsden County, Florida and Decatur County, Georgia to determine progress being made by growers to integrate IPM practices into their production systems. By this, UF/IFAS extension efforts could also be measured to discover how successful they have been in getting the message out concerning these new practices, in particular the use of UV-reflective mulches during the Spring.

Survey results showed that all growers scouted their fields weekly, while 82% scouted twice per week. Insecticide sprays for thrips averaged 15-20 times per season. On approximately 2000 acres of Spring tomatoes, only 10% of the total acreage was grown on metallized mulches, accounting for 23% of growers utilizing it. Fifty-five per cent of growers used Actigard to aid in TSW management, while 50% planted TSW-resistant varieties. However, 28% of growers in North Florida and South Georgia still are not using either Actigard, resistant varieties, or metallized mulches as part of their pest management practices. As the scouting numbers confirmed previous research data, TSW incidence averaged 17% on black plastic, while only 2% on metallized mulch.

Those who did not utilize these new mulches stated there was not enough research data to convince them to make the switch from black plastic mulch to metallized. Others stated that metallized mulches were too expensive. However, one farm operation which uses metallized mulches showed that on a per acre basis, although metallized mulches are over twice as expensive as black plastic, only 36 boxes/acre were lost on these mulches with 2% TSW infection compared to 306 boxes/acre on black plastic with 17% TSW infection. This ultimately led to a return to the farm totaling $882 on metallized mulch at the end of the season.

Further research has shown that a strategy that integrates metallized mulch, Actigard, and weekly insecticide sprays can reduce incidence of TSW up to 75-80%. Current recommendations now suggest using metallized mulches (with $75% reflectance) for mid- to late planted Spring tomatoes, along with Actigard early at a rate of 3/4 oz. (max) per 100 gallons of spray, and alternating reduced-risk pesticides (such as Spin Tor) in the regular spray program.

(Josh Mayfield, ext. agt., Gadsden Co., Tim Momol, Joe Funderburk, Julie Stavisky and Steve Olson, NFREC-Quincy, Joel Hudgins, Decatur Co. Ext., Bainbridge, GA - Vegetarian 03-04)


"Graywall" in Tomato Production

Recently, I received a phone call from a client with the following question: Is the tomato disorder called ‘graywall’ the same as ‘blotchy ripening?’ Not being quite sure and having limited access to the campus library, I decided to look for answers in publications available on the Internet. The search engine, Google.com, was very helpful as usual. I was able to access several extension publications from the leading Land Grant Institutions, the Canadian Food Inspection Agency, and a few resources from other countries.

It seems that researchers often disagree in the identification of these physiological disorders and the cause of them. Some scientists recognize ‘blotchy ripening’ and ‘graywall’ as two different disorders with similar symptoms, while others are classifying blotchy ripening, graywall and internal browning as the same disorder.

The graywall/blotchy ripening is a serious problem in field and greenhouse tomato production. The greenhouse varieties, yellow fruit tomatoes, plum and beefsteak types may be effected.

University of Florida researchers and Florida tomato growers are using the term ‘graywall’ to describe a blotchy/uneven ripening of tomato fruit produced in Florida. In South Florida, poor quality of tomatoes caused by this disorder can lead to serious reduction in tomato yield in some years. This production season 2002/2003 is one of these difficult years with plenty of "graywall" in the fields and growing frustration among growers.

From my conversations with tomato growers and scouts in the Homestead area, I found out that there is also a difference in the severity of symptoms between two leading field varieties grown in the Homestead area. During the 2002/2003 season ‘FL 47’ appears to be more affected by this disorder than ‘Sanibel’ variety. Growers are also observing severe incidents of graywall on some yellow and plum varieties. In some cases, the whole harvest from affected fields had to be classified as unmarketable.

The symptoms of graywall are first observed as blotchy, flattened areas on the wall of green tomato fruit. The color of the blotches is usually brownish-gray. As the fruit matures and changes color into red, these areas may remain gray or turn yellow causing uneven ripening. In some cases, it is quite difficult to see the graywall symptoms because they may be less visible on the outside wall of ripe fruit. When fruit is cut, the dark brown vascular tissue is visible. This darkening of the vascular tissue is still visible in ripe fruit. See Figure 1.

Figure 1. Advanced graywall at harvest and after ripening. (Photos: S.A. Sargent)

The causes of blotchy ripening and/or graywall are not simple and difficult to pinpoint. Certain weather conditions in combination with some cultural practices seem to favor development and intensity of graywall symptoms. Experienced tomato growers in the Homestead area identifying cloudy weather as the most important cause of graywall development. According to my unofficial survey of growers, a combination of three or more days with cloudy conditions followed by sunny weather and warm temperature is a "proved recipe" for graywall. In addition, an excessive nitrogen fertilization causing strong vegetative growth of tomato plants almost always guarantees the development of these disorders. Results of dry tissue analyses of plants affected by graywall often show lower amounts of potassium in leaves.

These observations by growers are in line with information published in Extension publications that I was able to access on the Internet. According to researchers, the conditions favoring graywall development are 1.) High nitrogen/plants growing rapidly, 2.) Low potassium, 3.) High soil moisture, 4.) High humidity, 5.) Temperature fluctuations, 6. Low light intensity.

Other disorders sometimes mimicking the graywall are symptoms produced by the tobacco mosaic virus leading to blotchy, uneven ripening of the fruit. Sweetpotato whitefly feeding can also produce symptoms of blotchy ripening but there is a significant difference in the internal color of the tomato fruit. The internal tissue stays whitish and hard and there is no vascular browning.

The role of potassium in preventing of the development of the graywall symptoms is not very clear. At least in my Internet research, I could not find a definite answer. More research needs to be conducted to help growers reduce crop losses related to graywall and other physiological disorders.

(OlczykVegetarian 03-04)
 


Commercial Packaging Options for Beit-Alpha Cucumbers

Production of Beit Alpha-type cucumbers (Cucumis sativis L.) is increasing in greenhouses from Mexico to Canada and Florida. While these high-quality cucumbers have been popular for some time in U.S. markets of middle-eastern immigrants, major supermarket chains are becoming savvy to their market potential. Three years ago Beit-Alpha cucumbers had significant postharvest losses during handling and shipping through commercial channels in Florida. This led to a storage study in which we found that chilling injury developed during storage at temperatures below 50oF (10oC). (see The Vegetarian, June 2001).

Questions remained as to which package types would best serve these cucumbers. In this test we studied how five commercial packaging methods affected postharvest quality of Beit Alpha cucumbers during simulated commercial conditions. Cucumbers were stored for 21 days at temperatures above the recommended 50F (10C), but frequently encountered during commercial handing, namely 54F (12.5C) or 59F (15C).

Cucumbers (cv. Sarig) were harvested in July, 2001, at a commercial greenhouse and stored overnight at 54F (12.5C). The following day, the cucumbers (about 1 inch diameter and 5 to 6 inches in length; 25 mm D and 125 to 150 mm L) were warmed to room temperature and treated as follows (see Fig. 1):

1) Unwaxed (UW) in waxed carton.

2) Waxed (W) in waxed carton. Brushed-on, oil-emulsion wax (Sta-Fresh 711,  FMC FoodTech; 1:5 dilution). UW and W treatments were place-packed in waxed, corrugated cartons (½ bushel; PCA 4411-1002 107528) in this order: a thin, foam liner on bottom, one layer of non-data fruit, experimental fruit layer, non-data fruit layer and a foam liner sheet on top. Storage relative humidity: 85- 90%.

3) Unwaxed, over-wrapped tray (OWT). Six unwaxed fruits on expanded polystyrene tray and over-wrapped (Stretch-tite, Polyvinyl Film, Inc.). 

4) Unwaxed, small clamshell (SC). Three fruits in unvented “Herb Pac” container (Ultra Pac 4070-125, polystyrene).

5) Unwaxed, large clamshell (LC). Nine fruits in hinged  “salad pack” container (Ultra Pac, polystyrene).


Figure 1.

Cucumbers were evaluated weekly and all data was subjected to analysis of variance; treatment means were compared using Duncan's Multiple Range Test or l.s.d. (P<0.05 level).

RESULTS

Beit-Alpha cucumbers retained excellent quality in all packaging methods for 14 days at 54F and 59F (12.5C and 15C). However, by 21 days quality differences became evident. Moisture loss is a principal cause of postharvest loss in slicing cucumbers, however in this study, unwaxed Beit-Alpha cucumbers remained acceptably firm after 21 days, despite >2% fresh weight loss in some treatments. Unwaxed fruits stored in cartons at either temperature lost about 50% more fresh weight than waxed fruits after 7 days, and more than twice the fresh weight of those stored in OWT, SC or LC after 21 days.  (Fig. 2 top: 54F/12.5C; bottom: 59F/15C).


Figure 2.

Firmness remained about 15 N during 14 d storage at both temperatures (data not shown). After 21 d, cucumbers at 15 C were firmer (15.2 N) than those at 12.5 C (13.6 N); those stored in the large clamshell were softest (12.7 N) (data not shown).

After 21 days of storage, the cucumbers were sliced; the cut vascular bundles in the epidermis exuded the same clear, viscous solutes that were observed at harvest (Fig. 3a), further evidence that turgidity remained high throughout storage. Small, edema-like protuberances formed during extended storage (by day 21), independent of storage method, and were possibly caused by continuous, internal pressure acting on senescing epidermal tissue, (Fig. 3b).


Figure 3a.


Figure 3b.

The change from initial color was calculated for epidermal color values (Lightness value, hue angle, and chroma value. After 21 days the epidermis of cucumbers stored in the Small Clamshell remained closest to initial color values, followed by those stored on the Overwrapped Tray, Unwaxed/carton, Large Clamshell and Waxed/carton (Fig. 4). The epidermis and pulp tissues (Fig. 4 and Fig. 5) of waxed cucumbers became more yellow than those from the other treatments (lower L* value and hue angle; higher chroma value), particularly those stored at 54F (12.5C). This may have been due to the wax interfering with lenticular gas exchange, entrapping endogenous ethylene in inter-cellular spaces and promoting senescence. It is unclear why this was more apparent at the lower temperature, although it was consistent with our previous tests.


Fig. 4. Lightness value, where 0=black, white=100; hue angle, where 90°=yellow,
 180°=green; chroma value, where the higher the value, the more intense the color tone.


Figure 5. Shrivel symptoms at the stem end became apparent by 28 d storage.

After 21 days, informal sensory panelists noted that cucumbers stored at 59F (15C) were crisper and had better overall appearance than those stored at 54F (12.5C), concurring with firmness and color data. However, fruits from both temperatures developed a slight “grassy”, off-flavor. Unwaxed fruits stored at 59F (15C) had bitter locular gel, whereas fruits from other treatments had no bitterness (data not shown).

There was slight condensation in SC, LC and OWT packages, however it did not promote decay.

We have also made the following observations:

a)       significant air exchange occurs via lenticels in the fruit epidermis, as shown in this submerged fruit under slight vacuum (Fig. 6a); 
b)       exposure to 20 ppm ethylene for 24 hr was sufficient to accelerate chlorophyll breakdown and allow growth of secondary pathogens during storage (Fig. 6b);
c)       production during cooler months can favor growth of sclerotinia rot during storage (Fig. 6c).


Figure 6a.

Figure 6b.

Figure 6c.

CONCLUSIONS

Unwaxed Beit-Alpha cucumbers place-packed in 3-layers in waxed cartons maintained good quality during 14 days storage at 54F or 59F (12.5 C or 15 C). However, serious consideration should be given to use of consumer packs, particularly rigid clamshell or over-wrapped tray, to minimize injuries and weight loss during handling and shipping and to promote marketing at retail level. Extended storage to 21 days resulted in off-flavors at both temperatures. Lowering the storage temperature to 50F (10 C) could permit longer storage with higher quality using these package types.

This article summarizes a poster presented at the 2002 Meeting of the International Society for Horticulture Science, Toronto. “Commercial Packaging Options for Beit-Alpha Cucumbers Grown Under Protected Culture”. By Steven A. Sargent1  and Abbie J. Fox, Horticultural Sciences Department, PO Box 110690, University of Florida, Gainesville, FL 32611 USA and Suzanne C. Stapleton, formerly at North Florida Research & Education Center-Suwannee Valley.

 (Sargent - Vegetarian 03-04)

Extension Vegetable Crops Specialists

Daniel J. Cantliffe
Professor and Chairman
Ronald W. Rice
Assistant Professor, nutrition
John Duval
Assistant Professor, strawberry
Steven A. Sargent
Professor and APRIL EDITOR, postharvest
Chad Hutchinson
Assistant Professor, vegetable production
Eric Simonne
Assistant Professor, vegetable nutrition
Elizabeth M. Lamb
Assistant Professor, production
William M. Stall
Professor, weed control
Yuncong Li
Assistant Professor, soils
James M. Stephens (retired)
Professor, vegetable gardening
Donald N. Maynard
Professor, varieties
Charles S. Vavrina
Professor, transplants
Stephen M. Olson
Professor, small farms
James M. White
Associate Professor, organic farming
Mark A. Ritenour
Assistant Professor, postharvest
 

Related Links:
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

This page is maintained by Susie Lonon.... if you have any questions or comments, contact me at zsf@mail.ifas.ufl.edu