The Vegetarian Newsletter
A Horticultural Sciences Department Extension Publication on
Vegetable and Fruit Crops
Eat your Veggies and Fruits!!!!!
South Florida Vegetable Variety Testing Program
By Monica Ozores-Hampton ‘Vegetable Specialist’
Making the correct choice of which varieties to plant each year is a cornerstone of a successful vegetable industry. The University of Florida/SWFREC variety testing program provides unbiased information about the adaptability and performance of vegetable varieties in Florida’s diverse environments, thereby allowing growers to make informed decisions (http://www.imok.ufl.edu/vegetable_hort/variety_testing/).
The variety trials are being conducted in multiple locations (Collier, Manatee and Palm Beach) and multiple seasons (winter and spring) in cooperation with Eugene McAvoy (Hendry County Extension Service), David Sui (Palm Beach County Extension Service), Crystal Snodgrass (Manatee County), Mary Lamberts (Miami Dade County) and Richard Raid (UF/IFAS). In addition to yields and quality crop development, we collected information that may be pertinent to pests (diseases and insects) and post-harvest quality. In tomatoes, variety trials had been conducted since 2006 with tomato yellow leaf curl virus (TYLCV) and since 2009 with Fusarium crown rot (FCR) resistant as well as grafted varieties. Tomato yellow leaf curl virus is induced by a number of closely related begomoviruses transmitted by the whitefly Bemisia tabaci (Gennadius), and Fusarium crown rot is caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL). Symptoms of TYLCV infection include dwarfed leaves that are up-curled, thick and crumpled and that have chlorotic margins. Up to 90% of flowers may abscise after infection, resulting in poor fruit set and yield, especially when infections occur early in the season (Figure 1).
The testing program provided recommendation under low and high TYLCV pressure (Table 1) (Figure 2). However, variety trials demonstrate that TYLCV can be managed with resistant varieties, but the lack of consistent fruit quality is a major factor for not adopting TYCLV-resistant varieties by the Florida tomato industry. Fusarium crown rot resistant varieties are widely adopted by the tomato industry, but testing continues since new varieties are being released every year. In Florida, continuing disease problems, lack of land for ideal crop rotation periods, increasing markets for specialty varieties that do not have disease resistance, imperfection of soil fumigation and the impending loss of methyl bromide have contributed to increased interest in grafting tomatoes. Testing grafted rootstocks will continue with the help of US$2.2 million funding by USDA-SCRI for the project “Development of Grafting Technology to Improve Sustainability and Competitiveness of US Fruiting Vegetable Industry,” obtained by several states, including Florida.
Bell pepper yields have been increased dramatically recently due to continued introduction of new varieties resistant to bacterial spot. Loss in yield due to bacterial spot can be attributed to both defoliation and spotting or rotting of fruit. Ten races of X. euvesicatoria have been identified worldwide. A race (identified by numbers 1, 2, 3, etc.) is defined by how it can survive and grow on varieties with or without specific genes for resistance. Over the years, genes resistant to various races of X. euvesicatoria have been identified and introduced into commercial bell pepper varieties. Therefore, variety trials were conducted in multiple years, locations and seasons (Figure 3). Variety trials demonstrate that cultivars containing the added resistance to race 4, 5 and/or 6 reduced bacterial spot infection rates and increased yields compared with varieties with only resistance to bacterial spot races 1, 2 and 3 under natural disease pressure.
The Florida bunch radish is one of America’s most popular garnishes and is available fresh from October through June. Growers relay in non-hybrid varieties as the standard variety, which offer low yield and quality. Therefore, a variety trial was conducted in the fall, winter and spring 2009-10 seasons with 21 (hybrid and non-hybrid) varieties assessing yield and quality (Figure 4).Results indicated that hybrid varieties can increase radish yield and quality for Florida growers.
Florida ranks first nationally in production, acreage and total fresh market value in snap beans. The majority of Florida's snap bean crop is produced for the fresh market, with only a small percentage destined for processing. Growers rely on new varieties to increase bean yields and quality and to maintain leadership in the USA market. Therefore, a variety trial was conducted in the winter 2010 with 13 bean varieties in two locations. Preliminary results based on one season indicated yield and color followed by yields are the most important attributes for Florida bean growers.
Low TYLCV Pressure
Low TYLCV Pressure
HA 3075 (Hazera), S-50257, VT-60774, and VT-60780 (Zeraim Gedera).
3078, 3074 (Inbar) and 3075 (Ofri) (Hazera)
Roma: Shanty (Hazera).
Tygress (Seminis) & 3074 (Inbar) (Hazera).
Roma: 5808 (Sakata).
Tygress & SVR200 (Seminis).
Security 28 (Harris Moran) & Charger (Sakata).
SVR 200 (Seminis)
SVR (Seminis), Tygress (Seminis), Grafting
BHN 833/Tygress (BHN/Seminis).
BHN 745 &Tygress (Seminis).
Security 28 (Harris Moran), BHN 745 and 765, 3091 & 3075 (Ofri) (Hazera), and 5443 (Sakata).
BHN 765, 8845 (Harris Moran).
Tygress and SVR 200 (Seminis).
Homestead : Tycoon (Hazera)
RFT 9773 (Syngenta)
The Weekend the Fuzz Froze off the Peaches
Mercy Olmstead, Ph.D., Stone Fruit Extension Specialist
One of the biggest concerns for any fruit grower is the threat of a frost or a freeze killing flower blossoms or fruit. On the evening of February 11th and morning of the 12th, 2012, low temperatures caused by two different frost/freeze events heavily damaged peaches in North Central Florida, including two research sites in Citra and Hastings, FL.
There are two main types of cold events that can cause damage to flower buds or newly set fruit, radiation frosts and advection freezes. Radiation frosts occur on clear, calm nights with low humidity. Heat from plants and the soil gained during the day escapes into the upper atmosphere, allowing cold air to settle near the ground. In these cases, site selection is extremely important in areas where a slope exists, as cold-tender or low-chill varieties should not be planted where cold air typically settles (Figure 1).
Figure 1. Proper orchard site selection can help to avoid cold air pockets at the bottom of slopes and to ensure cold air drainage.
Several methods can be used to “warm” the air near the ground in radiative freezes, including warming air near the surface (using orchard heaters), using wind machines to mix the air and bring warm air near the surface, and using ice formation to encase the buds or fruit (Evans, 2008). Ice formation on plant tissues keeps tissues at 32°F. In addition, water emits a small amount of heat as the ice layers form. This “latent heat of fusion” releases energy as the water moves from a liquid to solid state. If the temperature of the ice layer on plant tissues can be maintained at 31-32°F throughout the freeze period, then the tissue encased in ice can be kept at 32°F, preventing damage. However, if the water application rate is halted (due to a frozen sprinkler), or the volume required is insufficient due to the presence of wind (Figure 2), the tissue could drop to the wet bulb temperature, causing more severe damage than if no water was ever applied. The wet bulb temperature is measured using a sling psychrometer with a piece of wet material (typically a sock) attached to the end of the bulb. This temperature can also be calculated with a number of assumptions taken into account using FAWN online: http://fawn.ifas.ufl.edu/tools/irrigation_cutoff/about.php.
Critical temperatures for peach buds and flowers can be found in a Washington State University Publication available online: http://treefruit.yakima.wsu.edu/weatherbuds/budhardiness/BudCharts/Peach%20Bud%20Chart%20EB0914.pdf.
Figure 2. Volume of water required to use ice formation as an effective method of frost protection (Gerber and Martsoff, 1965).
Dry Leaf Temperature (°F)
Wind Speed (mph)
0 - 1
2 - 4
5 - 8
10 - 14
18 - 22
Acre-inches per hour needed for freeze protection
Advection freezes can often be more severe because cold air is accompanied by windy conditions, rendering the aforementioned techniques ineffective. These windy freezes are often part of a large cold air mass accompanied by steady wind speeds of at least 5 mph. Unlike radiation frost events, thermal inversions (warm air rising, cold air sinking) do not form, despite minor radiation loss from plants and the soil.
On the night of February 11th, 2012 and into the morning of the 12th, our research orchard at Citra experienced an advection freeze event. We had sustained winds of at least 10 mph throughout the night (Figure 3). Based on the data available at the time, irrigation to begin the ice formation process began at approximately 3 AM. The wind speed had begun to drop, and there was sufficient water pressure and volume to start the ice formation process.
Figure 3. Minimum temperature (°F) at approximately 2 feet above soil level (blue line) and maximum wind speed (mph) (red line) on February 11-12th, 2012 (FAWN data).
The following night, February 12th, was a clear, fairly calm night with lower relative humidity that resulted in a radiation freeze event(Figure 4). On this night, the water was turned on earlier than February 11th with calm winds and dropping temperatures. However, two successive nights of ice loads damaged some of the trees in the orchard, especially the ones that had not yet been pruned (‘UFSun’; Figure 5). The ‘UFSun’ suffered severe damage; some trees were damaged on 3 out of the 4 scaffolds. Although these trees will be kept through the season for observation, if sufficient buds do not form to replace lost scaffolds, they will be pulled from the orchard and replanted.
Figure 4. Minimum temperature (°F) at approximately 2 feet above soil level (blue line) and maximum wind speed (mph) (red line) on February 12-13th, 2012 (FAWN data).
Figure 5. Ice loads on pruned ‘Flordaprince’ trees (left), and on unpruned ‘UFSun’ trees (right) at the Plant Science Research and Education Unit in Citra, FL, February 2012.
Figure 6. Peach flowers encased in ice.
Figure 7. Freeze damage on peach flowers.
Good ice formation occurred on the 2nd night (Figure 6), but damage was already visible from the 1st night of the advective freeze (Figure 7). Three days later, fruit were sampled from the orchard to determine the degree of fruit damage from the two nights of freezes. Fruit that were still alive were green, with a white embryo and pit still in the process of forming, while dead fruit had brown mush, indicating a dead embryo (Figure 8).
Figure 8. Sectioning fruit to detect alive (left) and dead embryos (right).
So, what did we learn from this frost/freeze event? We definitely will finish pruning all of our orchards by Christmas this year to avoid tree damage from successive ice loads. With the warm winter, we had nickel-sized fruit and some canopy already on some of the low-chill varieties like ‘TropicBeauty’ and ‘UFSun’, which further weighed down tree branches.
It is very helpful to have a weather station or temperature recorder that you can access via the Internet, if your orchard site is not outside your back door. As technologies advance and become less expensive in the future, many commercial operations would benefit from investing in on-site temperature monitoring. The UF blueberry program has recorded at least 1-2 degree differences in our fields from the Citra FAWN station, which is 2 miles to the west of our field plots.
This year, FAWN rolled out a text message “freeze alert” system that has a $50.00 fee per season (http://fawn.ifas.ufl.edu/freeze_alert/). Using this system, you can set a number of parameters, such as the freezing threshold for different stages of bud of flower development, and then the system will send a text message or alert as an indicator of when to begin frost/freeze protection activities.
Finally, this advective freeze event was the first that I have experienced since coming here to Florida 2 ½ years ago. Although January-February 2009 was a tough year, successive ice loads from several radiation freezes were the downfall of many of the scaffolds in our research orchard. As water use gets more highly regulated, alternative frost protection methods will need to be investigated, and are being researched among faculty here at University of Florida for several specialty horticulture crops.
Here is to hoping that next year is a better year and we have a good cropload! Cheers.
Evans, R. 2008. The ABCs of frost management. Available online:
Florida Automated Weather Network. 2012. Data from Citra Station in Alachua County, FL. Available online: <http://fawn.ifas.ufl.edu/>
Gerber, J. F. and J. D. Martsolf. 1965. Protecting citrus from cold damage. Univ. Fla Ext. Cir. 287.