FLORIDA AGRICULTURAL EXTENSION SERVICE
,I',.- UNIVERSITY OF FLORIDA
'.- INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Ve"et l'(c (Cropjs DeJ)parlt Iment
October 24, 1966
TO: COUNTY AGRICULTURAL AGENTS
IN THIS ISSUE: J
1. Controlled Atmosphere (CA) Storage. '< r
2. Foreign Competition. l
3. Short Subjects.
(a) New Publications.
(b) Cabbage Diseases.
(c) Dimethoate (cygon)
(d) Dr. Jim Montelaro
1. Controlled Atmosphere (CA) Storage. Dr. B. D. Thompson
In recent years, much interest has been shown in the possibilities of
applying during transit the basic information on controlled atmospheres
developed more than 30 years ago. Within the past 5 to 10 years, increased
emphasis has been given to artificial inducement of the storage atmosphere
for fruit storage rather than natural equilibration due to respiration of
the stored fruit.
The ready availability of liquid nitrogen as a refrigerant during
transit and as a replacement for the normal 217 oxygen in the storage
atmosphere has stimulated interest in modified atmospheres for transit
of fresh vegetables. Unintentional modification of atmospheres has
occurred frequently in completely sealed film wraps in early prepacking
work and can occur in tight transportation vehicles. The promotion of methods
of modifying atmospheres during transit has tended to be more rapid and
aggressive than impartial research studies or objective appraisal of overall
Controlled atmosphere (CA) storage is the term applied to the practice
of holding produce in a room in which the concentrations of gases are
maintained at levels other than normal. Oxygen generally is much lower
than normal and carbon dioxide slightly above normal. The normal atmosphere
may be modified to obtain these desired concentrations by several means.
Modification of transit atmospheres can be achieved through replacement
of the normal atmosphere with nitrogen as the primary refrigerant or a
supplement to mechanical refrigeration units, or a prescribed artificial
atmosphere can be generated and added to the transit vehicle as a
replacement for the usual atmosphere. Some efforts are now being made to
unitize this atmosphere in an individual package.
COOP EMATIViE XTENSION WOHK IN AGRICULTUIrL AND HOME ECONOMICS. STATE OF FLORIDA
FCrr F CF GRICU.T RVE, U NlVLEiSITY OF F-LQ IDA., UNIT- 1 STATES DEPARTMErNT OF AC.RICULTUR.E, AND TRCARDS Or COUNTY COMMISS N4- COOPERATING
Theoretically, a reduction in oxygen concentrations or an increase in
carbon dioxide concentrations should reduce the respiration rate of fresh
vegetables resulting in an extended storage life. There are, however,
many complex biochemical pathways of respiration and all of these do not
respond in the same way to changes in concentration of these gases. In
most cases, a reduction of oxygen below minimum undetermined for most
fruits and vegetables results in an abnormal pattern of respiration, toxic
compounds may accumulate, and undesirable odors and flavors develop, some
permanent and others temporary. Although low oxygen is the primary cause
of abnormal respiration, an increase in carbon dioxide may result in
changes of cell pH causing changes in permeability and respiration
patterns. Accumulation of other gases such as ethylene may induce further
patterns of abnormal respiration.
In spite of all of these possible abnormal situations, if gas
concentrations and temperatures can be precisely controlled some benefits
may be derived from controlled atmospheres, One California company has
made more than 1,500 "test" shipments of lettuce and is pleased with
Much of the research to evaluate current uses of these early-discovered
fundamentals has been done by the USDA. Some results of this and other
work are summarized here.
Lettuce. Russet spotting was reduced in atmospheres of 1 to 8% oxygen.
Some reduction in butt discoloration in atmospheres of k to 1% oxygen.
Low temperature reduced decay more than low oxygen. Some reduction in
respiration rate in low oxygen, but savings in refrigeration small and
increases in shelf life were not proportionally greater. Oxygen concen-
trations below 1% or C02 above 5% was injurious. Lettuce held at 360 F.
was superior to that in modified atmospheres at higher temperatures unless
russet spotting was a severe problem.
Tomatoes. It has long been known that ripening of mature green tomatoes
is retarded by low oxygen or high CO2. Oxygen concentrations below 1% and
CO2 above 5% may increase the incidence of decay. Tomatoes held in 100%
nitrogen decayed before ripening when removed from the modified atmosphere
to a ripening room. Modified atmospheres accentuated chilling injury, and
mature green tomatoes appeared more susceptible to injury from low oxygen
or high CO2.
Strawberries. Softened more rapidly in 100 percent nitrogen than in
air. Less decay developed in the modified atmosphere and off flavors were
sometimes detected. Oxygen concentration of 1% had little effect on
respiration, decay or flavor.
Brussels sprouts. The quality of brussels sprouts held at 320 F, in
air was equal to or better than that of those in modified atmospheres of
higher temperatures. Complete ranges of CO2 and oxygen have not been
Cauliflower was injured by CO2 concentrations above 5% but the injury
becomes apparent only after cooking when the curds become grey and soft
with an off flavor.
Potatoes were injured by low oxygen and periderm formation was inhibited
at oxygen concentrations below 5%. High concentrations of CO2 retarded
formation of reducing sugars, induced sprouting and increased susceptibility
to black spot.
Green beans. Concentration of oxygen of 2 to 5% and CO of 5 to 10%
resulted in better retention of chlorophyll than air storage. Maximum
storage life at 450 was about two weeks however regardless of storage
Sweet potatoes were not benefited by modified atmospheres and when
stored in 2 to 4% oxygen, 20% CO2 or 100% nitrogen; developed off flavors;
and when moved to normal air, necrotic spots and browning of tissues occurred.
Chemicals other than carbon dioxide and oxygen are known to have an
effect on respiration mechanisms. Compounds of nitrogen, cyanide, carbon
monoxide and other chemicals are in this group. At least one commercial
operation has utilized this knowledge. With more research, applications of
benefit to the vegetable industry may result, However close attention must
be given to alternative methods of handling already available, emphasis must
be given to speed and care in handling, and a proper evaluation made of
the effects of any extension of a normal marketing period.
Modifying and controlling the atmosphere surrounding fresh vegetables
in an individual package, transit vehicle, or storage room may become a
recognized supplement to recommended handling practices, Most research
to date indicates very narrow limits between benefits and serious damage.
Precise control of atmosphere and temperature is essential. Properly
planned and carefully evaluated shipping and storage tests continue to be
valuable sources of information, but extensive applications should be
approached with caution.
2. Foreign Competition.
We hear a great deal of talk about the danger of foreign competition
to the Florida vegetable industry. Mexican vegetable exports into the U. S.
have steadily increased for the last several years. The enclosed bulletin
on Mexican Vegetable and Melon Production should be studied to get the
Strawberry production is not covered in this publication. The picture
is this, acreage increased from 4,400 acres in 1955 to 11,000 acres in
STRAWBERRIES, FRESH: U. S. imports
from Mexico 1/
Month Year beginning November 1
1960 1961 1962 1963 1964 1965
Nov. -- 13 41 394 -464 746
Dec. 23 201 103 708 931 1256
Jan. 26 187 576 210 722 1945
Feb. 10 150 702 538 729 1849
Mar. 305 329 319 1357 1273 2288
Apr. 19 72 595 354 921 1519
May 4 14 113 233 111 47
Total 387 966 2449 3794 5151 9650
3. Short Subjects.
(a) New Publications.
1. Commercial Growing of Sweet Corn, USDA FB No. 2042.
2. Survey of Mexican Vegetable and Melon Production, USDA, FAS-1
178. (Copy enclosed)
3. Aquatic Weed Control, Fla. Ag, Ext, Cir, 219B.
4. Tomato Production Guide, Fla. Ag, Ext. Cir, 98C.
5. Florida Agricultural Experiment Stations Vegetable Variety
Trials for 1964 and 1965, Cir. S-176.
6. Career Brochures. (Copy enclosed)
(b) Cabbage Diseases,
Every fall, we receive inquires and observe cabbage diseases in
the field which are the results of infected plants being planted. This
begins the long winter cycle of diseases in the cabbage growing areas.
The diseases are primarily bacterial. Black rot being the most prevalent
and the most difficult to eradicate. The growing or purchase of clean
plants for the early fall transplanting would eliminate a lot of the
problems not only in these plants but in subsequent plantings. Hot water
seed treatment as outlined in Ext. Cir. 193E is the only control.
Bacterial leaf spot has also been found in plants imported into the state
this fall. It also is controlled by the hot water seed treatment. Cabbage
yellows a soil fungus disease has also been brought in on infected plants.
The only control for this disease is resistant varieties.
For a good description of these diseases look in Fla. Ag. Exp.
St. Bull. 492, Diseases, Deficiences and Injuries of Cabbage and other
Crucifers in Florida.
(c) Dimethoate (cygon)
The interval for application of Dimethoate (cygon) on tomatoes
has been reduced from 21 days to 7 days.
(d) Dr. Jim Montelaro
Dr. Jim Montelaro is at present hospitalized by a heart attack.
He will be on a rest cure for at least several months. We are sure he
would be happy to hear from you, but it will be sometime before you
hear from him. Be patient, we'll do the best we can to meet your most
F. S. son, Chairman
Vegetable Crops Department
Mason E. Marvel
Assoc. Vegetable Crops Specialist
Vegetable Crops Specialist