Evaluation of Elevated CO2 for Control of Greenhouse Whiteflies on Poinsettias During Transit 1993 Proposal
sweetpotato whiteflies on poinsettias
A. SUMMARY
Infestation of whitenies on poinsettias still remains a major
challenge for many commercial
growers. The problem arises frequently from purchased cuttings
that were infested with whiteflies in the
propagation area. Growers face difficulties with conventional
sprays because eggs and pupae are
resistant to most insecticides. in addition, the increasing pressure
from many states restricting the
amount and type of pesticide used in greenhouses has forced the
industry to examine other non-chemical
methods to control common greenhouse pests.
I propose to continue my investigation on the use of short-term
elevated CO2 to eliminate
whiteflies that may remain on poinsettia cuttings after propagation.
The short-term elevated CO2
treatment can be applied prior to shipment, during transit, or
at the final destination. Studies conducted
in our laboratory indicated that adult whiteffies are highly
susceptible to the elevated CO2 treatment.
Ninety-five percent of the adult greenhouse whiteflies (Trialeurodes
vaporarium) died after exposure
to 25% or 50% CO, for 10 hours. We are currently evaluating the
effectiveness of these treatments on
other stages of whiteflies. There are reasons for us to believe
that the proposed technique is effective
against other stages of greenhouse whitefly. Unlike other techniques
currently available, the proposed
technique is not dependent upon the direct chemical contact of
insects for effective control but rather on
the assumption that living species require O2 for respiration
and other metabolic activities. The elevated
CO2 treatments drastically reduce the oxygen level, thus smothering
the insects to death. Even stages
such as eggs and nymphs which are resistant to chemical spray
are metabolically active and require
oxygen. Eggs and nymphs may not be as active as adult whiteffies
and may require longer exposure time
for effective control. The objectives of this study are (1) to
complete our investigation on the duration
of CO2 treatment required for eradication of all stages of whiteffies
and (2) to compare differences in
sensitivity of poinsettia cultivars to elevated CO2.
The proposed study will benefit the industry by providing growers
an environmentally safe
method of controlling whiteflies. The relatively simple set up
will enable all growers to establish their
own min-quarantine treatment, if desired. This will allow growers
to start their poinsettia’s season with
clean, non-infested cuttings, and thus, reduce the hazards and
expenses associated with application of
pesticides.
B. DETAILED PROPOSAL
1. Introduction and background information
Poinsettias have been the leading flowering potted plant in the
United States for many years. Despite
the extensive research conducted on this crop, elimination of
greenhouse and sweetpotato whiteflies
(Trialeurodes vaporariorum and Bemisia tabaci, respectively)
still remains a major challenge for many
poinsettia growers. The problem arises frequently from purchased
cuttings that were infested with whiteffies
in the propagation area. Thus, the best management strategy in
controlling the outbreaks of whitefly is by
prevention of their entry into the greenhouses. Recent devastation
of California crops by a strain of
sweetpotato whitefly further raised the attention and the awareness
of the potential damage that can be
caused by this insect.
Current control of whitefly includes the use of chemical and nonchemical
methods. Egg and pupal stages
are largely resistant to chemical pesticides. Effective control
relies on frequent spray targeted against early
nymphs or at adults emerging on the underside of leaves. Nonchemical
control strategies using biological
agents such as the parasitoid Encarsia formosa or certain species
of fungal pathogens can be useful in
greenhouse settings but require careful and constant monitoring
as well as reapplication. The success of this
method also relies on relatively low insect population on the
plant materials. Control of sweetpotato whitefly
has proved to be more difficult. Extensive studies have found
this species of whitefly to be resistant to many
of the conventional means of control. Furthermore, the increasing
pressure from many states restricting the
amount and type of pesticide used in greenhouses has forced the
industry to examine other environmentally
safe methods to control common greenhouse pests.
Currently, most of the small greenhouse operations in the United
States purchase poinsettia cuttings
from nearby operations that are licensed to propagate. These
plant materials frequently arrive with some
whitefly population that will later develop into a heavy infestation.
Finding a means to completely eliminate
those whiteflies should be the priority for the industry. I propose
to continue my investigation on the use of
short-term elevated CO2 treatment for eradication of whiteflies
in poinsettia cuttings. The treatment can be
applied prior to shipment, during transit, or at the final destination.
If shown to be effective, all poinsettia
growers can be assured of clean plant material at the beginning
of the season.
Commercially, elevated CO2 treatments are used for long-term storage
of some edible commodities.
The limitations is that treatment of bulky tissues frequently
results in anaerobic respiration and alters the
flavor of the commodities. On the other hand, floricultural crops
have been shown to tolerate much higher
levels of CO2 with no adverse consequences. The levels are much
higher than those reported to eradicate many
insects. Success of the method will not only drastically reduce
the outbreak of whiteflies from purchased
infested cuttings, but, in doing so, will drastically reduce
the use of pesticide, will protect groundwater from
pesticide contamination, will increase profitability by reducing
the cost of pesticide and by increasing the
quality of the products, and will reduce the risks of public
health from pesticide application.
2. Review of significant literature
Use of modified atmosphere (MA) for long-term storage and pathogenic
control on edible crops has
been intensively investigated. The method refers to changes in
the composition of the air surrounding the
commodity. Usually this involves reduction of oxygen levels and/or
elevation of carbon dioxide levels.
Response of plant species to MA include reduced respiration,
inhibited initiation of ripening, inhibited
production and action of ethylene, retarded chlorophyll degradation,
and reduced chilling injury. Prolonged
exposure of edible crops to the modified atmosphere frequently
causes anaerobic respiration, and
consequently, results in the accumulation of ethanol, acetaldehyde,
and other volatile compounds in the tissues
(Davis, et al., 1973; Norman and Craft, 1971; Pesis and Avissar,
1989).
Commodities differ in their susceptibility to modified atmosphere
and the recommendations for the
level of tolerance to reduced O2 and/or elevated CO2 varies.
The differences are suspected to be due to the
variations in structural (anatomical) rather than metabolic differences
among commodities. MA studies have
shown floricultural crops to have a higher tolerance to elevated
CO2 or reduced O2 as compared with edible
commodities. Vase life anthuriums (Akamine and Goo, 1981), carnations
(Hanan, 1967), daffodils (Parson
et al., 1967), gladiolus, roses, and snapdragons (Thornton, 1930)
were reportedly extended by MA under
various combinations of O2 and CO2 concentrations. More recently,
the possible use of MA to suppress
pathogenic activities in floriculture crops was investigated.
The study was initiated to appraise the possible
use of MA to prolong the storage life of various species of cut
flowers (Joyce and Reid, 1985). Results from
the study demonstrated that many floriculture crops can tolerate
very high concentrations of CO2. Exposure
of cut lilies, iris, carnation, gypsophila, daffodil and cyclamen
to 60% CO2 for 7 days had no deleterious effects
on the flowers. This level of CO2 was significantly higher than
those normally considered harmful for edible
crops. The authors indicated that one major difference between
flowers and many other horticultural
commodities is their high surface/volume ratio. This may reduce
the CO2 injury caused by CO2 accumulation
in bulky organs exposed to similar concentrations of the gas.
The possible use of MA for insect control has been investigated
in many edible crops. Studies have
been conducted for two purposes: (a) insect control in long-term
storage areas or (b) short-term exposure of
MA as a quarantine treatment for postharvest insect control.
In most cases, MA combinations needed for
long-term insect control could not be tolerated by the commodities
and resulted in more rapid deterioration.
In contrast, short-term exposure to MA has been reported to cause
no detrimental effects on the appearance
or nutritional value of oranges (Ke and Kader, 1990) and other
edible crops and could possibly be used as a
quarantine treatment on imported edible crops. The composition
of atmosphere required for effective insect
control is dependent upon the species of insect. Both elevated
CO2 and reduced O2 have been investigated.
The former was more effective than the latter in eliminating
Caribbean fruit fly (Benschoter, 1987). A carbon
dioxide level of >/= 50% is required for effective control of
codling moth (Soderstrom and Brandl, 1987). A
lower CO2 concentration was reported to be as effective as higher
concentrations for controlling the eggs and
larvae of Caribbean fruit fly (Benschoter, 1987). Exposure of
eggs and larvae of Caribbean fruit fly to CO2
concentrations of >/= 20% for 7 days resulted in complete eradication
of the insects.
Results from last year’s funding indicated that whiteflies are
highly susceptible to an elevated level
of CO2. To conduct the experiments, aspirators were constructed
to collect adult whiteflies. The aspirators
were constructed with two venting holes allowing us to introduce
a constant flow of a known concentration of
CO2. Aspirators for the control treatment were vented with atmospheric
air (0.03% CO2). Each treatment
consisted of 3 replicate aspirators with approximately 80 - 100
whiteflies per aspirator. Our first experiment
revealed that adult whiteflies are very sensitive to high level
of CO2. All whiteflies appeared dead after
exposure to 25% and 50% CO2 for 80 and 20 minutes, respectively.
Subsequently, we found that these short-
exposure time only caused temporary unconsciousness of the insects
and the majority of them revived after
they were transferred back to the atmospheric air. Further studies
revealed that exposure of adult greenhouse
whiteflies (Trialeurodes vaporarium) to 25% or 50% CO2 resulted
in 100% death in less than 12 hours
(Table 1). To investigate the sensitivity of different stages
of whitefly to elevated CO2, plant materials infested
with uniform stages of whiteflies are needed. We have developed
a system, as described later in the Materials
and Methods section, to accomplish this purpose. One obstacle
which still requires investigation is obtaining
a large number of eggs laid on the same day. We had attempted
twice to inoculate a tomato cultivar with
whiteflies but had limited success. We are currently growing
poinsettias from cuttings and will inoculate
these plants once they are established in the greenhouse.
We had studied the tolerance level of poinsettia cuttings to elevated
level of CO2. Rooted cuttings of
’Supjibi’ and ‘Lilo’ were exposed to 50% CO2 or air (control)
for 24 hours and were then potted up and grown
in a glasshouse for evaluation. Results revealed significant
differences in the tolerance level of the 2 cultivars
to elevated CO2. Eighty-five percent of the cuttings of ‘Supjibi’
developed severe toxic symptom on the mature
and expanding leaves from the CO2 treatment whereas only 5% of
the ‘Lilo’ cuttings developed minor toxic
symptoms. The initial toxic symptom appeared as upward curling
of the leaves which later abscised. All
expanding and mature leaves in ‘Supjibi’ cuttings were affected
whereas only a few mature leaves were
affected in ‘Lilo’. This result indicated vast differences in
the sensitivity of different cultivars of poinsettias
to an elevated level of CO2 and suggested that more cultivars
should be evaluated. Additionally, a lower level
of CO2 (25%) should be tested on poinsettia cuttings since this
level of CO2 has been shown to effectively
control the adult whitefly (Table 1).
When Dr. Peter Konjoain, a commercial greenhouse grower in Andover,
MA and an adjunct professor
at the University of Massachusetts, was informed of our findings
he was excited by the potential of using the
technique as a mini quarantine treatment that could be conducted
in the greenhouse establishment. The
feedback from Dr. Konjoain was a further confirmation of the
validity of this project and its potential impact
on the industry.
3. Objectives of proposed research project
I propose to continue my investigation on the efficacy of elevated
CO2 for insect control of whitefly
on poinsettia cuttings. Studies conducted in our laboratory indicated
promising control of whitefly with the
proposed technique. Data pertaining to the tolerance level of
different stages of whiteflies to elevated CO2
and the responses of different cultivars of poinsettia cuttings
to short-term elevated CO2 treatment still remain
to be investigated. Additionally, we will expand and include
sweetpotato whitefly in our investigations. The
objectives of this proposal are: 1) to determine the effects
of elevated CO2 on survival rate of eggs, pupal and
nymph, and adult stages of greenhouse and sweetpotato whitefly;
2) to determine the tolerance level of
different cultivars of poinsettia cuttings to elevated CO2; 3)
to investigate the effects of elevated CO2 on
rooting capability of unrooted poinsettia cuttings; and 4) to
examine the effects of elevated CO2 on
establishment of rooted cuttings.
4. Materials and Methods
The research to be conducted under each objective is outlined
independently. Plant materials will
initially be obtained from Paul Eche Ranch. Plants will be grown
in the Department of Plant and Soil Sciences
glass-covered greenhouses (18′C night temperature) and placed
in cages covered with fine screen in order to
maintain clean, non-infested plant materials.
The modified atmospheric chambers used in this study are containers
of various sizes, ranging from
test tubes and jars to aquarium tanks. All containers have lids
with two venting holes for CO2 exchange. The
appropriate size container will depend on the volume required
to conduct each experiment. The chambers will
be situated in a 20′C temperature controlled incubators with
12 hr of 25 umol*m-2*s-1 light. The elevated CO2 will
be applied by venting chambers with a constant flow of factory-mixed
gases. The construction of these
chambers is simple, thus making it feasible for all growers to
construct their own quarantine chambers, if
desired. The proposed technique is not intended for use in the
greenhouse for whitefly control as the high
level of CO2 needed for effective control of whiteflies is toxic
to human beings and the amount and the cost
of CO2 required to raise the greenhouse atmosphere to the necessary
level are not justifiable.
(a) Optimum level of CO2 levels for maximum control of the insect
To understand how different developmental stages of whiteflies
respond to the elevated CO2
treatments, plant materials infested with uniform stages of whiteffies
are needed. For this reason, we will
inoculate non-infested plant materials with adult whiteflies
for one day and the adults will be released the
following day. All eggs will, therefore, be laid on the same
day and further development of stages can be
coordinated. This approach will enable us to apply elevated CO2
levels separately to eggs, nymphs, pupae, and
adults. The survival rate of the various stages of whiteflies
to the treatments can be assessed.
Custom-made aspirators will be used to collect adult whiteflies.
After collection of the adults into the
aspirator, the system can be connected directly to a constant
flow of CO2 and used to investigate the
susceptibility of the adults to the CO2 treatments. Additionally,
adults collected in the aspirators can also be
released for inoculation of plant materials as described earlier.
Greenhouse and sweetpotato whiteflies at different developmental
stages will be placed in atmospheric
chambers vented with a constant flow of variable concentrations
of CO2 at predetermined levels. Control
treatments will be vented with air (0.03% CO2). Chambers will
be vented with modified air for various
amounts of time and thereafter, vented with air. Survival rate
for egg and larval stages will be calculated
following the passage of sufficient time for the development
of insects into pupae and emerging adults.
Normally formed puparia and adults will be counted as survivors.
(b) Tolerance of different cultivars of Poinsettia cuttings to
elevated CO2 atmosphere
Due to the great differences in the responses of ‘Supjibi’ and
‘Lilo’ cuttings to elevated CO2, other
commercial available cultivars will be evaluated. Both unrooted
and rooted, will be placed in atmospheric
chambers vented with a constant flow of variable concentrations
of CO2 at predetermined levels. Control
cuttings will be those treated with constant flow of atmospheric
air. Immediately after the 12-, 48-,or 96-hr
exposure, signs of physiological disorders such as discoloring
or wilting of the leaves and stems will be noted.
Cuttings will then be placed in a simulated shipping environment
for 0 to 7 days. The extent of chlorophyll
degradation from the shipment will be recorded. Results from
this study should indicate to us the maximum
level of CO2 poinsettia cuttings can withstand without any subsequent
deteriorating effects.
Effects of elevated CO2 on rooting of poinsettia cuttings
The purpose of this study is to evaluate if elevated CO2 treatment
on unrooted cuttings affects their
subsequent ability to root. Unrooted poinsettia cuttings will
be placed in atmospheric chambers as previously
described. After the treatments, cuttings will be divided into
2 groups. Half of the cuttings will be placed in
a simulated shipping environment for 2 days before propagation,
the other half will be propagated immediately
after the treatment. Cuttings will be planted in pasteurized
medium and placed in the propagation house under
mist for 21 days. Cuttings will be planted and grown at 18′C
night temperature greenhouse. Data will be
collected on the number, length, and dry weight of the roots
at 2 and 3 weeks after propagation.
Effects of elevated CO2 on establishment of rooted cuttings
The purpose of this study is to investigate how elevated CO2
treatment on rooted cuttings affects the
establishment of the cuttings in growers’ site. Rooted cuttings
will be placed in atmospheric chambers as
previously described. Cuttings will be divided into 3 groups
immediately after the treatments. Two groups
will be placed in a simulated shipping environment for 2 and
7 days before planting. The third group will be
planted immediately. The cuttings will be planted in 10cm diameter
pots and grown in a 17′C night
temperature greenhouse. Data will be collected on the height
and dry weight of the shoots at 4 and 6 weeks
after planting.
5. Facilities and Equipment Available
All facilities and equipments needed for this project, including
greenhouse bench compartments,
propagation benches, temperature-controlled incubators, gassing
chambers and gas chromatography are
available at the University of Massachusetts.
6. Literature Cited
Akarnine, E.K. and T. Goo. 1981. Controlled atmosphere storage
of anthurium flowers. HortScience 16(2):
206-207.
Benschoter, C.A. 1987. Effects of modified atmospheres and refrigeration
temperatures on survival of eggs
and larvae of the Caribbean fruit fly in laboratory diet. J.
Econ. Entomol. 80:1223-1225.
Davis, P.L. and W.G. Chace, Jr. 1969. Determination of alcohol
in citrus juice by gas chromatographic
analysis of headspace. HortScience 4:117-119.
Hanan, J.J. 1967. Experiments with controlled atmosphere storage
of carnations. Proc. Amer. Soc. Hort. Sci.
30: 370-376.
Joyce, D.C. and M.S. Reid. 1985. Effect of pathogen-suppressing
modified atmospheres on stored cut flowers.
In: Blankenship (ed.). Controlled atmospheres for storage and
transport of perishable agricultural
commodities. Hort. Report. No. 126. NC State Univ., Raleigh.
Ke, D. and A. A. Kader. 1990. Tolerance of ‘Valencia’ oranges
to controlled atmospheres as determined by
physiological responses and quality attributes. J. Amer. Soc.
Hort. Sci. 115(5):779-783.
Norman, S.M. and C.C. Craft. 1971. Production of ethanol, acetaldehyde
on postharvest quality of
mechanically harvested strawberries for processing. J. Amer.
Soc. Hort. Sci. 104:242-264.
Parsons, C.S., Asen, S., and Stuart, N.W. 1967. Controlled atmosphere
storage of daffodil flowers.. Proc.
Amer. Soc. Hort. Sci: 90:506-514.
Pesis, E. and I. Avissar. 1989. The postharvest quality of orange
fruits as affected by pre-storage treatments
with acetaldehyde vapor or anaerobic conditions. J. Hort. Sci.
64: 107-113.
Soderstrom, E.L. and D.G. Brandl. 1987. Controlled atmospheres
for postharvest control of codling moth
on fresh tree fruits. California Tree Fruit Agreement, Sacramento.
CTFA 1986 research report.
Thornton, N.C. 1930. The use of carbon dioxide for prolonging
the life of cut flowers, with special reference
to roses. Amer. J. Bot. 17: 614-626.
7. Detailed Budget
The funds requested will fund a part-time technical support to
work on the project. The request for supplies
is to support purchase of gas cylinders, pots, growing media,
and other materials which will be required to
conduct this research.
Salaries (part-time technical support) $5,000
Supplies $1,500
Publication $ 500
Total $7,000
C. PROJECT LEADER QUALIFICATIONS
The principal investigator has a Ph.D. degree in plant physiology
from the Univ. of California-Davis
and a M.S. in floriculture from the Univ. of Missouri-Columbia.
This unique educational background has
enabled me to conduct both basic and applied research that are
critical to the floricultural industry. Our
laboratory is well equipped for the proposed study. In addition,
we have already constructed aspirators for
collecting adult whiteflies, screened cages for growing non-infested
materials, and venting chambers for the
CO2 treatment.
