Evaluation of Controlled Atmosphere Anoxia Treatments as a Potential Disinfestation Technique for Thrips and Spider Mites in Greenhouses. Progress Report — June 1997
Date:5/23/97
Title of Project:Evaluation of Controlled Atmosphere Anoxia
Treatments as a Potential Disinfestation Technique for Thrips and Spider
Mites in Greenhouses.
Institution where work is being conducted: University of Kentucky
Amount of Endowment Grant: $7,500
Covering Period: 7/96 to 6/97
Anticipated Date of Project Completion /Final Report: June 1998
Individual(s) Conducting Project:
(List Project Leader First)
Daniel A. Potter - Title Professor
Telephone Number: 606-257-7458
Robert G. Anderson
David W. Held
Disinfestation
Goal of Project:
This project seeks to evaluate the potential for using controlled
atmosphere (CA) treatments to control thrips, aphids, and twospotted spider
mites on common bedding plants. CA is a standard technique for managing
post-harvest pest problems on fruits, vegetables, and stored grain.
It employs low oxygen (anoxia) and high carbon dioxide and nitrogen environments
to suffocate insects. If successful, it is feasible that truckloads
of bedding plants could be disinfected with CA as they travel to their
destinations, or simply overnight before shipment. This would especially
benefit large cutting and plug producers who may inadvertently distribute
insect pests, as well as hundreds of smaller growers whose pest infestations
may originate from plant stock that they have purchased. Before CA
technology can be adapted for greenhouse pest management, the effects of
anoxic treatments on key pests must be determined. Our project differs
from the limited. previous work on anoxia in that it pertains to greenhouse
production systems, and because it considers effects of CA on plant growth
and quality, as well as pests.
Progress to Date:
From the onset, we have worked closely with an agricultural engineer
whose input has enabled us to build and monitor our CA system. The
test chambers are 10L vacuum desiccators modified to facilitate airflow.
Half of the chambers receive the CA treatment, and half get compressed
air as a control. Gases are regulated by flow meters and delivered
to the chambers by 1/4″ PFA tubing. Before any mortality tests could
be done, extensive system checks were run using gas chromatography to ensure
consistency of the test environments.
After checking the system, initial experiments were conducted
with twospotted spider mites. These tests gave variable and disappointing
results. We have since learned that mites are notoriously difficult
to control with CA, and were probably a poor target for initial mortality
tests. We followed with tests using flour beetles, a non-greenhouse
pest that is known to be susceptible to elevated nitrogen atmospheres.
Overnight exposure gave 100% mortality of flour beetles, verifying the
integrity of our system and providing a “standard” insect species for comparisons
in later tests. Interestingly, we found that beetles placed on leaves
required longer to kill than those in the normal flour medium. This
indicates that greenhouse pests must be exposed on living foliage to obtain
realistic evaluation of anoxic effects.
Next, we conducted tests on aphids and thrips on bean foliage
in a high-nitrogen environment. These results are highly encouraging:
100% of the aphids or thrips were dead after 6 or 12 hours, respectively.
Further tests suggested that high C02 atmospheres are less effective than
using elevated nitrogen levels. We are proceeding with experiments
to determine precise lethal exposure thresholds for various life stages
of these pests.
Another objective is to evaluate compatibility of anoxia with
bedding plants, since any adverse effects would obviously render the technique
less useful. ‘Carpet Lilac’ petunia plugs were exposed to 0,6, and
12 hours of 100% nitrogen or compressed air. No adverse effects were
noted at 48 hour evaluations. Next, we gassed plugs of ‘Super Elfin
Lilac’ impatiens for 6,12, or 24 hours. The plugs were transplanted
into flats and grown for 4 weeks. Thrips were also placed in the
chambers to test for mortality in the presence of plant material.
For plant evaluations, we measured root mass, shoot mass, number of breaks,
days to flowering, and % flowering by 4 weeks. This test was repeated,
for 2 independent trials. There were no differences between treated
and control plants, except in one trial where treated plants required slightly
longer to flower, and had slightly lower flowering percentages. Finally,
we tested ‘Vodka’ begonias in the same manner. Treatment effects
on begonias were much more severe than on other plant species tested.
Begonias exposed to 12 or 24 hours of 100% nitrogen were killed by the
treatment. A 6- hour exposure did not seem to have the detrimental effect
of longer exposure. These results suggest that possible plant effects
must be considered in evaluating costs and benefits of CA technology.
Future Directions:
As can be seen from the aforementioned research, CA treatment
is effective against thrips and aphids, but more testing is needed before
this technology can be developed for commercial use. Some areas we
hope to investigate include:
1) Efficacy against spider mites. Longer exposures (up to 36 h)
will be run to establish lethal thresholds for mites, as compared
to thrips and aphids.
2) Interaction with light and plant material. Metabolic activity
of plants may be adding oxygen, even though the atmosphere is being exchanged
every 30 minutes. We need to confirm lethal thresholds in the presence
of realistic amounts of living bedding plants. Also, light regime
may influence stomatal activity and thus gas exchange by the plant.
We have preliminary data suggesting that lethal thresholds for pests may
differ under light or dark exposures.
3) Further evaluation of effects of anoxia on various bedding plant
species. It must be established that anoxic treatments that are lethal
to pests will not harm the plants, and to identify the plant species with
which this technology is compatible.
Note: We have submitted a request to AFE for extension of funding for
an additional year
Plans for Dissemination:
This work forms the basis of a Master’s degree research project
being conducted by David Held (under supervision of the senior investigators).
Results will be presented at the 1997 national meeting of the Entomological
Society of America, and at several greenhouse conferences this fall and
winter. The work will submitted for publication in both refereed
journals (probably Journal of the American Horticultural Society) and trade
magazines.
