Evaluation of Controlled Atmosphere Anoxia Treatments as a Potential Disinfestation Technique for Thrips and Spider Mites in Greenhouses.
Date:5/29/98
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: 7/97 to 6/98
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
The greenhouse industry faces many problems in pest management including
resistance of insects and mites to insecticides and a limited palette of
alternative pest control options. Currently the EPA is debating the
cancellation of registrations of organophosphate and carbomate insecticides
under the Food Quality Protection Act. This, as well as public concerns
about pesticide usage on ornamental commodities, requires the industry
to search for alternative methods of pest control that address these issues.
The goal of this project is to evaluate the potential use of controlled
atmosphere anoxia (low oxygen) treatments to control of key pests of bedding
plants. Such a system might be useful to disinfect propagules or
cuttings before shipment, or upon receipt. Our project has the following
objectives:
To develop and test a replicated controlled atmosphere test system.
To evaluate thresholds for mortality of important greenhouse pests
in the developed
system.
To evaluate lethal treatments for arthropod pests for compatibility
with common bedding plant species.
Progress to Date:
A replicated system was constructed under the supervision of an Agricultural
engineer. Vacuum desiccators modified for air flow serve as the treatment
chambers. Once the system was constructed and tested for consistency,
a series of experiments was conducted to study variability of response
of arthropod species and life stages, effects of different anoxic gases,
influence of plant material and light exposure on lethal thresholds for
pests, and effects of anoxic treatments on plant growth and quality.
In a 100% nitrogen environment, we found significant variability in mortality
response of arthropod species over time. Time required for 100% mortality
was 6 h for aphids, versus 1 2 h for Western flower thrips. Anoxia
by either carbon dioxide or nitrogen resulted in 100% mortality of twospotted
spider mites and thrips at 1 2H. In addition, mite eggs treated for
12 H in either a 100% carbon dioxide or nitrogen environment had 0% hatch.
Therefore, we conclude that both active life stages and eggs of twospotted
mites are susceptible to anoxia.
Preliminary experiments using Tribolium castaneum, a flour beetle, as
an indicator species suggested that the presence of plant material might
influence effectiveness of anoxic treatments. Survival of Tribolium
castaneum was higher when the beetles were exposed on leaf disks that for
beetles exposed in a dry flour medium. This potential confounding
effect was tested with greenhouse pests using Impatiens plugs inside treatment
chambers and nitrogen as the test gas. In addition, different exposures
of either light or dark were used in a factorial experiment with or without
Impatiens plugs. Fortunately, presence of plant material did not
influence the effectiveness of the anoxia in either light or dark.
The final objective of these pilot studies was to evaluate some common
bedding plant species for their tolerance to treatment conditions that
are lethal to arthropods. Three common bedding plant species, begonias,
impatiens, and petunias were tested in separate experiments. The
results suggest that there is variability in response of plants.
For example, begonias tested for 6, 12, and 24 h in a 1 00% nitrogen environment
showed that this species is intolerant of elevated nitrogen, even for only
6 h. Petunias that were treated in a 1 00% nitrogen environment for up
to 12 h showed negligible adverse results. Impatiens were tested
for 6, 12, and 24 h in a 100% nitrogen environment. The plants were
grown for 4 weeks post-treatment and harvested to determine growth impact.
There was a reduction in days to first flower and percent flowering in
the 1 2 and 24 h anoxia treatments when compared to controls. There
was no difference in root and shoot mass between airand nitrogen-treated
plugs. Therefore, there may be species-dependent effects of these
anoxia treatments on different plants.
Future Plans:
Over the course of many experiments we often have observed variable
mortality within the lethal treatments. For example, mortality of
thrips at 1 2 h could be 60-70% in one experiment, while it could be 1
00% with the same exposure in another experiment. This variability
may be due to variation in oxygen amounts in the bottled gases used for
this work, To test this hypothesis we plan to use specially mixed gases
with 0.5 and 1.5% oxygen levels (remainder nitrogen) over time to determine
if this seemingly small difference in oxygen can account for variation
in arthropod response. Another priority is to determine how broadly
this technology can be applied. We will compare the mortality of
several other pests not previously tested, including whiteflies and mealybugs,
in simultaneous exposures with mites, thrips or aphids. This project
has been successful in demonstrating both the potential effectiveness of
anoxia in controlling insects and mites, as well as some of the sources
of variation and problems that still must be resolved before commercial
systems can be developed for use by the greenhouse industry.
