Thrips–TSWV/INSV Control Systems
Team Leader: Michael P. Parrella
Department of Entomology, University of California at Davis
Application for Continued Funding
Research Project Title: Thrips — TSWV/INSV Control Systems
Thrips and topoviruses represent a formidable problem facing
floricultural producers across the US. Here we propose a research/implementation
program which combines recent research with the development of new information
to combat this problem in a multi¬ódisciplinary/multi-state research proposal.
Priorities:
1. Sampling/Identification
a. Validation/implementation of a monitoring/identification
program for thrips across a variety of floriculture crops. This program
developed in California, will be evaluated in the western US in addition to
Vermont and Texas.
b. Economic thresholds for western flower thrips have been
developed for roses, and research will extend this to other crops. The
sampling/threshold work will include development of a monitoring system for
detecting the presence of viruliferous thrips in samples. This system and a new
immunology method for tospoviruses will be used to provide growers with an early
warning system for tospoviruses to assess thresholds for viruliferous thrips.
2. Pesticides
a. Develop practical recommendations for more effective
use of the fungus Beauveria
b. Evaluate new ‘reduced risk’ pesticides as they
become available
c. Determine compatibility with natural enemies of thrips
and other pests
3. Biological control of Thrips
a. Evaluate recommendations for use of commercially
available natural enemies
b. Evaluate the entomopathogenic nematode, Thripinema
siddiqui and parasitoids in the genus Ceranisus
4. Postharvest Control
a. Evaluate different methods of postharvest disinfestation
techniques
b. Develop new methods using novel pesticides and/or
controlled atmospheres.
Researchers:
| Dr. Michael P. Parrella Dr. Diane Ullman Dr. Elizabeth Mitcham Dr. Arnold Hara Dr. Kevin Heinz Dr. Michael Brownbridge Dr. Karen Robb Ms. Julie Newman Mr. Steve Tjosvold |
Department of Entomology, UC Davis Department of Entomology, UC Davis Department of Pomology, UC Davis |
Department of Entomology,
University of HI, Hilo
Department of Entomology,
Texas A&M, College Station
Department of Entomology, University
of VT, Burlington
UC Cooperative Extension, San
Diego Co.
UC Cooperative Extension,
Ventura and Santa Barbara Cos.
UC Cooperative Extension,
Monterey and Santa Cruz Cos.
Proposed Project Duration
Start: 7/1/98 Completion: 7/1/02
Total Estimated Cost
Year 1: $126,000
Year 2: $192,000
Year 3: $196,000
Year 4: $200,000
Team Leader: Michael P. Parrella
Department of Entomology, University of California at Davis
Project Research & Anticipated Industry Benefits
The main thrust of this project is to combine researchers
from across the country to help solve the thrips/tospovirus problem. Each of
these individuals brings a unique set of skills to the table and is responsible
for developing a piece of the Thrips/Tospovirus IPM puzzle. Michael Parrella
(California) is concentrating on developing and validating sampling plans,
thresholds, and identification keys for thrips attacking floriculture crops. In
addition, he is examining the performance of reduced risk pesticides and their
compatibility with natural enemies. Michael Brownbridge (Vermont) is looking at
ways to improve the performance of the fungus, Beauveria bassiana, for thrips
control. Kevin Heinz is evaluating the potential of a new biological control
agent of thrips, the nematode Thripinema. In addition, Dr. Heinz is
determining the utility of commercially available natural enemies such as
predatory mites in the genus Amblyseius. Diane Uliman (California) is trying to
understand the population dynamics of viruliferous thrips in floriculture crops
in the field and greenhouse. Dr. Ulimam is also developing a rapid bioassay to
tell if an individual thrips is a virus vector. Beth Mitcham (California) and
Arnold Ham (Hawaii) are examining various postharvest treatment methods to
control western flower thrips. The Farm Advisors in this project (Karen Robb in
San Diego, Steve Tjosvold in Santa Cruz and Monterey, and Julie Newman in Santa
Barbara and Ventura) will be heavily involved this coming year as we try to
implement and validate this holistic IPM program with growers throughout
California. The Farm Advisors are receiving funds from the USDA-ARS National
Floriculture Initiative to cooperate in this project.
Each of us is making good progress and we have an agreement
with GrowerTaiks to submit five articles (one from each of us) in the coming
year of this project. This may be compiled and published separately as a booklet
by GrowerTaiks (see attached email correspondence) We are also in discussion
with GrowerTaiks regarding the publication of the identification key for thrips
attacking floriculture crops in the US. The company Hortitechnia (Marta Pizano
hortitec@openwaycom.co) has expressed interest in publishing this in Colombia.
One of us (M. Parrella) visited Colombia this past year and presented
information on the management and identification of thrips in greenhouses. Many
of us particpated in SAF’s Pest Management Conference and contributed articles
to the proceedings. Two of us (Parrella and Heinz) were on the organizing
committee for an international workshop on thrips to be held in Canada in June
(2000) and members of this research team will present data at this meeting (AFE
provided financial support for this conference).
Summary of Professional/Published Information
Parrella: Twenty one species of thrips have been found to
attack floriculture crops in the US and Hawaii and a ‘user friendly’ key
has been completed for their identification. In roses, we recommend using blue
or yellow sticky cards at a placement density of approximately 5 per
5000 square feet. We find that at this number there is a relationship between
the number of thrips on the cards and the number in developing rose flowers. Approximately
20 thrips per card per week represents 1-2 thrips per flower this is the
threshold. Any more than this number, and treatment is recommended. The results
with chrysanthemum is not as clear. Thrips are difficult to control with
insecticides ¬ó one of the more effective new materials is Conserve (Dow). No
product that has come along recently is as good. The product Thiamethoxam
(Flagship by Novartis) while effective against a wide range of pests, is
ineffective against western flower thrips.
Brownbridge: Data on improving the performance of microbial
control agents (specifically the fungus Beauveria bassiana) suggest that the use
of smaller nozzle tips at closer proximity to target plants provides more efficient
deposition of spores. Wide-angle cone nozzles were inefficient and a large
proportion of the spores sprayed did not land on the target plant. This not only
reduces potential efficacy but is economically imprudent. A series of
quantitative tests over the next year will further resolve issues related to the
optimization of spray application techniques. Our objective in the coming year
is to test a limited number of nozzles (5) under conditions that mimic a
sprayer moving over a full plant canopy. We will do this at 2 rates of movement,
at 2 pressures and at 2 angles. The cold fogger and electrostatic sprayers
provided the best and most efficient spray coverage throughout the canopy. While
the hydraulic sprayer provided effective deposition, patterns were more
variable. All three sprayers were similar in the effective reach of their spray
stream. Use of a reduced spray volume, e.g., with a cold fogger, may reduce
spray costs. However, the deposit must also be of a concentration that is
efficacious for management of, and is readily acquired by, the target pest.
Ultimately, the same amount of active ingredient may be required to achieve the
same level of efficacy so other factors may play a more influential role in the
type of sprayer selected, e.g., time taken to spray a crop.
When smaller nozzle tips or equipment such as foggers with
narrow diameter tip orifices are used, there is a greater potential for
clogging. This makes aspects of spray technology related to the formulation of
fungal materials increasingly important. Preliminary experiments with fungal
formulations have shown that wettable powders do not perform as well with
sprayers that form very fine or mist spray streams. Additionally, each
formulation has special physical parameters such as viscosity, evaporation
speed, and stability of suspension, that can affect spray quality. We propose to
evaluate specific formulation components and adjuvants that are traditionally
added to spray suspensions for ULV application to determine their effect on the
distribution of fungal conidia within a plant canopy.
Heinz: The biological attributes of a potential biological
control agent, the nematode Thripinema, have been studied to gather information
that is needed before larger scale efficacy trials can be correctly carried out.
We have found that Thripinema survival is strongly influenced by
temperature. Unprotected nematodes on an exposed leaf surface may live only a
few hours under typical greenhouse conditions. This is reflected by the fact
that Thripinema is more commonly found in buds and flowers than on
leaves. We have also examined the ability of Thripinema to suppress
thrips populations. In a small-scale laboratory cage study we found a 3.5 fold
lower thrips population in cages where infected and healthy thrips were both
included than cages having only healthy thrips. This reduction occurred in the
3rd generation after the thrips were initially put into the cages. Thripinema has an advantage over thrips predators and parasitoids. The nematode resides
in buds and flowers which are often too tight and narrow for other natural
enemies to invade but are preferred places for thrips. In biological control, Thripinema
might be combined with other natural enemies that attack different thrips
life stages. The mite Hypoaspis miles, which lives in the soil and
attacks the soil borne stages (pupae) of thrips could be combined with Orius bugs
that eat thrips larvae in the plant canopy and finally with Thripinema attacking
thrips in the buds and flowers.
Ullman/Robb: Tospoviruses can only be transmitted by an adult
thrips if it fed on an infected plant as a larva. Thus, only virus host plants
that support thrips development from egg to adulthood are important to virus
spread, because they are the only plants that can produce infective thrips. This
concept is central to constructing any management program for tospoviruses
because these viruses can infect well over 600 crop plant and weed species.
Removal of all potential host plants in an area is usually not possible. The
industry urgently needs a means for locating those plants that produce infective
thrips and are therefore important to virus spread. Plant removal and thrips
control efforts could then be directed to locations where infective thrips are abundant and
treatment will have the greatest impact. To address these needs, we have developed a monitoring system
that deploys petunia indicator plants as a rapid means for locating sources of
infective thrips. We have shown that this system serves as an early warning to
growers and helps locate sources of infective thrips. We have further shown that
control actions based on information from the petunia indicator plant monitoring
system dramatically reduces virus incidence and improves production of high
quality plants.
The monitoring system works as follows: Indicator plants show
distinctive lesions 3-7 days after feeding by an infective thrips. Previously,
we demonstrated that petunia indicator plants could be used with directional
traps to locate sources of infective thrips and that removal of these sources
could dramatically reduce virus incidence in field cut flower and bulb crops (to
less than 1%). Under the current grant, in the 1998/1999 funding cycle, we
showed that directional sticky traps could be used at a relatively low rate, but
that petunia indicator plants could not be decreased accordingly. We were able
to maintain very low virus incidence using directional sticky traps and petunia
indicator plants to provide the grower with information that directed management
decisions. During the current funding cycle, we streamlined our monitoring
strategy in field grown flowers for maximum efficiency and expanded our research
program to greenhouse production areas. With supplemental funding from the
Hansen Trust we also expanded our monitoring program to include greenhouses in
Ventura county. We also began assessing actions that growers could take in
response to monitoring information, e.g. using hydrated lime under benches in
greenhouses lacking cement floors, using spinosad based products to control
thrips, and keeping greenhouse doors closed in areas where infection was shown
to come from outside the greenhouse. In addition, we continued to test the
potential of jasmonic acid for inducing resistance to thrips and limiting
tospovirus spread. Finally, we developed a list of plants that support thrips
and tospovirus development. These are most important to virus spread and should
be the focus of control programs.
Mitcharn/Hara: The tolerance of chrysanthemum cuttings to
insecticidal controlled atmosphere treatments was tested. Cuttings were exposed
to 1% 02 and 20 or 40% CO2 for various lengths of time at 5¬?C
(41¬?F). The tolerance to 1% 02 for up to 12 days was excellent, and longer
times have not yet been tested. Tolerance to 20% CO2 was between 4
and 7 days, and tolerance to 45% CO2 was less than 2 days.
These results indicate that low oxygen atmospheres have more potential than
elevated carbon dioxide atmospheres for chrysanthemum cuttings. Research on
insect mortality at these controlled atmosphere treatments is underway.
Acetaldehyde is a volatile compound naturally produced and metabolized by plant
materials, and may be considered as Generally Recognized as Safe (GRAS) by
regulatory authorities. A 1-hour fumigation with acetaldehyde provided for
control of melon aphid, western flower thrips and two spotted spider mites with
0.6, 0.9, and 2.0% acetaldehyde, respectively. Early data indicate that
mortality may occur in less than a 1-hour exposure. Mortality of western flower
thrips was nearly complete after a 30-minute exposure to 2% acetaldehyde (Fig.
3). Additional work is needed to determine the effects of concentration and
exposure time on aphid, thrips and mite mortality. This information will guide
the development of treatment parameters.
