AFE Research Reports

August 18, 2003 - 11:49

Ever wonder about how your contributions to the American Floral Endowment are spent? These three research reports will give you a taste.

p class=MsoNormal>Since 1961, the American Floral Endowment (AFE) has invested
$11 million in scientific research and educational programs. The Special
Reports are a result of Endowment-funded scientific research projects at
universities throughout the United States. The reports are written by some of
the industry's most respected researchers and are set up to provide readers
with a basic understanding of the projects, the results and how results can
improve horticulture. They are intended to assist in the production of
high-quality plants and flowers, improve the care and handling of flowers, and
help increase profitability.

The Special Reports are part of the Endowment's Special
Report Notebook Program, a project started several years ago to disseminate key
scientific and educational research. Each year, donors receive new Special Reports,
annual progress reports and, if available, consumer marketing articles. This
information is inserted in a special three-ring binder called the Special
Report Notebook and is an important reference tool. Special Report Notebooks
may be obtained by making a contribution to AFE. Contributions to the Endowment
are tax deductible as allowed by law and support the funding of scientific
research for new knowledge and technology, fund educational programs to attract
talented people to the floral industry, and support the only industry-based
statistical/marketing research and data collection program.

The following are three Special Reports from the 2003
Notebook.

Effective Release of Natural Enemies

By Kevin Heinz, Texas A&M
University

Biological control has been proposed as a method for
controlling insect pests of floricultural crops for many years. Although
effective across many pest-crop systems, the 3-10 fold increase in the monetary
costs typically associated with biological control prevents some growers from
embracing it as a regular practice.

Currently, approximately 50 species of parasitoids,
predators and pathogens are available from commercial insectaries for use to
control arthropod pests of greenhouse and nursery crops. Two questions are
central to their efficient and economical use. When should biological control
be initiated, and how should natural enemies be optimally released to maximize
their efficacy? Answers to these questions are needed not only to make
biological controls effective in the specific systems utilized but also for the
general practice of biological control in greenhouse and nursery crops.

When To Release For Mites

In a commercial greenhouse, plants infested with two-spotted
spider mites (Tetranychus urticae) were arranged into three groups based on
their planting date. Within each age group, plants were allocated to one of two
treatment groups: biological control or grower derived chemical control
program. Each age-by-treatment group was replicated four times. Two
Phytoseiulus persimilis were released weekly per pot for the biological control
treatments, while the grower applied insecticides as perceived in the chemical
control treatments. In all three treatments (recently potted plants, plants in
mid production and plants near harvest), releases of P. persimilis provided
biological control of T. urticae. However, plants in mid-production and near
harvest harbored moderate to high densities of mites prior to achieving
successful biological control. Thus they had significant crop damage. In
contrast, releases initiated at the beginning of the crop cycle yielded
damage-free plants. Also, insect control was significantly greater than the
chemical control program.

Cost for the biological control program was almost 10
percent less, and the level of control was greater than the weekly spray
program used by the grower. Southwest greenhouse growers are now using regular
releases of P. persimilis to control mite problems on foliage plants and
miniature roses.

How To Release For Aphids

Aphids are serious pests of floricultural crops worldwide.
Because outbreaks can occur rapidly, aphid control requires that sufficient
numbers of natural enemies be released and that natural enemies rapidly locate
patches of infestation.

Greenhouse studies documented the ability of green peach
aphids to spread over an area of 120 sq.ft. per day after infesting a single
potted chrysanthemum. Natural enemies must be capable of spreading at least
this rapidly to prevent local infestations from becoming problematic.

In greenhouse studies, green lacewing larvae, used as model
predators, were incapable of navigating among potted chrysanthemums placed on
solid benches. Although lacewing larvae voraciously consume aphids once
discovered, successful biological control requires placement of lacewing larvae
onto each individual plant infested with aphids.

By comparison, studies with the parasitoid wasp A. colemani
demonstrated that it could spread over an area of 147 sq.ft. per day. From
these results, we determined that the most effective biological aphid control
could be obtained by releasing A. colemani from points no greater than 12 feet
apart within a potted chrysanthemum greenhouse.

The release technology developed was evaluated in commercial
chrysanthemum greenhouses in terms of pest control, economic feasibility and
grower acceptance. The effectiveness of natural enemy releases was determined
by comparing aphid populations in grower-treated ranges with aphid populations
in experimental ranges receiving natural enemy releases using a haphazard
release method or an optimal distance. Each treatment was replicated three
times. Natural enemies were released weekly into each of the ranges at a rate
of one wasp per plant.

Use of the optimal release distances (4x) resulted in significantly
greater aphid biological control than the haphazard method (1x) and in
comparison to plots not receiving any wasps. Use of the optimal release rate
cost the grower 1.2-1.3 times the cost of insecticide applications. In
contrast, haphazard releases cost the grower 2-3 times the cost of insecticide
applications. The quality of plants harvested from the optimal release distance
were equivalent to those harvested from the insecticide check plots and
significantly greater than plants harvested from the haphazard and no release
plots.

Adaptation of this approach to other biological control
programs should improve efficacy and reduce costs.

Managing Thrips and Whiteflies with Fungi

By Michael Brownbridge,
Margaret Skinner and Bruce Parker, University of Vermont

Methods of plant protection are undergoing major changes as
many of the "standard" pesticides are withdrawn from the market.
Insect-killing fungi are an important new weapon in the IPM arsenal, but
information describing their effective use is needed. In these studies, we
tested two "off-the-shelf" sprayers for application of the fungus
Beauveria bassiana for control of western flower thrips on chrysanthemum and
silverleaf whitefly on poinsettia.

MATERIALS AND METHODS

Spray equipment. The sprayers tested were a high-volume
hydraulic sprayer (Dramm Corp.) and an electrostatic sprayer (ESS).

Application. Plants
were artificially infested with thrips or whiteflies and sprayed with
BotaniGard WP at the recommended rate.

Chrysanthemums.
Plants were sprayed every five days (total four treatments) using a standard
spray gun at 200 psi or the ESS sprayer. Efficacy was evaluated by sampling
thrips from flowers.

Poinsettia. Plants
were sprayed using a five-nozzle extension lance, spraying up into the leaf canopy.
Four sprays were applied at seven-day intervals. Whitefly populations were
sampled every seven days. Spore deposition and persistence were determined
using a leaf press technique.

RESULTS

Chrysanthemums were in flower at the start of the trial, a time
when thrips populations can dramatically increase. Even so, compared to the
untreated "checks," both sprayers suppressed the increase in thrip
population. The high-volume spray provided better levels of control (See Figure
1, page 20), but high levels of thrips infection were obtained with both
sprayers (See Figure 2, page 20).

Interestingly, infected thrips were also recovered from the
untreated check plants, indicating movement of infected insects from sprayed to
non-sprayed areas. This natural "spread" may be an important benefit
when using fungi in a control program. Á

On poinsettia, high-volume sprays successfully suppressed
the whitefly population (See Figure 3, below). Greater efficacy may have
resulted from better targeting of spores to the underside of the lower leaves
where the highest whitefly populations are found. Spore counts taken directly
from the leaf surface confirmed this. Spores remained viable throughout the
spray process and remained viable on the leaves for less than six days.

CONCLUSIONS

Under grower conditions, control measures would be applied
before pest populations reached the levels used in these trials. Thus, fungi
are best used as preventatives. Increased levels of thrip and whitefly control
were obtained with the hydraulic sprayer, probably because of better targeting
of the pests. Also, the higher spray volume may have provided better leaf
coverage and movement of the spores to infestation sites in flowers and
infection sites on the insects.

IMPACT TO THE INDUSTRY

(1) Plants must be scouted regularly so that fungal sprays
can be initiated before pest populations reach outbreak levels.

(2) Growers can use fungi within an IPM strategy to regulate
thrips and whiteflies. Their unique mode of action makes them ideal for use in
resistance management.

(3) Targeted spray applications using a high-volume sprayer
appear to provide the best levels of control.

(4) When fungi are used within an IPM program, pesticide
residues on plants handled by retailers and wholesalers will be significantly
reduced.

Management of a New Powdery Mildew on Poinsettia

By M. Daughtrey, Cornell
University, and J.M. Byrne and M.K. Hausbeck, Michigan State University

In 1988, a new powdery mildew first appeared on poinsettia
crops in North America. Few powdery mildew fungicides were labeled for use on
poinsettia, and the biology of the fungus, an Oidium species, was relatively
unknown. Research was initiated to obtain information critical for disease
management.

MATERIALS AND METHODS

Fungicides. Sixteen
preventive fungicide treatments were compared on poinsettia 'Freedom Red'.
Powdery mildew inoculum was introduced 48 hours after the first fungicide
treatment on October 14. Colonies were counted weekly on four previously
selected leaves and bracts of each plant.

Infection was studied in relative humidity (RH) chambers
providing 35-92 percent RH at 59, 68 and 77° F. Inoculated leaf disks were
incubated for 48 hours, stained with "cotton blue" and examined
microscopically.

Spore production.
The effect of temperature on spore production was measured using leaf disks
held on agar disks in petri dishes for 14 days at 59 or 68° F. Spore
numbers and chain length were counted microscopically.

Symptoms of infection.
Symptoms of powdery mildew are often latent until fall, when greenhouse
temperatures become lower than 86° F. Colonies on leaf undersurfaces may be
hard to detect. Careful scouting and early detection are essential for precise
management of powdery mildew on poinsettias.

CONCLUSIONS

Greenhouse Control Study normal'>. Untreated controls developed 12 colonies per leaf and 22 colonies per
bract by December 10. No powdery mildew was observed on plants treated every 14
days with sterol biosynthesis inhibitors Systhane 40WP, Terraguard 50WP and
Strike 25TOF or with Pipron 84.4 EC or Nutrol applied every seven days (applied
with Latron B-1956 spreader-sticker). Excellent suppression was also obtained
with 3336F + Latron B-1956, Phyton 27 21.8EC, Milsana 114UBF/FL and ZeroTol 27
percent applied every seven days and with Cygnus 50WDG, Compass 50WG and
Heritage 50WG applied every 14 days.

Most treatments were free from phytotoxicity, but some bract
spotting was observed with ZeroTol and Milsana. Residue was moderate to heavy
in 3336F, Milsana and Nutrol treatments. Residue in treatments with 3336F used
alone was reduced by alternating treatments of 3336F and First Step.

Microscopy Studies

Environmental effects on infection style='font-weight:normal'>. Infection was most efficient at 68° F and RH
of 35-50 percent. All steps in the infection process were slower at 59° F.
Earlier studies showed that 86° F inhibits infection.

Environmental effects on sporulation style='font-weight:normal'>. Sporulation began nine days after inoculation. The
spore chains were longer at 68° F than at 59° F. Only 50 percent as
many spores were produced at 59° F as at 68° F.

IMPACT TO INDUSTRY

(1) Knowing the effects of temperature on this powdery
mildew allows growers to manipulate environmental conditions to slow the
development of an epidemic. Less inoculum will be produced if temperatures are temporarily
lowered from 68-59° F. This allows environmental control to be used as one
component of an IPM program that also uses scouting and appropriate fungicides.

(2) Growers may utilize the appropriately registered
fungicides found to be effective in this control trial to significantly reduce
disease. Growers can choose materials with demonstrated low residue and minimal
chance of phytotoxicity. In order to reduce fungicide residue, growers may be
able to use the strategy of alternating a high-residue material with a
bicarbonate.

(3) Retailers and wholesalers have a reduced risk of
purchasing poinsettias with powdery mildew. Because it thrives at moderate
humidities, this particular powdery mildew may become much more visible during
retail or in churches, homes or lobbies. Thus, careful management in greenhouse
production is critical for retail performance.

About The Author

Steve Martinez is executive vice president of the American Floral Endowment, Glen Carbon, Ill. For more information on the Endowment's programs, please contact Steve by phone at (618) 692-0045 or E-mail at afe@endowment.org.

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