|
|
|
Phytoseiulus persimilis Spider Mite Predator Adapted from the Applied Bio-Nomics
Manual PO Box 1555, Ventura, CA 93002 800-248-2847 * 805-643-5407 * fax
805-643-6267 e-mail bugnet@rinconvitova.com www.rinconvitova.com |
|
|
Phytoseiulus persimilis Two-Spotted Mite Predator (Acarina: Phytoseiidae)
Common Name: Persimilis
Target
pest
Two-spotted spider mite (Tetranychus
urticae)
Description
Persimilis is a tropical predatory mite that was one of the
first greenhouse biological control agents available commercially.
·
Eggs are oval and <1/50 inch (0.3 mm) long, oval shaped;
pale translucent yellowish pink color; deposited near spider mite populations
and about 3 times larger than spider mite eggs.
·
Larvae are inactive, a pale salmon color and have 6 legs.
·
There are two nymph stages; both are a pale salmon color,
have 8 legs, and are very active predators.
·
Adults are bright reddish orange, with long legs and
pear-shaped bodies, 1/50 inch (0.5 mm) long.
Both adult and immature predators move rapidly over the
leaves and both feed on two-spotted mite eggs, nymphs, and adults. Unlike its
prey, Persimilis does not spin webbing.
Use in
Biological Control
·
Persimilis is very effective against two-spotted spider
mites in greenhouse vegetables and ornamentals, interior plantscapes, and
conservatories. It is also used in mild climates on field crops, such as
strawberries, melons, cucumbers, vegetables, mint and hop.
·
Optimum conditions are 68-81°F (20-27°C) and relative humidity
over 60%.
·
At temperatures of 64-81°F (18-27°C), the predators reproduce
faster than spider mites. At warmer or cooler temperatures, however, the spider
mites reproduce faster.
·
At temperatures warmer than 86º F, the growth rate does not
keep up with the spider mite growth rate because the eggs dry out.
·
At 68ºF Persimilis breeds twice as fast as TSSM.
Monitoring
Tips
·
Persimilis are usually easy to tell from their prey, which
are slow-moving, pale green mites with two darker spots on their sides.
·
In winter, some two-spotted mites turn a reddish color, but
they can still be distinguished from the predators by the pair of dark spots on
their sides and slow movements.
·
Weekly inspections of leaves to determine ratio of predators
to spider mites can be done along with pruning or picking. It is difficult to
estimate numbers due to a clumped distribution.
·
Spider mites can easily increase ten-fold to threatening
levels before they are detected, predators purchased, and the pests controlled.
·
The best method is to count the mites on random leaves or
leaflets to determine numbers and whether they are going up or down
·
Time of day can affect counts as the spider mites move up
and down.
A complete life cycle takes from 5 days at 86°F (30°C) to 25 days at 59°F (15°C).
·
There are 4 times more females in the population than males
(a sex ratio of 4:1).
·
Females lay 2-3 eggs per day for an average of 60 eggs over
their 35-day lifetime. The eggs hatch in 2-3 days. They are oval and twice the
size of two-spotted mite eggs.
·
Newly hatched predators do not eat, but later stages and
adults feed on all stages of prey. Each predator consumes between 5-30 prey
(eggs or mites) per day.
·
Adults may live for 30-35 days at cooler temperatures and
deposit 30-60 eggs. Adult Persimilis feeds on all stages of target pest,
consuming 5-30 target pest/day, and rather than eating all spider mite eggs,
females lay their eggs amid spider mite eggs to assure survival and wide
distribution
·
Persimilis does not diapause, therefore remains active
year-round in greenhouses.
Product
Information
Persimilis is sold either in a granular carrier (usually
vermiculite) or on bean leaves. Both formulations should be applied the same
day they are received as the quality of the product drops with storage. If
Persimilis must be stored, hold only at 50-59°F (10-15°C).
Temperatures above or below that range cause mortality. Release predators in
areas with highest pest densities.
Using the vermiculite product
When Persimilis are refrigerated they tend to clump
together. If the package is cold, lay the container on its side at room
temperature (out of direct sunlight), for 15-20 minutes, to allow the mites to
warm up and move apart.
·
Check the product by sprinkling some of the vermiculite onto
a sheet of white paper; the active predators should be easy to see.
·
Gently rotate the bottle to mix the mites with the carrier
and distribute the contents over the plants.
·
Avoid placing the predatory mites in direct sunlight. If
transporting in a hot vehicle we suggest keeping the mites inside an insulated
chest with cool pack until ready for release.
Using the bean leaf product
·
Place leaf pieces from the container onto each infested leaf
of crop plants. The bean leaves eventually dry out and become inconspicuous.
·
Advantages of this product are that all life stages are
present, which introduces all ages of predators into a crop. It provides ideal
humidity and a food supply for the predator in transit.
·
It can be used in interior plantscapes where the vermiculite
carrier would be unsightly.
Note that although the bean leaves contain a few two-spotted
mites, this does not add to the pest problem because the predators quickly
eliminate them. The presence of this food enables Persimilis to start
reproducing immediately, which improves biological control.
Introduction
Rates
Persimilis is most effective when applied at the very first
suspicion of the presence of
two-spotted mites. Because of its high reproduction rate, Persimilis
usually exhausts its food supply and eventually dies out, therefore repeated
introductions are recommended until all sites with spider mite infestations
have Persimilis present. General releases to achieve a high enough predator to
prey ratio are more effective than fixed rates per unit area. A general fixed
rate can be from five to twenty predators per plant or from 20,000 to 80,000
per acre.
General Introduction Rates
·
5 Persimilis/10 ft2 (m2) or 20
Persimilis/infested leaf, weekly, as needed. Apply predators to each infested
plant.
Field strawberries, melons, cucumbers, vegetables, mint,
hops
·
1 Persimilis to 10 spider mites including eggs, or 8000 per
acre (20,000 per ha), or 4-5 Persimilis per 10 ft2 (m2) will yield control in
14 days at less than 86ºF and above 60% humidity
·
Provide a complex of natural enemies controls spider mites
except when trees are over-fertilized, over-pruned, and sprayed with
non-selective pesticides that kill all the natural enemies. When the ratio of
predators to pests is too high, selective acaracides can be used that do not
harm the non-mite natural enemies.
·
Releases are made by a slow-release system early in the
season or by simultaneous uniform distribution of spider mites and Persimilis.
Persimilis disperses in 18 days to every spider mite colony from a release onto
every tenth plant
Specific Crop Programs
·
Greenhouse cucumbers — 6
Persimilis/10 ft2 (m2) or 100 Persimilis/infested
plant, weekly or as needed. For larger areas use 60,000 / hectare (24,000 /
acre). Persimilis works well because cucumbers can tolerate up to 30% damage of
leaf area. If too hot, Persimilis hides beneath the lowest leaves, leaving
spider mites at the growing tops
·
Greenhouse tomatoes — Apply at a ratio of 1 predator to
10-20 spider mites. The glandular hairs on tomato leaves are toxic to
Persimilis so females will lay fewer eggs than on other crops. For best
results, use the predators shipped on bean leaves as these are more easily to
apply to tomato leaves than vermiculite.
When its food becomes scarce, Persimilis disperses
throughout the crop. The predator moves better within a crop when the leaves of
adjacent plants are touching. It tends to moves upward on plants, so it can be
applied to the trunks of large plants in interior plantscapes.
When predators are found on each infested leaf it usually
means that the biological control program will be successful. It may take
another 2-6 weeks for new plant growth to show improvement, depending on growth
rates.
For Best
Results
·
Be very proactive and preventive and do not let spider mites
become a problem.
·
If spider mite numbers are high with visible webbing and
clusters of mites stringing down from leaves, knock them down with a compatible
pesticide before releasing predators. Organic options are GCMite or other OMRI
listed insecticidal soap and/or light horticultural oils that may have neem oil
added. Fenbutatin oxide (Vendex® )
will also reduce pest numbers.
·
Persimilis needs relative humidities greater than 60% to
survive, particularly in the egg stage. In low humidity conditions, raise the
humidity by lightly misting plants or wetting walkways.
·
Where humidity above 60% RH can be maintained, the predator Feltiella acarisuga can also be used
with Persimilis.
·
Where humidity is below 60% RH, the predatory beetle Stethorus punctillum can be used with
Persimilis. Stethorus feeds on all
stages of spider mite and is effective at detecting individual mite colonies.
·
If average temperatures are often below or above the 68-81°F (20-27°C) range for optimum use of
Persimilis, introduce Amblyseius fallacis
along with Persimilis.
Predatory mites require
proper conditions such as adequate humidity and compatible management practices
to be effective. Start with clean plants and use good sanitation practices to
avoid spreading mites. Carefully inspect new plant material with a 10X to 15X
hand lens before bringing it into the greenhouse; disinfest plants if they
harbor mites.
·
High foliar nitrogen levels can favor outbreaks of some
mites. Do not apply more nitrogen than necessary, and when possible use less
soluble forms.
·
Bending rose canes to increase flower production increases
humidity within the lower canopy, providing a more favorable environment for
predatory mites than in traditional trellis production.
·
Pest mites thrive under hot dry conditions; properly
watering plants dislodges some mites and slows pest mite dispersal.
·
When using predatory mites, regularly monitor pest and mite
populations to evaluate control efficacy. If releases are not proactive, they
may not be effective, and pesticides may be warranted.
·
Control dust around crops; use plastic dust barriers, impose
speed limits on dirt roads, and cover bare soil.
·
If there was a severe infestation, which was not controlled
by early September, it is likely that an early attack by over wintered mites
will occur next spring. Some pest mites can over winter at ground level and
will emerge from between the overlaps of floor coverings or backs of rows, roof
supports, at purling, etc. Treat these areas in fall with Hypoaspis.
·
Remove piles of plant debris, especially heavily infested
plants. Reduce potential over-wintering sites, such as pots and covers.
·
Check regularly for signs of an early attack, concentrating
on patches where the damages was seen last season, and near possible over
wintering places. Release Phytoseiulus persimilis near TSSM infestations and
repeat weekly until each leaf has predators.
·
As soon as you observe any damage by spider mites, introduce
predators. If the initial damage is severe or caused by the red over wintered
population, the spider mite numbers must be reduced with a suitable pesticide.
·
Apply OMRI or NOP listed oil, soap, or other miticide with
relatively low impact on predators to reduce pest populations, and then
introduce predators after leaves dry.
·
Insecticidal soap, horticultural oil, and essential oils
have low residual toxicity and provide control if applied thoroughly on plants
where mites are feeding.
·
Essential oil products, such as GCMite (containing
cottonseed, clove and garlic oils) Ecotrol (rosemary, peppermint, and
wintergreen oils) may work better than less expensive soap and oil treatments
because of their multiple modes of action in controlling mites and other pests
in 3 – 5 days, allowing the beneficial insects to come back quickly.
·
Oil has little impact on predatory mites and can be a good
choice if spraying is needed when natural enemies are present. For crops and
growing situations where phytotoxicity is a concern, reduced rates (1% soap or
0.25-0.5% oil) can provide control.
·
The habit of N.
fallacis to overwinter in crevices can be used to advantage in the early
spring with a pre-bloom horticultural oil application. This greatly reduces the
number of European red mite eggs while not affecting predatory mite
populations.
·
Avoid using persistent pesticides for at least several weeks
before releasing of predator mites.
Conventional
Pesticide Controls
For effect of pesticides on Persimilis, see Pesticide
Toxicity Chart.
·
To reduce mortality of predatory mites from pesticides, find
out the length of residual harm on the Pesticide Toxicity Chart before
releasing predators.
·
Hot Pepper Wax and IGRs are effective low risk controls with
no residual harm to predators.
Cinnamaldehyde may have a little or no residual. Abamectin has a
two-week residual.
·
Fenbutatin oxide (Vendex®) is sometimes used on
hot spots in a Persimilis program but it is a Pesticide Action Network Bad Actor
Chemical. It does not harm Persimilis, but avoid over spraying, which reduces
the predator’s food supply and their ability to reproduce.
·
Spreader-stickers, supreme oils and soaps are harmful to
predators contacted by the spray, but have little residual activity.
·
Overuse of mist-applied sulfur can suppress predator
reproduction and reduce effectiveness and may have some residual effect on
predators.
·
A single application of a chemical considered highly toxic
to Persimilis at any time during the season will have a large negative impact
on its abundance.
ã Rincon-Vitova Insectaries, Inc.
2008