Improving your bottom line
Integrated Pest Management (IPM)
The Tomato Magazine
“Integrated Pest Management (IPM) in Greenhouses” was
the topic of a fact-filled presentation by Dr. R. Chris Williamson
at the Wisconsin
Fresh Fruit and Vegetable Conference, held earlier this year in Stevens
Williamson is with the Department of Entomology, University of Wisconsin.
Greenhouse insects are difficult to manage, the speaker pointed out.
Among the reasons are multiple generations (up to 20 per year), lack
of natural enemies to reduce populations, almost unlimited food supply,
constant environmental conditions, some life stages are not susceptible
to treatment and growing major insecticide and miticide resistance.
“ The foundation of successful pest management begins with a comprehensive
understanding of the biology of a pest,” he told the group. It
is important to know the life cycle, behavior/habits, ecology and vulnerable
IPM (integrated pest management) is a decision-making process that considers
and utilizes all available pest management options or strategies to prevent
economically damaging pest outbreaks below an acceptable, pre-determined
injury level or action threshold while reducing risks to human health
and the environment, Williamson explained.
“ IPM does not preclude the use of pesticides,” he emphasized. “IPM
is not merely a biological or ‘organic’ pest control program.
IPM is a decision-making process, not a stringent or rigid management
Components of an IPM program include: monitoring and sampling (inspect);
pest identification (what pest); decision-making (what action); intervention
(take action); follow-up (re-inspect); record-keeping (write it down,
history); and education (learn), the speaker said.
When monitoring and sampling, thorough and consistent inspections (scouting)
before pest(s) cause problems is important, Williamson warned. Tools
include the use of sticky cards (aphids, whiteflies, fungus gnats, thrips
and shoreflies); potato slices (fungus gnat larvae); and indicator plants
(petunias or fava beans for thrips).
Place sticky cards at a minimum rate of one card per 1,000 square feet,
he suggested. Space them equally in a grid pattern. Place additional
cards near entrances and vents to detect migration from the outside.
Check and change cards weekly. Blue sticky cards are used to detect thrips
(1-2 inches above crop canopy); yellow cards are used to trap aphids
(vertical), fungus gnats and shore flies (horizontal), and whiteflies
Proper Pest Identification
Accurate identification of pests is essential, the speaker warned. If
unsure, ask a knowledgeable authority, such as a county agent, colleague,
vendor, etc. Otherwise the action strategy selected will be ineffective
and costly in terms of wasted time and money.
IPM decisions are guided by “action thresholds,” Williamson
cautioned. These are flexible guidelines that justify a treatment or
intervention. Such action thresholds are determined by the greenhouse
Based on the information collected, what is the “best” action
to take? the speaker asked. Responding to his own question, he stressed
that the cost of intervention, value of the crop, potential for damage,
impact of damage and the effectiveness of intervention must all be weighed
There are three types of possible intervention (control strategies),
Williamson noted. These include: (1) biological; (2) cultural (mechanical/physical),
and (3) chemical (pesticides).
Biological control equates to the use of any living agent to suppress
pest populations (predators, parasitoids, bacteria, fungi or nematodes),
Cultural controls include: (1) inspecting new plants thoroughly; (2)
keeping doors, screens and ventilators in good repair; (3) using clean
or sterile soils or media; (4) eliminating pools of standing water on
floors; (5) cleaning greenhouses thoroughly after each production cycle;
(6) avoiding over-watering and promoting good ventilation; (7) maintaining
a weed-free greenhouse; and (8) removing and destroying heavily infested
Chemical control, he added, equates to the use of pesticides to reduce
pest(s) to an acceptable or tolerable level (threshold). Included here
would be the use of insecticides for insects and miticides for mites.
Not Always First-line of Defense
Pesticides are extremely valuable tools when used judiciously, Williamson
said. However, they should not always be the first-line of defense.
“Follow up,” he counseled the group. “Evaluate the effectiveness
of the intervention implemented. Did it work? If not, why not? What is
your next step?”
Record keeping is very important, he stressed. Maintain records of problems
and solutions. Such information is invaluable for future situations.
Also, records can serve as a legal document for potential litigation
Education is also important, he stressed. Attend workshops, field days,
short-courses and seminars. These are vital to learning about the most
current and innovative pest management strategies or approaches and keeping
informed on developing pest problems.
In his presentation, Williamson showed the difference between “incomplete” and “complete” metamorphosis.
In “incomplete” metamorphosis, only eggs, nymphs and adults
occur. On the other hand, in a “complete” metamorphosis,
there are four life-stages: egg, larva, pupa and adult. The importance
of this is because larvae of insects with complete metamorphosis have
much different feeding habits than adults and often cause the most damage,
Focusing on insects with piercing-sucking and rasping-sucking mouthparts—hemiptera,
homoptera and thysanoptera—Williamson explained that the order
homoptera includes aphids, mealybugs, scales and whiteflies. Here, there
is incomplete metamorphosis, sucking mouthparts are involved and there
are two pair of membranous wings, he said.
Aphids are soft-bodied insects that may or may not have wings, he said.
They may transmit viruses and can breed without mating. Aphids reduce
plant vigor and cause stunting and malformation.
Among the numerous types of aphids are green peach, cotton, potato, foxglove
Williamson showed the impact of green peach aphids on peppers and encouraged
regular monitoring. When monitoring, check as many plants as possible,
he advised. Look at terminal buds and lower leaf surfaces. Cast skins,
honeydew and sooty mold are indications of aphid infestation. Yellow
sticky traps can help monitor winged aphids. Aphid parasitoids can sometimes
help, he said, showing examples of several types.
Aphid IPM includes sanitation (remove weeds inside and outside of greenhouse),
screening vents and windows, limiting the use of quick-release fertilizer
and the use of beneficial insects (green lacewings, ladybeetles and
parasitic wasps), Williamson told the group.
“Rotate chemicals every two to three applications to prevent insecticide
resistance,” he cautioned, adding that organophosphate resistance
is common. When using Marathon, remember a drench is better, he said.
With Endeavor, expect a slow kill but the aphids do stop feeding fast.
Other options are Thiodan, Orthene, Talstar, Azatin, Avid and Beauvaria.
Tracing the mealybug life cycle, Williamson described the types of damage.
Mealybugs feed at stem tips and leaf junctures, he said. They prefer
tropical foliage plants. Stunting, yellowing, defoliation and wilting
are common. They play a role in honeydew and sooty mold. Citrus mealybugs
can inject a toxin while feeding.
When monitoring for mealybugs, visually inspect both leaves and stems,
he suggested. Yellowed or wilted foliage may indicate underground infestations.
Mealybug IPM calls for inspecting plant material on arrival. Heavily
infested plants should be destroyed. Remove soil and compost piles from
growing areas, the speaker urged.
As for Mealybug chemical control options, use insect growth regulators
when beneficial insects are present, Williamson advised. Two to three
treatments over 10 to 14 days will be required as the eggs and adults
are somewhat protected. Recommended materials include Orthene, Marathon,
insecticidial soap, Permethrin, Scimitar, Neem oil and Beauvaria.
When dealing with different types of scale, Williamson recommended regular
monitoring. Visual inspection of lower leaf surfaces and stems is important,
he said. Yellowed foliage may indicate a scale infestation or the presence
of honeydew on leaves. There is a wide host range of foliage plant pests.
Scale IPM and Chemical Control
For scale IPM, remove and destroy heavily infested plants, the speaker
advised. Wash off honeydew and dislodge crawlers with water sprays.
Inspect new plant material on arrival.
For scale chemical control, spot treat if there are two or more adult
scales or large numbers of crawlers per leaf. Two to three treatments
will be needed at 10-day intervals. Insect growth regulators (azadirachtin)
and soaps will control soft scales.
Williamson then updated the audience on thrips and the kinds of damage
they can cause. Their rasping-sucking mouthparts puncture plants surfaces.
Egg-laying also damages plants. Injury appears in streaks rather than
spots. Blossoms become brown, petals are distorted and buds fail to
To determine the level of thrips damage, look for wet, varnish spots
in feeding injury sites, the speaker informed. Most of the damage is
on flowers and in new growth. Check the underside of the leaves of foliage
plants. Use blue sticky cards to monitor thrips.
Thrips IPM calls for good sanitation, screening windows, vents and fans
and paste pasturizing soil to kill immature thrips, Williamson detailed.
Remove weeds that act as a thrips refuge. Remove and destroy crop residues
after harvest, and remove all soil debris from the greenhouse.
On the chemical control side, treat thrips at three to five day intervals
with very good coverage, he recommended. Rotate chemicals to prevent
Western Flower Thrips (WFT) resistance. Recommended materials include
Mesurol, Spinosad (Conserve), Avid and Pedestal (IGR).
Williamson also talked about the order Diptera, meaning flies, gnats,
mosquitoes and midges. Adults have piercing-sucking or sponging mouthparts
and larvae have chewing mouthparts and feed on roots, stems and fruit.
To monitor fungus gnats, the speaker suggested monitoring with sticky
traps placed horizontally at the crop canopy. Another practice is to
place potato discs on growing medium surface to monitor larval populations.
Fungus gnat and shore fly IPM calls for eliminating breeding areas. Drain
wet areas, he counseled. Dispose of infested growing media and remove
all plant debris. Avoid over-watering plants as well as over-fertilizing
plants; the latter promotes algae growth.
For chemical control of fungus gnats and shore flies, Williamson recommended
Citation, Orthene, Dursban, Adept, Distance, Sanmite, Permethrin, the
use of nematodes for fungus gnat and Gnatrol (B.T.I.).
There are three types of major mite concerns: spider, cyclamen and broad
mites, the researcher said. Two-spotted spider mites are oval, yellow-green
in color with two large, dark spots. They cause webbing, bronzing and
stippling and are worse in hot, dry conditions. Mites feed in protected
plant parts, particularly the underside of leaves.
On the chemical control side, mites are not insects, thus most insecticides
do not control spider mites. As a result, miticides are required. Floramite,
Hexygon, Ovation, Tetrasan, Cinnamite, Avid, Talstar and Sanmite are
among the miticides commercially available.
Cyclamen mites can also be a challenge. These microscopic creatures hide
inside buds and flowers and inject a toxin while feeding. They are favored
by low temperatures and high humidity. Damage mimics physiological disorders.
On the chemical side, the can be controlled in a water bath at 110ºF
for 15 minutes or by using Avid, Thiodan and possibly miticides, although
the latter recommendation is unclear.
Broad mites can be another challenge to greenhouse growers. These mites
attack up to 60 families of plants. Chemical controls include Avid, Thiodan,
sulfur (not pyrethroids) and the possible use of miticides, although
unclear. Eliminate weed sources (clean cultivation).
“Always read and follow label directions,” Williamson cautioned,
adding that pesticide labels change frequently.
Editor’s note: Dr. Chris Williamson can be
contacted by e-mail at: Rcwillie@entomology.wisc.edu.
© 2006 Columbia
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