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Integrated Pest Management (IPM) in Greenhouses

The Tomato Magazine
June 2006

“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 Point, Wis.

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 life stage(s).

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 regime.”

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 (vertical).

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 manager.

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 appropriately.

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), he explained.

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 plants.

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 problems.

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, he warned.

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 and melon.

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
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.

Thrips Damage
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 open.

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 Publishing

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