Greenhouse Pests Insect & Mite Pests. David J. Shetlar, Ph.D. The “BugDoc”. The Ohio State University, OARDC & OSU Extension Columbus, OH. © November, 2003, D.J. Shetlar, all rights reserved. Greenhouse & Interiorscape Pest Management.
Greenhouse Pests Insect & Mite Pests David J. Shetlar, Ph.D. The “BugDoc” The Ohio State University, OARDC & OSU Extension Columbus, OH © November, 2003, D.J. Shetlar, all rights reserved
Greenhouse & Interiorscape Pest Management Managing insect and mite pests in greenhouses should be a simple task! If you believe in laws of thermodynamics (i.e., matter can be neither created nor destroyed), the biological corollary should be: living organisms must come from living organisms! In short, we know that pests can not spring forth from “primordial much” which was a common thought during the Dark Ages! In short, if you start with a clean greenhouse and clean plants, then pests should not be a problem!
Greenhouse & Interiorscape Pest Management (cont’d) • The most common sources of insect and mite pests in greenhouses are: • Preinfested Stock(Cuttings and seedlings often have pests when purchased. Start clean!) • “Typhoid Mary” Plants(Stock that is infested and isn’t removed before the next crop is begun. University greenhouses are notorious for this! Smaller greenhouse operations that grow a variety of crops continuously are also guilty!) • Fly-Ins (Greenhouse doors, cooling vents and air vents are not properly covered allow flying insects to enter)
Major Greenhouse Pests • Whiteflies • Mealybugs & Scales • Mites (spider mites, broad mites, & etc.) • Thrips • Leafminers • Nuisance Pests (fungus gnats, shore flies, & etc.)
Greenhouse Whiteflies • Greenhouse (Trialeurodes vaporariorum) • Sweetpotato (Bemisia tabaci) • Silverleaf (Bemisia argentifolii) • Bandedwinged (Trialeurodes abutilonea) Best site on Internet: The Whitefly Knowledgebase http://whiteflies.ifas.ufl.edu/
Notes: The greenhouse whitefly has been the traditional whitefly found in greenhouses. In the mid 1980s, another whitefly which was slightly smaller, slimmer and had a more yellowish body became common in Florida and the Carolinas. This new whitefly was a major problem on certain greenhouse vegetables and flowers such as poinsettias, gerbera daises, and hibiscus. This whitefly was eventually identified as the sweetpotato whitefly – Strain B, but this pest was subsequently described in 1994 as the silverleaf whitefly. At present, the greenhouse and silverleaf whiteflies are the most common pests in greenhouses, but the sweetpotato and bandedwinged whiteflies are occasionally encountered. It is important to identify each species since they have varying susceptibilities to biological and chemical controls.
Egg Nymph I (=crawler) Nymph II (=“scale”) Nymph III (=“scale”) Nymph IV (=“Pupa”) Adult Whitefly Life Cycles At 70ºF, the greenhouse whitefly life cycle takes: 6-10 days for egg hatch, 3-4 days as a nymph I, 4-5 days as nymph II, 4-5 days as nymph III, 6-10 days for the pupa. Adults can live for 30 to 40 days.
Greenhouse whitefly pupa, note raised upper surface and long, glass-like spines. Greenhouse whitefly adults hold the wings flatter over the body and they are more white in base color.
Greenhouse whiteflies: note wings held wider and more flat on body, and pupae with long spines. Silverleaf & sweetpotato whiteflies: note wings held closer to sides of bodies, and pupae have no spines.
Other whitefly species can be found, especially in southern greenhouses. Fortunately, most are not significant problems in production settings. Palm whitefly adult and “pupae.” Many whiteflies have such characteristic waxy fringes. A giant whitefly and its nymphs plus an old pupal exoskeleton.
Whitefly Management • Monitoring – visual inspection of plants, upper leaves for adults, lower leaves for nymphs; yellow sticky cards. • Cultural Control – sanitation, resistant plants • Biological Controls – parasitoids & diseases • Chemical Controls – emphasis on insect growth regulators, rotating chemistries, etc. • Integrated Programs – combining cultural and biological controls with chemical controls selected to have minimum adverse action on biologicals.
Whitefly Monitoring • Yellow sticky cards • Visual Inspections – adults prefer to lay eggs on younger foliage; undisturbed females lay eggs in circles; various thresholds (e.g., whitefly nymphs and/or pupae per leaf) have been developed for certain crops. Note rings of eggs that indicate that the females were undisturbed for a considerable time!
Whitefly Cultural Controls • Start Clean! – start a crop with “clean” plant material and keep rooms separated. • Sanitation – keep weeds and other vegetation surrounding greenhouses mowed, or eliminated with herbicides or ground covers. • Exclusion – screen vents, air cooling pads, etc. with material with screens fine enough to exclued white flies. Doors should be under positive air flow (e.g., air flows out when opened). • Use Resistant Plants – some cultivars appear to be less able to support whitefly populations. Be sure to ask seed dealers about resistant cultivars.
Whitefly Biological Controls • Parasitoids – mainly Encarsia and Eretmocerus species, many usage techniques (e.g., mainly introductions or “banker” systems). • Predators – green lacewings are often helpful in field crops, lesser so in greenhouses. See: http://www.umass.edu/umext/floriculture/fact_sheets/pest_management/slwf.html
Encarsia formosa, a commonly used parasitoid. Parasitized pupae turn black. Can you find the two adults?
Development Times for Greenhouse Whitefly
Scheduling Short Residual, Contact Insecticides for Control of Greenhouse Whitefly (assuming “pupae” are resistant) At 85º: Eggs=3 Nymphs=7 Pupae=7 Adult Preovi=1 Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 At 65ºF: Eggs=11 Nymphs=17 Pupae=12 Adult Preovi=2 Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
Whitefly Chemical Controls • Soaps & Oils – best on foliage plants because of phytotoxicity potential; kills mainly eggs, crawlers and scale states by contact. • Contact Insecticides – most pyrethroids kill by contact and most have some residual action. Eggs and “pupae” may be resistant, so reapplications may be necessary to catch the crawlers or adults that may emerge after an application. • Systemic Insecticides – systemic insecticides are usually effective for actively feeding stages of whiteflies. • Insect Growth Regulators – have been very effective, especially as alternate chemistries.
Whitefly Chemical Controls ALTERNATE CHEMICAL CONTROLS! Whiteflies are notorious for developing resistance to pesticides. Their high reproductive potential and short generation time make them excellent at developing resistance. While there is considerable debate on resistance management, do not use the same pesticide again if satisfactory control was not achieved with a recent application. It is often recommended that managers alternate chemical groups on a regular basis if whiteflies need continual control. Without cultural and biological controls, chemical controls will eventually fail.
Greenhouse Mealybugs & Scales • Mealybugs (citrus, longtailed, Mexican, etc.) • Soft Scales (brown soft scale, hemispherical scale, black scale, nigra scale, etc.) • Armored Scales (oleander, fern, Boisduval, false Florida, cactus, etc.) Sites on Internet: http://www.ipm.uiuc.edu/greenhouse/insects/index.html http://floriculture.osu.edu/archive/oct97/mealybug.html
Greenhouse Mealybugs • Citrus (Planococcus citri) • Longtailed (Pseudococcus longispinus) • Mexican (Phenacoccus gossypii) • “Unnamed” (Phenacoccus madeirensis) • Root Mealybugs (Rhizoecus spp.)
Citrus mealybugs, early ovisacs, and a couple of crawlers. Longtailed mealybugs – crawlers, nymphs, and adults.
Phenacoccus madeirensis All stages on chrysanthemum. Ovisacs and crawlers. A male.
Other mealybug species often occur in lath-house ornamentals in southern states. Striped mealybugs Pink hibiscus mealybugs being tended to by fire ants.
Mealybug Hosts • Citrus – 27 families of plants; begonia, coleus, amaryllis, cyclamen, and dahlia are most commonly attacked in greenhouses. • Longtailed – 26 families of plants; Dracaenia & ferns most commonly • Mexican – mainly chrysanthemum, English ivy, geranium, Gynura, hollyhock, Ixia, lantana, and poinsettia. • “Unnamed” – mainly chrysanthemum & poinsettia as well as foliage plants. • Root – numerous long-lived greenhouse plants but most damaging to African violets.
Mealybug Life Cycles • Citrus - males known but not obligatory; up to 600 eggs per ovisac; 10 days for egg hatch; 50-60 days per cycle. • Longtailed - males obligatory; up to 200 eggs per female, no ovisac, possibly live birth; two to three months per cycle. • Mexican – males known; up to 400 eggs per elongate ovisac; cycle can be completed in 47 days. • “Unnamed” – males known; up to 300 eggs per elongate ovisac; cycle can be completed in 30 days. • Root – not much known; several species that lay small numbers of eggs in compact ovisacs; slow developing.
Greenhouse Soft Scales • Brown Soft Scale (Coccus hesperidum) • Hemispherical Scale (Saisseta hemisphaerica) • Black Scale (Saissetia olea) • Nigra Scale (Parasaisetia nigra)
Hemispherical scales – all stages! Can you tell which ones are parasitized?
Soft Scale Life Cycles • Brown Soft Scale – ovoviviparous, males uncommon; 60 days to mature. • Hemispherical Scale – parthenogenic; up to 1000 eggs per adult; 40 to 105 days to mature. • Black Scale – parthenogenic • Nigra Scale – parthenogenic; lays eggs over long period of time; 40 to 60 days to mature.
Greenhouse Armored Scales • Oleander (Ivy) Scale (Aspidiotus nerii) • Cactus Scale (Diaspis echinocacti ) • Fern Scale (Pinnaspis aspidistrae) • Bifasciculate Scale (Chrysomphalus bifasciculatus) • Boisduval Scale (Diaspis boisduvalii)
Oleander scales are irregularly round in shape. Males are smaller and more oval in shape. Cactus scales are sexually dimorphic, females being rounded and males being slender, elongate forms.
Fern scale females are generally brown and oystershell shaped. Males are white with a medial ridge running down the waxy cover.
Boisduval females are irregularly rounded and males are elongate, white and with a medial ridge in the waxy covering. Settled nymphs produce a patch of elongate waxy threads as they form their covers.
Armored Scale Hosts • Oleander Scale – numerous woody plants • Cactus Scale – various cacti & orchids • Fern Scale – ferns and Aspidistra • Bifasciculate Scale – palms, rubber plants, & figs • Boisduval Scale – palms, banana, cacti, & orchids
Armored Scale Life Cycles • Oleander Scale – males & females common; 90 eggs per female; 30-35 days to mature. • Cactus Scale • Fern Scale – males and females common; few eggs per female; ~30 days to mature. • Bifasciculate Scale • Boisduval Scale – males & females common; 200 eggs per female; 23 to 32 days to mature.
Mealybug & Scale Management • Monitoring – early detection of mealybugs and scales is important to achieve good control. • Cultural Control – sanitation/start clean, throw away severely infested plants! • Biological Controls – parasitoid wasps are common • Chemical Controls – emphasis on systemics, following spray schedules, etc. • Integrated Programs – combining cultural and biological controls with chemical controls selected to have minimum adverse action on biologicals.
Greenhouse Mites • Twospotted Spider Mite (Tetranychus urticae) • Lewis Mite (Eotetranychus lewisi) • Southern Red Mite (Oligonychus ilicus) • Broad Mite (Polyphagotarsonemus latus) • Cyclamen Mite (Phytonemus pallidus) • Bulb Mite (Rhizoglyphus echinopus)
Twospotted spider mites have typical spider mite life cycles. They have egg, six-legged larval, eight-legged nymph I & II, and adult stages. Between every molt, the mites settle down and don’t move for a day or more, depending on the temperature.
Typical twospotted spider mite population. The eggs are completely spherical. Most of these are adults. The male in the middle is “guarding” a female nymph II that is in the process of molting into an adult.
Larva (above); egg, nymph I & II in molt rest, cast skins (right); nymph II female and male guarding (below).
When monitoring for spider mites, the tell-tale stippling is easily spotted. The mites will be on the underside! If left uncontrolled, twospotted spider mites will completely encase the foliage in their fine silk. Note that the mites use the webbing as a walkway. Plants this heavily infested should be thrown away!
If left uncontrolled, spider mites can eventually kill their host plants. When this is about to occur, the mites often cluster at the tops of the plants in order to balloon to other plants. This is one such ballooning cluster. Remember that an unmated female that is blown to a new plant can start an entire colony. When unmated, she can only produce eggs that will develop into males. However, the female can live long enough to mate with one of her sons and then she can begin to produce eggs that will develop into females!
Development Times for Twospotted Spider Mite
Longevity & Fecundity for Twospotted Spider Mite
“Red Mites” Greenhouse managers often talk about “red mites” or “red spiders” when they are referring to spider mites. This is unfortunate, since there is no such species such as a “red mite”! Twospotted spider mites take on a red or orange hue when chilled in fall conditions (above) Southern red mites and European red mites have conspicuous spines and a reddish color (right).
Spider Mite Management • Monitoring – early detection of spider mite activity is important to achieve good control, look for stippling. • Cultural Control – start clean; remove weeds surrounding greenhouse environment; regularly syringe with water. • Biological Controls – numerous predatory mites are available and useful. • Chemical Controls – soaps & oils work well by contact; new miticides often have ovicidal activity, etc. • Integrated Programs – combining cultural and biological controls with chemical controls.