Floriculture Indiana Vol. 12 No. 3 Summer 1998 Page 7

Insect Pests of Greenhouse-Grown Pansy Raymond A. Cloyd Entomology Department, Purdue University 1158 Entomology Hall,West Lafayette, IN 47907-1158 Phone: (765) 494-4575 Fax: (765) 494-2152

Pansy {Viola X wittrockiand) is one of the plant quality, nutrition, and temperature. Adult most widely grown bedding plants in U.S. green aphids may be winged orwingless. Young develop houses. Like many ornamental bedding plants into wingless adults unless the host (plant) be pansy is susceptible to various insect pests. Pests comes crowded in which case the young develop maybe present in the early stages of plantgrowth into winged forms. This allows aphids to spread or appear later when plants are in flower. The rapidly to other areas of the greenhouse. Aphids major insect pests of pansy are aphids, fungus can overwinter outside thegreenhouse as eggs. In gnats, shoreflies, western flower thrips, and cater thespring, eggs hatchand theyoungdevelop into pillars. Whiteflies and two-spotted spider-mites winged females that fly intothegreenhouse. Once are generally considered minor pests. inside thegreenhouse, theyproduce live, wingless female offspring. If winged adults are found on Aphids yellow sticky cards this indicates that a heavy Aphidsgenerally attackpansyinthespring population is present and management strategies and/or late summer. They are usually located on need to be implemented immediately. young terminal growth. Aphids feed on plant tissue with theirpiercing-sucking mouthparts caus Fungus Gnats ing plant stunting, wilting, leaf yellowing, and Fungus gnatlarvae cause direct damage by upward curling of leaves. A by-product of their feeding on roots (roothairs). They areespecially feeding isa sticky, honeydew substance that coats destructive to seedlings and young pansy plants plantleaves. This honeydew serves asamediumfor that are becoming established. Theirrootfeeding blacksooty mold fungus. The presence of black reduces the plants ability to take-up water and sooty mold fungus and/or aphid cast-skins can nutrients, and creates wounds which serve as an reduce the marketability of a pansy crop. entrysite for fungal pathogens. Larvae can also Aphids are soft-bodied insects that have directly introduce fungal pathogens such as tubes (cornicles) on the end of their abdomens. pythium root rot and black root rot. Fungus gnat Females can give birth to live young. Theyoung adults are generally considered a nuisance, but females produced can then produce their own they have been implicated in transmitting fungal youngin 7 to 10days. Females cangive birthto 60 diseases through their fecal droppings or through to 100live youngper dayfor a period of 20 to 30 spores that are attached to their body. days. This ability to quickly reproduce can result Fungusgnatadultsaresmall, slender,mos in tremendous numbers of aphids within a short quito-like black or dark-brown insectsabout 1/8 period of time. Aphid reproduction depends on inch long. Each wing possesses a distinctive "Y" Floriculture Indiana Vol. 12 No.3 Summer 1998 Page 8 shaped vein. They have long legs and antennae anadult. Ageneration can becompleted in 15to that are longer than the head. Adults are weak 20 days. Each female canlaybetween 300 to 500 fliers and are usually found flying over the me eggs where algae is present such as medium sur dium surface orlower leaves. Fungus gnat larvae faces, benches, and floors. Eggs hatch in 2 to 3 are whitish with ashiny black head. It is approxi days. Larvae thatemerge are located under thetop mately 1/4inch long atthe final stage ofdevelop layer of the medium surface where they feed on ment. Thelife cycle consist ofaneggstage, 4larval algae. Thelarval stage lasts approximately 7 to 10 stages, a pupae stage, andanadult. Ageneration days. Pupation occurs in the medium. Adults can be completed in21 to40days. Fungus gnat emerge in 4 to 5 days and liveabout 3 to 4 weeks. adults are highly attracted to fresh medium or Adults move very rapidly on medium and leaf medium that is approximately 2 to 4 weeks old. surfaces. Females deposit eggs in cracks on the medium surface. Eggs hatch in3 to 5 days, giving rise to Western Flower Thrips (WFT) white larvae. Larvae are generally found within Thrips generally attack pansy when the thetop 1inchofthemediumsurface oftenaround plants are in flower. Feeding by WFT causes a theinterior edge ofpots or flats. Larvae feed and scarring of the petals, this is most apparent on develop inabout 2weeks. Pupation occurs inthe darker-colored flowers (white streaks are particu medium. Adults emerge after 4 to7 days. Adults larly noticeable). In addition, deformation of live about 7 to 10 days and females can lay flowers occurs when WFT feeds in flower buds approximately 150 eggs. before they open fully. Western flower thrips aresmall (less than2 Shoreflies mm) insects that have piercing-sucking mouth- Shoreflies are primarily a nuisance pest. parts. Females arethe predominant sex found in Shorefly damage consists of excrement ("fly greenhouses, especially when populations build specks") left on the foliage. Larvae feed onalgae up. Males, which are smaller than females, are and do notnormally injure plants through direct present when populations arelow. The life cycle feeding. However, larvae have the potential to consists of an egg stage, two young stages, two transmit pathogens suchaspythium rootrotand pupal stages, andanadult. Development from egg black root rot. Shoreflies are usually a problem to adult istemperature dependent withoptimum under excessive moist conditions and where algae temperatures between 80 to 85°F. Females canlive is present. from 27to45days andcanlaybetween 150to300 Shoreflyadults looklike house flies. They eggs during theirlifetime. Eggs, which arelaidin are1/8inchlongandareblack incolor. Shoreflies leaves, hatch in two to four days. Young feed on have dark-wings with approximately 5 light-col leaves and flowers for one to two days before ored spots on each wing. Antennae are shorter molting. WFT then pupates in the medium, leaf than the head. They are stronger fliers than litter, or otherprotected place. The pupalstages fungus gnat adults. Larvae areyellowish-brown last approximately six days before adults emerge. with no head capsule. They are 1/4 inch long when mature. Shorefly has a life cycle consisting Caterpillars ofanegg stage, 3 larval stages, a pupae stage, and Caterpillars arethelarvae (young) ofmoths Floriculture Indiana Vol. 12 No. 3 Summer 1998 Page 9

(adults). They can invade greenhouses causing phytotoxic to pansies. Iffeasible, test materials on considerable damage to pansies. Generally, adults several plants before exposing theentire crop toan migrate intogreenhouses through vents, sidewalls insecticide. Be sureto cover both upperand lower or doors when left open. Theadults lay eggs on plant surfaces in order to get maximum control plant foliage. These eggs hatch into the typical with "worm" stage. They are usually noticed in this foliar-applied insecticides. For more information "worm" stage. Caterpillars can do considerable oninsecticides registered forbedding plants, which damage in a short periodof timeifleftunchecked may include pansies, consult theextension publica byfeeding on the foliage. Common caterpillars tion ID-218 Spring Greenhouse Bedding Plant thatare found in greenhouses are beet armyworm, Insect/Mite and Disease Management. black cutworm, andvariegated cutworm. 3. BIOLOGICAL Management Strategies Parasites {fiphidius colemani ), predators 1. CULTURAL (Green Lacewing), beneficial nematodes (Nemasys®), and beneficial fungi (Naturalis-O®/ A. Sanitation Botaniguard®) may be used on pansies to control Remove allplantandmediumdebris from various insect pests. However, biological controls the greenhouse and place it far away from the must be applied early enough before pestpopula greenhouse interiorand exterior. These are places tions getoutofhand. It isbest tocontactextension were fungus gnatadults canlayeggs andWFTcan or university personnel on the proper procedures pupate. Eliminate weeds inside the greenhouse for effective use of biological controls. Order and aroundthe perimeter. Weeds serve as refuge biological controls from a reliable supplier and for pests to hide. Reduce algae inside the green check before releasing to besurewhatyourelease is house. Algae serves as a breeding sitefor fungus alive. Biological controls arecompatible withmost gnatsand shore flies. biorational insecticides suchasinsect growth regu lators, neemproducts, and Bacillus thuringiensis. B. Plant Culture Avoid overwatering and underwatering 4. SCOUTING plants as stressed plants are more susceptible to insects. Do not over-fertilize plants, especially Scouting consists of looking at plants or withexcess nitrogen asthisresults insoftsucculent yellowstickytraps onaregular basis forthepresence growth thatishighly susceptible toinsects. Excess of insect pests. Place yellow sticky traps approxi moisture fromoverwatering cancreate conditions mately 2 per 1000 fA Place the traps approxi for algae growth. As mentioned above, fungus mately 1inchabove the cropcanopy. Checksticky gnats and shore flies breedin algae. traps weekly. Besure to replace trapsat least every twoweeks. Usea 1OX hand-lensto identifyinsects 2. CHEMICAL on sticky traps. Visually inspect plants for the presence ofnon-winged insect pests suchas aphids Read the label to make sure pansies (i. e. and immature WFT. bedding plants) arelisted as some materials can be