Many tropical plants are in homes, interiorscapes, zoos and aquariums with people and animals continually present. Biological controls are increasingly popular in these spaces as using beneficial insects reduces the use of pesticides in the environment.
Always inspect new plants and cuttings and consider placing all incoming plant material in quarantine for a short time to watch for any developing pest or disease issues. Pests may be present in soil, so treat accordingly.
Start your biocontrol program by identifying all current pest problems, as well as potential pests that commonly occur. Establish a scouting program with yellow sticky traps as well as visual inspection to monitor pest pressure weekly. Keep records of this information, which pests are present, when did the infestations occur, and on which crops they were found. Many biocontrol agents work best preventatively. Plan a budget for your biocontrol program and commit.
Following is a list of the common pests on tropical plants and their biological control agents.
Mealybug and Scale
Mealybugs
The most common species of mealybug on tropicals is citrus mealybug. Other species that may occur are long-tailed, obscure, citrophilus, grape and ground or root mealybug. They damage plants by sucking the sap and their feeding causes distortions, stunting and yellowing of foliage. They also produce honeydew, which supports the growth of unsightly sooty molds on leaves and attracts ants. It’s important to control ants as they will attack beneficial insects to protect their food source.
Soft and Armored Scales
Black scale, hemispherical scale, brown scale and nigra scale are soft scale (Coccidae) that attack many foliage plants. California red scale and purple scale are examples of common armored scales (Diaspidae). Some biological controls only attack certain species of scale, therefore correct identification is essential.
Biological Control Agents for Mealybug and Scale
Aphytis melinus is a parasite of hard scale. It will attack California red scale, San Jose scale, ivy scale and oystershell scale. Females lay their eggs under the immature scale and can lay over 100 eggs during her two-week lifespan.
Rhyzobius are ladybird beetles that resemble Cryptolaemus, although smaller. They are used for soft and hard scale. Adults and older larvae feed on all scale life stages. Adult females live for two months.
Adalia bipunctata, the two-spotted lady beetle, is a generalist predator that feeds on most soft bodied insects including scale and mealybug. Adults live for two to three months.
Chrysoperla rufilabris, the green lacewing, is a generalist predator. The larvae feed on all types of soft bodied pests and persist for two to three weeks. Also known as ‘aphid lions’ lacewing larvae voraciously attack their prey by seizing them with large, sucking jaws and inject paralyzing venom. The hollow jaws then draw out the body fluids of the pest.
Micromus variegatus, the brown lacewing, is also a generalist predator, but both the larval and adult forms aggressively eat pests. The nocturnal Micromus is active at temperatures down to 39F making it ideal for cool season pest control.
Cryptolaemus montrouzieri, also known as the mealybug destroyer, is a generalist predator. They are most effective when mealybug numbers are high and when conditions are warm and humid. They are most active in sunlight and are not as effective during darker winter months.
Other Measures to control scale and mealybug
Prune out and destroy severely infested branches before releasing biological controls. Mist plants with water to remove honeydew. Spray infested plants with insecticidal soap to reduce pest numbers before releasing biological controls. Soap is most effective on the crawler stage of scales.
Spider Mites
Two-spotted mites, Tetranychus urticae, are the most common mites on ornamentals. Spider mites are often a problem in very warm and dry areas, such as during the summer and at the top of tall plants nearest the glass in a greenhouse. Their feeding causes white stippling on the leaves, and in severe infestations the leaves turn yellow and die. Webbing indicates a spider mite infestation.
Biological Control Agents for Spider Mites
Phytoseiulus persimilis is a specialist predator for two-spotted spider mites. Introduce Persimilis at the first sign of spider mite damage, in all infested areas. Distribute them on middle and upper foliage, in early morning. Monitor progress by inspecting new growth weekly to determine whether spider mite damage continues to occur.
Galendromus occidentalis are more effective predator of citrus red mite than Persimilis and can also be used to control two-spotted spider mites. They do well under high or low temperatures and are more effective than Persimilis in tree top foliage and on hairy leaves. They feed primarily on spider mite nymphs and adults, but not on eggs and will feed on pollen if mite populations are low.
Amblyseius californicus and Amblyseius fallacis persist better that other species as they also feed on pollen and a variety of small insects and mites, helping them persist over a longer period. Californicus does well in extremely hot conditions and fallacis can reproduce at lower temperatures than other predatory mites.
Other Measures for Spider Mite Control
Mist plants frequently to raise humidity, but do not hose down the foliage, which would dislodge predators. This slows the feeding and reproduction of spider mites making conditions more favorable for predatory mites.
Thrips
Several species of thrips cause problems in tropicals, including western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci), echinothrips (Echinothrips americanus) and Thrips parvispinus. Thrips damage leaves and flowers by sucking the cell contents, leaving a silvery, stippled and distorted appearance. Western flower thrips can also transmit Tomato Spotted Wilt Virus, which kills some ornamentals. Pesticide resistant strains of this species are common.
Biological Control Agents for Thrips
The following three species of biological controls are compatible and can be used together.
Stratiolaelaps scimitus is a soil-dwelling mite that feeds on the immature stages of thrips in the soil or growing media. Strats alone cannot control thrips infestations, but it contributes to the effectiveness of biological control when used with other predators. They will also feed on fungus gnat larvae, springtails and root mealybug.
Amblyseius cucumeris feeds on immature stages of thrips as well as pollen. Cucumeris is available in a loose bran carrier, which is sprinkled onto leaves, and in slow-release sachets which are hung on plants. Release predators at the first sign of thrips, or, ideally, before thrips are present on susceptible plants. Establishment of cucumeris takes 4-8 weeks, so start before thrips problems occur.
Orius insidiosus, the minute pirate bug, feeds on all stages of thrips. Orius is most effective from March to September because they do not reproduce if day length is less than 16 hours. Supplemental lighting can remedy this. Release at least 500 Orius at one time and use banker plants like ‘Purple Flash’ peppers to establish a breeding population.
Aphids
Green peach aphid, Myzus persicae can be a serious problem on tropicals. Foxglove aphid, Aulacorthum solani, and potato aphid Macrosiphum euphorbiae, may also occur. Aphids reproduce quickly on favored host plants causing distorted foliage. They also produce honeydew, which coats leaves and allows sooty molds to grow and attracts ants.
Biological Control Agents for Aphids
All three biological control agents listed below can be used together for long term control.
Aphidius spp. are a group of native parasitic wasps used to control aphids. They are outstanding searchers and can locate new aphid colonies even when aphid populations are low. After the females lay an egg in an aphid, the aphid becomes a swollen brown ‘aphid mummy’ and a new wasp hatches out.
Aphidoletes aphidimyza, the aphid midge, is a predator of over 60 species of aphids. The adult female midges lay their eggs near aphid colonies and the resulting orange larvae attack aphids. Use preventatively before aphids appear.
Chrysoperla, Micromus and Adalia are also aphid predators. See above.
Other Measures for Aphid Control
Prune out heavily infested branches, wash aphids off plants with a strong spray of water or apply insecticidal soap sprays before releasing biological controls. Control ants, which may be protecting aphid colonies from predators.
Whitefly
The most common whitefly on tropicals is greenhouse whitefly (Trialeurodes vaporariorum). The feeding of immature whiteflies drops sticky honeydew onto foliage below, which become covered with unsightly sooty mold, reducing the vigor of plants.
Monitoring Tips
Use yellow sticky traps to monitor for whiteflies. Plants highly attractive to whitefly, such as Lantana, Jerusalem cherry or Fuchsia can be used as indicator plants to detect early infestations of whitefly.
Biologicial Control for Whitefly
The biological controls listed below are compatible and can be used together.
Encarsia formosa is a tiny wasp that parasitizes immature stages of whitefly. As the wasp develops, the greenhouse whitefly scales gradually turn black. Encarsia are less effective during cool weather and overcast periods and short winter days.
Delphastus catalinae is a small, black, lady beetle. Both adults and larvae feed on whitefly eggs and immature stages. Delphastus is sold as adults and should be applied as soon as whitefly are detected. Delphastus works well with Encarsia because it avoids feeding on parasitized whitefly scale.
Other Measures for Whitefly Control
Start with a clean crop. Keep growing area weed free. Use yellow sticky cards to trap and monitor whitefly. If adults whiteflies populations are over 10/leaf, spot spray affected areas with insecticidal soap.
Black Vine Weevil
Black vine weevils are dark brownish gray, 1/3 inch long “snout beetles”. They are all females and cannot fly. The adults are active at night; they chew half-circle notches in the edges of leaves of various ornamentals. The larvae feed in the roots of rhododendron, azalea, yew and other ornamentals and can stunt or kill plants. Check leaves for signs of new notches from May onward, which indicates adults are present and will soon begin laying eggs.
Biological Control Agents for Black Vine Weevil
Entomopathogenic nematodes are very effective at controlling root weevil larvae in plantscape conditions. They must be applied after the eggs have hatched and larvae are present in the soil, usually from July onward. Three soil drenches of nematodes mixed in water, 7-10 days apart, are usually required. Nematode products vary, so always follow product recommendations for rates.
Other Measures for Black Vine Weevil Control
At night when adults come out to feed, knock them off plants onto sheets where they can be collected and destroyed. Apply a sticky substance like Tanglefoot Insect Barrier around the circumference of the trunk to stop beetles from reaching the foliage.
Content Courtesy of Applied Bio-nomics Ltd
