Know your enemies

The increased cost of food and concerns for food-borne diseases has fueled gardeners demand for vegetable bedding plants. Growers need to produce high quality pest-free vegetable transplants to meet this increased demand.
 

Start clean, stay clean

Pest management of vegetable bedding plants begins with a clean, weed-free, disinfected greenhouse. Grow transplants off the ground in a well-ventilated house. Avoid overfertilizing transplants, especially with nitrogen-based fertilizers to prevent lush growth that is more susceptible to aphids, whiteflies and spider mites.

If feasible, use separate houses for vegetable seedlings and ornamental bedding plants. Advantages to operating separate houses include:

• Vegetable seedlings are protected from any pests that may migrate from ornamentals and plants that are held over.
• Vegetable seedlings are protected from tospoviruses and cucurbit seedlings are protected from powdery mildew-infected verbena.
• It is easier to treat the vegetable seedlings if pesticides are needed.
   

Early problem detection

Regular, weekly scouting helps to detect problems early. This early detection and treatment result in better pest control since plant canopies are smaller and better spray coverage can be achieved.

Use yellow sticky cards to trap and detect adult stages of fungus gnats, thrips and whiteflies. Inspect and replace the cards weekly to keep track of population trends. Focus on scouting indicator plants, which are those plants or cultivars that have serious, persistent pest problems every year. Examine the undersides of leaves for insect and mite pests and inspect root systems to determine whether they are healthy.

Some common arthropod pests on vegetable bedding plants include aphids, broad mites, fungus gnats, shore flies, spider mites, thrips, and whiteflies.
 

Biological controls

Vegetable bedding plants with only one or two key insect pests, or with a longer production schedule are potential candidates for biological controls. Purchase natural enemies from a reliable biological control supplier. This will ensure a consistent supply of viable, high- quality natural enemies that are shipped in a timely manner. Obtain specific directions from biological control suppliers on proper release rates and timing.

For information on the compatibility of pesticides and natural enemies, consult the online databases of Koppert (www.koppert.com) or Biobest (www.biobest.be). Check under “Side Effects.” Biobest also has a side effects mobile app.
 

Aphids

Green peach, melon, and foxglove aphids may occur on vegetable transplants. Large numbers of aphids will stunt and deform plants. Foxglove aphids cause significant leaf distortion.

Examine the foliage, along stems and new growth of peppers, tomatoes, eggplants, cole crops, and leafy greens. Signs of aphid activity include shed white skins, shiny honeydew, curled new leaves, distorted growth and the presence of ants.

Yellow sticky cards help detect the entrance of winged aphids into greenhouses from outdoors. Yellow cards will not, however, allow you to monitor aphids within the crop, as most aphids are wingless.

Controls: Insecticides labeled for aphids include acetamiprid, azadirachtin, azadirachtin and pyrethrins, Beauveria bassiana, dinotefuran, horticultural oil, insecticidal soap, Isaria fumosorosea, pyrethrins, and spirotetramat.

Predatory midges (Aphidoletes aphidimyza), parasitic wasps, ladybird beetles and lacewings (Chrysoperla spp.) are commercially available as biological control agents. Aphid parasitoids are selective in which aphid species they attack, so proper aphid identification is important. Some suppliers offer a mix of different parasitoid species.

Aphid banker plants are used to support a healthy beneficial population of Aphidius colemani. Banker plants are also available from several biological control suppliers.
 

Fungus gnats

The damp, moist greenhouse environment favors fungus gnats. Young seedlings and transplants are vulnerable, especially when overwatered. Adult flies can be monitored with yellow sticky cards placed close to the growing medium surface. Fungus gnat larvae can be monitored by placing potato discs on the growing medium surface. After two days, inspect the medium under the potato and the potato disc for the black headed larvae.

Controls: Treatments are best directed against the damaging larvae. Some options include acetamiprid, azadirachtin, azadirachtin and pyrethrins, Bacillus thuringiensis subsp. israelensis, and pyriproxyfen.

Soil dwelling predatory mites (Hypoaspis (Stratiolaelaps) miles), entomopathogenic nematodes (Steinernema feltiae) and rove beetles (Atheta (Dalotia) coriaria) are commercially available natural enemies. In unsprayed greenhouses, the parasitoid Syncara pauperi may occur. More greenhouse growers are also seeing more hunter flies (Coenosia attenuata) that prey upon fungus gnats and shoreflies.
 

Shore flies

Adult shore flies are often confused with fungus gnats and hunter flies. Shore fly adults are often seen resting on leaf surfaces. Their fecal spots or droppings can also be unsightly. Shore flies do not directly injure plants, but can carry root rot pathogens from diseased to healthy plants.

Controls:  Shore flies are best managed by controlling algae, their food source. Commercially available natural enemies include: Steinernema carpocapsae (Millenium), Hypoaspis (Stratiolaelaps) miles, and Atheta (Dalotia) coriaria.
 

Whiteflies

Sweet potato and greenhouse whiteflies may occasionally occur on vegetable bedding plants such as tomato, eggplant, and pepper. Look on the undersides of one or two leaves per plant for immature stages and adults. Yellow sticky traps can be used to detect adult whiteflies once populations have reached higher densities.

Controls: Some insecticides labeled for whiteflies include acetamiprid, azadirachtin, azadirachtin, and pyrethrins, Beauveria bassiana, buprofezin, dinotefuran, horticultural oil, insecticidal soap, Isaria fumosorosea, pyrethrins, pyriproxyfen, and spirotetramat.

Whitefly parasitoids (Encarsia sp. for greenhouse whitefly and Eretmocerus sp. for sweet potato whitefly), predatory mites (Amblyseius swirksii) and the predatory beetle, Delphastus catalinae are commercially available natural enemies.
 

Thrips

As thrips feed with their rasping mouthparts, white streaks will be seen on the expanded leaves. Infested new growth may curl under and leaves are often deformed. Yellow or blue sticky cards and indicator plants provide easy ways for detecting the onset of an infestation.

Eggplant, tomatoes and peppers are especially prone to thrips infestations. Many common greenhouse weeds harbor both thrips and tospoviruses. If tospovirus-infected western flower thrips feed on tomatoes and peppers, these virus-infected plants may suffer from reduced yields in the garden.

Controls: Some insecticides labeled for thrips include: azadirachtin, Beauveria bassiana, chlorfenapyr, dinotefuran, horticultural oil, insecticidal soap, Isaria fumosorosea, and pyrethrins.

Predatory mites (Hypoaspis (Stratiolaelaps) miles, Amblyseius cucumeris, Amblyseius swirsksii), Amblydromalus limonicus, and predatory bugs (Orius sp.) are commercially available natural enemies.

Entomopathogenic nematodes (Steinernema feltiae) may also be used against thrips pupae in the soil and immature thrips on the foliage.
 

Spider mites

As spider mites feed, leaves become stippled or mottled as chlorophyll is removed. Spider mites often develop as localized infestations on beans, tomatoes and eggplants. Turn over the leaves, and with a hand lens, check for the presence of spider mites.

Controls: Some miticides labeled for spider mites include bifenazate, chlorfenapyr, horticultural oil and insecticidal soap.

Predatory mites (Phytoseiulus persimilis, Amblyseius californicus, Amblyseius andersonii and others) and predatory gall midges (Feltiella acarisuga) are commercially available natural enemies.
 

Broad mites

Broad mites are closely related to cyclamen mites. They can be distinguished from cyclamen mites by their eggs, which are covered with “bumps” that look like a row of diamonds.

Adults and larvae walk rapidly on the underside of leaves.

Broad mites can also attach themselves to whiteflies and use the whiteflies as a carrier for their dispersal. With a 20x hand lens, inspect the underside of the leaves for the broad mites and their eggs. And they migrate to peppers or tomatoes from, infested ornamental crops. As they feed, broad mites inject toxic saliva, which results in twisted, distorted growth. Leaf edges often curl downward or terminal buds may be killed. Do not confuse broad mite injury with herbicide injury, nutritional (boron) deficiencies or physiological disorders.

Controls: Insecticidal soap and chlorfenapyr. Discard heavily infested plants. Predatory mites (Amblyseius cucumeris and Amblyseius californicus.)
 

Before you apply controls

Remember that the product and label uses must be approved for your state or region. Follow the label directions. Try new materials on a small scale before widespread use.

Information in this article is for educational purposes and does not constitute endorsement of products or criticism of products not mentioned. Consult with your local extension specialist and growers.

Pundt is an extension educator at the University of Connecticut and a frequent contributor to Produce Grower. Have a question? You can reach her at leanne.pundt@uconn.edu.

All Photos Courtesy Of Leanne Pundt