In the latest issue of the Organic Growers School newsletter, you recommend planting flowers to attract parasitic wasps and flies for the control of harlequin bugs. Can you offer any advice on what the maximum effective distance should be between your flowers and your crops?
First a comment about harlequin bugs; from personal experience …these are bad guys with a capital “B”. I would not count on a few flowers to keep them in check, but would be very proactive as soon as I spotted even one. Meanwhile, you can plant flowers that attract beneficial insects as part of a holistic approach to gardening ~ that may eventually make headway with the harlequin bugs. ATTRA advises imagining your beneficials are a mini-livestock “herd” that you build on every year.
Texas A & M defines beneficial insects as “any insect that has a life style that is advantageous to [humans]. Insects that preserve the balance of nature by feeding on others, pollinators, and recyclers are examples of beneficial insects.” Today we will focus on beneficial insects that feed on or disrupt the life cycle of “bad bugs”. The subject of pollinators, recyclers, and other beneficials (like bats) may be addressed in a future column, however it is important to note that many of the same plants that attract and nourish beneficial insects, will also attract butterflies and bees. Generally we are hoping that the good guys (ladybugs, parasitic wasps, ground beetles, syrphid flies, lacewings, predatory bugs and wasps, tachinid flies, etc) will eat, parasitize, or otherwise out-compete the bad guys (the bugs eating our crops).
Let’s explore why flowers are useful to benefical insects … ideally, beneficials want lots of the food that they like, and they want it easy to find and in a predictable location. Flower nectar provides just that! Nectar provides insects with sugar and the energy to look for prey, to mate, and to lay eggs. In addition to nectar, the protein and fat in pollen aids in egg development, and flowers provide a site where insects can locate mates. Extrafloral nectaries (these are nectar-producing glands on the plant that are physically apart from the flower) are also an important supplemental food source that contains about 95% sugar. Well-fed beneficials produce exponentially more eggs…which means much larger populations of upcoming good guys.
Mike, I would locate the flowering plants as close as possible (and practical) to the crop you want to protect with beneficial insects, but within at least 200 ft. Make it easy for the beneficials to find and eat the pest.
A few options include ~ planting your beneficial-attracting plants in your actual garden beds, in a hedgerow along the border of your garden, in rows adjacent to your crops, or in clumps dispersed around your garden area. If you have a 1000 sq. ft. garden, plant about 50 -100 sq. ft. (or 5-10% of your garden or neighboring area) with plants that attract beneficials. You can “gardenscape” with annuals, cover crops, perennials and trees, or a mixture of these. The layout and scale of your garden, and your personal gardening style, will be the determining factors. For instance, if you till the entire garden annually, perennial plantings are impractical within the main garden.
Utilize flowers that the beneficial insects you hope to attract & retain are known to enjoy. Local entomologist, Dr, Richard McDonald says “Plant it and they will come!” Set the table, and invite them to sit down and have dinner.
Consider whether the flower structure of the plant is easily accessible to the beneficial in question. For instance, tiny parasitic wasps have short mouthparts, so they prefer to obtain nectar from small, shallow flowers such as those in the parsley (umbrel) and sunflower families. The ATTRA link below is an excellent resource for determining which good bugs eat which bad bugs, and the flowers that they prefer.
Year-round plantings are considered ideal. The objective is to have plenty of flowers blooming all season that will attract and nourish beneficial populations and their young – by the time the unwanted insects show up. Remember to plant early and late
blooming flowers to extend your bloom time to cover the entire season. Plant annuals successively, and deadhead both annuals and perennials throughout the season to encourage continual flowering. If you allow periods without blooms, your beneficials may disperse to greener pastures.
Try planting bands of cover crops between your crop rows to attract beneficials. Clovers and vetch will produce nitrogen, as well as attract beneficial insects. Buckwheat can be planted every 2-3 weeks, attracts beneficials, and is loved by the honeybees that pollinate most of our food crops. Grains also attract beneficials. When you mow the cover crop, consider mowing alternate bands of the cover crop, while leaving some strips in place to provide continued habitat for the beneficials. Avoid using a rotary mower when you mow the cover crop, so that you disturb/damage the beneficials as little as possible. Where farmers might mow with a sickle bar, gardeners could try using hand-held hedge shearers, or a weedeater with a blade (rather than strings) and swiping an area only once.
Gardener Jeff Ashton planted both ends of his 12’ raised beds with an 18” band of tansy, yarrow, lovage, and Queen Ann’s lace (all perennials). The predatory wasps were especially attracted to the lovage and the whole affect was very pretty. The planting was kept in bounds by pruning, and Jeff provided auxiliary water for the insects in a cake pan filled with gravel. Richard McDonald (Dr. McBug) has a special fondness for bronze fennel. This tall perennial returns every year reliably, produces yellow umbral flowers that resemble dill flowers, reseeds readily, and is beautiful. It is a host plant for black swallowtail butterflies, and provides excellent habitat for beneficials. Farmer Patryk Battle has experimented with an array of techniques to attract beneficials ~ outdoors and inside his greenhouse. Richard and Pat have both taught classes about beneficials at the Organic Growers School Spring Conference, so keep your ears open for this year’s conference schedule (to be held on March 3-4, 2012).
Beneficial insects can be mail-ordered and released into your garden to target a particular pest. Commercially-produced beneficials should be given a brief adjustment period (30 minutes?) in a cool spot, and released as soon as possible after receipt. When the beneficial insect has eaten most of the targeted pest in your garden, your “gardenscaping” will help retain them for continued pest control in the area. If they have no food nearby, they will have to exit your area in order to survive and reproduce.
FYI ~ Using beneficials inside the greenhouse
is becoming more mainstream every year. In our area alone…Banner Greenhouse, Van Wingerden Greenhouse, and the NC Arboretum use beneficials regularly and pro-actively. They scout for pests at least weekly, and order beneficials accordingly or receive them on a pre-determined schedule. However, they don’t wait until an infestation is out of control, since it takes about a week to receive the beneficials in the mail. Our resident expert, Tom Elmore (Ask Tom) has lots of experience using beneficials in his greenhouse, and hopefully he will share his expertise in a future column.
It seems like a no-brainer, but please realize that any broad spectrum insecticide – even organic ones – that you use on a pest (bad bug) may affect your beneficial insect population (good bugs) simultaneously. Use insecticides with restraint. If you do use them, try the softest approach first ~ such as insecticidal soap, horticultural oils, and botanicals, etc. ~ and strive to target a particular pest with a suitable control (for instance, Bt targets only soft-bodied caterpillars) rather than killing everything with a “big gun” approach. Conventional (NON-organic) sprays are designed to last, so a “one spray” knockdown can keep killing beneficials as well as target species for weeks.
Permanent hedgerows will provide shelter, a windbreak, and nectar & pollen for many beneficials, butterflies, pollinators, and other wildlife. Providing habitat for wildlife in general is an important way every gardener can contribute to re-balancing nature ~ since human-created habitat loss has put pressure on many differing species. It is important to keep in mind that we are talking about a delicate balance here. To help prevent fungal diseases, site any plantings with an eye for air movement around your garden (if the plant harbors beneficials, but stifles air movement you will have a different problem to address). Be observant.
This season, many of us had drought-stressed plants that succumbed more easily to other pressures ~ like insects and diseases. Utilizing beneficial insects will add one more tool to your toolbox, but merely planting some flowers will not replace the need for common sense, on-going attention in the garden. Projects of this nature require the gardener to hone their observational skills, monitor (good and bad) insect population numbers regularly, rotate crops, recognize nutrient deficiencies, and attend to the basics ~ like weeding and watering. In any garden, thinking holistically is always a great idea!
SEASON OF BLOOM for Various Beneficial Insect-attracting Plants:
Alyssum (likes cool weather), Borage, Buckwheat (flowers 3 weeks after planting), Clovers, Coriander/Cilantro (not the slow-bolt varieties), Grains, Lovage, Mustards (wild), Norway Maple, Parsley/Parsnip, Peony, Pussy Willow, Tulip Poplar, Vetch
Bachelor Button, Borage, Buckwheat, Clovers, Coriander /Cilantro(not slow-bolt varieties), Coreopsis, Cosmos, Dill, Lovage, Mints, Yarrow
Black-eyed Susan, Bronze Fennel, Caraway, Coriander /Cilantro (not slow- bolt varieties), Coreopsis, Corn, Cosmos, Dill, Fennel, Jerusalem Artichoke, Kenaf, Mints, Queen Anne’s Lace, Sunflowers, Sweet Potato, Tansy, Yarrow
Black-eyed Susan, Bronze Fennel, Coriander/Cilantro (not slow-bolt varieties), Coreopsis, Cosmos, Dill, Jerusalem Artichoke, Mints, Queen Anne’s Lace, Sunflowers, Tansy, Yarrow
Alyssum (likes cool weather), Bronze Fennel, Buckwheat (blooms until frost), Chrysanthemum, Golden Rod, Queen Anne’s Lace, Sedum ‘Autumn Joy’, Sunflowers
TYPE OF PLANT:
Tulip Poplar, Pussy Willow, Norway Maple
Perennials (comes back every year):
Peony, Yarrow, Mint, Bronze Fennel, Black-eyed Susan, Jeruselum Artichoke, Queen Anne’s Lace, Chrysanthemum, Golden Rod, ‘Autumn Joy’ Sedum, Yarrow, White Clover, Tansy, Lovage
Annuals (replant every year): Alyssum (early & late), Buckwheat, Sunflowers, Dill, Coriander/Cilantro, Bachelor Buttons (reseeds readily), Parsley (bi-annual), Clover, Mustards, Grains, Borage, Cosmos, Caraway, Kenaf, Corn, Sweet Potato (replant many of these about every 3 weeks for maximum continual flower production ~ especially buckwheat, dill, coriander, and sunflowers)
Extrafloral Nectary Plants:
a few of the over 2000 plants….Peony, Sweet Potato, Bachelor Button, Cowpeas, Vetch, Passion Flower Vine, Elderberry, Trumpet vine, Callicarpa, Willow, Black Locust
Good luck Mike!…and see the additional resources below.
Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School
Gardeners: Got a question for Ruth? Email it to us at
ADDITIONAL RESOURCES ~
Sources for Insects:
Organic Growers School Spring Conference Library:
The Good, The Bad, and the Ugly: Attracting Beneficial Insects in the Home Harden (2011), Patryk Battle
ATTRA Farmscaping: (Well worth the price! This document includes: Plants that Attract Beneficials, Pests and Associated Beneficial Insects, and Seed Blends, Plants and Sprays to Attract Beneficial Insects)
Biological Control: A Guide to Natural Enemies of North America
Author: Ruth Gonzalez
Ruth Gonzalez is a former market farmer, gardener, and local food advocate who wants to see organic farms proliferate and organic gardens in every yard. She serves on the Organic Growers School Board of Directors, and in her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.