Marigolds and Insect Pest Management
Marigolds tolerate the heat and alkaline soils, but come in many shapes, colors, and heights. Shapes range from single to frilled to massive round balls. Colors include yellow, gold, orange, ivory, mahogany,and bicolor combinations. Heights range from 6 to 36 inches. With this kind of variability, you can hardly go wrong with marigolds.
The African marigold (Tagetes erecta) is the tallest variety and has the pompom type flowers. Now, there are also shorter varieties of African marigolds available. French marigolds (Tagetes patula) are shorter and bushier usually reaching a height of 6 to 12 inches. Signet or dwarf marigolds (Tagetes tenuifolia) have small (1/2 inch) blooms and lacy, fragrant foliage. All marigolds do best in full sun and require a minimum of six hours of direct sunlight. Prepare soil as you would for a vegetable crop by adding composted organic matter, a little phosphorus, and some soil sulfur if you have highly alkaline soil. Nitrogen should be applied sparingly. Too much nitrogen will produce lots of foliage and few flowers. They can be grown easily from seed or nursery transplants. Do not over water marigolds and allow the soil to dry somewhat between watering. Seeds can easily be collected and planted in the following year.
Marigolds are relatively pest free and many people interplant them in their vegetable gardens to deter insect pests. While the data is lacking as to whether marigolds actually deter insect pests, they definitely attract beneficial insects such as lacewings, ladybeetles, and parasitic wasps. A vegetable
garden with some planted flowers is also more attractive and this makes it more enjoyable to work in.
Recent research indicates that marigolds contain compounds toxic to root knot and other plant-parasitic nematodes (microscopic round worms that damage plant roots). Root knot nematodes are not native to our area, but can be brought in with infected plant materials (see the July 7, 1999 Backyard Gardener for more information). The research showed that marigolds, especially certain varieties of French marigolds, significantly reduced root knot nematode populations the following year. Varieties of French marigolds shown to have nematocidal properties are: Bolero, Bonita Mixed, Goldie, Gypsy Sunshine, Petite, Petite Harmony, Petite Gold, Scarlet Sophie, Single Gold,
and Tangerine. If you would like to try using marigolds to manage root knot nematodes, here
are some recommendations:
At the end of the growing season, remove as many roots as possible from the soil by pulling, plowing or tilling. Doing so will reduce the number of safe places where nematodes can survive during the winter.
In winter, till the soil several times to expose nematodes to the sun and weather. You may also want to solarize your soil (see the May 21, 2003 Backyard Gardener).
In spring, plant half of the garden with marigolds and half with root-knotresistant vegetable cultivars (a few are available – look for the “N” on the label). Plantings in blocks or strips are easy to manage. Strips may comprise one or several rows of vegetables. You will need about 300 marigold plants per 100 sq. ft.
Use a marigold variety listed above.
Space marigold plants, or thin seedlings, so they are 7 inches apart.
Fertilize as needed or according to soil test recommendations. Nutrien imbalances can make nematode problems worse.
Keep weeds under control.
Before the first frost, remove as many seed-bearing flower heads as possible. Then, you will have seed for next year's marigold patches, and fewer volunteer marigolds will sprout among your vegetables.
Till the remaining marigolds into the soil.
The following spring, repeat the process with this exception: plant marigolds where you planted vegetables the previous year and vice versa. Enjoy those marigolds! The University of Arizona Cooperative Extension has publications and information on gardening and pest management. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. Gardeners prize marigolds (Tagetes spp.) for their easy-to-grow nature and the bright colors they add to a sunny garden. This plant's hardy nature makes it perfect for numerous landscape settings, such as in a container or as a border plant, throughout U.S. Department of Agriculture plant hardiness zones 1-10. While marigolds are typically pest-free and not bothered by most insects, occasional problems may arise with a few common garden pests. Sponsored Link Aphids Organic Control Organic Control for Aphids to avoid Aphids from Farms, Fields & Gardens ozonebiotech.com/Bug-Buster Aphids Aphids come in many colors, such as green, red or yellow, and feed on the marigold plant's stems and leaves. Except in severe cases, aphids will typically not kill a mature marigold but will simply cause leaf curling and other aesthetic problems. Shooting your affected marigolds with a strong blast of water from a garden hose is often enough to dislodge and control this pest. In more serious cases, spraying the aphids with neem oil or insecticidal soap will kill the pests on contact.
Earwigs
Earwigs are reddish-brown pests that measure approximately 3/4 inch long and sometimes feed on the leaves of marigolds in the evenings. Simply removing common hiding spots, such as fallen plant debris, yard rubbish and weeds, will often fix this problem. Otherwise, trapping can control this pest. Pour 1/2 inch of vegetable oil into the bottom of a small container, such as a rinsed-out tuna fish can, and bury the can next to your marigolds so that the lip of the can is level with the surrounding soil. The oil will attract the earwigs, and the bugs will fall into the oil and die. No Matches Found. Please try your search again.
Caterpillars
The larvae of some butterflies and moths will occasionally feed on the foliage of your marigolds. Keeping your garden weed-free will generally suffice in fixing this issue, since weeds are one of the most common hosts for caterpillars. Otherwise, pick the caterpillars off of your marigolds by hand and drop them into soapy water to kill them.
Leafminers
Leafminers look like little black-and-yellow flies. They sometimes lay eggs in your marigold's leaves. The resulting larvae then "mine" through the foliage, leaving little lines in the leaf tissue. Keeping your marigolds well-watered is generally enough to prevent this problem since leafminers tend to target weakened, drought-stressed plants. If you notice the telltale signs of leafminer activity, cut off the infected foliage and discard them. Snails and Slugs
Snails and slugs may attack low-hanging sections of your marigolds, or young marigold seedlings or transplants. Eliminating slug and snail hiding spots, such as surface debris, can manage this pest. Picking the pests by hand and dropping them into a solution made of one part household ammonia and nine parts water will also effectively kill them.
Spider Mites
Spider mites are very small and look like tiny orange or black dots that create white webbing on your marigold's foliage. They're generally not problematic, although severe infestations can weaken or kill a young or stressed marigold plant. Since this insect is drawn to drought-stressed plants, keeping your marigolds well-watered will often control the problem sufficiently. Otherwise, spray the affected parts of your marigold with any insecticidal soap.
Thrips
Thrips are small, flying insects that suck the sap out of a marigold's leaves. Healthy plants tend to tolerate an average thrip attack. If your marigold is succumbing to the infestation, hang a blue sticky trap -- available in most garden stores and nurseries -- on one of your marigold's branches. Thrips are attracted to this color and will get stuck and die. Replace the sticky trap once its surface is covered with insects.
Whiteflies
Whiteflies feed on the sap in a marigold's leaves and stems and are most common during warm weather. Pruning off leaves that are covered in whiteflies will generally keep this pest's population at levels too low to cause lasting damage. Alternatively, use a hand-held vacuum to suck the flies off of the leaves. For the best results, attack this problem in the early morning or late evening, when the insects are slower.
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