Root-knot Nematodes: Biocontrol with French Marigold
Root-knot nematodes (Meloidogyne
spp.) can be effectively managed in home gardens without pesticides. One
alternative to using nematicides is to intercrop and rotate vegetables with
marigolds. Most cultivars of African marigold (Tagetes erecta) and French marigold (Tagetes patula) are effective in reducing the most common root-knot populations—Meloidogyne incognita and M. javanica (Table 1).
Table 1. Some marigold cultivars effective against the root-knot nematode Meloidogyne incognita.*
*Ploeg AT. 1999. Greenhouse studies on the effect of marigolds (Tagetes spp.) on four Meloidogyne species. J Nematol 31(1):62-9.
||'Crackerjack' and 'Flor de Muerto'
||'Bonita Mixed,' 'Gypsy Sunshine,' 'Scarlet Sophia,' 'Single Gold,' and 'Tangerine'
The roots of
these attractive flowering plants contain chemicals that kill nematodes.
As a method of biocontrol, growing marigolds is not only pleasing to the
eye but economical and environmentally sound as well. One drawback, however,
is that the benefits are not realized until the following year. Also, the
treatment frequently needs to be repeated with marigolds and vegetables grown
in alternate years.
Be careful when you
buy marigolds to help control nematodes. Not all marigolds sold as bedding
plants are effective against nematodes. Tagetes signata cv. Tangerine Gem, for example, will not control root knot.
To use marigolds to manage root-knot nematodes, follow these steps.
- Collect a soil sample
from the root zone of a living, but apparently unhealthy, plant. Include
roots in the sample. Submit this sample to the Nematode Assay Section of
Agronomic Division to verify that root knot is the problem. It is also a
good idea to send a soil sample to the Soil Testing Section for lime and
- 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.
- Apply lime according to soil test recommendations.
- In spring,
plant half of the garden with marigolds and half with root-knot-resistant
vegetable cultivars. Plantings in blocks or strips are easy to manage (Figure
1). Strips may comprise one or several rows of vegetables. Contact your
county Cooperative Extension agent for Plant Pathology Note 6, which lists
nematode-resistant vegetable varieties. Table 2 indicates the amount of
marigold seeds or plants needed based on area.
- Use a marigold variety known to be Tagetes erecta or T. patula.
- Space marigold plants, or thin seedlings, so they are 7 inches apart (Figure 2).
- Fertilize according to soil test recommendations. Nutrient imbalances can make nematode problems worse.
- Early in the growing season, cultivate between marigolds regularly to keep weeds under control.
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.
- In the
fall before crop residue destruction, take another soil sample for nematode
assay from the marigold area, if you want to monitor effectiveness.
- 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.
Figure 1. Strip-crop arrangement.
Figure 2. Detail of marigold spacing on 7-inch centers.
Table 2. Marigold seed or plant requirements per treatment area.
|Total Area in Marigolds
|100 sq. ft.
||6 packets (~350 seeds)
|1,000 sq. ft.
on nematode problems can be obtained from your county Cooperative Extension
office. Assistance in interpreting the nematode control recommendations can
also be obtained from the NCDA&CS regional agronomist for your area.
For more information about the Agronomic Division and its services, see our
website at www.ncagr.com/agronomi/ or call 919-733-2655.
revised December 2000
NCDA&CS AGRONOMIC DIVISION
Mailing address: 1040 MAIL SERVICE CENTER, RALEIGH NC 27699-1040
Physical address: 4300 REEDY CREEK RD., RALEIGH NC 27607-6465
Phone: (919) 733-2655
Last Updated August 29, 2003