Zac asks: My beets seem to be growing well, but when I harvest them some of the beet roots have knots or nodules on them which I suspect are root knot nematode damage. What can I do to get rid of the nematodes?
Tropical Gardener Answer: Sadly, these microscopic critters are in a lot of soil and gardens in Kona. They do cause unsightly damage to root crops and often bring about severe plant distress. There are several things you can try short of replacing the soil, which is not advised and might not even work.
The worms in the species Meloidogyne attack a variety of plants including beets and carrots. They are especially harmful to root crops as their knots make the crop unsaleable. The nematode knots are actually part of the root and are not easy to remove.
Root-knot nematodes usually attack plants that are stressed. The dry conditions we have had recently are probably stressing your plants and encouraging the nematode attacks. Keeping your soil and plants very healthy and adequately irrigated can help prevent these attacks.
The incorporation of manure or compost into the soil as well as regular mulching on top can increase microbial activity which will help reduce the nematode population.
A practice called solarization has shown some success with nematode suppression. If your garden is in full sun, you can try covering the moist soil with clear plastic for a month or more during the hottest time of year. This may be summer unless you are at upper elevations where cloud cover will hamper the operation. Maintaining high soil temperatures between 125° and 130° for about 30 minutes a day for between four and six weeks can kill the nematodes.
Planting nematode suppressive plants like sunn hemp (crotalaria) or certain marigolds including Tagetes species and French marigold varieties (Nemagold, Petite Blanc, Queen Sophia and Tangerine) can be effective. You should plant them for a season then till them into the soil. You can also interplant marigolds in small gardens to some effect. A UC publication at http://ipm.ucanr.edu/PMG/PESTNOTES/pn7489.html is very informative and might offer some other helpful suggestions.
The chitin in products like crab shell meal can also reduce the number of nematodes in the soil. Pleasant Valley Farm Supply in California sells crab shell meal at groworganic.com. They also sell a liquid called Monterey Nematode Control. Check it out to see if it will work against root knot nematodes.
I have an anecdotal report from a gardener who used a steamer on soil against nematodes and found it worked. The soil temperature must reach 130° down at least 6 inches for best effect.
Currently a nematode resistant beet has not been developed though some corporations are working to produce a genetically modified one, if that’s any solace.
Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.
Gardening Events
Wednesday: “Papaya Crop Insurance Listening Session” from 9 to 10 a.m. USDA is seeking feedback on crop insurance program for papayas. The conference call number is 888-844-9904 and Access Code 8604877. For more information contact Risk Management Specialist, Kale Horton at 816- 823-2883 or email kale.horton@rma.usda.gov.
Friday &Saturday: “Maona Community Market” from 9 a.m. to 8 p.m. both days at 84-5097 Keala o Keawe Road off Route #160 (Puuhonua o Honaunau Road) on the left just before Painted Church Road (on the right). Check it out on Facebook at https://www.facebook.com/maonacommunitygarden/.
More information by contacting maonacommunitygarden@gmail.com or Bridget and Leisha at 808-430-8568 or 808-989-4780 or Chantal: 808-937-9800.
“Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.
Farmer Direct Markets
Wednesday: “Sunset Farmers Market” 2 p.m. to sunset at the north makai corner of the Kmart parking lot.
Wednesday &Friday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay
Friday: “Pure Kona Market” 9 a.m. to 5 p.m. at Amy Greenwell Garden in Captain Cook
Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center
“Kamuela Farmer’s Market” from 7 a.m. to noon at Pukalani Stables
Sunday: “Pure Kona Green Market” 9 a.m. – 2 p.m. at Amy Greenwell Garden in Captain Cook
Tuesday–Saturday: “U-Pick greens and produce” 10 a.m. to 4 p.m. Tropical Edibles Nursery, Captain Cook.
Plant Advice Lines
Anytime: konamg@ctahr.hawaii.edu
Tuesdays &Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892
Mon., Tues. &Fri: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu