Jerry asks: I have had problems with root knot nematodes in the past. Currently, one of my tomato plants looks like it is dying. Could that be the cause? Is there anything I can do to save the plant?
Tropical Gardener answer: Once root knot nematodes infect the roots of a plant, not much can be done. It will likely be very weak or die. The only way to do a positive identification of this problem is to inspect the roots. Wet the soil and dig into a small part of the root zone. Look for hard nodules, called galls on the roots. When present they prevent the plant from getting adequate water and nutrition which can be deadly. Sometimes nodules on the roots of nitrogen-fixing plants in the bean family can look similar but if the knots are on your tomato plant, nematodes are probably present.
Nematodes are microscopic, eel-like roundworms that live in the soil and can be beneficial as well as damaging. The most damaging nematode species is the root knot, Meloidogyne species. This species creates galls on the roots for them to develop and feed. They attack a wide range of plants, including vegetables, fruit trees and ornamentals. If they are present you need to avoid spreading them on tools, boots or in the soil of infested plants.
Though difficult to eradicate, several cultural practices can reduce nematode numbers and keep your plants healthy enough to resist their attack. Amending your soil with organic matter will increase its water and nutrient holding ability, improve plant health and reduce the nematode population. Adequately irrigating your plants during dry times can avoid water stress which makes plants vulnerable to nematode attack.
One of the best control mechanisms for home gardeners to reduce nematode problems is to plant nematode suppressing species. African marigolds (Tagetes erecta) and French marigolds (T. patula including “Nemagold,” “Queen Sophia,” “Petite Harmony,” “Gold” and “Blanc” varieties) release a substance that deters nematodes and other disease promoting organisms. Avoid “Tangerine Gem” and “Signet” marigolds, T. signata or T. tenuifolia, which can host nematodes. The UH publication at http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-35.pdf has more on this.
Crotalaria or “Sunn hemp” can also help reduce nematode damage while fixing nitrogen in the soil. See the UH publication at http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-32.pdf for more on using crotalaria as a deterrent.
Solarizing is another effective way to reduce nematode populations in the upper layer of soil, though not always practical in small gardens. This technique is described in many publications and videos online. One site: http://homeguides.sfgate.com/kill-nematodes-soil-49404.html describes solarization as well as other techniques for killing these nematodes. Check it out.
Some questions that appear here were originally directed to Kona’s Certified Master Gardeners. You may contact them with questions at konamg@ctahr.hawaii.edu.
Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.
Gardening events
Tuesday: “Community Seed Library Round Table” at 5 p.m. at the Kailua-Kona Public Library with Nancy Redfeather. Discussion will include: invasive species, planting the right plants at the right time in the right place and more. Bring gardening questions and seed donations. Info: Natalie at nehamah47@gmail.com.
Wednesday: “Grafting Talk Story” from 1 to 2:30 p.m. at the UH Cooperative Extension office in Kainaliu with Joe Sabol answering grafting questions.
“Grafting Workshop” from 4:30 to 6:30 p.m. at the UH Cooperative Extension office in Kainaliu with Joe Sabol. Hands on grafting lesson. $10 fee includes all supplies. Registration required at http://hawaiicoffee.weebly.com/grafting-workshop.html.
Farmer direct markets
Wednesday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at the Sheraton Kona Resort & Spa at Keauhou Bay
Wednesday: “Sunset Farmers Market” 2 p.m. to sunset at the north makai corner of the Kmart parking lot.
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: “South Kona Green Market” 9 a.m. to 2 p.m. at Amy Greenwell Garden in Captain Cook
Monday–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
Thursday: 9 a.m. to noon at UH-CES in Kainaliu – 322-4892
Monday, Tuesday and Friday: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu