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How To Stop Dahlia Nematodes – Treating Dahlia Root Knot Nematodes

How To Stop Dahlia Nematodes – Treating Dahlia Root Knot Nematodes


By: Mary H. Dyer, Credentialed Garden Writer

Nematodesare microscopic worms that live in the soil. Most are beneficial,cycling nutrients and helping keep pests in check. Some, including dahlianematodes, are extremely destructive little pests. How do you recognize dahliaroot knot nematode damage? Can root knot nematodes in dahlias be treated orcontrolled? Read on for more information on dahlia nematodes.

Symptoms of Dahlia Root Knot Nematode Damage

The primary symptom of root knot nematodes in dahlias isswelling or galls on the roots. The swellings make tiny, pimple-like bumps aslarge as an inch (2.5 cm.) across. If you aren’t sure, carefully dig the plantand shake off the loose soil to see what you’re dealing with.

Dahlia root knot damage may also include yellowing of theleaves and wilting, especially during hot weather when the plant is waterstressed. Galls on the roots make it difficult for the plant to absorbmoisture.

Preventing and Treating Dahlia Root Knot Nematodes

Dahlia root knot nematodes are difficult to control andthere isn’t much you can do. Professional growers use nematicides,but the chemicals haven’t been approved for home gardens. You may need to startover with new dahlias in an unaffected area of your garden. Be sure to look fornematode-resistant varieties.

You can also take these preventative measures in the gardenwhen plantingdahlias:

  • Add a generous amount of manure, compost or other organic material to the soil, especially if your soil is sandy. This won’t get rid of dahlia nematodes, but it will give the plants a fighting chance by getting more moisture to the roots.
  • Grow marigolds as a group throughout the summer. Most marigold varieties are known for controlling dahlia nematodes. However, avoid signet marigolds, as these may actually attract the nematodes you are trying to control.
  • You can try solarizing the soil as well. This is often helpful on a temporary basis. Water the infected area, cover it with clear plastic, and secure the edges. Leave the plastic in place for at least four to six weeks. Solarizing is effective only in hot weather.

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Are Nematodes Eating My Plants?

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Not an insect and not always a pest, a nematode is a microscopic, unsegmented worm that lives in the soil. It has been around for millions of years, and it remains one of the most prolific animals on earth. Some nematodes benefit the garden by feeding on other pests, but about 10 percent cause damage to plant roots, particularly the root knot nematode (Meloidogyne spp.) Nematode victims range from trees and shrubs to vegetables to flowers. Although the worms may kill annuals, the bigger threat to sturdier plants is damage that allows entry to bacteria and fungi.


How to Kill Nematodes in Soil

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Nematodes are microscopic worms that can live in your soil or water. Some nematodes are beneficial, controlling grubs and other insects in the soil. Other nematodes are harmful to plants, burrowing into roots and making their way up the stems and leaves. The damage makes it difficult for plants to absorb nutrients, resulting in weak, small or even dead flowering and vegetable plants. There is no chemical control approved for use by homeowners, but there are other ways to limit the damage caused by the parasitic worms.

Remove all vegetation from the area. Wet the soil, then cover it with two sheets of clear plastic to raise the temperature in the soil and kill the nematodes. Dig the edges of the plastic about 6 inches into the soil to keep it in place and hold in the moisture. Place the plastic during the hottest months of the summer, and leave it in place for four to six weeks.

Plant cool season crops rather than warm season crops. Nematodes are less active in the cooler months, so there is less chance they will damage plants. Plant nematode-resistant plants all year long to limit damage. Nematode resistance is indicated on the seed or plant label.

Amend soil with plenty of organic matter prior to planting. Till or dig the organic matter several inches into the soil. The organic matter will help suppress the nematodes and keep them from causing as much damage.

Keep contaminated areas of the garden from spreading. Do not move plants from infested areas into clean areas. Water infested areas separately so the runoff doesn't get into clean areas. Clean gardening tools with alcohol between uses to keep from transferring nematodes on the tools.

Water your plants frequently don't let them dry out. Plants are more susceptible to nematodes if they are stressed from lack of water.

Allow the planting bed to lie fallow for one or two seasons. Water the planting area and keep it moist so the nematode eggs will hatch, but keep the planting zone free of weeds and other vegetation. If the nematodes hatch and have nothing to eat, they will die.

Remove plants and dig up the roots at the end of each growing season to remove the nematodes' food source. Dispose of the plant matter. Till the soil after removing the plants to dry the soil and expose the nematodes to sunlight, which kills them. Till the soil again every few weeks to dig up more of the nematodes and expose as many as possible before the next planting season.