Sometimes it’s the Little Things That Count
August 6th, 2005
Nematodes are especially active in warm weather. There are microscopic worms that bore into roots of susceptible plants, causing galls and knots and weakening the plants. Here are two ways to significantly reduce large populations of nematodes.
Solarize the Soil:
Solarization- using the effects of the sun’s rays- is the method to use only when nematode and fungus problems are acute and unbearable. It kills useful organisms, including worms and beneficial fungi, along with the bad ones. (This works best where summer days are hot.)
Pull out all the plants, including the roots and thoroughly soak the soil with water. Cover the area with clear or black polyethylene plastic that’s 1 to 4 millimeters thick. Prop up the top layer with wire hoops or bamboo frame, peg it down around the outside, and bury the loose edges.
Solarization works in the same way as a greenhouse where a transparent covering, in this case the plastic sheeting, traps the sun’s heat. After several days of sunshine, soil temperatures rise to as high as 140 degrees at the surface and over 100 degrees as far down as 18 inches — hot enough and far enough down into the soil to sterilize it. It takes four to six weeks of sunny weather to pasteurize the soil at these temperatures.
Many people think marigolds repel nematodes, but the truth is they attract them. Root knot nematodes entering marigold roots are killed by a natural plant chemical before they have a chance to reproduce. Marigolds can be used to rid the ground of these pests. In spring, solidly plant the area to be treated with French marigolds, place in a 7-by-7 inch pattern. Leave marigolds in place for a full 120-day season of growth.
With either method, nematodes will gradually return, but they’ll be discouraged if you regularly add a lot of organic soil amendment. They don’t like humusy soil.