Wednesday, April 5, 2017

Nematodes





 Nematodes are microscopic roundworms. There are both good and bad nematodes. Many nematodes live in our soils and are beneficial.  But there are a number of harmful species that attack plants. These nematodes insert their stylet mouth-part, much like a  hypodermic needle, into the  tissue and suck out the plant juices.  

Plants which are infested with nematodes may exhibit symptoms of stunting, yellowing and wilting. Further symptoms may be smaller and fewer leaves, and smaller fruit.  Also, due to this feeding, the root knot nematode, in particular, will cause the plant cells to rapidly enlarge, thus developing characteristic bumps or knots on the roots. 



What to do?  If root knot nematodes are in your garden, take it seriously. Eradicating the garden of nematode pests is highly unlikely, but they can be managed with good sanitary procedures. Here are some measures:
·      Apply organic matter (OM) to the soil.  OM will encourage the growth of beneficial organisms, fungi, bacteria and good nematodes. They, in turn, will ‘attack’ the plant parasitic nematodes and deplete their numbers. A note of interest, there is one species of fungus that forms loops with its fungal threads. Nematodes will become stuck in these loops, which will actually tighten, and eventually the nematode dies. 

·      Crop rotation  Do not replant the same crop or any susceptible crop into infested soil.  For instance, if you discover root knot nematodes on your cucumbers, plant a resistant crop, like garlic or corn, in place of the cucumbers. For best results, do not plant with a susceptible crop for 3 years.

·      Keep the soil fallow. A more drastic form of crop rotation is simply keeping the infested area fallow. This starves the nematodes. Do not allow any crop, even weeds to grow there. But do add organic matter. Again, 3 years is best.

·      Soil sterilization  This involves covering the infested area with a piece of clear plastic for at least one month and preferably two. This should be done during the hottest part of the year.  In hot climates with clear skies, enough heat can be produced underneath this tarp to kill most of the nematodes. 

·      Plan resistant varieties. The best control against nematodes is to use resistant varieties. You may notice on a tomato seed package the letters VFN.  This means that the variety is resistant to the fungus, Verticillium and Fusarium and to the root knot nematode.  Such varieties include Celebrity and Better Boy. Asparagus, corn, garlic, onion, strawberry, zinnia, salvia and marigolds are also resistant to root knot nematode.  

Most Important: DO NOT SPREAD CONTAMINATED SOIL
Perhaps the most important aspect of controlling nematodes is to stop them from spreading throughout the garden.  If your tomato patch is newly infested with nematodes, keep those nematodes there. Nematodes will slowly spread in the soil by themselves. Don’t help them by carrying soil from the infested area to other areas, or by carrying around contaminated dirt clinging to garden tools and shoes. Work in an infested area last. Always clean tools and shoes.  Be cautious when receiving potted plants from other gardens or even from a nursery that has non-sterilized soil.    

Marigolds have been reported for many years as a way of reducing the nemotode populations. The French marigolds are most effective; varieties include Nemagold, Petite Blanc, Queen Sophia, and Tangerine. Unfortunately, planting a few marigolds next to each susceptible plant will NOT eliminate the problem. To be effective, the entire infested area needs to be planted in marigolds, each plant about 7 inches apart. The flowers must be planted for a minimum of two months and then turned under. The area also needs to be kept free of weeds. Then, root knot sensitive plants can be planted back into that area the following planting season. Replanting marigolds every other year will almost certainly be necessary.