Root Knot Nematode

 

There are many species of nematodes of which a few hundred species attack plants and animals. Root knot nematode is a microscopic worm that is non-segmented, i.e., if you magnified it many times, it would look like a snake. The female lays eggs which hatch into a juvenile nematode, which has the ability to penetrate plant roots. Once inside the root, the nematode pierces a cell with a very fine needle-like mouth and begins drawing nutrients from the cell. The injury to the cell is so slight that the cell continues to function normally. In fact, in the case of root knot, it functions better than normal, and secretions from the nematode stimulate the cell to grow and cause other cells in the immediate vicinity to also become super active. This results in the gall formation you see. Each gall has one to several nematodes feeding inside it.

 

Root knot nematodes are a common and serious landscape and garden problem in the sandy soils of the Central Coast. Anytime you have plants that are growing poorly, losing vigor, declining or dying prematurely, or are smaller than nearby plants of the same kind, you should suspect the presence of nematodes. Galled and deformed roots are the underground symptoms of the presence of root knot nematode.

 

Control of this pest is difficult. One of the reasons strawberry growers fumigate their fields is to control nematodes. Soil fumigants and some other soil-applied chemicals are the only effective way to control nematodes, and this control is only temporary. Another means of control is to grow plants that will not be a host to the nematode. Unfortunately, there are very few plants on which root knot nematode does not feed. Grasses and marigolds are good plants to use where nematode populations are found in your garden. There are a few vegetables which have resistance to nematodes. The N in VFN tomato varieties indicates resistance to nematode attack. Finally, use of high amounts of organic matter as a soil amendment can help suppress nematodes and help stimulate healthy plant growth. Unfortunately, I know of no comprehensive list of nematode-resistant plants, so the gardener is pretty much left to trial and error in developing a landscape that will grow and do well in the presence of nematodes.