Plant Disease Profile: Nematodes

Almost every plant, which means your customers' lawns, is susceptible to some type of nematode.

Many nematodes are saprophytes that consume dead matter and help recycle nutrients in the ecosystem. Some species of these roundworms can attack animals and insects, and a small group actually causes plant damage. These plant parasitic nematodes range from a millimeter or less in size and can live in the soil and roots of plants, making them unidentifiable to the eye. And there are currently no controls for the lawn industry to fight back.

So Lawn & Landscape spoke with Frank Wong, technical service specialist at Bayer Environmental Science, to better understand the different types of nematodes, and how LCOs can identify, prevent and control them.
 

Species. There are two groups of plant parasitic nematodes, endoparasitic and ectoparasitic. Endoparasites, like root-knot and lance nematodes, live inside the roots of a plant, while ectoparasites, like sting, stunt and spiral nematodes, live on the outside and feed on plant roots.

Plant parasitic nematodes are usually whitish or translucent and about a millimeter long, Wong says. "To see them accurately you need to look at them under a microscope to identify what nematode is involved," he says.
 

Damage and identification. The majority of plant parasitic nematodes attack the root system. Wong offers a few examples.

Nematodes have needle-like stylets in their mouths, he says. They poke holes inside the root cells with the stylets and then suck up what comes out of them.

"Some of the endoparasitic nematodes – a good example is the root-knot nematode – what they'll do is penetrate into the root and make a home there," Wong says. "In the process, they actually make plant hormones to cause the roots to gall up and swell. That gives them a great home to just sit there and keep eating. Those root knots are stressful for the plant because it's a nonfunctional root and the plant is tricked into putting a lot of energy into forming those knots."

Nematodes cause stress to the root system, which reduces turfgrass vigor and growth, "symptoms that look like general plant distress," Wong says.

However, there are not specific symptoms for nematode damage, he says. In order to determine nematodes are eating turfgrass or other plants, proper testing must be done. A soil test and microscope exam can be done to look for nematodes and identify if there is a high enough infestation to harm the plant.

"Because you have the different types of nematodes that attack – the outside versus the ones that burrow the inside – you may have to do both types of test to determine which nematode, if there is one present, is causing the damage," Wong says.
 

Prevention and control. Nematodes are in the soil already, making it difficult to prevent them in most situations, Wong says. For example, if a homeowner has infested Bermudagrass, takes it out and plants new Bermudagrass, there's a chance the nematodes will infest the new grass because they're still in the soil.

"Often times it's very difficult to prevent nematodes from establishing in a planting," Wong says. "It's very important for landscapers to make sure that they are getting clean material. If you have a new site, with ground that has never had turf on it, then there is a good chance that you probably don't have a very high nematode population that affects turf. But if you go to the sod farm and they have a huge infestation in their turf, and you bring all of that material to your new planting, you're going to transfer all of those nematodes with you."

Currently there aren't chemical control options for turf on the residential and commercial side of the industry, Wong says, so proper maintenance is a LCOs best bet at prevention and management. Nematodes tend to be a stress disease, so healthy turfgrass is usually less susceptible than stressed.

The author is an associate editor at Lawn & Landscape. She can be reached at clawell@gie.net.