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Wayward worm at New Mexico's door

Reniform nematodes have spread west through Southeastern states for four decades, and are now just a county away in the Texas Panhandle, said Stephen Thomas, a nematologist with NMSU's Agricultural Experiment Station.

"Cotton is most threatened, but reniform nematodes potentially affect every crop we grow in New Mexico, with the possible exception of alfalfa," Thomas said. "There's no varietial resistance to reniform in any known crop, and the fall-back solution is expensive pesticides and nematicides."

Symptoms of reniform nematode damage include stunted plants that yield poorly, because of damage caused when the tiny worm sticks its needle-like mouth part, called a stylet, into a root to suck out nutrients. The worm also uses its digestive system to inject toxins into the plant, disrupting the cotton plant's metabolic processes.

Another consequence of finding reniform nematodes is that other states seeking to prevent the introduction of this petite pest can functionally halt the movement of crops out of New Mexico, he said. That means once the reniform nematode is known to occur here, other states can require that New Mexico ensure any product produced comes from a reniform-free field.

"This is going to be very costly and time-consuming because we would have to certify every field, a relatively complex process that requires periodic sampling," Thomas said. "If a field is found to be infested, it's out of production for import to other states from that time on. It becomes a huge regulatory problem for growers."

Today, New Mexico is already infested with another type of nematode, the southern root-knot nematode. Heavy infestations can cut cotton yields by as much as 25 percent. This microscopic worm acts as a plant parasite and infests about half of New Mexico's cotton acreage.

The more damaging reniform worms attack roots and can cause yield losses in cotton of 10 to 75 percent. Discovered in Georgia and Louisiana in the early 1940s, the tropical pest has now spread to all Southern states. Over the past two decades, reniform nematodes have become significant pests across the Cotton Belt, taking a heavy toll on Southern cotton production.

Gary Lawrence, a plant pathologist at Mississippi State University, said reniform nematodes are becoming serious pests in 11 Southeastern states, led by Mississippi, Louisiana, Alabama and Georgia. They infest about 1.2 million acres, or 19 percent of the region's cotton, he said. Infestation levels range from 1.4 percent to a stunning 55 percent.

Under the right conditions, reniform nematodes are quite prolific. One female reniform nematode can produce 70 or more eggs in a 25-day cycle. Three generations later, 24 million individuals are possible.

Introduction of reniform nematodes to New Mexico would most likely come from the West Texas Panhandle, where equipment and soil frequently cross the border into New Mexico. There's one positive point, though. The West Texas reniform nematode population is centered in New Home, a small farming community 15 miles south of Lubbock, said Terry Wheeler, a plant pathologist at Texas A&M Agricultural Research Center at Lubbock. Being that far away from the reniform hot spot allows New Mexico producers enough time to closely monitor any westward movement, she said.

Reniform nematodes can move up and down in the soil a few feet, but they're not going to cross the state line unless they are carried in soil. That soil can enter New Mexico on equipment and transplants, and even the tires of pickups. Even a little bit of soil can carry some eggs, and that's all it takes for reniform nematodes to take hold, she said.

To determine if the pests are in the field, growers need to sample around stunted plants in cotton or green bean land and find out which pests they have, NMSU's Thomas said. Since reniform nematodes are not easily detected early in the season, the best time to take soil samples is in late summer or early fall when populations are high.

One factor making reniform nematodes so difficult to eradicate is the distance they can put between themselves and any control measure, he said. Many can survive 36 inches to 48 inches deep in the soil. As a result, infestations often go undetected until the damage is already underway, since the pests leave few, if any, warning signs.

No control measure will completely eradicate the pest, Thomas said. Rotation to crops like corn or grain sorghum for one to two years, which helps control root-knot nematodes on peanuts, will not help against reniform nematodes in New Mexico, he said.

Chemical controls of reniform nematodes can be costly. Nematicide treatments run about $25 to $100 an acre depending on the chemicals. In addition, after using these chemicals nematode populations have completely recovered by the end of the season because treated plants produce a healthier root system, which creates a larger food source.

"Any time a nematode pest gets introduced, it's impossible to eradicate," Thomas said. "With control options decreasing, the importance of keeping new pests out becomes that much more important."

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