It's the great root-knot nematode control, Charlie Brown

Close-up photo of Root-Knot Nematodes

Root-knot nematodes are tiny parasitic worms that infect plant roots. They form galls or knots on the plant roots that block the flow of nutrients and photosynthesis products. (Texas AgriLife Extension Service photo by Robert Burns)

OVERTON — Root-knot nematodes are common visitors to East Texas fields of pumpkins and many other vegetables, but their presence is anything but a holiday treat for growers, according to a Texas AgriLife Extension Service expert.

“Root-knot nematodes are the biggest problem that many of our East Texas vegetable growers have to face,” said Dr. Karl Steddom, AgriLife Extension plant pathologist.

Steddom recently completed trials comparing various fumigants and biological controls for root knot nematodes on pumpkins.

“The pleasant surprise is that one of the biological controls was one of the most effective,” Steddom said.

Dr. Karl Steddom at field site for root-knot nematode study

In his root-nematode study, Dr. Karl Steddom, Texas AgriLife Extension Service plant pathologist, tested products considered industry standard fumigants, a relatively new fumigant for which there wasn't a lot of test data yet, and two biological controls. (Texas AgriLife Extension Service photo by Robert Burns)

And he said the results should be applicable to all the crops affected by the pest. The list is considerable. Root-knot nematodes can knock back yields and quality on pumpkins, tomatoes, sweet potatoes, beets, cucumbers, carrots, peaches, watermelons, and okra. Even ornamental plants such as roses that have been started from rootstock can be hammered by the pest.

“Some watermelon varieties are marginally affected, but they can flat-out kill some crops like okra,” Steddom said.

Root-knot nematodes are tiny parasitic worms that infect plant roots. They form galls or knots on the plant roots that block the flow of nutrients and photosynthesis products. The pest is found worldwide but thrives in the sandy soils common to East Texas, he said.

“One of the biggest problems with these is that their eggs can lay dormant in the soil for years,” he said. “They’re very difficult to get rid of, and once a grower gets nematodes in a field it can be a big issue for their production for years to come.”

The infestation may start out in a small area of a field and at first may not be at high enough levels to cause significant losses in crop yield or quality, Steddom said. But if the field is left untreated, it’s almost a sure bet that the nematode population will grow and spread throughout, he said.

Steddom began the study because there wasn’t a lot of field data on two of the label products. He could have tested the products on a number of different crops, but he chose pumpkins because they’re less labor intensive to harvest, he said.

He tested nine different combinations of products on a site at the Texas AgriLife Research and Extension Center at Overton.

He conducted the tests in a field with a field that had a sandy loam soil and a high population density of root-knot nematodes.

One of the treatments tested was Vapam and Vydate, a chemical combination considered an industry standard. Another fumigant was Paladin, a relatively new product for which there wasn’t a lot of test data, he said. The other two products were biological controls, one already on the market, another still in the experimental, testing stage.

Three of the treatments were of Actinovate, a biological fungicide that uses the bacteria, streptomyces lydicus  to control nematodes. The three treatments were at 6, 12 and 18 ounces per acre.

Steddom also tested NI-9, an experimental biological control product not yet on the market, at various rates.  And he tested a mixture of Actinovate and NI-9.

For the test crop, he used pumpkins in raised beds, 40-inches wide and 6-inches high, under plastic mulching, a system that is comparable to what’s commonly used in commercial vegetable production.

All the treatments were applied through drip-irrigation tubing.  He harvested the pumpkins on Nov. 5 and compared yields as well as the extent of root galling.

Although Steddom did not find pumpkin yield differences among the various treatments, there were differences in the amount of visible galling on roots. Microscopic counts of root-knot nematode eggs per ounce of root were collected at another laboratory.

Surprising, in terms of eggs per ounce of root, the best control was achieved by Actinovate at the lowest rate of 6 ounces per acre, he said.

Pumpkin field where root-knot nematode study was done

For a test crop in the root-nematode control study, Dr. Karl Steddom used pumpkins in raised beds, 40 inches wide and 6 inches high, under plastic mulching, a cropping system that is comparable to what's commonly used in commercial vegetable production. (Texas AgriLife Extension photo by Robert Burns)

The root-gall index, which is largely a visible-eye rating, was also lowest with the 6-ounce rate of Actinovate. The 18-ounce rate of NI-9 achieved similar results.
“While yield was not impacted during this study, the reduction in reproduction rates has significant implications for future crops in this field,” Steddom wrote in his official report. “Neither phytotoxicity nor differences in plant vigor were observed at any time during this study.”

The other pleasant surprise is that Actinovate is by far more user-friendly than the standard fumigants. Though the fumigants rapidly degrade and pose no risk to the end user, Steddom said, they are dangerous to those who apply them. A private pesticide license is required to purchase and use the fumigants, but the biological control is available to homeowners without a license.

Root-knot nematode galls on pumpkin roots

Root-knot nematodes formed galls or knots on these pumpkin plant roots. (Texas AgriLife Extension Service photo by Robert Burns)

The study was funded by the U.S. Department of Agriculture’s IR-4 Project, which is also referred to as the Minor Crop Pest Management Program.

The full results of the root-knot nematode study will be available on the IR-4 website ( ) sometime in early 2011, he said.

“Growers or homeowners wanting more information about root-knot nematodes and their control should contact their local county Extension agent,” Steddom said.

A county-by-county directory of AgriLife Extension agents can be found at .


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