Lowly Ring Nematode Suppressed with Biological Control

A beneficial bacterium and soil solarization are an effective biological control combination against a ring nematode species wreaking havoc on peach trees in the southeastern United States, an Agricultural Research Service plant pathologist reports.

The beneficial bacterium, Pseudomonas sp (BG33R), was isolated in the early 1990s from soil that was known to suppress the ring nematode (Mesocriconema xenoplax) in South Carolina, according to Andrew Nyczepir of the ARS Southeastern Fruit and Tree Nut Research Laboratory in Byron, Ga. The bacterium was isolated by Daniel Kluepfel and Jane Lawrence of Clemson University, Nyczepir’s colleagues in this research. BG33R was first shown to inhibit M. xenoplax reproduction under laboratory and greenhouse conditions.

Soil solarization is a special mulching method that uses a transparent plastic covering to trap the sun's heat, according to Nyczepir. After months of sunny weather, many soil microorganisms are suppressed. This disinfestation method gives beneficial bacteria, such as BG33R, a competitive edge by lowering the native population of bacteria and killing harmful pests like the ring nematode. Soil that has been solarized also allows plants to draw on nutrients more readily.

Introducing BG33R after solarization treatment will help reduce the dependence on nematicides--pesticides used specifically to manage or prevent damage caused by nematodes, according to Nyczepir. He has searched for alternatives to chemical control of the ring nematode in the past, and has used other biological controls such as crop rotation or ground covers to suppress the pest.

Nyczepir and Kluepfel found that combining BG33R and soil solarization in peach orchard field plots resulted in ring nematode populations at or below nematicide treatment thresholds for about 18 months, unlike unsolarized plots.

Nyczepir first demonstrated that this species of nematode was a key component to peach tree short-life disease (PTSL), which causes peach tree losses estimated at over $6 million a year in South Carolina alone. The PTSL disease complex occurs when ring nematodes cause trees to weaken, leaving them vulnerable to such factors as cold injury, bacterial canker or both.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.