Nematodes: A Rotational Concern

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Soil sampling probe filled with soil

Recent research out of Arkansas suggests that row rice producers who rotate to soybeans should be concerned about potential yield loss from southern root-knot nematode feeding.

“What we are learning is that furrow-irrigated rice may allow for an increased carryover of nematodes when compared to flooded rice production systems,” says Travis Faske, University of Arkansas nematologist. “If we are sustaining nematode populations in row rice production, that could allow for higher nematode populations in the subsequent soybean crop.”

Furrow-irrigated rice, also known as row rice, is increasingly popular throughout the Mid-South. In Arkansas, acres planted to row rice jumped from approximately 40,000 acres in 2017 to 125,000 acres in 2019 and 200,000 acres in 2020. That number is expected to increase again in 2022.

Despite this drastic increase in row rice production, little is known about the survival of root-knot nematodes in a row rice production system where water levels fluctuate and the upper third of the field remains relatively dry.

To remedy that, Faske and his team at the University of Arkansas have ongoing studies to evaluate the host sustainability of hybrid rice to the southern root-knot nematode, Meloidogyne incognita.

Early indications suggest that hybrid rice is a suitable host for the southern root-knot nematode.  However, the conditions in which furrow-irrigated rice is grown, silt loam soils and irrigation practices will limit the impact on rice production.

Faske’s three-year study evaluated eight rice hybrids for host suitability. The greenhouse studies found that all eight hybrids were hosts for the pest. Under these conditions, southern root-knot nematode populations can increase 8- to 14-fold in one growing season.

In the 2019-2021 studies, eight rice hybrids were planted alongside corn and soybean as companion crops. Although rice was a suitable host to the southern root-knot nematode, it was a less favorable host than corn or soybean. With corn or soybean, the nematode numbers can increase by 25- to 35-fold. 

“Hybrid rice appears to be a less susceptible host as compared to soybeans, but it is susceptible to southern root-knot nematode feeding,” Faske says.

Additionally, soil samples pulled from harvested row rice fields in the study confirmed the presence of root-knot nematodes in the loam and silt loam soils.

“We found one-tenth the nematode populations in the bottom third of furrow-irrigated rice fields that we found in the top one-third of the field,” Faske says. “The greatest nematode populations were noted in silt loam soils, as compared to loam fields, and in the upper end of the field that was relatively dry compared to the lower end.”

This finding suggests that growers could see higher southern root-knot nematode populations when fields are rotated to soybeans after rice, at least compared to flooded rice production systems.