SDSU: Stunted yellowing corn could signal nematodes


Are you spotting stunted yellowing corn in patches? It could be due to corn nematodes, said Emmanuel Byamukama, Assistant Professor & SDSU Extension Plant Pathologist.

“Several plant parasitic nematodes infect corn leading to reduced plant vigor, stunted growth and yield loss,” he said.

A microscopic worm-like organism that lives in the soil, the plant parasitic nematode has a “feeding straw-like” structure called a stylet that is used to injure the plant roots and suck nutrients from the plant cells.

“Some of the nematodes feed from the outer surface of the root without entering the root (ectoparasites), whereas other types enter the root and feed from within the root (endoparasites),” Byamukama explained. “Infected roots have reduced water and nutrient uptake and wounds created by nematode feeding can be entryways for fungal pathogens.”

Byamukama added that the organisms, in general, are slow movers.

“They are spread through tillage and water movement within the soil,” he said. “This is the reason corn plants with severe nematode infection appear in patches,” he said.

The infection in corn usually goes unnoticed or can be mistaken for other diseases such as root rots or nutrient deficiency. Yield loss due to nematode infection can still occur without necessarily observing above ground symptoms.

Sampling for Corn Nematodes

The first step to effective nematode management, Byamukama said is diagnosing the type and density in the soil.

“Since corn nematodes can be inside the root and also on the surface of the root, diagnosis of these nematodes requires sampling both soil and corn roots,” he explained.

For fields suspected to be infected, four to six plants should be carefully dug out without injuring the roots when corn is still young.

To increase chances of determining if nematode infection is causing the symptoms being observed, Byamukama encourages growers to collect another set of four to six plants from parts of the field with no symptoms.

To sample the soil, use a probe or a shovel to obtain 20 cores of soil between 6 to 8-inches within the root zone. Soil from non-symptomatic areas should be collected separately to determine population densities in symptomatic and non-symptomatic areas.

Corn Nematode Management

“What determines the need to apply corn nematode management practices is the type and density of nematodes infecting corn in a given field,” Byamukama said.

For instance, he explained, the threshold for needle nematode is 10 nematodes/ 100 cubic centimeters of soil whereas for spiral nematode, the threshold is 1000 nematodes.

“That is why it is important to have the soil and corn plants tested in the lab to determine the type and density of different nematodes infecting corn,” Byamukama said.

The most common management practice is crop rotation. However, some nematodes that infect corn can also infect other crops such as soybean.

“Therefore, this practice alone may not be effective against certain nematodes that have a wide host range,” Byamukama said.

Nematicide seed treatments are another corn nematode management practice. The commercially available nematicide seed treatments include Aveo, Avicta Complete, Nemastrike, and Poncho Votivo.

Tags: Agriculture News, Farming, Crops
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