Nematodes

Encyclopedia Article

Description and Symptoms 

Every field in Iowa has plant-parasitic nematodes feeding on corn roots; however, they rarely cause economic damage. Multiple nematode species feed on corn. Symptoms of nematode damage can occur any time during the season and include poor or uneven stands, chlorosis, stunting, and small or poorly filled ears. Often, symptoms occur in patches where nematode numbers are highest. Because these symptoms are not unique, damage is often attributed to causes such as weather, soil conditions, or fertility. Root symptoms depend on the type of nematode involved, and can include stunting, root swelling and malformation, and discolored lesions. 

Scouting

The best time to scout for nematodes are when symptoms of damage are observed, but no later than R3 (milk) growth stage. A scouting tip is to collect 15 to 20 12-inch-deep soil cores from the root zone of symptomatic plants. Also, collect five or six root systems if crop ia at V6 growth stage or younger. More damaging in dry fields with low fertility and can be more of a concern in sandy areas. Moisture stress and poor fertilization will contribute to greater nematode damage. 

Management

It would not be surprising to discover SCN in any field in Iowa in which soybeans have been grown. SCN is widely distributed in the state, and once an SCN infestation becomes established, the nematode can survive for ten or more years without a soybean crop being grown.

Managing SCN should involve coordinated use of multiple tactics, including growing nonhost crops (such as corn), growing SCN-resistant soybean varieties, and using nematode-protectant seed treatments when soybeans are planted. Also, it is very important to grow SCN-resistant soybean varieties with different sources of resistance in successive soybean crops, if possible, but there are few resistant soybean varieties available with a source of SCN resistance other than the common PI 88788 resistance.a

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