Drought Highlights Damage Caused by Nematodes

By CnAgri2012-07-09 20:25:59 Print

The drought throughout Indiana is intensifying nematode damage in farm fields, says a Purdue Extension nematologist.

The needle nematode, soybean cyst nematode and lance nematode all are causing more problems for grain farmers in a year when crops already are stressed by extreme heat and lack of rain.

Jamal Faghihi explained that nematodes, microscopic roundworms, can be found in fields every year, but the damage is worse during a drought season. "The severity of symptoms shows because of the stress in plants," he said.

Faghihi stressed that nematodes and their damage will be found in patches in the fields.

"They're not going to be uniformly distributed all over the field," he said.

Farmers should know if they are having nematode problems at this point in the summer. "They've always been there if you looked hard enough," Faghihi said. "Now, you can't miss it."

The needle nematode exclusively feeds on corn and grasses and is found in sandy soils. Oftentimes, the needle nematode poses a problem in the spring when the weather is cool and wet. Although the needle nematode is sensitive to heat, Faghihi speculates that this year the early warm weather created an opportunity for the worm to do its damage early. He advised farmers to inspect the plant roots early in the season for abnormalities, which include poor development, club-shaped roots and damage resembling herbicide injury.

The lance nematode is found in corn and soybean fields. Similar to the needle nematode, the lance nematode causes damage to plants that results in yellow, stunted growth with abnormal roots. The lance nematode is not deterred by hot weather.

The soybean cyst nematode attacks soybean plants and causes the plant to become yellow and stunted. This nematode starts as a microscopic worm and ends its one-month life cycle as a cyst containing 200-300 eggs. Earlier in the season the cysts are brown, but this time of year they are white or yellow, the size of a sugar granule and can be seen by the eye.

Faghihi said farmers should inspect for the presence of the cysts by digging out the root, placing it in water and checking for cysts. The cysts are durable and can survive extreme conditions.

Faghihi said most soybean cyst nematode-resistant cultivars contain the same source of resistance, PI 88788. Nematodes, however, are overcoming that resistance. He said farmers need to understand which resistor is being used in their crops and consider switching to soybeans with another source of resistance.

Soybeans with resistance derived from peking are something that Faghihi said farmers should consider as they determine the best course of action for managing the soybean cyst nematodes. Crop rotation is another important step farmers can take to weaken the stability of the nematodes because the worms feed exclusively on specific plants.