By Adriana Murillo-Williams, Alyssa Collins, Paul D. Esker
Plant parasitic nematodes
(PPN) are microscopic roundworms that feed from living plant roots and other plant parts. Plant parasitic nematodes that have been reported to feed on soybeans include the lance, sting, lesion, root knot, and cyst nematodes. However, within the long list of soybean disease-causing agents in the United States, more yield is lost to Soybean Cyst Nematode (SCN) than any other nematode, bacterial or fungal pathogen. In plants affected by SCN, water and nutrient uptake by the root will be impaired, the number of nodules formed on the roots will be reduced, and when above-ground symptoms are visible, plants will look yellow and stunted. Lemon-shaped females are visible on the roots 5 to 6 weeks after planting.
Soybean cyst nematode cysts can contain up to 250 eggs. This picture shows a burst SCN cyst and the eggs.
What makes SCN so damaging?
- The masked yield robber: SCN may be present in a soybean field without causing any above-ground symptoms and reduce soybean yield by 10%. It can go unnoticed for several years. When symptoms are visible, yield losses may already be as high as 50%.
- Easy spread: Although SCN cannot move long distances by its own power, the adult nematode and the cysts (dead female bodies full of eggs) spread through anything that moves soil, like agricultural implements, tractor wheels, flood water, and strong winds. SCN has already spread through 80% of all soybean growing areas in the country.
- High reproductions rates: The nematode’s life cycle can be completed in 24 days; therefore 3-6 generations of nematodes can occur during a growing season. With each generation, more cysts containing eggs will be produced and can remain viable in the soil for up to 10 years.
- Many hosts: A short list of known SCN hosts include cowpeas, sweet clover, hairy vetch, crimson clover, scarlet clover, alsike clover, birdsfoot trefoil, white lupine, yellow lupine, chickweed, wild mustard, and pokeweed.
- Interaction with other diseases: Lesions in the roots caused by SCN feeding are infection courts for the pathogens that cause Sudden Death Syndrome, Brown Stem Rot, and Charcoal Rot. Severity of these diseases can increase in SCN-infested fields.
- Broken resistance: One of the most important items in the toolbox for SCN management has been the use of resistant varieties, along with rotation to non-host crops. However, in recent years, SCN has adapted to the resistant varieties. The ability of SCN to reproduce on those varieties has dramatically increased.
Where is SCN?
Soybean cyst nematode was found in Lancaster County in 2002; however, no further findings have been reported in subsequent surveys conducted by the PA Department of Agriculture. Additionally, SCN infestations have been reported in eight counties along PA borders, including three in Ohio, two in Maryland, one in Delaware, and two in New Jersey. The first report of SCN in New York occurred in 2017.
We need to raise awareness!
Preliminary results from a survey in PA (n=54) during the past winter indicated that 83% of the participants (farmers, crop consultants and agronomists) had never scouted/soil sampled for SCN and 81% were not aware of the source of resistance in the varieties they use. Therefore, as part of a collaboration Penn State Extension
, the SCN Coalition
, and the PA Soybean Board, we will be offering a free nematode testing program.
How is SCN diagnosed?
Any integrated pest management strategy starts with the correct diagnosis. The best way to diagnose and quantify SCN levels in the field is by sending soil samples to a professional diagnostic laboratory.
How can you get a free SCN test?
Free testing is being offered for soybean growers during the 2019 planting season. You can request a soil sample at your local Penn State Extension Office. The soil bags contain sampling instructions, a label that needs to be filled out, and a field history form that must be returned along with the soil sample to your local Penn State Extension Agronomy Educator. There is a limited number of bags per county, so hurry up and contact your local extension educator. The deadline for sampling collection is June 20th.
The easiest way to collect soil samples for nematodes is with a soil probe. However, when there is no access to a soil probe, subsamples can be collected with a spade or a trowel at 8 inches deep. If the soil will be collected in a field where soybeans were grown last year, take the samples from within the row, in the root zone, where chances of finding cysts are highest. If your field has not been sampled for SCN, it is a good idea to start by sampling areas of high risk of introduction, like field entry ways, areas prone to flooding, and along fence lines.