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¶ What:
The typical above‐ground symptoms of nematode damage in corn are the depressed, circular, or elliptical areas of stunted plants in sandy areas of the field (70% sand or more). The size of affected areas may range from one‐half to five acres. Plants may appear to have normal color, but are stunted. Plants may also be yellowed or may show mid‐day wilting.
The shortest corn plants are found in the center of the area. Plant height may increase steadily from the center of the area to the edges of the area,
which are normal height.
¶ Figure 1. Healthy vs Nematode Affected Corn Plants
¶ When:
Samples for needle and sting nematodes are best collected from the sandy areas of the field during the spring, before planting. Don’tcollect samples if soils are very wet (saturated) or frozen. Collect in‐season samples up to the R3 growth stage (milk stage).
Many nematodes that feed on corn may be deep in the soil profile, and some, including needle nematodes, can migrate down as the growing season progresses. These nematodes are missing or underrepresented in the typical soil samples taken for fertility management. Greater sampling depth may be needed later in the season as nematodes have migrated downward. Soil samples collected at mid‐ to late‐ season soil samples may yield nematode population densities that are deceptively low.
¶ Where:
Collect samples from plants showing obvious damage symptoms. The highest nematode populations are often at the edges of the affected area, not in the center.
It may be prudent to collect two samples. Take one sample from the center of the affected area, but avoid sampling plants that are dead or nearly dead. Take the second sample from the apparent edge of the affected area, from what appear to be more healthy corn plants.
¶ Need:
- soil probe
- shovel or trowel
- heavy‐weight, freezer‐grade, zip‐lock plastic bags, quart‐size or larger
- cooler with ice packs (e.g. “Blue Ice”)
- marking pen (“Sharpie”) for labeling bags
- knife or shears to trim roots
- proper sample submission form (see below)
¶ How ‐ Sampling:
- Select a plant to sample. Kick aside or remove the top two tothreeinchesofsoil. Therewillbefewnematodesinthis soil layer, because it is often too hot or dry for nematodes to survive
- Place soil probe about two to three inches away from the base of the plant (four inches, if tall corn)
- Push soil probe in through roots (should hear crunching). The sample must include both soil and live root tissue
- Early to mid‐season: Collect soil core that is 8 inches long. Actual sample depth will be 2‐to‐10 inches or 3‐to‐11 inches
- Mid‐ to late season: Sampling to 18‐inch depth may be advisable
- Remove soil core from the probe and place directly into labelled sample bag.
- Repeat 12 to 15 times
- Emergence to V6: Dig up root mass from every third plant sampled. Carefully shake off soil. Make sure that root tips are present and seminal roots have not been stripped off. Cut off and discard top of plants. Place root mass in separate, labelled plastic bag
- V6 to R3 (6‐leaf to milk stage): Collect soil cores only
- R4 (dough stage) to harvest: Sampling is not recommended
¶ Figure 2. Collecting Root Mass
¶ How ‐ Packaging:
- Label plastic bag with marking pen for proper sample identification
- Mix sample in bucket very gently, inverting once or twice by hand. Do not damage live roots while mixing
- Remove representative sample of soil and live roots (three or four handfuls). Place in plastic bag and seal
- Nematodes are soft‐bodied animals that can be ruptured and destroyed by blunt physical force. Don’t throw or drop soil sample bags
- Place sample immediately in cooler and out of direct sunlight and/or heat. Enclose ice packs if temperatures will exceed80°F.HeatandUVlightcankillnematodes. (Treat sample as you would treat fishing worms.)
- If samples cannot be shipped immediately, store by refrigerating , but do not freeze
¶ How ‐ Shipping:
- Avoid shipping samples late in the work week. Otherwise they may sit over the weekend in a delivery truck or unconditioned warehouse that is not air conditioned
- Handle sample gently, protecting them from physical impact and high temperatures, which may result in inaccurate results
- Pack samples in a sturdy cardboard box. Cushion sample bags well with crumpled newspaper or sufficient absorbent paper packaging material to prevent shifting of contents while in transit
- Ship via UPS, FedEx, or other carrier using ground service. Sending via next‐day air can just a waste of money
- Ship via US Mail if diagnostic laboratory is close. USPS Priority Mail can take two to three days or longer
¶ References
Dappen, G. Nema‐Test: Preparing a Sample. (www.nematest.com/prepare_sample.htm accessed 07/28/2014)
Tylka, G. Stunted, Yellowing or Wilting Corn: Could Nematodes Be the Cause? Integrated Crop Management News, Iowa State Univ. Coop. Ext. Serv., Ames, Iowa. (http://www.extension.iastate.edu/CropNews/2012/0529tylka.htm accessed 07/28/2014)
Tylka, G., et. al. 2011. Sampling for Plant‐parasitic Nematodes in Corn Strip Trials Comparing Nematode Management Products. Plant Health Progress, Plant Mgmt. Network. 01 Sept. 2011 (http://www.plantmanagementnetwork.org/pub/php/diagnosticguide/2011/nematode/ accessed 07/28/2014)