RALEIGH — With the growing season for summer agronomic crops underway and many landscapes actively growing, it is an excellent time to utilize diagnostic testing to identify existing abnormal growth problems.
The N.C. Department of Agriculture and Consumer Services’ Agronomic Services Division offers a range of services to help optimize crops and yards.
Soil testing, nematode assay, and plant tissue analyses are usually used for predictive, routine testing, but they can also help identify a current growth concern or problem. With soil testing, clients receive reports with crop-specific lime and fertilizer recommendations. A nematode assay will provide crop-specific control measures based on nematode species and populations. Plant tissue analysis provides the existing plant nutritional status of a crop that is currently growing.
Usually when growth concerns occur, there are some areas of a field, landscape or lawn where growth is normal or “good” and other areas where growth is poor or “bad.” It is important to acquire samples from both good and bad areas. Soil samples for fertility purposes from these areas can be taken randomly from within the defined good and bad zones. Soil should be sampled to the depth of the root zone, typically four inches for areas that are not tilled and six inches for tilled areas. If plants are very young, sampling a lesser depth equal to the rooting depth is advised. About 10 to 12 soil cores randomly taken in the good and bad areas should be acquired for each sample, using a clean, plastic bucket and a non-galvanized sampling tool.
Areas affected by nematodes typically are circular in shape and if plant roots are examined, growth abnormalities can sometimes be seen. Nematode populations will be greatest at the edge or perimeter of this circular area, where healthier plants adjoin those that are growing poorly. To acquire a sample for nematode assay, soil from this edge or perimeter should be sampled. Sampling through actively growing roots to acquire root material is best. It is also recommended that a “good” sample be taken in a nearby area where growth is nearly normal. About one pint of soil is needed for each nematode sample. The soil should be placed in a plastic bag to prevent it from drying. Also, it is important that the sample is not exposed to hot sun since high temperatures can kill nematodes.
Plant tissue samples, both good and bad, can also be taken randomly from plants from within areas where good and bad soil samples are taken. The most recently mature leaf is the leaf to sample for most plants. Typically, this is a fully expanded leaf about four leaves back from the growing point or bud of the plant. Leaves that are dead or decayed should be avoided. For small leaves, a couple of handfuls of plant material is usually sufficient; for large leaves like fully developed corn or tobacco, 10 to 15 leaves are sufficient. For turf, typically the top growth that is normally mowed is appropriate to sample; scissors can be used or grass can be taken from a mower bag. Tissue samples should be placed in paper bags or envelopes since plant material will decompose in plastic bags.
Samples submitted to any of the above services require a sample information form that can be found at http://www.ncagr.gov/agronomi/pubs.htm. Information forms for soil and nematode samples can be submitted online. Fees for nematode assay and plant tissue analysis are $3 and $5 per sample, respectively. Soil testing is free except during the peak season months of December through March.
Commercial growers needing help in diagnosing growing problems are encouraged to contact their NCDA&CS regional agronomist for a farm visit. You can find contact information for your regional agronomist at www.ncagr.gov/agronomi/rahome.htm . Homeowners may contact their local county extension service office where they can also find supplies for soil testing and nematode assay.