Andy Kness, Extension Educator, Harford County
Nematodes are a highly successful and diverse group of roundworms that have adapted to nearly every terrestrial and aquatic ecosystem; in fact, they are the most numerous multicellular animal species on earth. One tablespoon of soil can contain thousands of nematodes of many different species, each contributing different ecosystem services. Many are free-living nematodes that feed on bacteria and fungi, others may feed on organic matter and contribute to the natural cycling of nutrients, and others may be plant-parasitic nematodes; which are the one’s that can cause serious problems in production agriculture.
Plant-parasitic nematodes have highly specialized, needle-like mouthparts that they use to feed on plants. While some nematodes feed on leaves (foliar nematodes), most plant-parasitic nematodes feed on plant roots. These nematodes find susceptible hosts by following chemicals exuded by the roots. In many cases, these chemicals also trigger their eggs to hatch. Once they find the roots, they begin to feed. Different species have different feeding habits. For example, some nematodes, like the sting nematode (Belonolaimus longicaudatus), are ectoparasites, meaning that they feed and complete their lifecycle outside of the plant root. Others, like the root-knot nematode (Meloidogyne incognita), are endoparasites, feeding and completing their lifecycle inside the root. Regardless of their feeding behavior, plant-parasitic nematodes disrupt the flow of water and nutrients into the plant and can cause severe root deformities and stunting, leading to decreased plant vigor, water stress, nutrient deficiencies, and overall poor growth and yield reduction.
If left unchecked, plant-parasitic nematode populations can increase to the point where production of susceptible crops is nearly impossible. If you suspect nematodes to be a problem in a field, the first step to proper management is to identify the culprit. In some cases this can be easy. For example, if you dig up symptomatic tomato plants and notice large galls on the roots, then you know you have root-knot nematode. However, diagnosing a nematode problem is not always that easy; and suppose you’re farming new ground and want to determine if nematodes are a potential problem? Fall is the time to sample and begin taking action against nematodes.
In general, sampling soon after the crop has been harvested in the fall is the best time to sample for nematodes. To take a sample, use a soil probe and sample 6-8 inches deep in between plants in the row. Take 20-25 samples across the field and mix all the cores together in a clean plastic bucket. After mixing thoroughly, place one pint of soil (I use two scoops of an 8 oz. yogurt cup) in a plastic bag and seal it. The sample can be kept in the refrigerator until you’re ready to ship it to a lab for testing. Do not let the sample dry out or get hot (i.e. don’t leave it in your hot truck all day); nematodes need to be alive in order to enumerate their populations in your soil. Remember, your test results will only be as good as your sample.
For our region, Virginia Tech is the closest lab to send samples. Mail samples (keep cool) and appropriate form to: Nematode Assay Laboratory, 115 Price Hall, 170 Drillfield Drive, Blacksburg, VA 24061-0331. For forms and more information, visit their website or call your Extension Office for assistance.
Once you get your results, you can begin weighing your management options, which will vary depending on the nematode species present and your cropping system. As a rough guide, here are some management options that are generally applicable to managing most species of plant-parasitic nematodes; however, you should do more research and/or consult with your local Extension Agent to discuss management options for your specific situation.
- Crop rotationto non-host crops is typically one of the first steps taken when nematodes are identified as a problem. This can be an effective management strategy if populations aren’t too high. Rotation out of host crops for at least 1-2 years is recommended. Crop rotation may also include leaving a field fallow.
- Planting resistant varieties. Resistant varieties may not always be available, especially in specialty crops. Also, nematodes can overcome resistance genes due to their high fecundity, so check to make sure the resistance gene is still effective.
- Sanitation should be high on the list of priorities, regardless if nematodes are a problem. Properly cleaning your tools and equipment before moving to a new field or a new area of the farm can prevent the spread of nematodes, diseases and weeds. This also includes purchasing certified, clean seed.
- Fumigation is often the most effective way to manage nematodes, but it can be expensive and therefore often limited to high-value crops. An alternative to synthetic chemical fumigation is biofumigationusing brassicas (mustard and rapeseed). Some cultivars (such as Caliente 199) have been bred specifically for fumigation purposes. If done properly, this method is highly effective at knocking back populations of nematodes and other soilborne diseases. However, if done incorrectly, this method can actually increase some nematode populations, so do your research before attempting biofumigation.
- Soil solarization can sterilize the top 8-12 inches of soil and kill plant-parasitic nematodes. This method needs to be done during the hottest part of the summer, as temperatures need to exceed 130 ºF for at least 5 minutes under the plastic. This is a temporary solution and is only viable for shallow-rooted annual crops.
- Seed treatmentscan offer short-term protection against some nematode species. Seed treatments are typically more common on field crops such as corn and beans and less common for vegetables. Seed treatments protect the root for a couple of weeks during germination and will wear off quickly as the season progresses.
If you experienced, or suspect that you experienced, nematode problems this growing season, fall is the time to start managing the issue. Having a grasp on the exact problem will allow you to better manage the issue and save you time and money in the long run. Contact your local Extension Agent for assistance. You may also contact me with any questions.
