Clay Higgins, New Jersey

Question about nematode studies

March 18, 2015

Categories: American Daffodil Society, General

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As a master gardener I’ve noticed that the NC State University that sponsors the Extension service in NC has a standard statement when it comes to fighting nematodes and that is to “apply lime so that the soil Ph is from 6.5 to 7.0.” That’s for just about all gardening.

NC has a very serious nematode problem in Northeast North Carolina. Don’t take this as “gospel” but I think it is from the long term agriculture production of tobacco, cotton and other products. This past summer 2014 was “wet” for our area regardless if drier then most, however in the hot and moist climate nematodes attacked everything from boxwood and other bushes to most gardening plants.

Has there been any studies done on nematodes and moisture? It seems that dry weather and high Ph in the range of 6.5 to 7.0 is the best way to counter nematodes. Along with a lot of chemicals that I would rather not use.


2 responses to “Question about nematode studies”

  1. Keith Kridler, Texas Keith Kridler, Texas says:

    Soil PH of 6>7 is really not going to limit the ability of nematode species to survive. Ideal soil PH in gardens will allow various garden crop type plants to grow at their maximum ability as the soil nutrients are going to be more available. There are thousands of known species of nematodes. The Bulb and Stem nematode that infests Daffodils and members of the lily/amaryllis’ families are KNOWN to infest over 450 other species of weeds, grasses, crops, shrubs and even some trees. The below information is from the link right below my comments. Notice if you go to the whole link that some crop plants can “tolerate” an infestation of over 1,000 nematodes in a 100 ML. (3.3 OZ) of soil. And you can still harvest a “commercial” crop. This would/could be a Gazillion nematodes of just one species, to the acre. Notice the bulb and stem nematode is probably in almost all old farming areas of the temperate world by now. Depends on if you have a truly high infestation or not. It is extremely hard to actually find ANY nematode expert that has the time to identify all of the samples that come into their laboratories. Very hard to tell the difference between these species. Plant pathologists normally will look at the species of plant, look at the damage and tell you on say a tomato plant that “it is infested” with “nematodes”. There maybe 100’s of different species of nematodes on the roots and soils clinging to these roots from one sample sent to a pathologist.

    Bulb and stem nematodes can spread through lawn clippings and some of the “organic mulches”. They move down hill with water flow. They move up hill on your shoes and tools. Notice that 100 female bulb and stem nematode eggs can hatch out and mature in less than 20 days at 59*F (15*C) and lay another 200 to 500 eggs. Everyone should be “hot water” treating their bulbs, every time they dig them!

    Keith Kridler

    Bulb and stem feeder (Ditylenchus spp.): There are two important species in commercial crops: Ditylenchus dipsaci and Ditylenchus destructor.

    Ditylenchus dipsaci: This is one of the most devastating plant parasitic nematodes, especially in temperate regions. It is known to have more than 10 biological races, some of which have a limited host range while others infect over 450 different plant species, including many weeds. The principal hosts are alfalfa, faba (fava) beans, onion, garlic, leek, maize, oat, pea, potato, rye, strawberry, sugar beet, tobacco, bersem, clover, and tulip. It has also been reported on carnation, celery, lentil, rape, parsley, sunflower, and wheat. It is found almost everywhere that these crops are grown with variable severity.

    See Figure 2. White flagging symptions caused by Ditylenchus in alfalfa.

    D. dipsaci is a migratory endoparasite that feeds upon parenchymatous tissue in stems and bulbs, causing the breakdown of the middle lamellae of cell walls. Feeding often causes swellings and distortion of aerial plant parts (stems, leaves, flowers) and necrosis or rotting of stem bases, bulbs, tubers and rhizomes that begins in the field and continues in storage. In onion plants at 59 ° F (15 ° C), the life-cycle takes about 20 days. Females lay 200 to 500 eggs each. Fourth-stage juveniles tend to aggregate on or just below the surface of heavily infested tissue to form clumps of “eelworm wool” and can survive under dry conditions for several years; they may also become attached to the seeds of host plants (e.g. onions, lucerne, Trifolium pratense, faba beans, Phlox drummondii). In clay soils, D. dipsaci may persist for many years. Cool, moist conditions favor invasion of young plant tissue by this nematode. Alfalfa plants tend to be stunted with very small ‘mouse-eared’ leaves, stems with shortened internodes and swollen nodes and with pale yellow or white shoots (often called white flagging, Fig. 2). This symptom is readily observed at green-up in the early spring or just after the first cutting. Infected stems are brittle and tend to break off from the crown, and infected crowns are not firm and may be spongy in consistency. Infected areas of the field are about 2-3 weeks slower to green-up in the spring compared to non-infected areas and appear to have winter kill. Plants will die and the stands become patchy with blank spaces. Stand decline increases weed pressure within affected fields. We observed high incidence of other soilborne fungal pathogens such as Rhizoctonia associated with alfalfa affected with alfalfa stem nematode in sandy soil.

    In onion, nematode penetration into the leaves causes leaf deformation and leaf swellings or blister-like areas on the surface; leaves grow in a disorderly fashion, are often wilted and chlorotic; and high nematode numbers can actually kill younger plants. The bulb inner scales are usually more severely damaged than the outer scales, the bulbs soften and show the scales in concentric circles when cut open. In garlic, leaf yellowing and death occur without any leaf deformation or swelling. It can be carried on dry seeds and planting material of host plants. In the field, fourth-stage juveniles can withstand desiccation for many years with gradually decreasing survival over years without a host plant. Nematode survival and damage are greater in heavy soils as compared to sandy soils. The nematodes are spread to new areas by surface water runoff, irrigation, wind-blown crop debris, soil and crop debris clinging to equipment, humans and livestock, and with seed. Runoff water is very important in the spread of stem nematodes within a field and to adjacent fields.

  2. David Adams, New Zealand says:

    Thanks Keith for such a detailed description. We have not been reminded of such information for some time. I think an important element of your notes is that there are a plethora of nematode species some of which are plant specific. I know our chrysanthemum exhibitors often talk of a nematode that affects their plants.
    I remember once being told that ditylenchus can live on decaying bulb material for up to six years which means that infected soil should be thoroughly sterilized, or not used for bulbs for a long time.
    It is interesting that when we export bulbs to both the USA and the European Union that the only pathogen they worry about is the potato cyst nematode which has been known in New Zealand. Somehow they can identify the species during soil inspection. At my place they identify a nematode that affects clover but don’t consider it a problem for exporting bulbs.