Nematodes(Phylum Nematoda)-Roundworms
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ematodes(Phylum Nematoda)-roundworms that are U.S. is the presence of the sting nematode (Belonolaimus among the most abundant animals on Earth (Fig. longicaudatus), considered the most damaging plant-parasitic N1)-are found in all aquatic environments, on plants nematode known to feed on turfgrass. Fortunately, it does not and in soil, animals and humans. They are common both as survive cooler climates and has not been found north of human and animal pathogens and as free-living organisms that southern North Carolina. feed on algae, bacteria, fungi and other nematodes. Although less than 10per cent of the described nematode genera are considered Not just a U.S. problem to be plant pathogenic, these organisms are responsible for In Canada, the issue of plant-parasitic nematodes on turfgrass billions of dollars in damage worldwide. has been debated for quite some time. A study on population Plant-parasitic nematodes feed on a variety of different crops, dynamics of these root-feeding animals on golf course greens including corn, potatoes, soybean, strawberries and various was conducted in Ontario in 1998 and numerous nematodes herbs, to name just a few. On turfgrass, we rarely think of plant- known to be parasitic on turfgrass were found in the soil. Last parasitic nematodes as problematic in the northern part of this year, I also came across a number of golf course green samples continent, but they are definitely present whether or not symptoms appear each year. Superintendents are more likely to Figure 1: The root-gall nematode, associate nematodes with controlling grubs and other insect Subanguina radicicola pests rather than with turf damage. Many turf managers in Canada do not seem to be familiar with these potentially damaging microscopic pests. Plant- parasitic nematodes have been known to be extremely damaging to turfgrass in the southern parts of the continent, especially the southern U.S. Many nematodes reproduce more quickly in warmer climates and the year-round growing season present in the southern U.S. offers an ideal environment for population growth. In contrast, the harsh winters experienced in much of Canada are believed to have a detrimental effect on nematode populations, possibly leading to a decline in numbers coming into the spring (although many nematodes are adept at surviving colder climates through dormancy, much like plants). Another factor that increases nematode damage in the southern 18 April 2007 GreenMaster from throughout Canada with rather high levels of plant- Figure 2: Generalized symptoms of nematode parasitic nematodes. There is no doubt these pathogens are damage, including thinning of the turf stand present in golf course greens soils, but the real challenge is and premature death. trying to associate visible symptoms with nematode damage. Nematodes that feed on turfgrass plants are root feeders and therefore cause relatively general symptoms, including yellowing of turf, thinning of turfgrass stands, drought intolerance and premature death (Fig. 2). In northern climates, most of these symptoms do not become evident unless the turf is under some sort of stress, as is the case with many other root pathogens (For more information on root pathogens, see GM, vol. 42, issue 1, pgs 38-42.). In addition, many of the plant-parasitic nematodes we see in Canada are more actively present and feeding in the spring and fall, while symptoms of damage do not appear until the summer. Finally, the presence of feeding nematodes may not cause symptoms on its own, but rather predispose the turf to other stress-related diseases such as anthracnose (Colletotrichum cereale), bacterial wilt (Xanthomonas translucens) or summer patch (Magnaporthe poae). All of these factors make it very difficult to associate turfgrass stand symptoms with feeding nematode populations. The primary nematodes dealt with in Canada are the stunt more recently, the root gall nematode (Subanguina radicicola). nemtaode (Tylenchorhynchus spp.) , the spiral nematode These pests cause varying levels of damage, in part because of (Helicotylenchus spp.) , the ring nematode (Criconemella spp.) , feeding habits. The spiral, ring and stunt nematodes are the lance nematode (Hoplolaimus spp.) , the root-knot nematode considered ectoparasitic feeders, meaning they feed from outside (Meloidogyne spp.), the cyst nematode (Heterodera spp.) and the root by inserting a needle-like mouthpart (called a stylet) cur, RAKE AND ROLL! <fIfpa'BJ!JfI)~ g,! ~~;J H-l1fIl Our unique tungsten A new level High performance carbide tipped blades are of dethatching. turf.roller system. designed to outperform Our proven turf dethatching Superintendents trust the and outlast conventional technology is engineered greenslRON 3000 to achieve products. Available for for durability and efficiency. consistent, championship most OEM greens, fairway, Free floating sections putting greens. Add our Turf grooming and spiking conform to undulations. Ventilator and Turf Broom mower applications. Hardened steel construction attachments to create means extra durability. the ultimate greens maintenance system. n Call Toll Free: 1-800-661-4942 for more information or visit www.woodbayturftech.com GreenMaster April 2007 19 Figure 3: Extensive damage to a golf course amount of traffic and wear on the turf, irrigation practices and green due to feeding by root-gall nematode, fertility programs. These all influence the health of the turf Subanguina radicicola. stand, and as a result, the potential for you to see symptoms from nematode feeding. This allows for an important tool in determining whether or not nematodes are a problem on your site-the use of damage thresholds. A damage threshold is simply the population level of a given pest at which you are most likely to see plant damage. In many agricultural crops, thresholds are used as part of integrated pest management (IPM) programs to determine when damage is most likely to occur and to properly time chemical applications, if needed. In the North American golf course industry, the use of thresholds, especially with fungal pathogens, becomes a bit more difficult due to high expectations of end users and, subsequently, low tolerance for any kind of turf damage. This is especially the case on greens. With plant-parasitic nematodes, however, damage thresholds can be used because healthy turfgrass plants are often able to withstand a certain level of feeding before the symptoms become evident above ground. The specific threshold value depends on a number of factors, I including the damage potential of the pest, climatic conditions, ~ Q) t soil type, irrigation or rainfall levels, wear on the turf and ::J 8 cultural practices. As such, published threshold levels B should only be used as a guide, as they were more than likely o ..s:: c.. determined under different conditions . If you think you may have problems with plant-parasitic into plant cells to extract nutrients. Most nematodes within these nematodes, your best bet is to develop your own thresholds genera need to be present in relatively high numbers to cause visible damage, as their effect on the host is primarily indirect. Figure 4: Visible galls on roots caused by root-knot Effects of their feeding include stunted roots, chlorosis and nematode (Meloidogyne graminis) and root-gall weakened turfgrass stands, but expression of these symptoms nematode (Subanguina radicicola) (below). will depend on population levels and overall turfgrass health. Lance, root-knot, cyst and root gall nematodes all enter the plant root directly. They are potentially much more damaging (Fig. 3) because in addition to extracting nutrients, their physical presence in the plant may lead to blocked vascular tissue in the root system. In addition, the root-knot nematode releases enzymes that lead to the creation of giant cells upon which the nematode feeds. This further weakens the turfgrass plant by diverting essential nutrients to the feeding site of the nematode pathogen. Determining population levels While all of these nematodes have, at one time or another, been found in golf course greens soils throughout Canada, the important question is whether or not they are present at damaging levels. Most soils that support plant growth will eventually develop population levels of plant-parasitic nematodes. One of the largest contributing factors to increased levels is the age of a green, as it takes time for populations to build up. On golf greens, nematodes can be transferred by a number of different carriers, including golfers' shoes and maintenance equipment. Fortunately, the presence of nematodes does not always lead to visible damage. There are often other factors that bring about symptom expression, most of which are related to the general health of the turf. These include turfgrass height of cut, soil health, the 20 April 2007 GreenMaster Figure 5 and 6: Sampling methods for bag and sent toa diagnostic laboratory that routinely performs- determining nematode population levels- nematode extractions and has the ability to-identify the pests. or whether unexplained turf damage is If you are experiencing unexplained symptoms and want to caused by nematodes (below). find out if they can-be attributed to nematode feeding, you should take two separate sets of samples-one from a healthy area of turf and one from the edge of the symptomatic area(s) (Fig. 6). Take the same size cores as mentioned above; about 10-15 cores from each area should suffice. Be sure to separate the samples and label them appropriately. This may allow a diagnostician to associate symptoms with nematode populations, though numerous factors such as time of year and type of nematode may affect the levels in the soil. If you pull up a core and notice galling, you should remove a cup cutter sample where you see symptoms and send that sample to the laboratory as well. Asymptomatic Unfortunately, if you do find plant-parasitic nematodes in your turf, there are very few treatment options. There are no post-plant nematicides registered for use on turf in ~@)~ • - -.'- Canada.