Nematode control
Plant parasitic nematodes are small, microscopic, thread-like animals that utilize a stylet to puncture and feed from plant cells. In turf, these nematodes are root parasites. Nematodes are important turf pests in South Carolina, particularly in sandy native soils of the Sandhills and coastal regions. They are also important in artificial, sand based, root zone mixes fro greens and athletic fields. Nematodes contribute heavily to the decline of turf, this depends on the type of nematode and the amount of them in the soil. Nematodes are often blamed for weak turf when, poor cultural practices, fungi, insects, nutrient problems, soil compaction, poor drainage, or other environmental problems may be the more serious factors leading to the decline. All of these other stresses can also make nematode damage worse. Therefore, correct diagnosis is important to adequately address the problem and determine if the use of a nematicide is warranted. Nematicides are generally highly restricted in their use and vary in their effectiveness against different species of nematodes. It is critical to carefully consult the label to be sure that product can be used on a particular site.
ABOVE GROUND SYMPTOMS:
The yellowing of turf followed by willting(slow recovery), poor responce of turf to fertilization and eventfull thining in irregular shapes followed by weed invasion are all symptoms that occur over months and years.
ROOT SYMPTOMS:
Short, stubby roots with few branch roots compared to healthy roots. Roots may have a dark brown color, and sometimes (with sting or stubby root nematodes) exhibit swollen root tips. In sod with severe infestations, the sod strength is low.
SOIL SAMPLING:
Soil sampling is necessary for accurate diagnosis. Quart-size plasic bags will help you submit the samples to the nematode assay laboratory at Clemon University. These bags can be obtained from the Cooperative Extension Service office in your county. The number of nematodes recovered from soil vary greatly, depending on, the time of year and the stage of crop or plant development at that time. Many other factors can be involved. Samples taken during the Winter and early Spring are less reliable, and in some situations certain nematodes may be missed entirely. In general, for routine assays, sample during the time of year that the turf is growing is the most suitable time. For warm-season turfgrasses, June or July is a good time to detect high populations if they exist. For cool season grasses, late spring or early summer should detect damaging populations, if they exist. Diagnostic assays (those taken to determine if nematodes may be a factor) can be taken at any time: if high populations of damaging species are encountered, then certainly nematodes are a factor. However, if nematodes are not found in damaging numbers, it still doesn’t preclude their role if the time of year the sample was taken is unfavorable for their survival. If nematode populations are high, determine the best approach to the problem including: improved turf management practices, planting new grass type, or chemical control. Usually a combination or integrated approach leads to the best success.
Improve Turf Management Practices. Most grasses can withstand moderate numbers of different kinds of nematodes. Deep, infrequent waterings encourage deeper rooting of the turf, allowing grass to obtain more water and nutrients than a turf. This will give turf a short root system due to shallow, daily waterings. Avoid excess nitrogen fertilization, as this encourages lush, succulent roots conducive to nematode population buildups. Avoid stresses to turf such as mowing too short. Alleviate compacted soils and correct any nutrient deficiencies.
Plant a Different Grass. Planting another grass type may be a choice if the new grass provides acceptable quality and is adapted to the site. Sometimes nematodes are attacking a particular grass and damage is severe because it is not adapted to the site. However no variety of any turfgrass is known to have true resistance to all nematodes. Using proper turf management practices (see above) and best adapted turf species is a more practical approach than simply switching varieties.
Nematodes and the Grasses Most Affected by Each
| Turfgrass | Sting1 | Ring2 | Stubby-Root3 | Lance4 | Root-Knot5 | Spiral6 |
|---|---|---|---|---|---|---|
| Warm-season | ||||||
| Bahiagrass | ? | X | X | |||
| Centipedegrass | X | X | X | X | ||
| St. Augustinegrass | X | X | X | X | X | |
| Bermudagrass | X | ? | X | X | ? | X |
| Zoysiagrass | X | ? | X | X | X | X |
|
Cool-season |
||||||
| Creeping bentgrass | X | X | X | |||
| Tall fescue | X | X | X | |||
| Ryegrasses | X | X | X | |||
| Bluegrasses | X | X | X |
2. Ring nematodes are widely distributed. Found on all turfgrasses but are considered major pests on centipedegrass. If populations are high enough, they can damage bermudagrass and zoysiagrass.
3. Stubby-root nematodes occur in most soil types in South Carolina.They cause damage similar to sting nematodes. However they are particularly encountered in bentgrass greens, but populations capable of causing severe damage are much higher than sting nematode populations capable of causing severe damage.
4. Lance nematodes are widely distributed. They attack all turfgrasses in South Carolina, but are especially damaging to and frequently associated with St. Augustinegrass. Lance nematodes also attack bermudagrass and may become a predominant nematode in old greens where sting nematode has been controlled with nematicides.
5. Root-knot nematodes are widely distributed. Found frequently in St. Augustinegrass, zoysiagrass, and bermudagrass. The effects of these nematodes on turf are not well known, but they are believed to be injurious at high population densities.
6. Spiral nematodes are frequently found on all turfgrasses, but are not believed to cause serious damage in most circumstances.
CHEMICAL CONTROLS
Because crop rotation, varietal resistance, biological control and several other disease management strategies are not always practical or effective for turfgrass nematode control, the use of chemical nematicides is currently the most reliable approach to reducing parasitic nematode levels in turfgrass stands. Chemical nematicides can be applied as preplant fumigants and as post-plant non-fumigant contact chemicals. Fumigants are toxic to plants and should only be used before establishment of the turfgrass stand. In established turfgrass stands contact nematicides come in granular or spray formulations and are always watered immediately after application. They also have some insecticidal activity. All nematicides are extremely toxic to humans and animals and should be handled with all precautions indicated on the product label. No single product is effective against all nematodes on a given turfgrass species.
Soil Fumigation Before Planting
Soil fumigants are chemicals applied as gases or liquids that are ready to vaporize. They are very toxic to the turfgrass but can be used to treat soil prior to seeding or planting to reduce populations of plant parasitic nematode, weeds, fungal pathogens, and other soil-borne microorganisms. Turfgrasses established in fumigated soil show more uniform and vigorous growth. The fumigants used in turf are the gas methyl bromide, the liquids 1,3-Dichloropropene (Telone II), 1,3-dichloropropene-chloropicrin (Telone C-17) and metam-sodium (labeled as Vapam, Sectagon or Busan 1020). All three fumigants are Restricted Use pesticides that usually require special equipment and application by licensed professionals especially when large areas are to be treated. A granular material, Basamid Granular can be applied with a drop spreader but this generates a fumigant, methyl isothiocyanate, that is toxic to nematodes. Basamid Granular carries a ‘warning’ signal on the label.
Methyl bromide is a very effective broad-spectrum biocide that has "served" the turf industry well. It is standard practice to fumigate new greens, tees and areas being replanted with methyl bromide. For treatment of small areas, methyl bromide is available in small cans ( e.g., Brom-O-Gas) used under a plastic tarp seal. This is achieved not by injection but by allowing the gas to diffuse into the pores of the soil. Cans contain 1 or 1.5 lb of methyl bromide, enough to give excellent control of pests and weeds at a rate of 1 lb per 50-100 square feet. However, the commercial production of methyl bromide was scheduled to stop in the year 2001 because it was associated with ozone depleting and a potentially serious environmental pollutant. Methyl bromide will therefore not be available for nematode control after the phase-out period.
When fumigants or Basamid is used, the best results are usually obtained when the old sod is first stripped from the area to be treated. This should be followed by thorough tilling of the soil at least two weeks prior to the application of the fumigant to allow adequate decomposition of old roots. Tilling loosens the soil and permits more rapid and uniform diffusion of the fumigant. At the time of application the soil should be moist (not water-saturated). Too much fumigant escapes in dry soil and too little diffuses when pores are filled with water. The temperature of the soil should be about 50 to 80°F (at a depth of 4 inches). Too much fumigant evaporates from hot soil whereas diffusion is too slow in cold soil. For maximum effectiveness, the treated area should be sealed immediately with plastic tarp for several days. It is extremely important that the fumigated area is not recontaminated by accidental introduction of nematodes in soil clinging to tools, equipment, footwear, in run-off water, or in infested soil. Pests introduced into partially sterilized soil usually reproduce rapidly because of the lack of competition from microorganisms.
Nematicides for Established Commercial Turf
Only two chemical nematicides are currently available for use on established turfgrass stands. They are the non-fumigant organophosphates fenamiphos (Nemacur 10G or 3 EC) and ethoprop (Mocap 10G). They can only be used on commercial turf (including golf courses, cemeteries and industrial grounds) where the risks of exposure can be minimized. The active ingredient in the granules or emulsifiable concentrate must be carried into the soil by an adequate amount of irrigation and rain water (enough to reach the root zones and give effective control of nematodes but without product loss through leaching).
Nematicide applications should be made in autumn or spring (before nematode populations peak) during periods when soil temperatures are above 60°F according to the product label. For granular formulations, gravity or "drop-type" granule spreaders are preferred (or required) over centrifugal types for more accurate application and for ensuring the safety of animals, humans and non-target plants. Other applicator types are still being tested. For example, the suitability of shallow injection of narrow bands of granules in the turf that is popular for application of granular insecticides for mole cricket control is being tested for nematode control. Experiments comparing the effectiveness of broadcast application of granules vs. subsurface injection of granules have shown similar effectiveness. Subsurface injection in fairways is practical and should reduce the potential for off-site movement of material.
Prior to application, physical soil treatments that aid soil penetration by water (such as core cultivation, vertical mowing and mechanical thatch removal) may aid in effectiveness. Applications should be followed by adequate overhead irrigation in order to wash the active ingredient into the soil and avoid exposure of people, pets and wildlife to the chemical.
The following rules are required for fenamiphos use on golf courses in Florida. These measures are designed to reduce the risk of exposure to birds and aquatic organisms. It is suggested that others consider adopting these guidelines as good stewards of the environment as well as for the product. No more than 10 acres per golf course per day may be treated with Nemacur (3 EC or 10G). There must be a three-day interval before an additional 10 acres could be treated. Do not apply Nemacur closer than 10 feet from bodies of water and surface fairway drains. Nemacur should not be applied to golf course turf between noon and sunset from June 1 to September 30 to avoid movement of pesticide by sudden downpours into bodies of water. It must not be used to control mole crickets. Total product application must not exceed 200 lb per acre per year.
At this juncture, instructions for the use of Nemacur remain the same as stated on the most current product label for other states in the Southeast. The safest guidelines are always on the product label. The product must be distributed evenly over the area to be treated and it must be washed immediately into the soil with at least 0.5 inches of water (usually up to the point when 1 inch of the top soil has become wet). Total irrigation should not result in puddling and runoff. Do not apply Nemacur where water runoff is likely to occur. The 3 EC formulation is not recommended for use on greens and tees. The purchase and use of all formulations of Nemacur are restricted to certified applicators for uses authorized by their certification, or to persons under their direct supervision.
The effects of nematicides are only temporary. Fumigants leave behind no residual active ingredients, so nematodes that survived the treatment (i.e., were too deep to be reached by it) or were brought in on the new sod can begin to re-colonize the normal turf root-zone immediately. The non-fumigant nematicides that may be applied to living turf must remain in the root-zone (top 4-10 inches in which most turfgrass roots normally grow) for several weeks to be effective. However, they will eventually dissipate from that region as a result of combined effects of leaching and decomposition. These products do not necessarily kill all nematodes that are exposed to them, but "inactivate" or paralyze many of them. Therefore, when the chemical is gone, there are usually some nematodes ready to resume feeding and reproducing. With either kind of nematicide, the treatment only provides a limited period of relief from nematode stress. The treatment cannot result in the desired improvement in turf health unless other stresses are also controlled and the nutrients (especially potassium) and water that are needed for good root growth are available.
OVER-USE OF NEMATICIDES
No nematicide is equally effective against all nematodes. When one is used frequently, nematodes that are least affected by it will have a distinct advantage over those that are most affected by it. For instance, prolonged frequent use of a product that affects lance nematodes less than other species enables lance nematodes to become dominant in that population. We believe that this has happened with Mocap in some cases, at least in part because Mocap is not systemic (absorbed into the live root tissues) and therefore cannot reach endoparasitic nematodes that are living inside those roots.
Enhanced biodegradation is a phenomenon that can reduce the effectiveness of soil-applied pesticides where the same product has been used over a prolonged period of time. Repeated application of the same chemical to soil encourages build-up of bacteria and other microbes which can metabolize ("digest") that chemical, so they can destroy it much more quickly than was the original case. The net effect is a shorter period of control from a given treatment. Enhanced microbial degradation has been reported for over 200 soil-applied pesticides, including nematicides, which have been used too frequently on a particular site. Enhanced biodegradation of Nemacur has been documented in several Florida turf sites. Therefore, it is prudent to use all soil pesticides as little as necessary, to reduce chances of developing such soil microbial populations. It also seems wise to rotate or alternate among all products that are legal and effective for a particular problem, to avoid prolonged selection for microbes that can build up on a particular pesticide.
Soil fumigants used pre-plant to control pests such as nematodes and weeds.
| Liquid Soil Fumigants | Rate of Product/Broadcast | Comments |
|---|---|---|
| Telone II (1,3-dichloropropence, 94%) |
9-18 gal/A - mineral soils 24-36 gal/A - muck or peat soils |
These fumigants are injected into the soil with tractor-mounted equipment. Maximum effectiveness is achieved when soil is covered with a plastic tarp for one to several days. Telone C-17 contains chloropicrin, which is an effective fungicide as well as a nematicide. Restricted Use Pesticides. |
| Telone C-17 (1,3-dichloropropene 78.3% + chloropicrin 16.5%) |
10.8-17.1 gal/A - mineral soils 21.8 gal/A - muck or peat soils |
|
| Vapam (metam sodium, 32.7%) |
50-100 gal/A | Apply either as a drench in water or inject by chisels. Cover after the treatment with a plastic tarp for maximum benefit. Restricted Use Pesticides. |
| Vapam HL (metam sodium, 42%) |
30-75 gal/A | |
| Gaseous Soil Fumigants | Rate of Product/Broadcast | Comments |
| Methyl Bromide Terr-O-Gas |
1-2 lb/100 ft2 | Inject by chisels and cover immediately with a plastic tarp. Restricted Use Pesticide. |
| Brom-O-Gas | Available in small cans (1 lb or 11⁄2 lb per can) for small area treatments. Must be covered with a plastic tarp to be effective. Restricted Use Pesticide | |
| Granular Soil Fumigant | Rate of Product/Broadcast | Comments |
| Basamid Granular (dazomet 99%) |
255-450 lb/A | This material carries a warning signal word, and is not a restricted use pesticide. It generates a gas when exposed to water, which fumigates the soil. It is more effective when tarped, but can be used with a water seal |
Minimum levels of common nematodes that may justify nematicide application to established
turfgrasses and expected relative effectiveness of nematicides for their control.
| Kind of Nematode | Thresholds (no./100 cc soil) |
Comparative Effectiveness of Nematicides | |
|---|---|---|---|
| Nemacur | Mocap* | ||
|
Sting, Awl Lance Stubby-root Spiral Ring Sheath, Sheathoid Root-knot |
10 80 100 1000 500*** 200 100 |
G** G G G G G M |
G-M P M G M M P |
* Mocap will injure many cool-season turfgrasses
**G = Good M = Moderate P = Poor
***Ring nematode populations over about 150/100 cc soil may injure centipedegrass; other grasses apparently tolerate much higher levels.
Nematicides for commercial turfgrass use.
| Nematicide | Rate | Comments |
|---|---|---|
| Nemacur 10%; Turf and Ornamental Nematicide (fenamiphos 10%) |
2.3 lb/1000 sq.ft. or 100 lb/A | Golf courses, cemeteries, industrial grounds; DO NOT USE on residential lawns or public recreational areas other than golf courses; not for use on turf being grown for sale or other commercial use as sod, or for commercial seed production, or for research purposes. Irrigate immediately with at least 1⁄2" of water; do not allow puddling or run-off to occur. Do not treat newly-seeded areas until plants have developed secondary root systems. Restricted Use Pesticide. See product label for further application restrictions. Not to exceed 200 lbs/acre/year. |
| Nemacur 3 Turf (fenamiphos 35%) |
9.7 fl oz/1000 sq.ft. or 3.3 gal/A | Use on golf courses, cemeteries, and industrial grounds, not recommended for tees or greens. DO NOT USE on residential lawns or public recreational areas other than golf courses; not for use on turf being grown for sale or other commercial use as sod, or for commercial seed production, or for research purposes. Apply dosage in minimum of 1⁄2 gallon of water per 1000 sq.ft. (min. 20 GPA). Irrigate immediately after treatment with a minimum of 1⁄2 inch of water. Do not treat newly seeded areas until plants have developed secondary root systems. Do not apply more than twice per year. Restricted Use Pesticide. Do not apply to more than 10 acres per golf course per day; wait 3 days before treating any additional area. See product label for further application restrictions. |
| Mocap 10G (ethoprop 10%) |
2.3 to 4.6 lbs/1000 sq.ft. or 200 lbs/A | Pesticide for golf courses only; not for domestic turf. May be applied to bermudagrass, St. Augustine, centipede, zoysia, and bahia-grasses; cool-season are very sensitive to Mocap. Mocap may be applied over perennial ryegrass overseeding, without injury as long as it is thoroughly watered-in. Do not apply nematicidal rates to greens, tees, or other turfgrass cut to height of less than _ inch. Do not use on newly seeded areas until grass is well established. Do not apply to wet foliage. Do not apply rates greater than 200 lbs/acre at any one time, or more than 400 lb/acre/year in any combination of treatments. Application must be followed immediately by at least 0.1 inch of irrigation or rainfall. |