Nematode problems of turfgrasses in Florida and their control.

Research data and observations during the past 10 or more years have shown that several species of nematodes limit quantity and quality of turf grass production in Florida. A sting nematode, Belonolaimus longicaudatus, and a lance nematode, Hoplolaimus galeatusy have proven to be highly pathogenic and of wide spread occurrence on most of the major turf grasses grown in Florida. Several other nema todes also cause significant diseases of the roots of turfgrasses. Adequate chemical control meas ures are available for use in most cases. During the past 5 years new, effective organophosphate nematicides have been made available for use on commercial turf. These new chemicals are somewhat selective against certain nematodes and as a result, sting nematodes have been controlled very effectively but lance nematodes have not been controlled. Thus, in a few years severe lance nematode problems have become prevalent on turf where sting nematodes have been controlled. Newer compounds are continu ally being evaluated for control of lance and other nematodes. Introduction Stylet-bearing nematodes are abundant in turf from all areas of Florida. Several thousand samples of turf taken throughout Florida have been routinely examined for the presence of plant parasitic nematodes since 1953. In the great majority of cases from 1 to 10 species of obligate plant parasites were present and usu ally in numbers sufficient to cause injury to the grasses involved. Nematode parasites have been found on all Florida Agricultural Experiment Station Journal Series major turfgrasses grown in Florida. The more pathogenic species occur more commonly and in greater numbers on the various types of bermuda, zoysia, centipede and St. Augustine grasses. The bahiagrasses apparently support lesser populations although some deleterious effects have been found in some locations. Patho genic capabilities have been determined experi mentally with some of the nematodes involved but much information is lacking. Experiments involving the use of nematicides have provided additional data to indicate levels of pathogenicity. Thus, considerable efforts during the past 10 years have been devoted to the elucidation and control of nematode problems of turfgrasses in Florida. Some of the findings are herein reported. The Nematode Parasite op Turfgrasses in Florida The following is a list of the nematode para sites most frequently encountered in turf sam ples. Comments pertaining to the pathogenic capabilities are based on the references listed or on control experiments and observations by the authors or both. 1. Sting Nematode—Belonolaimus longicau datus Rau. A severely pathogenic ectoparasite which is more damaging to turfgrasses than any other nematode species (7). It is widely dis tributed in soils with high sand content, and is relatively easy to control with chemical nemati cides. 2. Awl Nematode—Dolichodorus heterocephalus Cobb. This ectoparasite is also severely pathogenic, but it occurs much less frequently than does the sting nematode. It is usually asso ciated with wet soils such as around ponds, lakes, and streams. 3. St. Augustinegrass Cyst Nematode Heterodera leuceilyma Di Edwardo and Perry. A highly pathogenic sedentary endoparasite (1), which attacks St. Augustinegrass only as far as known. It is limited in distribution but causes severe injury when present. It is diffi cult to control with current nematicides, and, therefore, the use of St. Augustinegrass is not recommended where this pest occurs. 4. Root-knot Nematodes—Meloidogyne spp. 490 Florida state horticultural society, 1970 These are endoparasites and the species M. graminis (Sledge & Golden) Whitehead is wide spread on golf courses. This species is moder ately pathogenic (2,3) and moderately difficult to control. 5. Lance Nematode — Hoplolaimus galeatus Sher. This species is widely distributed in all soil types, and is moderately pathogenic (7). It probably should be classified as a migratory endoparasite or a semiendoparasite since it may partially or totally enter roots. It is difficult to control and in some cases, has become a severe problem after the sting nematode was brought under control. 6. Stubby Root Nematodes—Trichodorus spp. These ectoparasites are widely distributed but in most cases the population levels are low. They are moderately pathogenic (6). 7. Spiral Nematodes—Helicotylenchus spp., Scutellonema spp. and Peltamigratus spp. These nematodes are widely distributed and one or more species of these ectoparasites frequently are found in turf samples. High population levels are considered necessary for significant injury but proof of pathogenicity in Florida is lacking. Perry et al. (4) showed that H. digonicus was pathogenic to blue grass in Wisconsin. 8. Ring Nematodes — Criconemoides spp. These ectoparasites are widely distributed and high population levels are found frequently. They are especially prevalent and pathogenic on centipedegrass (5). 9. Sheath Nematodes—Hemicycliophora spp. and sheathoid nematodes Hemicriconemoides spp. Various species of these ectoparasites are found frequently and oftentimes in high numbers. Pathogenicity data are lacking but observations indicate that high population levels are neces sary for significant injury. 10. Several other plant parasitic nematodes are found commonly in turf. Some such as root lesion nematodes—Pratylenchus spp. (migra tory endoparasits), stunt nematodes—Tylenchorhynehus spp. (ectoparasites), and dagger nematodes — Xiphinema spp. (ectoparasites) are considered pathogenic when rather high population levels are present. Control Since turf is a perennial, certain methods used to control plant nematodes on annuals, such as rotation, flooding, and fallow, are not feasible. This limits control possibilities either to the use of resistant grassses or to the use of chemical nematicides. Bahiagrasses appear to be resistant to a wide range of the nematodes listed above, but they are sometimes attacked by the more highly pathogenic parasites such as sting and root-knot nematodes. Other varieties or types of grasses with resistance to the more injurious nematodes have not been found. Thus, the only effective control measure generally available to day involves the use of chemicals. Many experiments using numerous chemicals for the control of plant parasitic nematodes affecting turf in Florida have been conducted during the past 10 years. To be acceptable the chemicals must control nematodes and cause little or no injury to the grasses, and applica tion procedures must be practical. Initially, two such chemicals were recommended and used in Florida. These were V-C 13 (0-2,4-dichlorophenyl 0,0-diethyl phosphorothioate) and DBCP (1,2dibromo-3-chloropropane). Each is prepared as a water emulsion and applied as a surface drench. Very high rates of each are required and sometimes they are phytotoxic to the turf. Sarolex, which is a nematicidal formulation of the insecticide diazinon, [0,0-diethyl 0-(2isopropyl-4-methyl-6-pyrimidinyl) phosphorothi oate] was developed for use on turf and has been used since 1965. Rates of 20-30 lbs/acre a.i. are effective against the sting nematode. The above 3 compounds have been labeled for use on home lawns as well as golf courses, com mercial turf, etc. The newer nematicides with potential for use on turf are highly toxic to mammals and are limited to professional turf areas, such as golf courses, sod farms, and cemeteries. The nematicide-insecticide Dasanit (0,0-diethyl 0-(p-methyl sulfinyl)phenyl phosphorothioate) has, since about 1967, become the nematicide most widely used on golf courses in Florida. It is used for treating fairways as well as greens. There is little danger of phytotoxicity with Dasanit and thus the chemical can be applied to large areas before being watered in. Only the granular formulation is used and from 10 to 20 lb/acre a.i. have proven effective especially for sting nematode control. As is the case with other chemicals discussed, about %-l inch of water is required to move the chemical into the soil for contact with the nematodes. Nematicides currently recommended for use on turf as Dasanit, DBCP, Sarolex, and Mocap (0-ethyl S,S-dipropyl phosphorodithioate). Of PERRY, SMART, HORN: NEMATODES TURFGRASSES 491 these four DBCP is effective against ectoparasitic nematodes, but has little effect on endoparasites. The emulsifiable concentrate must be used, and it is often improperly applied or applied under improper conditions, or both. Therefore, good results are not always obtained. Sarolex and Dasanit are especially effective against other ectoparasites. Sarolex must be applied as an emulssifiable concentrate, and, therefore, in volves more care and time for application than most homeowners are willing to take. Dasanit and Mocap are not available for use on home lawns but certainly are the easiest to apply since granular formulations are used. For, the above reasons, research to provide nematicides which are more effective and easier to apply continues. Several new experimental compounds show promise of filling one or more of the needs alluded to above. Results of three tests are given below. In Table 1, rates of Nema cur (Ethyl 4-(methyl thio)-m-tolyl isopropylphosphoramidate) and Tirpate (2,4-dimethyl-2formyl-1, 3-dithiolane oxime N-methylcarbamate) are compared for control of the sting nematode. Note that excellent control was pro vided for 3 months by Nemacur, but a lesser degree of control was provided for 2 months by Tirpate. The higher turf rating received by Tirpate at 8 lb/acre a.i. in June indicated a quicker nematode kill. In Table 2, rates of Nemacur are compared with each other and with DuPont 1410 (S-methyl 1 -(dimethylcarbamoyl)N [(Methylcarbamoyl) Table 1. Effect of Nemacur and Tirpate on popula tions of the sting nematode, Belonolaimus longicaudatus on 'Ormond1 bermudagrass. Nematicides were applied May 27, 1970, Nematicide & Rate Turf No. nemas/100 cc soil Formu