Golfdom, July 2017

THE FOUR TO WATCH FOR Nematodes on northern turfgrasses By Nathaniel A Mitkowski Ph D N ematodes are everywhere Theyre found in all but the most extreme environmental conditions in soils oceans rivers streams on plants in plants and even in animals and humans Fortunately most nematodes are innocuous eating bacteria and occasionally each other Of the thousands of nematode species few are pathogens But despite the small proportion that is pathogenic all plants grown in natural soils are attacked by nematodes no matter where they are grown Nematodes are most severe in tropical and subtropical climates Because winter temperatures in these areas usually are above freezing nematodes can remain active in the soil for extended periods and do not freeze In areas where the ground does freeze such as the northern United States nematodes have some protection against sub zero temperatures and eggs often can remain in soil unaffected for months by temperature In addition to winter conditions the growing season in areas like the southern United States is longer than in the North which translates into more nematode generations and more plant damage One significant exception is the soybean cyst nematode which is widely prevalent and causes substantial devastation from Minnesota to Florida Turfgrass parasitic nematodes are similarly more destructive in southern regions than in northern areas but northern nematodes still cause substantial damage when population numbers are high NEMATODES OF THE NORTH Four plant parasitic nematodes in the northern U S regularly cause noticeable damage to turf the stunt nematode Tylenchorynchus spp the lance nematode Hoplolaimus galeatus the barley root knot nematode Meloidogyne naasi and the spiral nematode Helicotylenchus spp Frequently plantparasitic nematodes are not identified as to species There currently are 111 identified species of Tylenchorynchus and species identification can be extremely difficult and time consuming Other nematodes are found parasitizing northern turfgrasses but they tend to be less common and its unclear how much damage they cause These include the ring nematode Criconema spp Figure 1 the needle nematode Longidorus spp the cyst nematode Heterodera iri the lesion nematode Pratylenchus pentrans the pin nematode Paratylenchus spp and the sheath nematode Hemicycliophora spp And still others regularly attack roots but have not been cited as causing economic damage This demonstrates a major point when addressing turf parasitic nematodes Their mere presence doesnt mean they are causing symptoms or that damage levels are of concern Stunt and spiral nematodes nearly are universal on northern courses however levels of these nematodes must be relatively high before we observe damage symptoms Lance and root knot nematodes tend to be more sporadic in appearance but lance causes severe damage at lower levels than the other nematodes Lance nematodes spend some of their time outside of the root but also burrow through roots throughout the year Figure 2 This can cause catastrophic damage and makes it difficult to count their true population levels simply by soil extractions DAMAGE DETERMINATION To determine if a nematode population is causing damage to turf we extract them from the soil and count their numbers If the number exceeds a set threshold they may be a problem Use caution when interpreting thresholds however because thresholds are just estimates usually derived using specific environmental conditions type of grass season rooting depth height of cut etc 32 Golfdom July 2017 Golfdom com ALL PHOTOS BY NATHANIEL MITKOWSKI Super Science FIGURE 1 The ring nematode Criconema spp gets its name from the pattern of distinct rings that comprise the nematodes cuticle or outside layer similar to a pressurized skin While relatively common this microscopic nematode rarely reaches high levels in turfgrass stands and it is unclear how high nematode levels need to be to observe economic damage