Root knot nematodes damaging creeping bentgrass greens
Since I first discovered root knot nematode (RKN) affecting creeping bentgrass in southern Indiana 15 years ago, I have observed the problem with greater and greater frequency on golf courses north of the Ohio River. This spring, a number of cases of RKN infection have been revealed by a stressful (dry conditions and elevated temperatures) weather in the lower Midwest. Root knot nematodes are among the most destructive to turf systems because they are endoparasitic, i.e., they enter root tissues and migrate toward meristematic regions of the root, where they essentially remain and reproduce and complete the cycle of population growth. Compared to other (ectoparasitic) nematodes, relatively small RKN populations can cause significant damage. The plant’s response to RKN infection is abnormal cell growth—resulting in swellings (Figure 1) on roots and impaired root function. Turf exposed to environmental stress (heat, drought, and compaction) tends to wilt and die more quickly if also infected by RKN (Figure 2). More images were included in a blog posted in May 2015.
The strategy for RKN management is based on a two-pronged approach.
Practice good agronomy to promote dense healthy root systems, and then relieve drought, heat, and nutritional stresses through irrigation, syringing, and spoon-feeding. Raising the mowing height and substituting rolling where possible will certainly contribute to stress reduction.
This is difficult because, unlike fungal diseases, there are few products to stop population growth. There may be some help in the near future, but currently, only Nortica will help reduce nematode populations. Nortica (Bayer) is a biological product (Bacillus firmus I-1582) that may be effective under conditions of low to moderate stress. Applications in May (soil temp around 60-70°F) are probably most effective in limiting the new wave of infections each spring. Published research focused on control of RKN on cool season grasses remains scarce.
Until research generates a more comprehensive understanding of chemical effects on nematode populations, the best recommendations for avoiding damage are based on sound agronomy.