As soil temperatures continue to rise, we will see an increase in parasitic nematode feeding pressure and population size. This spring feeding is why nematode damage presents in the late summer months, as the nematodes have damaged the roots early putting the grass at greater risk of drought and/or heat stress in the summer.
Before you start to treat for nematodes, make sure you know what nematode species you have infecting your turfgrass. Our research indicates that there is a difference between ectoparasitic and endoparasitic nematodes, not just in feeding methods but in population dynamics as well. Sting nematode, an ectoparasitic nematode, will be in the top 4 inches of the soil column during the early to mid-spring months and then will drop below the root zone during the summer to a depth of at least 8 inches. From June to September, a majority of sting nematodes are found below 4 inches in the soil column. This area, while outside the root zone is also beyond the reach of most currently available nematicides and chemical applications are unlikely to reduce nematode populations significantly.
However, our results show that root-knot nematodes, which are an endoparasitic nematode species, stay within the rooting zone during the entire year. This study identified that the infective juvenile stage starts to increase in quantity in early spring and throughout the summer. Infective juveniles are the most vulnerable life stage for root-knot nematode as they are outside the roots, and are likely more susceptible to chemical management during this time. As an endoparasitic nematode, the adults reproduce inside the root, limiting the effectiveness of nematicides due to being protected within the roots.
The three newest nematicides to the market are: Divanem (abamectin), Indemnify (fluopyram) and Nimitiz (fluensulfone). All three nematicides are effective against ectoparasitic nematodes such as sting, lance and ring nematodes. These three products are also effective against endoparasitic nematodes, but are most effective against the juveniles outside of the roots. With a limited number of nematicide applications allowed each year, it is very important that we accurately time nematicide applications when nematodes are most susceptible and likely to be contacted by the chemicals.