Spiking, wetting agents, hydroject, aeration all may help avoid turf injury. Results have been very mixed. Cultural approaches will probably be more effective. Where nematode populations were high this spring, populations have not moved up appreciably. On other sites, nematode populations have varied from low to high.
Population density depends on the carrying capacity of the particular green.
Decline as a result of nematode infestation is more likely to express itself from now through August. Remember that decline is often the result of several factors and that nematode populations need to be ascertained before application of nematicide. After August, populations tend to decline, and while they may pick up again in the fall, nematode populations will be reduced over the winter months. Although I usually do not recommend a nematicide after August, suppression of nematode populations at the end of the summer will allow for better root development into the fall. Cyst nematodes are more vulnerable to nematicide after August 1 because the juveniles are moving from the cyst through the soil to the root.