Root-Knot Nematodes Galls on Parasitized roots.
If your mirliton vine begins to come back each year with less vigorous growth and fruit yield, root-knot nematodes (RKN) may explain the cause. They are especially a problem with older vines in sandy soil. In Mexico and Central America, RKN are such a pest that the large commercial chayote farms pull up all their plants every three years and replace them with new ones.
RKN can infest the roots of mirliton within three years, though we don’t normally see that problem in the Gulf Coast south. Nematodes are deceptive and hard to diagnose without digging up the roots and inspecting them for galls. RKN don’t suddenly kill mirlitons vines; instead, they gradually drain them of nutrients so that the most frequent symptom is little growth and low fruit yield.
When the vine begins to exhibit this slow decline, most growers often think it is due to a lack of fertilizer and try to solve the problem by piling on more fertilizer.
But the solution is simple. You can buy beneficial nematodes that kill the root-knot ones. You add the beneficial nematodes to a gallon of water and drench the soil in the early spring and late fall. That will wipe out the root-knot nematodes almost immediately, and will continue to contriol them if treated every three years.
You can buy them here.
View photos of the excavated roots here.