Sting Nematode Problematic for Young Trees

The sting nematode is the most serious nematode problem in young citrus groves, nematologist Larry Duncan reported at the Florida Citrus Growers’ Institute in April. According to Duncan, long before HLB, the sting nematode was widely encountered in groves on Florida’s Central Ridge and in Polk County.

The University of Florida Institute of Food and Agricultural Sciences professor said tree growth and fruit production were markedly reduced on trees with heavy sting nematode infestations. But trees were otherwise healthy pre-HLB, and groves remained profitable.

Sting nematodes are especially troublesome in young groves with HLB because small trees with few roots support many of the pests, Duncan said. On the other hand, large trees with many roots support few sting nematodes.

The sting nematode was first recognized as a widespread pest of young trees when growers were replanting after the 1980s freezes, Duncan said. Now, growers are replanting because of HLB.

A 1985 survey showed that all common rootstocks were heavily infested and damaged by sting nematodes, Duncan reported.

Sunn hemp, a cover crop, can suppress sting nematodes prior to planting, Duncan said. He added that perennial peanut can suppress the pests in row middles.

Monitoring is necessary in order to make rational treatment decisions, Duncan stated. Because sting nematode populations resurge following nematicide use, repeated applications are required in the spring and fall.

Recently registered chemicals offer new modes of action that are highly toxic to nematodes but much less toxic to mammals and birds than existing carbamate products. They also pose less risk to groundwater. These new products include Vydate L (oxamyl), Nimitz, Salibro and Velum Prime.

“Oxamyl effect on roots was superior among the nematicides tested,” Duncan stated. “However, the treatments did not increase yield enough to be profitable.”

“Ideally, sting nematode will one day be managed in citrus with a combination of cover cropping with non-host plants, rootstock tolerance/resistance, HLB avoidance and judicious use of nematicides,” Duncan concluded.

See his full presentation here. 

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