The two types of grapes grown in Florida, Muscadine (Vitis rotundifolia Michx.) and the American bunch (Vitis labrusca L.) grapes, are susceptible to attack from the grape root borer (GRB), Vitacea polistiformis (Harris). The GRB is the most important pest of grapes in the southeastern United States, especially in Florida, Georgia, and North Carolina. This pest causes substantial injury to the grapes, which results in declining vine vigor, yield reduction, and death of grapes. Although the muscadine grape is native to Florida, its increased demand and production put it under a lot of GRB pressure.
This ingenious pest starts as eggs laid by the adult female moths on grape leaves. The hatched larvae fall to the ground, dig into the soil to locate its food source – the grape roots. Because this injury phase (or infective stage) occurs inside the ground, and it is difficult for the grower to see the damage.
That it can take several months or years before symptoms show on the grapes adds another level of difficulty for the growers to know when to protect their grapes. By the time they realize they are under attack by GRB, severe damage may have occurred. Interestingly, the GRB larvae can remain undetected in the soil for almost 2 years.
Damage by the Grape Root Borer
The various Florida regions may see the adult moth at a different time of the year. The northern part of Florida sees GRB immigrating between June and October, while it is between July and August in central Florida, and may extend to December.
For more information about the grape root borer and management, please check out the following interesting topics:
The featured images are credit to Johnny N. Dell and James Solomon (USDA Forest Service), both from Bugwood.org.