Grape Root Borer-Background, Scouting, and Management

• The GRB is clear-winged moth whose appearance mimics paper wasps.
• The larvae feed on the mature roots of all grape species and hybrids.
• The young GRB larvae are spread throughout the root zone, while the older larvae are inside large roots closer to the trunk.
• The roots will have hollowed tunnels, sometimes packed with frass.
• They may cause increased susceptibility to cold injury; vines weaken and eventually die.
• GRB likely move into vineyards from wild vines.
• Adult moths live about 1 to 2 weeks and do not consume any food.
• The females emit pheromones to attract flying males for mating.
• After mating, females lay eggs (300 to 600) singly or in small groups over several days as the female moves short distances.
• After two to three weeks the eggs hatch and the small larvae quickly enter the soil.
• When the eggs hatch, <3% if the larvae typically survive and find suitable roots to feed on. The newly hatched larvae are capable of tunneling through 9 to 11 inches of soil to locate the roots. However, when surface protection and soil moisture decrease, the mortality rate of the larvae increases
   

  

• Once established on the root system, they thrive and typically spend their life cycle in one vine. They are uniformly distributed through the root system as young larvae and move toward the crown as they grow.
• Larvae (full-grown: 1” long, white with brown heads) feed on the roots for one, two, or three years, depending on the region. This stage causes extensive vine damage.
   

  

• Larvae move to within 2 inches of the soil surface, close (~12”) to the trunk when they are ready to pupate.
• Adults emerge 35-40 days later, typically July-August in our area.
• It can take many years (12-20) for populations to build in the vineyard, but once the infestation reaches a sufficient level and damage increases, production can decrease quickly over a few years.

• Pupae (3/4” long) and pupal skins can be scouted on the soil surface near the trunk, beginning about the first week of July.

  

• Adult GRB moths mimic the appearance of the Polistes or paper wasps, but they are clear-winged moths. The top of the head is orange; the antennae are orange with brown-black markings. The abdomen is dark brown with reddish-brown markings, with a very narrow yellow band on posterior edge of segments two, four, and sometimes six. The legs are orange with brown-black markings. The forewings are dark and mostly opaque.  
• Females are much larger than males, with an approximate 1-1.5” wingspan.
   

  

• The moths are most active in the afternoon, and mating also occurs during this time.
• Male moths are most commonly seen flying about the vineyard; females are usually sedentary in vines and fly sporadically. The number of males and females is typically equal.
   

  

• As females use pheromones to attract males, synthetic pheromones may be used to trap (1/variety block) and monitor male flight timing and populations.
• Traps at Great Lakes IPM - https://www.greatlakesipm.com/monitoring/ready-to-use-kits/clearwing/gltr32743k-trece-pherocon-grape-root-borer-grb-kit-3-station
• Lures at Great Lakes IPM - https://www.greatlakesipm.com/monitoring/lures/clearwing/gltr327403-trece-pherocon-grape-root-borer-grb-lures-3cs
   

  

• There is currently no known economic threshold, although 5% infested vines  may decrease production.
• Infected vines may have discolored and smaller leaves, reduced shoot growth, fewer and smaller berries, wilting leaves, and ‘slow vine decline.’

• Insecticides commonly used in the vineyard do not affect GRB populations.
• Research at Southwest Missouri State showed no significant difference in adult GRB emergence when comparing a totally vegetation-free vineyard, a 3-foot bare strip under the vines, a bark mulch, a hay mulch or grass, and weeds under the vines.            
• The same synthetic pheromone (EZ/ZZ) used to trap GRB may also be used as a control tactic, known as “mating disruption.” Isomate® GRB Pheromone ties (100 twist ties/A) are installed before moth emergence and the ubiquitous level of pheromone inhibits the male from finding the female, so mating does not occur.  This reduces population growth and new larvae colonizing the roots but will not impact those that have already infested the roots. (Regretfully availability of Isomate® GRB ties can be limited).
   

  

• You can monitor and control the moths as they emerge by keeping under-the-vine area around the trunk free of weeds and debris and visual scouting when they expand and dry on the lower trunk. They typically emerge in the mid to late morning (between 9-11 AM).
• Applying plastic mulch under the vines may inhibit emergence and larvae soil penetration, although this has not been widely tested and may not be feasible on a commercial scale.
• Lorsban-4E applied to the soil has been the conventional chemical control of GRB. However the active ingredient (Chlorpyrifos) is in the process of being banned—some special uses* may still be available; always check the label.  
• Biological control may be feasible by utilizing (Heterorhabditis) nematodes (e.g. Arbico Organics NemaSeek), although they have not been tested in our area, are somewhat expensive, and must be stored, handled, and applied correctly to be effective.  
• Hilling-up soil around the trunk (up to 1’ in height with a 3’ diameter) may inhibit pupal emergence. However, timing is critical, mounds must be removed promptly to prevent scion rooting, and it may increase soil erosion risk.
• Regretfully few viable management options are available to control GRB. However, well-maintained infected vines may continue to produce a (satisfactory) crop for many years.

*Federal law requires that insecticides and other pesticides list the sites where they can be used.  Always read the label carefully and follow the directions.