New Tools for Vineyard Ant Management

New Tools for Vineyard Ant Management

Gel Baits Can Provide Ant Control in Larger Vineyards
 
Contributed by Ted Rieger
 
UCCE IPM Advisor & Entomologist David Haviland
explains the composition & application of hydrogel ant
baits for vineyard ant management at a meeting in Lodi.
(Photo: Ted Rieger)
 
Reducing ant populations in vineyards is important for managing mealybugs that pose a significant threat to grapevines as leafroll virus vectors in addition to their potential for damaging the grape crop by direct feeding. Some ant species protect and tend mealybugs in order to feed on sugary “honeydew” produced by mealybug feeding activity in grapevines. As a result, ants disrupt integrated pest management (IPM) by interfering with natural predators and parasites that assist with mealybug control. In addition, ants can help spread mealybugs within vineyards, and help maintain below-ground colonies of mealybugs near vine trunks and on vine roots. 

Recent research and trials with polyacrylamide hydrogels combined with ant insecticides was funded by a grant from the California Department of Pesticide Regulation (DPR). Led by University of California Cooperative Extension (UCCE) IPM Specialist and Entomologist David Haviland, based in Kern County, this project is expected to lead to new ant control products that could receive regulatory and label approval this year. This research also produced a new University of California Agriculture and Natural Resources (UCANR) publication: "Ants of California orchards and vineyards: an identification and management guide." This publication will be available online in PDF format soon, in the meantime, contact Haviland (dhaviland@ucanr.edu) to receive an electronic file.

The Lodi Winegrape Commission (LWC) hosted an educational meeting and field day March 12 to present results of this research, information on monitoring ant populations, and how to use gel baits with insecticides to reduce ant populations. 

Ant Monitoring and Identification

More than 275 ant species have been identified in California, which include introduced or non-native species, but a small percentage are considered agricultural pests. Collecting, identifying ant species, estimating numbers and monitoring ants in vineyards is important in order to determine the need for, and the type of control measure based on the ant species' preferred diet. Recent studies indicate that more species exist that tend mealybugs in addition to the Argentine ant (Linepithema humile), which was originally the main focus in vineyards, and is the main species of concern in coastal California vineyards.

The new "Ants of California" guide lists 15 common ant species found in vineyards and orchards during the DPR research project with information about physical characteristics for identification, nest characteristics, behavior and preferred food sources. Growers can also collect ants and contact their farm advisor to assist with identification. Haviland said it is common to see up to five different ant species in a vineyard.

Ant species seen in San Joaquin Valley vineyards include the Native Gray or Field Ant (Formica aerata) that feeds on sugar and protein, and the Pavement Ant (Tetramorium immigrans) a generalist forager that feeds on insects, honeydew, nuts and fruit and is common in Lodi area vineyards.  

Other ant species listed in the guide as honeydew or sugar feeders and may be found in vineyards include: Bicolor Pyramid Ant (Dorymyrmex bicolor), Pyramid Ant (Dorymyrmex insanus), Dark Rover Ant (Brachymyrmex patagonicus), High Noon Ant (Forelius pruinosus), Pharaoh Ant (Monomorium pharaonis), and False Honey Ant (Prenolepis imparis). The Field Ant (Formica perpilosa) is the predominant species in the Coachella Valley and feeds on honeydew.  

The California Harvester Ant (Pogonomyrmex californicus) is seen in Southern San Joaquin Valley vineyards, but feeds mainly on seeds and dead insects. The Thief Ant (Solenopsis molesta) can also be found but primarily feeds on proteins. 

Other species—the Southern Fire Ant (Solenopsis xyloni) and the Red Imported Fire Ant (Solenopsis invicta) are mainly protein feeders and not a concern as mealybug tenders, but as stinging ants their control may be warranted as they are a potential hazard or nuisance for vineyard workers. Other ants more commonly found in residential settings may be encountered in vineyards. The Carpenter Ant (Camponotus spp.) is commonly found in wood, but is a generalist scavenger and may feed on honeydew from plants produced by aphids, whiteflies and scale.

Nathan Mercer, a researcher on the DPR research grant team who now works for the California Department of Food and Agriculture (CDFA), presented information on monitoring using cotton ball samples. Cotton balls saturated with sugar water can be an easy and effective way to sample and quantify ants in early spring (March, April) when ants begin foraging. Dissolve one part sugar in four parts water and soak cotton balls in this solution, then place them in the vineyard on the ground near the base of vine trunks.  After two hours in the field, return and inspect the cotton balls and record the number of ants at each site. Actual count numbers may be impractical, so use a rating scale such as: 1 for 1-10 ants, 2 for 11-49 ants, and 3 for 50+ ants. If unknown or different ant species are observed, collect samples for later identification.

Ant Control Materials and Methods

The broad-spectrum insecticide chlorpyrifos was formerly an option for ant suppression, but it was prohibited by DPR for agricultural use in California after 2020. Other ant bait products available differ based on their chemistry, method of application and the ant species diet.  Ant baits were primarily developed for residential use and for use in a bait station. Both liquid and granular baits are available for use with EPA-approved bait stations. While these can be effective, and may be useful in small vineyards, costs associated with the deployment and maintenance of bait stations make them impractical for widespread adoption in commercial vineyards. 

Research trials in vineyards show that granular baits applied by broadcast with a fertilizer spreader or seed spreader pulled by an ATV can be distributed more quickly and more frequently over a larger area and can be more practical for larger vineyards. Recent studies have focused on development of hydrogel-based baits that allow liquids to be field applied using a gelatinous substrate using traditional fertilizer or seed spreaders.

Mercer presented results of research trials, including two years of trials in Lodi vineyards, comparing effectiveness of five different insecticides applied with hydrogels. While each material worked to reduce ant populations, results showed that Syngenta Platinum (active ingredient thiamethoxam) worked best as a conventional material. For organic use, research suggested Corteva Entrust (active ingredient spinosad) as an effective product, and it is listed with the Organic Materials Review Institute (OMRI) for certain uses. Boric acid is another low toxicity material that may be suitable for IPM programs.

The polyacrylamide hydrogel preparation uses an off-the-shelf product such as Soil Moist from JRM Chemical, Inc., or Miracle-Gro Water Storing Crystals, sold in garden shops and hardware stores designed for use in potting mixes to retain soil moisture. Baits are made by placing a small amount of active ingredient toxicant into sugar water, then adding the dry hydrogel crystals and allowing the solution to absorb into the hydrogel beads.

Haviland demonstrated the hydrogel preparation and mixing process in 5 gallon buckets. Once mixed, the solution must be allowed to sit for a minimum of 4 hours for the gel to set into beads. Haviland then demonstrated the bead bait application, placing the beads in a hopper of a fertilzer spreader mounted on the back of an ATV. Detailed instructions for mixing and applying the hydrogel bait is in the new ant management guide.

Once applied in the vineyard, ants drink the liquid at the hydrogel surface, carry it into the nest, and distribute it as food within the ant colony to cause the colony to collapse over time. It is recommended the gel baits be applied under the vine row near vine trunks at a rate of 5 to 10 gallons per acre. Since the gel beads will evaporate over a period of about 1 to 3 days, they should be applied in mornings, or under cool or foggy conditions, to prevent the beads from drying out too quickly.
 
Hydrogel beads with ant baits can be applied with
fertilizer or seed spreaders on an ATV for ant
management in larger vineyards.
(Photo: Ted Rieger)

For organic use with spinosad, a different alginate hydrogel mix is recommended that can be easily made with materials that include sodium alginate, calcium chloride and potassium sorbate. Because these ingredients are considered food products, it is believed this gel mix will be more quickly approved by regulators and OMRI for use in organic vineyards.

Depending on seasonal and climatic conditions, and location, ants emerge from nests and begin foraging from March to May in California vineyards. Researchers are recommending two gel bait applications in vineyards, one around April 1 and one around May 1, when ants begin foraging. Once mealybug activity begins producing honeydew later in the season, this becomes the ants' preferred food source, and they will not likely be attracted to gel baits.

Napa County Cooperative Extension Viticulture Farm Advisor Monica Cooper has conducted trials to evaluate commercial and experimental ant baits for control of Argentine ants in Napa County vineyards, including the use of gels with boric acid applied with a broadcast spreader. For information on ant management in Napa County vineyards with a focus on Argentine ants, see: https://ucceviticulturenapa.wixsite.com/uccevitnapa/ants
 

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