Stephen Vasquez and Roger Baldwin

Vertebrate pests live in and around vineyard settings and can cause significant damage. Damage will depend on the vineyard location, surrounding habitat, and population size of the vertebrate pest in question. Gophers, ground squirrels, and rabbits are the primary vertebrate pests in the San Joaquin Valley and will cause long-term damage if left unchecked. Gnawing on grapevine roots and trunks will lead to large patches of dead vines. These pests can also damage irrigation systems and cause erosion by diverting water via their burrows. Although these pests have natural predators, growers should not rely on them solely for controlling large populations of vertebrates. Recently, Roger Baldwin and I held a field day that focused on gopher management in vineyard settings. Following are some of the strategies that were discussed at the field day.

Gopher Habitat
Visual identification of gophers may prove difficult since they rarely venture outside of their burrows. Living underground, gopher activity includes the building of an intricate burrow system that can only be detected by the distinct mounds found at each opening. Openings to the burrow matrix will typically be plugged, but recent activity can be indentified by the moist, friable soil that gophers push out of recently made burrows. Growers should focus their management efforts on these types of mounds and not the ones that are dry.

Injury
Feeding mostly on root systems of herbaceous plants, gophers will sometimes pull entire plants below ground or nibble on above ground plant parts near their tunnel entry. Grapevines are damaged when gophers gnaw on roots or bark below the soil line. Vines damaged by this type of feeding will look water stressed or will die as a result of girdling, a process that removes the cambium and does not allow for natural repair. Vineyards older than ten years of age display little damage from gophers, perhaps due to the larger root system characterized by the corky periderm protecting the inner bark layer and cambium.

Management

Traps
Traps, when set correctly, work well against gophers. Traps, like all control methods, are most effective when populations are low. Several types are available, but the two-pronged pincher types are the most popular (Fig. 1). When populations are high, trappers will need to focus their efforts in localized areas with high activity, setting traps multiple times throughout the season.  Once gophers are controlled in those areas, new efforts should expand out from these centralized areas until the whole vineyard has been controlled.

Setting Traps

• Locate main burrow using a probe (long screwdrivers work well) and open a section with a gardening shovel large enough so traps can be placed within the burrow.
• Place traps in pairs facing opposite directions (Fig. 2).
• Secure traps with a wire flag for monitoring and retrieval.
• Openings can be left open or covered. If you plan on covering the opening, use cut pieces of a dark fabric (or other material, e.g. plywood) to exclude light. Place soil around the edges of the fabric covering hole to help exclude excess light and encourage the gopher to continue using the tunnel. However, covering does not appear to influence capture success, so if setting numerous traps in a vineyard, leaving openings uncovered can save valuable time.
• Monitor traps daily, moving and resetting in a new location if necessary.

Baiting*
For large populations, toxic baits have often been used and can require less time to apply. Three different types are available to grower: Strychnine¹, zinc phosphide¹, and anticoagulants¹ (diphacinone and chlorophacinone). Baits can be applied by using hand applicators or by a tractor driven mechanical applicator that makes a pseudo tunnel. 

Hand Applications

• Using a gopher probe/applicator (Fig. 3), locate burrow near a fresh mound. It is important that bait be placed 12-18” away from burrow entrance on both sides of the opening. Bait placed too close to the opening or too deep will encourage the gopher to seal the burrow.
• Dispense bait into tunnel through probe.
• Cover the opening with soil or a rock to exclude light. Place soil around the rock or object covering hole to help exclude excess light and encourage the gopher to continue using the tunnel.
• Place bait in two to three locations within burrow.
• Monitor activity and reapply as needed.

¹. May be restricted use material depending on such aspects as concentration of the active ingredient, method for applying bait, and where bait is applied.  Restricted use materials require a permit for purchase and use. 

Mechanical Applications (Burrow Builder)

• Determine soil moisture. Soil should contain enough moisture so the pseudo-burrow will not collapse (too dry) or tractor does not get stuck (too wet). Late winter or early spring is the best time to use burrow builders (Fig. 4).
• Pseudo-burrows should be made down row centers between vine rows.  The perimeter of the infested area should also be baited.
• Check to make sure burrows are being properly made and baited.
• Limit vineyard equipment usage for several days in order to maintain the integrity of the pseudo-burrow. This will allow gophers to find the burrows and consume bait.
• Monitor activity and reapply as needed.
• NOTE: Burrow builders should only be used if populations are high. Making single tunnels the length of the vine row may encourage and increase gopher activity.

Fumigants*
Many fumigants are not very effective against gophers due to their ability to detect and seal off tunnels quickly. However, aluminum phosphide¹ works well during the late winter or early spring months when the soil is moist. Soil moisture helps retain the gas within the burrow. Burrows should be located using a probe and tablets dropped into the hole and sealed. Activity should be monitored to determine effectiveness of fumigant. Follow up with additional treatments if new activity is noticed. Fumigants should not be used in gopher burrows near or around buildings due to potential escape of the resultant gas into buildings.

¹ Restricted use material and requires a permit for purchase and use.

Gas Explosive Device
A device that combines propane and oxygen in a given mixture, which is then ignited, producing a violent explosion within a gophers burrow is also available. Through a concussive force, the burrow(s) and their residents are destroyed. Like fumigants, this device should not be used near buildings due to leakage and the potential damage caused by the explosion.

Final Thought
Gophers are a difficult species to control given that they reside underground. Because of this, gopher control is costly and time-consuming no matter which approach you use. Therefore, much effort should be made to keep gopher populations low within your vineyards. If you take the time to maintain consistently low gopher populations, you will experience substantially greater savings on gopher control and will likely see greater production from your crops than if you only deal with gopher populations after they reach high levels.

* Always read and follow label directions when using pesticides.

Figure 1. Traps

Figure 1. Two types of traps. 1a and 1c are not set. 1b and 1d are set and ready to place in a burrow.

Figure 3. Baiting

Figure 3. A) Correct application method requires that bait be placed on both sides of tunnel opening 12-18” away. B&C) Poor application methods encourage gophers to seal the burrow.

Figure 4. Burrow maker

Figure 4. Mechanical burrow builder and bait applicator.

European grapevine moth (aka European grape berry moth; (Lobesia botrana) was recently found in Napa County, a first known find for California. The insect has the potential to cause great economic harm to California’s diverse grape industries. The moth was trapped in Napa County’s, famous Oakville grape growing region known for high valued wines. Common to Europe and the Mediterranean, European grapevine moth has been intercepted from across the US where international travelers, cargo or mail disembark from planes originating from overseas. Currently, the Napa County Agriculture Commissioner is working with the CDFA and USDA to survey the area where the moth was first located in an attempt to detect additional European grapevine moths.

European grapevine moth identification

European grapevine moth can be confused with American grape berry moth (Endopiza viteana) native to the eastern United States or European grape berry moth (Eupoecilia ambiguella). Wings of the invasive European grapevine moth, L. botrana, have a mosaic shaped pattern with black-brown, cream, and gray-blue ornamentation (Fig. 1).  Larvae tend to develop a purple cast after feeding and will often be found inside the berry. Samples should be taken to a trained university or state entomologist for proper identification and documentation. It is important to note that samples should be enclosed in a sealed container, jar, or vial if found prior to moving the insect (all stages) from an infested site.

Damage

Damage can be seen to both grape flowers and developing fruit. Larvae feed on flowers prior to bloom and continue through bloom. As bloom peaks, larvae protect themselves by producing webbing around the damaged flowers and feeding on neighboring flowers and parts. Second and third generation larvae feed on berries hollowing and contaminating them with excrements (Fig. 2). Cultivars that naturally have tight clusters—like Chardonnay, Pinot noir and Zinfandel—will suffer the most damage. Much like infestations from other worm pests, feeding damage will lead to infections by bunch rot fungi. Raisin and table grape cultivars will also experience damage, especially when bloom is prolonged due to weather, making flowers less responsive to applications of gibberellic acid used for bloom thinning. Table grape cultivars with tight clusters have the least tolerance for the moth due to fruit feeding damage and contamination with webbing, excrements and rot. All life stages can be found in vineyards infested with European grapevine moth but larvae from the second and third generations have been found to be the most damaging when fruit is maturing.

Host range

The host range for European grapevine moth is diverse. In addition to Vitis vinifera (cultivated grape), they also feed on other important agricultural crops like apple, cherry, nectarine, persimmon, plum, pomegranate and olive. It has been documented that privet and some grape cultivars are preferred for oviposition. Plants should be inspected for eggs, larvae and pupae. Larvae can be found in flower or fruit clusters along with webbing and in berries or other fruits. Pupae are frequently found inside a silken cocoon in rolled leaves, inside clusters, and under the bark of any of the previously mentioned host. At this time there are no regulations in place regarding the movement of fruit or other plant material from Napa County but growers and industry representatives should be vigilant. Trapping beginning at budbreak, using a tested pheromone is the best approach to monitoring vineyards for activity. Pheromones attract males to traps and allow one to estimate a population of European grapevine moth. With cooler fall temperatures, adult moths will be absent and only the diapausing pupal stage inside a silken cocoon can be found protected by grapevine bark. Growers should consult with their County Agriculture Commissioner or University of California personnel to determine the best approach to monitoring and properly identifying European grapevine moth.

Stephen Vasquez the UC Cooperative Extension viticulture farm advisor in Fresno County. Walt Bentley and Lucia Varela are UC IPM advisors in Fresno and Sonoma Counties, respectively.

Lbotrana-moth

Figure 1. Adult European grapevine moth displaying mosaic. Photo credit: Chilean Wine Corporation A.G.

Lbotrana-MC

Figure 2 L botrana feeding on berries. Photo credit: M. Cooper

University of California (UC) researchers have extended information at Grape Days for 58 years.  Here is a brief history, as remembered by Amand (Kas) Kasimatis and L. Peter Christensen, Extension Specialist Emeriti, Dept. of Viticulture and Enology, UC Davis.

Commodity days were quite popular on the Davis campus in the early fifties; the first Grape Day was held there in Aug., 1951.  H. B. Richardson, Ext. Specialist, and A.J. Winkler, Chair of the Dept. of Viticulture and Enology, organized the first program.  At the time, there was a lot of field research being done in the University vineyard, so most of the Department faculty put on a demonstration. It included lunch on a lawn with shade trees around the Viticulture fieldhouse and had a luncheon speaker.  L. Peter Christensen remembers attending one of campus Grape Days in the mid 1950s.  “Nick Dokoozlian Sr. drove the van. It was very popular and awe inspiring for a farm boy.”  Amand Kasimatis took over in 1956 and chaired the campus programs yearly until the early 1980’s.  In January 1976, Kasimatis, in collaboration with California Association of Wine Growers, developed Wine Grape Day.  Additional Wine Grape Days were held every February through 1985, on the Davis campus, with the exception of one that was organized by Vince Petrucci (Professor of Viticulture, CSU Fresno), and held in Fresno.  No Grape Days have been held on campus since 1985, but the Department presents RAVE (Recent Advances in Viticulture and Enology) in March.

In the 1960s, Kas established several regional Grape Days at off campus facilities.  The first of these was the Coast Grape Day, at the Oakville Station, Napa Valley.  Grape Day at Oakville continued for some time, eventually under the direction of Jim Wolpert.  The first Grape Day at the Kearney Agricultural Center (KAC), also initiated by Kasimatis, was held in 1967, two years after the center was opened.  Kasimatis directed Kearney Grape Days until 1973, when Fred Jensen (Extension Specialist Emeritus, UC Davis) assumed those responsibilities.  In the mid 1980s, L. Peter Christensen became an Extension Specialist, and then was responsible for the Grape Day at Kearney until Nick Dokoozlian (former Specialist, Dept. of Viticulture and Enology, UC Davis) took over in the early 1990s.  Since 2005, Matthew Fidelibus has organized Grape Day at the KAC.  We hope you find this year’s program to be interesting and enjoyable, and that you will join us again in 2011.

 

Erineum mite populations seem to be exploding this season. In the past two weeks, a half-dozen samples have been dropped off at my office for inspection. Normally, a few samples are brought in from backyard vineyards, which I expect. However, the most recent samples and calls have been from commercial wine grape vineyards with concerns that it is downy mildew. First, let me assure you that it is not downy mildew. The Valley has not experienced an outbreak of downy mildew since the mid-90’s when a few table grape vineyards were identified with the disease after optimal weather; rain and warm temperatures. The recent erineum mite outbreaks in commercial vineyards are easily explained by a reduction in sulfur use for powdery mildew. Winegrape vineyards tend to experience more frequent outbreaks when wineries request a reduction in sulfur dust so it does not interfere with fermentation. Below is a summary of erineum mite life cycle.

Leaf

Grape displaying blistering.

Erineum mite

Grape erineum mites.