Although bird damage is not a serious problem for most San Joaquin Valley vineyards, some, particularly those along rivers and streams, may suffer significant losses to certain avian species.
Mike Taber, field products manager of Wildlife Control Technology, Inc. in Fresno, urges growers to sort out which species are actually causing damage and which are not, along with the legal restrictions involved, before they launch a bird control program.
At a recent grape symposium in Easton, Taber said house finches and starlings are the major bird pests in the valley, even though some growers may be convinced that valley quail and mourning doves are culprits.
“Quail and doves may be mating in your vineyards in large numbers, but for the most part, they are not causing damage to your grapes because they feed on much smaller things,” he said.
House finches, or linnets, are small birds that nest in March in the SJV and into the summer in cooler grape growing areas of the state. Although they are classified as a migratory species, their young remain around where they were born as they mature. They tend to flock and may feed on grapes as the fruit matures but cause wider damage in vegetables and other crops.
Late table grapes such as Autumn Royal and Crimson Seedless are the most vulnerable to house finches pecking at individual berries. Beyond that damage, juicing attracts fungal diseases that inflict further losses.
Permit to control
House finches are under the Federal Migratory Bird Treaty Act with management supervised by county ag commissioners. A permit is required for control measures, and the birds may be killed only to protect crops from depredation.
House finches or parts of them shall not be sold or removed from the area where they are killed and an estimate of the number killed shall be submitted to the local ag commissioner each month and at the end of the year.
Taber said permit holders are liable for damage to persons or property by the use of traps or shooting/hazing of the birds, and county officials will likely review their control program. No non-target birds shall be killed, and a copy of the permit must be in possession of the permitee or his agent or employees when shooting or hazing is done.
Shooting or hazing can be expected to be under greater scrutiny by county officials in areas close to urban settlements. Hunting licenses are not required for house finches, but Taber advised growers to get them also for full compliance with technicalities in state laws.
Starlings not protected
Starlings, since they form flocks of thousands, also contribute to the increasing pest bird population in Fresno County, in urban settings as well as rural. Starlings are not protected by federal or state laws and can be taken without permits.
One clue to which species is causing damage in grapes, Taber said, is berry damage. House finches peck at berries, and starlings consume whole berries, a large flock of them able to claim a third of a vineyard's crop. Damage from starlings is sometimes mistakenly blamed on the bees that congregate on damaged clusters.
Regardless of which species is the problem, growers need to monitor vineyards closely and prepare for a broad approach, using more than one control technique, for success in protecting the crop.
“Don't just put one type of control out and then walk away, expecting it to do the whole job,” he advised. Another tip is to place the control first at the edges of the vineyard, because the birds start feeding in areas that are closest to power lines or buildings where they feel more secure.
Modified Australian crow traps, which require permits, can be one of the most effective controls, especially if used year-round.
These traps consist of a framework covered with wire-mesh and equipped with feed (peach culls, grain, poultry pellets), water, and shade for trapped birds. Birds slip in through narrow slots in the traps but cannot escape. Non-target species are later separated and released, and target species are destroyed.
“If you use this technique, leave a couple of birds in the trap to draw more in, and remember to put the trap on level ground to keep the birds from escaping at the bottom,” Taber said.
To increase the effect, he added, doors of traps can be left open to allow birds to come and go after feeding. Once the birds become confident, the doors are closed.
Plastic netting can offer some control success when an established bird population is causing severe damage, but Taber said it's debatable whether it is the most effective. “It is not always the most cost-effective technique, depending on the pest species, the value of the crop, and the amount of loss.”
He said finches and some other birds are ground-based feeders and will try to enter through the bottom edges of netting to get to the fruit, requiring that the material be secured at the bottom.
In the case of starlings, however, since they move from the top down, netting over the top portion of the canopy can prevent them from getting through. In some cases, netting works best when combined with other means, such as gas cannons.
Taber said reflective balloons and strips initially stop birds from reaching the crop, but after few days the birds realize there's no threat and move in. “These may work close to harvest, so don't put them in vineyards in July and expect them to be effective until harvest. Wait until the last possible minute.”
He said rigging reflective strips on wires originally was effective for keeping predatory birds from fish farms, but in vineyards the close interval of wires themselves, not the reflective strips, interferes with flocks of birds alighting on vines.
Propane cannons to simulate gunfire can be very effective, but he said they have no effect on bird pests at night and are more likely to annoy neighbors.
Strobe lights, while widely documented as a way to make birds uncomfortable, are not well suited for vineyards because of the numbers that would be required.
Taber has little regard for plastic owls, even though many growers buy them as a way to make birds uncomfortable, are not well suited for vineyards because of the numbers that would be required.
Taber has little regard for plastic owls, even though many growers buy them every year. More than one account tells of target pest species seen perched on the head of one of the dummy owls. “If you want to do something with owls, put a nest box, and at least you'll get some rodent control from it.”
Noting he was not always enthusiastic about electronic bird controls, Taber conceded that recent technology has improved them, depending on the targeted species. Systems that broadcast a distress call may cause a targeted species to investigate the distress, although that same species may be frightened away by sounds of a hawk or other predator.
Bird repellants are normally not acceptable for use in raisin, wine, or fresh market grapes. Although some are registered, growers should check with packers or marketers to see if they are allowed. In general, no toxicant baits are available for use by grape growers.