WARM WINTER STORMS STIMULATE Ask a citrus grower to recall the fallout from the last major El Nino and there's a good chance high snail populations will be mentioned. "Snails were the No. 1 problem after the big storms in 1983," noted Nick Sakovich, a UC Farm Advisor for Ventura and Santa Barbara Counties. If the weeks ahead bring similar weather, it will take a complete program to protect against damage to leaves and especially fruit. Since the last big El Nino, UC researchers have developed a complement of cultural and chemical controls. Add the practice of using ducks to clean up snails and there's a wide range of options. But, said Sakovich, the first option is to use bait to knock down populations and follow through with IPM practices. While the decollate snail is a good predator of the brown garden snail, it's a long term solution, Sakovich cautioned. Depending on populations, it may take around five years before the "killer snail" gets the upper hand. It can also be an expensive control measure. Depending on supply and demand for the predator, costs have ranged from around 5 cents to 25 cents per snail. But as growers are well aware, a potential for high losses dictates using as many options as possible. According to the farm advisor, some growers put ducks in groves to feast on snails, a practice similar to the old strategy of using "weeder geese" for grass control. Among the more traditional cultural practices, Sakovich said skirt pruning does a "decent job" of keeping snails in check. A copper band around trunks is another element in a complete program. He noted that copper foil may be damaged by animals that seek out insects inside of bands. If you use a Bordeaux slurry instead of foil, Sakovich recommends adding a latex house paint. A slurry normally lasts about one season, but latex paint can extend the protection period to around two seasons. Success with cultural practices, however, depends on using baits to reduce snail populations. Sakovich has tested a number of different products the last several years. Last October, he did research in a lemon grove near Oxnard, evaluating Deadline, other metaldehyde products and Sluggo, a new organic bait. Deadline and Sluggo had the highest control ratings in replicated trials, he reported. Control was measured by counting dead snails on three different days over a 33 day period. On each date, counts were made after irrigating for 18 to 24-hours with a mini-sprinkler system that gave good water distribution. Of the two most effective materials, Sakovich said 40 pounds of Sluggo per acre had the highest kill, or 127 snails when averaged over five replicated test plots. Twenty pounds of Deadline was nearly as effective (105 dead snails) and control wasn't significantly different, he reported. He said Sluggo is the first organic bait he's tested that's highly effective and compares to a metaldehyde product like Deadline. After three irrigations and 33 days in the field, the organic material appeared to hold up well, he observed. The active ingredient in Sluggo is iron phosphate, a naturally occurring soil component. The iron salt is extremely low in mammalian toxicity and non-toxic to wildlife and pets. Regardless of the material used, Sakovich pointed out that placement is critical. Snails take more bait if it's placed under trees. Based on his experience, activity is usually concentrated on the north side of the area under the tree canopy. However, maximum control occurs when snails are dehydrated by sunlight after consuming bait. For best results, he recommends placing bait between rows and close to drip lines. As a general rule, he added, decollate snails can be released into groves around 60 days after bait is used. The best time to introduce the predator is from February to May when it's warm and damp. The decollate snail is effective under light infestations, noted PCA Scott Scarbrough of Western Farm Service, Goleta. "Control with either decollate snails or baiting is enhanced by copper banding or skirt pruning," he said. Ideally, both tasks should be done before the rains begin, with skirt management continuing throughout the season. Subtropical rains stimulated snail movement this winter, Scarbrough reported. Activity started in November, slowed with cooler weather in December and picked up again in January. January through March are key months for using bait. "Irrigation through the entire season may cause snail movement that should be treated if infestations are causing damage," he added. The PCA said most growers recognize the need to use cultural practices to supplement baits. But, he cautioned against stretching the protection period for Bordeaux slurries. Adding latex paint may extend effectiveness to about 1-1/2 seasons, but he prefers to see a slurry applied to trunks every season. "Snails definitely don't like copper" and a foliar spray is a good way to get them off of trees, he said. It's a good idea to incorporate copper into brown rot sprays, Scarbrough advised. The PCA observed that a warm wet winter has created a "perfect environment" for snails. He added that weather conditions have been similar to 1996, "which was a pretty good snail year." |
