Snail- aaainst~~ -- snail ---__-- - u- Theodore W. Fisher 0 Robert E. Orth 0 Stuart C. Swanson Thedecollate snail, Ruminu decollutu Lin- Agricultural Commissioners in four other neaus (Family Achatinidae, Subfamily Subu- counties. These well-established colonies im- lininae) attacks, kills, and consumes brown plied introduction perhaps as much as 10 garden snails, Helix uspersu Muller (Family years earlier. They included a citrus grove with Helicidae), especially those less than half a residence at Ojai (this property has never grown. This suggests the possibility that the had a brown garden snail population), and snail can be used as a biological control residential properties in Riverside, San Ber- The decollate snail against the brown garden snail, the most nardino, Rialto, La Habra, and San Diego. important pest land mollusk in California. Today on these properties brown garden feeds on brown garden Since 1972 the decollate snail has been snail is either absent or is present in low snail without harming observed in the laboratory and in outdoor numbers, and mature individuals dominate healthy plants or fruit. confinement cages, private gardens, citrus the size class distribution. Properties nearby groves, and freeway plantings. It displays but without the decollate snail generally have very little tendency to eat healthy leaves, high populations of brown garden snail re- ties. In March 1980 the decollate snail was flowers, or fruits still attached to the plant quiring bait applications for control. Proper- found in San Jose, Santa Clara County. but may vigorously feed on old leaves, ties that have had decollate snail for 15 or Neither the decollate snail nor brown gar- especially those in contact with the soil, and more years probably give a realistic sense of den snail prospers in natural (undisturbed) fallen bruised fruit. results to be anticipated from establishing habitats in southern California. Both species The decollate snail evolved in North new colonies, at least in southern California. appear to thrive in cultivated situations with Africa and is commonly found around the As this study progressed, it became ap- frequent irrigation. The climbing habit of Mediterranean Sea. It has been distributed parent that the decollate snail had been in- the brown garden snail is well known, but widely in commerce; because it is a burrow- troduced in specific locations 5 to 10 years the decollate snail climbs up tree trunks and ing species, the eggs, hatchlings, and before its discovery as an established popula- walls or fences only when heavy rains flood juveniles are not easily detected in the soil of tion. To date 13 counties are known to har- it out of its accustomed niche, which is in the plants being transported in containers. In the bor the decollate snail. Studies in citrus upper inch of soil. United States it was reported first from groves are in progress in the counties of Im- In home gardens feeding by the decollate South Carolina in 1813 and has since been perial, Los Angeles, Orange, Riverside, San snail has been reported on leaves of Dichon- found in Alabama, Arizona, California, Diego, Tulare, and Ventura. Studies of dru, baby tears, and violets, on cotyledons of Florida, Georgia, Louisiana, Mississippi, freeway plantings are being conducted in germinating seeds, on very young seedlings, New Mexico, North Carolina, Oklahoma, Fresno, Orange, Sacramento, San Bernardino, and on flower petals. It is not clear if the de- Texas, and Virginia. San Diego, Santa Barbara, and Ventura collate snail initiates this sort of feeding or if In California the decollate snail was counties. Observations are continuing at it follows mechanical bruising caused by discovered first in Riverside on January 12, private residences in Kern, Orange, River- pruning, mowing, human or animal traffic, 1966, and by April it had been reported by side, San Bernardino, and San Diego coun- or initial bites by primary plant feeders. It is difficult to differentiate feeding damage of decollate snail to green, living plants from that of other organisms that feed similarly on living plant tissue, such as brown garden snail, slugs, and pill bugs. After several true leaves have been formed, the decollate snail usually has little further interest in the plants. On 14 species of common garden orna- mentals and vegetables, an outdoor caged forced feeding test at University of Califor- nia, Riverside, demonstrated that the decol- late snail would feebly attack established growing plants. Carrots (roots) while still growing in the soil were only occasionally nipped on the aboveground exposed portion. Yet when those same carrots were pulled up and laid on the soil, the decollate snail fed on them extensively. Only very minor feeding on growing green leafy plants was observed in these tests, and in no instance was a well- established plant destroyed. However, new sprouts of recently sown seeds were attacked. 18 CALIFORNIAAGRICULTURE, NOVEMBER-DECEMBER 1980 Typical damage by brown garden snail. gation. This was not planned as an integrated pest management program, but in retro- spect, that is what it was. We hope the strategies and tactics that evolved during this study may serve as guides for future programs tailored to meet specific local conditions. The rate of decollate snail spread in citrus groves varied widely from grove to grove; frequency, duration, and type of irrigation were the main determinants. In general, greater movement between rows occurs under sprinklers than with drip systems, but the greatest movement occurs during light, warm rain. Acceptable biological control of brown garden snail has not yet occurred in the five groves shown in the table, possibly because the decollate snail is continuing to spread, and its population is not yet of suffi- Decollate snails have nested under fruit on ground without causing damage. This citrus cient density to effect economic control of grove has had a decollate snail colony for at least 15 years. brown garden snail. However, brown garden snail counts are declining in pockets within In San Bernardino along a well-irrigated migration onto the surface of the highway by the Baker grove (Orange County) test plots north-facing freeway planting of Baccharis, the decollate snail occurred, whereas where the decollate snail occurs in relatively Osteospermum, and later Carpobrotus, previous such behavior by brown garden large numbers. three years beginning in 1974 elapsed before snail had threatened to cause passing vehicles The high compatibility of decollate snail the progeny of succeeding generations of an to skid. with citrus production is indicated by the introduced colony of 1,900 decollate snails A combination of factors brought the following observations. The heaviest known had worked their way approximately 600 feet brown garden snail problem under control: population of decollate snail has been eastward. There was no migration to the replacement of some of the original ground reported from Yuma, Arizona, by a pest west because of a wide dry concrete apron cover, Osteosperrnum, with Carpobrotus; management consultant who estimated 22.5 beneath an overcrossing, or to the south into reduced irrigation; continued use of snail gallons of snails per acre in irrigation basins residential properties at the top of the ap- baits and repellents on the periphery; and of Valencia oranges. (There are approxi- proximately 45 O slope because of an in- predation mainly on juvenile brown garden mately 3,400 snails in the %- to l-inch size tervening path of bare soil 4 feet wide to snail by the decollate snail within the plant range per gallon.) There was no snail damage which Caltrans personnel liberally applied mass. Former practices that were discouraged to fruit, and brown garden snail was not ammonium sulfate as a deterrant to move- were broadcasting of baits into the ground present. Near Lindsay, California, in groves ment of snails. Further movement eastward cover, which reinforced the resistance of with large decollate snail populations, small was blocked by another wide dry concrete brown garden snail to metaldehyde (Ca/ifor- numbers of the snail have frequently been apron beneath an overcrossing. No massive nia Agriculture, June 1975), and excessive irri- seen beneath large green navel oranges rest- ing on the soil in depressions caused by their weight, but no feeding scars were apparent. When attempting to integrate decollate snails into a brown garden snail control pro- gram, there may not be enough available to inoculate all trees in a grove simultaneously, so an alternate method is to inoculate a cluster of core trees and monitor the spread. Results will be slow, as indicated in the table. Because both methiocarb (Mesurol) and 7 percent metaldehyde kill the decollate snail, it is important to provide an unbaited buffer zone between the expanding colony and that portion of the grove receiving poison bait. The maximum dispersal rate measured for CALIFORNIA AGRICULTURE, NOVEMBER-DECEMBER 1980 19 the decollate snail was 65 feet in three would be to broadcast, at first, 50 or more southern California have begun to mass- months in a sprinkler-irrigated grapefruit snails per tree over an entire grove. This produce decollate snail for release against grove near Hemet, Riverside County. release method presumes a ready supply of brown garden snail on their properties. Assuming the effectiveness of baits will be decollate snails and a relatively low initial dispelled within four weeks, a two-tree buf- population of brown garden snail, as would fer would suffice to protect developing col- be expected after a baiting program. This Theodore W. Fisher is Specialist, and Roberr E. Orth and Stuarf C. Swanson are Staff Research onies of the decollate snail. As the snails method may also be used as a preventive Associates, ofEntomology, Division disperse, the buffer zone should be advanced measure before brown garden snail moves of Biological Control, University of California, ahead of them.