Reducing African Snail Damageto Yams in American Samoa

SUMMARY
Yams are an important traditional crop in American Samoa. Giant African snails, first introduced into the territory in 1978, have become a serious pest of yams, feeding on the young plants shortly after sprouting. Some farmers cite anecdotal evidence that ash barriers can help protect yams and other crops from snail damage, but the practice has not been tested experimentally. This project found that ash barriers failed to protect sprouting yams from snail damage. This lack of efficacy may stem in part from the difficulty of maintaining ash barriers in the heavy year-round rains of American Samoa.

OBJECTIVES
· Assess the efficacy of ash as a deterrent to young yam plants from African snail
· Disseminate the knowledge gained to other farmers growing yams in their plantations

INTRODUCTION
Yams are important contributors to food security for American Samoa. Mature yams are protected in the soil from hurricanes and remain edible long after reaching maturity. They are part of a traditional mixed farm system that includes taro, breadfruit, bananas and a few other fruits and vegetables, often grown in weedy mulch. These systems are ideal hosts for giant African snail, introduced to American Samoa in 1978. The snails attack young yam plants, feeding on the exterior layers of stem tissue, reducing growth and sometimes killing the plants.

Many farm families in American Samoa still use traditional ovens for cooking at least once a week. From the wood fuel, the ovens produce ash, purported to deter giant African snail when spread around the base of susceptible plants. This project sought to test the hypothesis that ash barriers around young yams can protect them from damage from giant African snail.

METHODS
Sixty yam species were planted into a 700-square-foot area that had recently been hand weeded, with the pulled weeds left on the soil surface as mulch. A 2-foot-diameter circle was cleared around each plant, and a ring of ash applied around half of the plants at alternating points of the 4-foot by 4-foot planting grid. The sprouting plants were assessed for damage by giant African snail. Many of the seed pieces in the original planting did not sprout. These were replanted. The original planting was done June 29, 2003, and the sprouted yams from the planting were assessed for damage on July 31. Yams sprouted from seed pieces that replaced those that did not sprout in the first planting were assessed for damage on Sept. 19.

RESULTS
Few of the seed pieces in the first planting sprouted. By July 31, nine of 12 ash-treated plants (75%) that did sprout showed snail damage. Eight of 14 (57%) of the untreated plants that sprouted were damaged by snails. In the repeat planting, most seed pieces again failed to sprout. Of those that did, one of five (20%) of the ash-treated plants and one of five untreated plants were damaged by snails as of Sept. 19. The experiment provided no evidence that an ash barrier can help protect young yam plants from damage by giant African snails. A reason for the failure might have been frequent rains that washed away the ash.

Although ash barriers may work against giant African snails under drier conditions, heavy rains are the norm year round in American Samoa. However, care was made during the frequent rains to replace the ash barrier during the experiment, and as it failed to retard snail damage, the treatment may not work even under dry conditions.

BENEFITS OR IMPACT ON AGRICULTURE
None reported.

PRODUCERS ADOPTION
None reported.

REACTIONS FROM PRODUCERS
None reported.

RECOMMENDATIONS
Chemical control with poisoned bait remains the most effective tactic to protect crops from giant African snail. Some cultural practices can help reduce their damage, such as leaving an area of bare ground or spreading bands of sand around crops and hand-picking snails. However, farmers still need an effective, convenient nonchemical control method that can save money and minimized adverse impacts on nontarget organisms and the environment.

OUTREACH
The project plan had called for repeating the experiment, sponsoring a field day and printing fact sheets had the initial results been positive. The negative outcome precluded these activities. Still, the results have been shared with farmers and extension agents. The agents can now recommend against attempting to prevent giant African damage by using ash barriers.