Principal Investigators: Victoria Y. Yokoyama, Research Entomologist, and Gina T. Miller, Biological Science Technician, Horticultural Crops Research Laboratory, USDA, ARS, Fresno, CA 93727

Collaborators: National Hay Association, Organization of Kittitas County Timothy Hay Growers and Suppliers, and the California Department of Food and Agriculture

A multiple quarantine treatment to control Hessian fly in compressed hay exported to Japan was approved in December 1996 and the first shipments of hay certified free of Hessian fly under the new treatment program arrived in Japan in February 1997. The U.S. market for hay exported to Japan is valued at $240 million annually. Through competitive pricing, the multiple quarantine treatment will generate increased demand for U.S. hay and it will ensure a constant supply of quality hay for the race horse, dairy, and beef industries in Japan.

Compressed bales of hay exported to Japan are inspected for plant hosts of Hessian fly upon entry. The occurrence of such hosts has resulted in rejections of shipments that have been costly to the hay export industry. Hessian fly is not found in Japan and is of regulatory importance to the Japan Ministry of Agriculture, Forestry and Fisheries. A certified fumigation program for standard bale timothy hay was developed by the USDA-ARS in the 1970's but the procedure is not currently economically competitive with compressed bales of timothy hay exported from other countries.

Timothy, alfalfa, oat, Bermuda grass, Sudan grass, and rye straw are the primary species of hay exported from the U.S. to Japan. Research began in 1991 to develop a postharvest treatment to control Hessian fly in these hays. Compression of standard bales, a normal hay handling process for exports, followed by fumigation with hydrogen phosphide was developed as a multiple quarantine treatment. The results of dose-response tests were used to determine levels of fumigant needed to control the Hessian fly puparia, the life stage that may occur in hay. The fumigation phase of the treatment was established at 60 g/28.3m³ aluminum phosphide for 7 days at 20°C.

The basis of the multiple quarantine treatment is compression of standard size bales into compact bales. A greater quantity of bales can be loaded in freight containers after compression. Compressed hay is economically priced because the bales are easily handled by specialized machinery and generate a greater savings in ocean freight. Compression monitoring equipment in laboratory tests showed the effect of compression on survival of Hessian fly puparia. The relationship between insect mortality and amount of pressure on the bales was shown in field tests using variable forces produced by several commercial hay compressors. Research showed that compression alone at 80 kg/cm² or more controlled large populations of Hessian fly puparia placed in the bales. Compression has potential as a single quarantine treatment to ensure that Hessian fly would not be accidentally introduced into Japan through hay shipments.

Seasonal weather conditions and hay harvesting practices including cutting, drying, wind rowing, baling, and curing were shown to control Hessian fly puparia in laboratory and field tests. A survey of the distribution of Hessian fly in California revealed that infestations did not occur in wheat. Such cultural factors indicate that Hessian fly would not be found in export quality hays that were not biological hosts for this pest.

Two large-scale tests of the multiple quarantine treatment in 1995 resulted in 100 percent mortality of a large number of test insects. These tests allowed an on-site confirmatory test in the presence of a scientist from the Japan Ministry of Agriculture, Forestry and Fisheries in April 1996. The successful on-site confirmatory test resulted in approval of the treatment.

A recent investigation studied the effects of in-transit conditions that may affect survival of Hessian fly and the quality of hay during shipment by ocean freight. Also, film-wrapped bales have been in demand in Japan and studies have been initiated to determine the effect of film wrapping on the efficacy of the multiple quarantine treatment. Hay exporters have requested that the fumigation phase of the treatment be modified to shorten the time and lower the temperature of the fumigation. Such modifications will expedite handling time of shipments and allow fumigation outside of warming barns during the colder periods of the year.