The presence of newly discovered insects and diseases, crossing the border into Ontario from around the world, continues to plague this province's nursery growers. The Plum Pox virus, the latest disease to claim nation-wide headlines because of its potential threat to the tender stone fruit industry, promises to create serious havoc within the ornamental nursery industry in Ontario, and particularly those nurseries located in the Niagara region.

     There are several strains of Plum Pox virus. More serious strains result in a low sugar content and premature ripening of fruit such as peaches, plums and many varieties of cherries, causing these fruits to be unmarketable. The D strain, found in Ontario, however, is responsible primarily for cosmetic damage to fruit. Several orchard growers reported noticing this damage for the past 10 years and claim it has not affected the sugar content of the fruit. Plum Pox virus, in any strain, is not a threat to human health or even to the overall health and vigour of the affected trees.

     In an effort to control the spread of this disease while the potential for eradication measures are assessed, the Canadian Food Inspection Agency (CFIA) recommended a quarantine on all susceptible varieties of peach, plum and nectarines within the townships of Niagara, Lincoln and St. Catharines. This quarantine will also affect the shipment of all ornamental varieties of Prunus, including non-fruit bearing varieties such as Prunus triloba and Prunus cistena. "It is ironic," notes Tony DiGiovanni, executive director for Landscape Ontario (L.O.), "that although this is a disease that affects the fruit, because orchard growers do not move their trees, it is the ornamental grower industry, not the orchard industry, that will be most affected by this quarantine."

     The incidence of Plum Pox virus within Canada is now being determined by the CFIA through an extensive testing program that will see them systematically check for the presence of the virus in every orchard in Ontario. The assistance of government laboratories from across the country was solicited to generate as many results as quickly as possible to help the federal government determine the actual extent of this problem.

     While L.O. supports swift action to delay the spread of this serious disease, they are urging the government to consider the impact of their actions on other related industries and to consider alternatives when they exist. "Once in place, quarantines are very difficult to lift," notes Mr. DiGiovanni. In view of the fact that no prunus varieties are being shipped at this time of the year, and also that most nursery stock is shipped to non-production areas, L.O. requested the CFIA agree to a delayed quarantine, giving both the federal and provincial agricultural ministries more time to study this problem in detail.

     Although it was originally suspected that the Plum Pox virus moved into Ontario from Pennsylvania where it was first discovered in the U.S., the government's monitoring program and grower records have subsequently shown that this is almost certainly not the case, and in fact, the virus could have spread to the U.S. from Canada after its probable introduction here from overseas sources. The U.S. control programs also call for quarantine within infected areas, but do not restrict the movement of ornamental varieties. The quarantine proposed by CFIA would affect eight Ontario nurseries. While the total dollar volume is not yet known, it is expected to be anywhere from $3 to $4 million per year, says Mr. DiGiovanni.