News from the Diagnostic Centre of the Dutch Plant Protection Service
The Diagnostic Centre of the Dutch Plant Protection Service has published its Annual Report for 1993, and the following items can be noted.
1) Xanthomonas campestris pv. dieffenbachiae (EPPO A1 quarantine pest) has repeatedly been found in plants of Anthurium andreanum showing symptoms of yellowing and necrotic leaf margins, from South Africa. According to the EPPO Secretariat, the information on the occurrence of Xanthomonas campestris pv. dieffenbachiae in South Africa is new.
2) Pseudomonas solanacearum (race 1, biovar 4) (EPPO A2 quarantine pest) has been found in the ornamental Curcuma longa in two glasshouses of one nursery only. Rhizomes are generally imported from Thailand, Sri Lanka, China and Japan where race 1 is widespread. This is the first time that race 1 has been found under glass in the Netherlands. Infected plants have been destroyed and the glasshouses disinfected.
3) A new thrips Echinothrips americanus has been found in August 1993 during an export inspection on Syngonium The plants had been grown in a nursery in Schipluiden, where also Philodendron (Araceae) appeared to be infested. In November 1993, this pest was also found in a nursery at Bleiswijk on Homalomena (Araceae). The host range of E. americanus is not well known, and in Araceae, only Dieffenbachia was previously mentioned. The pest occurs in the Eastern part of the United States, from Florida to New York state. Outside this area, it has been found only incidentally in California, Quebec (CA) and Bermuda. In the Netherlands, E. americanus is regarded as a species deserving quarantine status and action must be taken after detection of the thrips. In the two localities, the pest has been eliminated after chemical treatment. It is stressed that the species can be easily overlooked during import inspection as symptoms are not always visible.
4) Cannabis sativa can be attacked by Liriomyza huidobrensis (EPPO A2 quarantine pest). This is a new host record.
5) Phytophthora root rot of raspberry is an increasing problem in the Netherlands. The disease occurs mainly on red raspberry (Rubus idaeus) and some of its hybrids, and to a lesser extent on black raspberry (Rubus occidentalis). In the Netherlands, four species have been found in connection with raspberry root rot: Phytophthora fragariae var. rubi (the most virulent species - EPPO A2 quarantine pest), P. megasperma var. megasperma (found a few times only), P. cactorum (very common but considered as a weak parasite, occurring under poor growing conditions), P. citricola (sometimes found). This confirmed the suspicions expressed in the previous Annual report concerning the presence of Phytophthora fragariae var. rubi (EPPO RS 94/193)
6) During the last few years, a decline of pear trees has been observed in several orchards. This disease is caused by pear decline phytoplasma (EPPO A2 quarantine pest). This pathogen causes a premature leaf reddening, early defoliation in autumn, and poor root growth. Growth of new shoots in spring is retarded, leaves are smaller and can wilt suddenly. The disease may cause severe symptoms after transplanting the trees from the nursery. However, in the Netherlands, most affected trees recover from the disease during summer or the following year. The severity of symptoms is highly influenced by environmental conditions, especially temperature and precipitation. It is expected that cold and wet summers will decrease the occurrence of this disease. In addition, though all pear varieties are susceptible to the disease, the most common rootstocks grown in the Netherlands are highly resistant. According to the EPPO Secretariat, this is the first report of pear decline phytoplasma in the Netherlands.
Annual Report 1993, Diagnostic Centre, Plant Protection Service, Wageningen, Netherlands, 102 p.