Apple witches’ broom disease more common than supposed


<p>In 2013, 115 occurrences of quarantine plant pests and diseases were found in horticultural production and 23 in potato fields. In horticultural production, the number was one-third higher than last year, due to the high occurrence of an insect called the sweet potato whitefly. The apple witches’ broom disease, which is new to Finland, was found particularly in Aland.</p>

Apple witches’ broom disease was investigated on 43 sites in all. The disease was identified on all 13 sites in Aland included in the survey, as well as on Finnish mainland in two apple orchards and one producer of apple tree saplings.

“The witches’ broom disease reduces the apple crop and impairs the fruit quality and flavour. It had not occurred to experts previously to connect the broom-like shoot growth to the witches’ broom disease of apples, so it may have been present in Finland for years. The disease spreads with infected apple tree saplings and locally through the jumping plant louse,” says Senior Inspector Sirkka Malkki from the Finnish Food Safety Authority Evira.

New occurrences of the strawberry red stele were found on 28 sites. Due to its common incidence, strawberry red stele cannot now be completely eradicated from Finland, but efforts to control the spread of the disease will focus on planting material of strawberry.

Sweet potato whitefly eradicated from greenhouses   

During the spring season, the number of sweet potato whitefly was exceptionally high in Finland. In greenhouse production, they were found in 2013 on a total of 81 sites, but eradication of all the occurrences was successful. Sweet potato whiteflies spread into flower cultivations particularly with planting material of Mandevilla and Poinsettia. They can spread viral plant diseases that are harmful to tomato and cucumber. 

No quarantine plant pests or diseases at all were found in vegetable production.

Quarantine potato pests and diseases successfully controlled

Potato ring rot was found on four new sites. Potato brown rot was not found. Yellow potato cyst nematodes were found on seven new plots, which is half of last year’s number. Due to the incidences of white potato cyst nematode in summer 2012, an extensive survey of potato cyst nematode was carried out in North Ostrobothnia during the growing season 2013. However, new occurrences of white potato cyst nematode were not found.

New colorado beetle infestations were found on 14 potato fields in south-eastern Finland.

Wooden packaging material harbours risk of pine wood nematode

No quarantine plant pests or diseases were found in Finnish forests or timber. One wooden pallet imported from Portugal was found to contain pine wood nematodes. Wooden packaging materials manufactured in countries infested by pine wood nematode are the most important route for the spread of the pest into Finnish forests. The pine wood nematode is classified worldwide as the worst plant pest affecting forests.

A plant disease or pest can be designated as quarantinable in plant health legislation, if it is not permanently present in Finland, it is particularly difficult to control, and the damage it causes is significant in economic terms.  

Further information on quarantine plant pests and diseases: 
Quarantine pests and diseases

Further information:
Senior Inspector Sirkka Malkki, tel. +358 (0)40 542 1965 (open-field horticultural production)
Senior Inspector Ulla Oksanen, tel. +358 (0)40 511 7274 (greenhouse production)
Senior Inspector Atro Virtanen, tel. +358 (0)40 704 9607 (potato production)
Senior Inspector Sanna Välimäki, tel. +358 (0)50 384 9612 (timber and wooden packaging material)


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