Michelle Grabowski, UMN Extension Educator
As the world becomes more internationally connected, common garden plants are being shipped across the country and in some cases across the ocean. This is not a problem unless there are plant pathogens hitching a ride on these garden plants. In 2009, tomato transplants from the south eastern United States were shipped to garden centers from Maine to Ohio. Unfortunately these tomato transplants were infected with the pathogen responsible for causing a devastating disease of tomato and potato known as late blight. The resulting disease epidemic spread from home gardens to commercial tomato and potato fields; from the east coast through Wisconsin.
Devastating diseases such as White Pine Blister Rust and Chestnut Blight are believed to have been brought into the United States on infected nursery stock. Other invasive pest problems, like Dutch Elm Disease and Emerald Ash Borer, are believed to have been moved across the U.S. on infected firewood. As responsible gardeners and plant lovers, it is important to choose garden plants wisely.
· Nursery plants
· Potting soil
· Wood or other plant products
How can you avoid stowaway pathogens?
Buy locally grown plants
· Locally grown plants have local plant disease problems, plants shipped from distant states or other countries may contain pathogens from those areas that were not previously found in MN.
· Vegetable and annual flower transplants grown from seed in MN greenhouses are grown March through June. Very few pathogens are active this time of year. The same plants grown in warmer climates may be exposed to many different fungi and bacteria before being shipped north.
· Shop for vegetable and flower transplants at local farmers markets.
· Ask at the garden center where transplants are coming from.
· Read plant labels and choose plants from local nurseries.
Start plants from seed
· Only a few pathogens can travel on seed. Many more can be carried in infected potted plants on roots, stems, leaves or in potting soil.
· Purchase seed from a reputable producer to avoid problems with contaminated seed.
· Purchase certified disease free seed when possible. This is more common with fleshy 'seed' like potatoes or bulbs than with true seeds.
· Plant seeds in new potting soil with new or sterilized pots and trays. For more information about starting plants from seeds, read the UMN Extension publication 'Starting Seeds Indoors'
Select container grown plants wisely
· Potted plants can harbor plant pathogens on roots, leaves, stems, flowers or in potting soil.
· Purchase plants from a reputable nursery.
· Choose locally grown plants whenever possible.
· Purchase certified disease free plants if possible. This is common with some plants like certified virus free roses, raspberries and hostas, but not all plants have a grower certification process.
· Inspect all plants prior to purchase. Reject any plants that have dark, soft or sunken spots on roots, leaves or stems. Reject any plants that have diseased neighbors in the garden center as disease spreads easily from one potted plant to another.
· Report diseased plants to the garden center management.
Do not move firewood
· Invasive insects and pathogens can be carried on wood from infected trees.
· Burn firewood in the same area from which the tree was harvested.
Learn more about the plant diseases in your garden and report suspected invasive pests
· Use the UMN Extension Online diagnostic tool 'What's wrong with my plant?' to identify pest problems
· Information about invasive pests can be found at the Minnesota Department of Agriculture web site