Plant Pathology Infobytes
March 31, 1999
Start Right with Disease & Nematode Free Nursery Plants
Spring gardening season is here! Nurseries and other plant outlets are doing a booming business, and thousands of shrubs and other ornamental plants as well as fruit and nut trees will go into the ground over the next few weeks.
But before the holes are dug and filled, gardeners and orchardists should exercise caution. Make sure those new purchases are free of disease and nematode pests which often cause down-the-road gardening headaches.
All types of nursery plants are susceptible to attack by fungi, bacteria, and other pathogens. Also, root-knot nematodes infect a wide range of ornamental and orchard plants. The result is poor plant growth, and in some cases, plants are killed by diseases and nematodes. So it pays start right with healthy plants.
When shopping for nursery stock, slip container-grown plants out of their pots and inspect the roots. Look for creamy-white colored roots, and avoid those with brown or blackened root tips. This could be a indication of root rot or a sign the plant was stressed earlier and may not grow properly.
Also, avoid "root-bound" plants. Root-bound plants can be identified by larger roots which tend to grow in a circular fashion around the outside of the root ball. Root-bound plants aren't likely to produce a healthy, spreading root system needed for proper plant development. It's best to pay more for top quality nursery stock with healthy roots.
What else should you look for? Fruit and nut-bearing plants such as apple, peach, pecan, blueberry, blackberry, and grape are all subject to crown gall, root-knot nematode, and fungal root rot. Crown gall is caused by a bacterium and can occur on roots, trunks, and limbs of infected fruit and nut trees.
The galls, which range in size from small swellings up to 1 or 2 inches in diameter, are most commonly found where the main plant stem enters the soil. Galls are normally dark brown to black and have a roughened appearance. They cut down the amount of water moving from the roots to the upper plant parts and eventually cause plant death.
Root-knot nematode infections on plants are more difficult to detect. The small swellings on roots, caused by the feeding of nematodes, are the same color as the roots. Unless the root system is carefully examined after removal from the container, root-knot infections can be easily overlooked.
As the nematodes multiply on roots over a period of several years, the roots take on a "knotted" appearance and are not able to pick up water and soil nutrients. Consequently, severely infected plants become stunted and produce poor yields.
Fungal root rots can cause a number of symptoms including death of small feeder roots and dark depressions on larger roots. Once again, when selecting plants, look for whitish-to-cream colored roots.
Plants with dark root masses signal future trouble and should be avoided. The fungi that cause root rot might be present and not cause any symptoms until after the plants are transplanted. Poorly drained soils are favorable for root rot development, and should be avoided as planting sites.
These diseases are difficult to control once they are established. Although the organisms that cause the diseases occur naturally in the soil, it would be advantageous not to introduce them if it can be avoided.
Most of the plants sold at garden centers are normally of excellent quality, but it is still important for the gardener to inspect them closely and return any plants that show the symptoms described.
Contact your county Extension office for further guidelines on selecting healthy plants.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.