Articles by Jim Gainan

As published in the Billings Gazette

Too much heavy spring rain can cause fireblight

I've always dreamt what it would be like to live in the Pacific Northwest. After the last couple of weeks it has become clear to me that the beauty of the water and the mountains is not an adequate trade for the amount of rain that that area is accustomed to. I think I will just stick to regular visits on sunny weekends.

I share the frustrations of so many customers who are late getting their gardens planted, preparing their annual beds and planting their perennials. In fact, all of my plant materials are sitting on a trailer waiting for a break in this weather to be planted.

Once we have that chance, it's important to note that, after all of this rain, many of the nutrients in the soil have been washed away. So this year more than ever, it is crucial to include a time-release fertilizer when planting and to fertilize regularly with garden sprayers to supplement. In addition, adding compost and other soil amendments will give the plants an extra boosts. Heavy spring rain and severe weather cause many challenges in the garden. I will attempt each week to address a few of them.

Prepare for an inordinate amount of fireblight to appear in our area. Two main contributing factors will be our wet spring and damage during the time susceptible trees and shrubs were blossoming. Fireblight is a bacterial disease primarily affecting apples, crabapples, pears, mountain ash, hawthornes, roses and cotoneaster.

The bacteria overwinter near the edge of a canker formed during the previous season, and become active during the warm weather in spring. Water is absorbed by the bacterial masses that swell and secrete ooze. This bacteria-laden ooze appears just as the buds turn pink in spring and may continue until mid-summer. Insects attracted to the sticky, sweet-smelling ooze will spread the bacteria as they travel from plant to plant. Birds, rain, mist and wind are also methods by which the bacteria spread.

The bacteria will enter the new host plant through wounds, natural openings and new succulent growth. The attack starts at the blossoms and moves up the twigs to main branches.

The first symptoms usually appear on the blossoms. They will look like they've been soaked with water before rapidly wilting and turning brown. Diseased fruit will become leathery and, along with affected leaves, will cling to the branches for months. Twigs and suckers shrivel, blacken and the ends curl into a shepherd's crook and appear burnt.

While there is no cure, there are methods of control. When considering new plantings, look for varieties that are resistant to fireblight and try not to interplant susceptible and resistant varieties. Select a site with low humidity, good air movement and enough sun to allow wet leaves to dry quickly. Avoid feeding with a high nitrogen fertilizer as this promotes a flush of succulent susceptible growth. Remove suckers to prevent entry of bacteria into their tender tissue as well.

Generally, during the growing season, infected twigs are cut out while avoiding heavy pruning as it may stimulate tender and susceptible new growth. Prune 6-8" up from the infected area. Immerse cutting tools after each cut into a sterilizing solution of 1 part bleach to 9 parts water or a solution of 3 parts denatured alcohol to 1 part water. If using the bleach solution, be sure to rinse tools and wipe them dry to avoid corrosion.

Remove all cankered limbs in late fall, winter or early spring. However, because of the widespread reach of fireblight this season, with the guidance of the MSU Extension office, pruning should be discontinued this season until after leaf drop, when dormancy sets in this fall. Remove all cankered limbs in late fall, winter or early spring before the bacteria are active. If a red discoloration is found just beneath the bark in larger limbs, a lower cut needs to be made. Do not save any part of the plant. Burn or discard all infected parts to prevent the spread of the disease.

Right now, a treatment of a copper soap (copper octanoate) fungicide and bactericide spray is recommended on the affected tree or plant and any other varieties that may be susceptible with a repeated application if there is a heavy rain, damaging hail or new visible oozing. Check for insects that may spread the disease and control them. Next spring, susceptible trees should be protected from infection by a streptomycin spray program following the directions on the label.