Today’s post can be heard on the public radio show Crop to Cuisine, hosted by Dov Hirsch.
There’s a thug lurking in your neighborhood, taking every opportunity to attack your precious tree fruit. With oozing droplets and a hoard of unwitting helpers, it moves from tree to tree, torching twigs and branches until the tree looks scorched. Evidence of the infection becomes more obvious as we head into June.
Fire blight is a bacterial disease that affects certain plants in the rose family. It is especially destructive to apple, pear, quince and crabapple. It attacks in spring, when temperatures reach 65 degrees F and frequent rain occurs, and then bacteria overwintered in cankers on the tree resume activity, multiplying rapidly.
Though the good news is that we’ve had some rain and humidity, the bad news is: the recent weather created good conditions for this damaging disease. This is when masses of bacteria are forced through cracks and bark pores to the bark surface, where they form a sweet, gummy exudate called bacterial ooze.
Insects such as bees, ants, flies, aphids and beetles are attracted to this ooze, pick up the bacteria on their bodies, and inadvertently carry the bacteria to opening blossoms. Bacterial ooze splashed by rain also can spread the disease.
Young branch tips can be infected through air openings on leaves, called stomata, air openings on branches, called lenticels, or, more commonly, through wounds created by pruning, insects, or hail storms.
Droplets of ooze can form on these infected twigs within three days and fruit may be infected through insect feeding wounds. Girdling cankers – areas of disease on the wood – eventually develop from branch or blossom infections. Leaves wilt, darken and curl to form a shepherd’s crook. This gives the tree a fire-scorched appearance, thus the name “fire blight.”
There is no cure for this disease, so prevention is the best solution. Fire blight control methods include use of resistant varieties, cultural practices, pruning and spraying. Using resistant varieties is the most effective prevention method, but keep in mind that resistance doesn’t mean immunity.
Remove and destroy newly infected young twigs as soon as possible, so that your tree doesn’t become the mother ship for disease in the neighborhood. Do this when no rain is predicted for at least two weeks. It may be best to leave pruning until winter when the bacteria are not active. This reduces infection on the tree and the number of bacteria available to infect healthy blossoms and shoots.
In young twigs, make cuts at least 12 inches below the dark, visible edge of infection to avoid slicing into the bacteria. Remove all blighted twigs and cankered branches. Prune larger limbs about 6 to 12 inches below the edge of visible infection.
After each cut, surface sterilize all tools used in pruning. Spray tools with Lysol or dip tools in 70-percent ethyl alcohol, or a 10-percent bleach solution. Bleach can rust tools, so if you use this to sterilize your pruners, wash them after you’re done and apply a light tool oil to keep them rust-free.