Fire Blight Treatments

What alternatives to antibiotics exist for the control of fire blight on fruits such as apple and pear in organic production? 

By Amber Lippert

If you grow pome fruits (such as apple, pear, and quince), chances are you know about fire blight. This destructive disease is caused by a bacterium, Erwinia amylovora, which forms cankers that can kill branches and tree trunks. Bacterial “ooze” infects flower blossoms and new shoots, and subsequently spreads into woody tissues. The bacteria can also be spread by rain and insects, including honey bees visiting blossoms for nectar. As plant tissue affected by fire blight dies, it turns black, with a characteristic “scorched” appearance.

In Canada, a handful of chemical controls are registered for use to control fire blight. These include copper products, a few biopesticides, antibiotics like streptomycin and kasugamycin, and a growth regulator, prohexadione calcium. Copper products are allowed in certified organic production, but antibiotics like streptomycin and kasugamycin, and growth regulators like prohexadione calcium, are not. Some biopesticides are compliant, but there are others which OMRI has not yet reviewed (hint to manufacturers: apply, if you haven’t!).

Pome fruit producers need to know about alternative treatments that are compliant with Canadian organic regulations. In accordance with organic standards, growers must use known preventive techniques, including the use of highly resistant varieties and rootstocks, and heavy pruning. If a pest control product is to be used, it must be composed of substances included on Table 4.2 — Substances for crop production (Column 2) of the Permitted Substances Lists (CAN/CGSB 32.311).

Although researchers continue to study the effective control of fire blight, current alternatives to antibiotics include: 

• Biological controls that compete with E. amylovora (the microbe that causes fire blight)
• Coppers
• Lime sulphur
• Peracetic acid
• Kaolin clay and oils, to help control insects that spread fire blight

All of these materials need to be applied at the correct time. 

Producers can find allowed products for fire blight at OMRI.org by searching for products in the categories Biological Organisms, Copper (Production Aid), Kaolin Clay, Lime Sulphur, Peracetic Acid and Summer Oils. Producers must check with their certifier before using a new product in an organic system.

This article first appeared in the fall 2015 issue of the OMRI Materials Review newsletter, and was revised in September 2023 by Research and Education Manager Peter Bungum.