Fixed Copper

No, we’re not talking about faulty wiring, or that jar full of pennies.

Copper (and sulfur) have been used as fungicides and bactericides in gardens and agriculture for a really long time. Unlike Bordeaux mixtures, which use highly soluble copper sulfate, fixed copper takes much longer to break down. Each time it gets wet, fixed copper releases just a little more metallic copper onto plants.

Protection provided by fixed copper

Fixed copper applications are active against many common fungal and bacterial diseases of fruit trees and vines, and ornamental plants. These diseases include:

• fireblight
• bacterial canker
• bacterial spot
• peach leaf curl
• apple scab
• cherry leaf spot

Copper kills bacteria and fungi by breaking down protein molecules within the organisms.

Pump sprayer are handy garden tools

Shopping for fixed copper

When shopping for fixed copper products, it is not uncommon to see a wide range of active ingredients. To get your money’s worth, look for higher “metallic copper equivalents” (MCE) on the label. MCEs are listed as a percentage by weight, with the most common rating being 8%.

Fixed copper can take any of these forms:

• tribasic or basic copper sulfate
• cupric hydroxide
• copper oxychloride sulfate
• copper ammonium complex

There is also a copper soap (copper octanoate) available that has shown good results.

How to use fixed copper

The effectiveness of fixed copper against fungal diseases can be improved by adding 1% of a horticultural (not dormant) oil. The oil will help the copper stick to plants longer. It will also reduce damage caused by aphids, mites, and scale. Fixed copper is normally applied using a hand pump spray tank (pictured) or a hose end sprayer.

Fixed copper should be applied while plants are dormant and it is important to get complete coverage. Once new buds and shoots begin to emerge, phytotoxicity can be avoided by spraying on days when the fixed copper will dry quickly.

Avoid using other foliar (leaf) sprays when applying fixed copper. According to the Michigan State University Extension, “[A]void the use of spray additives such as foliar nutrients, and any surfactants with penetrating characteristics when applying coppers. Fixed copper and lime should not be used with Guthion, Imidan, Sevin, Thiodan, Bayleton, captan, carbamate (Ferbam), syllit, or phosphorus acid-type compounds (Fosphite, ProPhyt, Phostrol, Agri-Fos, Aliette).” 

Problems associated with fixed copper
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Even though fixed copper is an acceptable organic control, excessive use can raise copper levels in the soil to toxic levels. Once in the soil, copper may leach into local groundwater. It can also be toxic to aquatic organisms and many animals (but not humans).

As with the use of any chemical in the garden, be sure to read the label completely and follow directions exactly.