Gardeners have lots of tips to improve their harvests, many sound absurd and border on quackery, many sound absurd and actually work.
Early blight is a disease that afflicts tomatoes, potatoes and some related crops, it strikes early in the growing season, which is why it is sometimes called "early blight", technically it is Alternaria Solani. Early blight is very common, it causes fruit rot and stem lesions in tomatoes, tuber rot on potatoes. It can cause damping-off, stem cankers, leaf blight as well. Fungicides to treat early blight are commonly copper based which work by coating leaf surfaces with minuscule particles of their active ingredients, copper coupled with various ingredients sometimes pyrethins or similar compounds. The copper particles react with surface moisture and release copper ions that eliminate bacteria and prevents fungal spores from germinating.
Somewhere along the line, some DIY old school gardener came up with the brainstorm of placing copper wire in his/her tomato plants instead of spending their hard earned dough on expensive copper fungicides. Damn - what doesn't kill your tomato plant makes it stronger ?! The theory is piercing the plants stem with a thin copper wire and allowing the copper ions to circulate through the plants circulatory system will circumvent the need for fungicide, making the plant wore resistant to fungus and expand on its overall health and yield.
My basic knowledge stored in my personal gray matter includes a fragment that tells me copper is bad , copper is toxic. Further research tells me that copper in ample amounts will kill off plant life, copper spikes driven into a tree are known to slowly kill the tree, copper is also used to discourage root growth near foundations.
An Aussie gardener who has a youtube channel [“Self Sufficient Me”] did an experiment and his conclusions were pretty predictable. Apparently the copper wire notion is a myth, he found no difference between the plants pierced with the wire so far as disease susceptibility is concerned as opposed to those that weren't 'wired' with the copper. In fact the plants pierced with copper did not last as long as the others, although they did yield an acceptable crop before dying off.
The copper wire didn't help at all, in fact it appears that the copper wire may have had a detrimental effect. Watch the Video