Potato foliage


Hello, I was noticing a lot of black flea beetles on my potatoes and I sprayed the foliage with a dawn dish detergent + water solution, and I haven’t seen them after. But the foliage is looking bad, is it because of the beetles or is it potato blight? Please advise what do I do?
Thank you.


Thank you for sending the video.  It was a big help.

Your potato growing operation is quite impressive.

Comparing your video to images of potato blight, I don’t think potato blight is the problem. The beetles have caused damage, leaving holes in the leaves.  The edges of some of the leaves show signs of damage.  This may be related to the spraying of the Dawn/water solution.

There is a difference between soap and detergent.  We use detergent to wash dishes and our clothes because it is a degreaser and an emulsifier.  The problem with this on our hair, skin and leaves of plants is that it strips the natural protection from the surface.  This is why dermatologists and pharmacists tell people with skin problems to NOT shower/bathe/wash everyday.  Those few who follow that advice find the dryness on their scalp, skin and hair is reduced.  The same holds true for plants.  In addition, the heat we have been enjoying (?) recently is another stress for some plants.  This stress can be exacerbated by adding detergent into the mix.

I am providing a link to an article explaining the difference between detergent and soap as well as one on how to use soap as a pesticide safely.  It is written from a scientific perspective and in lay language, explaining the thinking behind the comments above.

Other hygiene tips to consider:

  • Water the soil and not the leaves
  • Since the total surface area affected is small, remove the damaged leaves and put them in the garbage (not the composter)
  • Clean up any debris around the plants
  • Use insecticidal soap instead of detergent as an insecticide for plants
  • When using insecticidal soap, target the areas where there is evidence of insects and not the entire plant
  • When consulting “websites” that recommend home remedies, check with an expert.  As Master Gardeners we do not recommend home remedies. Many of these home remedies either don’t work or can do more harm than good.  The Toronto Master Gardeners are here for you.  Garden centres also have experts who can provide advice.

I hope your potato plants thrive and you get an excellent crop.

Dish Soap Can Damage Your Plants

Insecticidal Soap – Use It Properly