Question
I'm still working on the black spots on my Dipladenia. You recommended either baking soda (what concentration?) or Lysol.  I tried 1 treatment with Lysol but when I went to buy some I found that they weren't offering anything with lactic acid as the active ingredient as I used before, but only Lysol with a long chemical Alkyl (C12-C18) dimethyl benzyl ammonium chloride. The lactic acid Lysol spray seemed to begin to help after one spray. I tried the second Lysol spray and it was harsh, causing some leaves to lose pigment in spots. Anyway, should I try this again, more diluted? Or were you thinking only on the lactic acid preparation.
Long question, thanks in advance.

Answer
Jonathon,

The one I have used succesfully is the Lysol with a long chemical Alkyl (C12-C18) dimethyl benzyl ammonium chloride but I do not use it close up on any plant. I hold the aeresol can at least 12 to 18 inches away and just mist the plant lightly. You are illing the fungus and bacteria in the air around the plant along with on the plant. You don't have to get a lot on the plant to be effective.

I have not used the baing soda spray personally but below are some recipes I have found for using it on roses.

     Baking Soda Spray:

1 tbsp vegetable oil
1 gallon unchlorinated water
1 tbsp apple cider vinegar
1 tsp Listerine (yes, the famous mouthwash, not mint flavour, just regular)
1 tbsp liquid soap
1 ?tbsp baking soda
Pump sprayer (large)
       Mix the baking soda, soap, Listerine, and oil with 1 cup water. Add the vinegar last so that the mix won抰 bubble over. Pour the mixture into the sprayer and add 1 gallon water. Shake to combine. Spray plants thoroughly.

       This formulation may need to be reapplied after rain since it tends to wash off. One side benefit to the baking soda spray is that insects don抰 love it either!

Second Recipe From Canada  
The suggested mixing rate is 20 millilitres [ml] (4 level teaspoons) of baking soda in four litres (1 US gallon) of water. To improve the effectiveness (the sticking effect) it is also good to include 5 ml of a mild soap that does not contain phosphate. Examples would be Dawn or Ivory Liquid. It is important to mix the ingredients well (it will work better if you use warm water), and to keep the mix agitated as you apply it.

vThe spraying is likely best done weekly or every ten days once there is any sign of either fungus, and using one of the three in succession each time, tends to improve your chances because the race of fungus you have will not then get used to what you are using such as they often do when only one product is used.

Are you sure that the black spots are not the insect scale? Have you tried removing them with your fingernail or with a Q-tip dippied in rubbing alcohol? If they come off leaving the leaf intact they are an insect called scale. If so write back and I will tell you how to get rid of scale. Good luck.

Darlene   [email protected]