After watching the documentary show on “Spring Watch” I had learn the white foam on the plant is from spittlebug. The following is the source from “Gardening know how” which I find it interesting and hope this is useful tip for your garden.
Source – from Gardening know how
Signs of a Spittlebug Infestation
The tell tale sign of spittlebugs is plant foam. This plant foam will normally appear in the plant where the leaf attaches to the stem or where two branches meet. It will look like white foam, a pile of bubbles or a big gob of spit.
Is a Spittlebug Damaging to Plants?
Other than looking unsightly, spittlebugs do very little damage to a plant. They do suck some of the sap from the plant, but rarely enough to harm the plant. The plant foam serves mostly to hide the adult and immature spittlebugs.
Organic or Homemade Insecticide for Spittlebugs
When looking for an organic spittlebug killer, you must keep in mind that you are looking for something that will not only kill the spittlebug but will repel further infestation.
A garlic or hot based organic or homemade insecticide for spittlebugs works well. You can do a double whammy with the following organic and homemade insecticide for spittlebugs:
Organic spittlebug killer recipe
1/2 cup hot peppers, diced
6 cloves garlic, peeled
2 cups water
2 teaspoons liquid soap (without bleach)
Puree peppers, garlic and water together. Let sit for 24 hours. Strain and mix in the liquid soap. Wipe the plant foam off the plant and spray all parts of the plant.
Now that you know a little more about spittlebugs you know what bug leaves white foam on plants and what you can do to stop it.
BEFORE USING ANY HOMEMADE MIX: It should be noted that any time you use a home mix, you should always test it out on a small portion of the plant first to make sure that it will not harm the plant. Do not use on waxy or hairy-leaved plants. Also, avoid using any bleach-based soaps or detergents on plants since this can be harmful to them. In addition, it is important that a home mixture never be applied to any plant on a hot or brightly sunny day, as this will quickly lead to burning of the plant and its ultimate demise.