White spots on indoor flat leaf parsley

Asked January 23, 2020, 9:34 AM EST

I brought my potted deck flat leaf parsley inside to a south facing all glass sunroom for the winter. After 3 months the leaves are developing white ‘spots.’ Is the parsley still safe to eat, and is there a soap-based spray I should use to try and control the ‘white spotting’? I also brought in basil, rosemary, thyme, and chive. Should I be concerned about the ‘spots’ spreading to the other herbs? Thank you so much for taking the time to answer my questions.

Carroll County Maryland

1 Response

Photographs of the spots would help us determine the possible cause and whether it may spread. The delay in timing between bringing the plants in and the appearance of the spots causes us to think that environmental stresses are an unlikely cause. That said, were any sprays (even for cleaning glass) used in its vicinity? Sometimes tissue death is a result of phytotoxicity, where a chemical contacting the tissue results in damage. (This is also why it's important when using insecticides to use those specifically manufactured for use on plants, as opposed to home remedies that might not have the right ingredients in the correct proportions.)

Thrips are a common insect pest of indoor and outdoor plants. They feed on foliage, often on the undersides, and can create a stippling of bleached-looking tissue that sounds like a match for what you describe. They can be removed by rubbing fingers over the leaves under a strong jet of water (spraying them in a shower or with a hose on a mild day outside). Eggs or pupal thrips not yet on the foliage won't be affected and the treatment should be repeated a few times about one week apart. Similarly, a pesticide safe for use indoors and on edible plants can be tried if this doesn't work. Horticultural-use oils and soaps would be good to try, provided the label states they can be used on houseplants and harvest-able plants. Often they will say when to discontinue use before harvest.

Damaged leaves are probably fine to eat. If there is an insect on the parsley, moving the other herbs a bit further away until the pest is controlled may help keep them from becoming infested, though not all insect pests are generalist enough to use every host available to them.