Good thing about herbs is that in most cases, they will re-grow rapidly after being trimmed. So go ahead and trim off and discard leaves or lengths of stems with leaves that are too bug-eaten ugly to eat yourself. New shoot buds will form from leaf nodes and they will grow, bushier.
As long as you have taken steps to eradicate the pests, the new tender shoots and leaves will grow and fill out.
A couple of my favorite ways to eradicate pests on edibles — obtain and release natural predators (my 1st choice) — ladybugs, predatory mites, predatory wasps...etc.
(if not utilizing natural Garden Patrol and am not concerned about killing the good guys — typically only on indoor plants)
- Horticultural/food grade diatomaceous earth is effective for most bugs if they are not too small like mites (not sure about thrips), I use a soft paint brush and dust the plant
- ... I use natural liquid soap called Dr. Bronner’s — I like peppermint for washing hands and use it at all the sinks — it is very strong so I use it cut in half with water in liquid soap dispensers. I wet my hands, suds up my hands with this, wet the herbs with water, put the suds on the herbs, and then rinse off. Probably all within less than 5 minutes. Very un-scientific. I think of it like giving them a “wash” and am more concerned about burning the plants by leaving the soap on too long. The way I’m doing it, the soap bubbles suffocate the bugs and make the weakened but often not quite dead bugs let go of the plant more easily when rinsed off.
Depending on the herb and how they are potted, I fill a container with tepid water and dunk the stems and leaves and swish around to rinse. If needing to hold the pot upside down, I wrap the pot and soil with plastic — put in plastic bag with opening twisted around the stem or use food wrap — so the soil (and plant) doesn’t fall out.
- I also take a spray bottle — about 8 oz to 16 oz, fill with water, a (dribble) of the diluted liquid soap, a drop or two of light salad oil like sunflower or safflower oil, maybe canola/rapeseed oil, and a drop or two of clear alcohol like vodka or rum, shake well and spray. I sometimes add a pinch of baking soda. I think actual recipe is something like a teaspoon to a quart or a tablespoon to a gallon. If oil is added, I don’t use when the plants are/will be in direct sunlight. If spraying, I follow by thoroughly spraying with filtered water or rinse off in the sink.
When there is a pest infestation, you need to dedicate yourself to treating the plants at least twice a week for a couple of weeks to break their life cycle and eliminate adults and eggs and newly hatched nymphs. If you need to wash them often, you need to be careful not to overwater, especially herbs that prefer drier conditions. You will also need to modify/reduce your watering regimen after cutting them back since there is less leaf surface to support and less to evaporate.