Worms can quickly grow and feed on lemon trees, destroying an entire lemon crop in a short period of time. To effectively kill the worms, a retail pesticide will work, but many times they will contain harsh chemicals that should not come into contact with the edible fruits on the tree. Instead, make a mild cleaning agent right at home that will kill the worms without putting toxins into contact with the lemons.
Pepper works as a natural repellent and as as pesticide that will kill worms on contact. Look in your kitchen cupboard to see what pepper spices and sauces you have available. Anything will work along the lines of Tabasco sauce, chili powder or pepper and cayenne pepper. You can also blend fresh hot peppers into a liquid form.
In a spray bottle, combine two cups of warm water with three teaspoons of any of the above items and shake to dissolve the ingredients. Spray this directly onto the worms, as well as plant leaves, as this will work as a repellent to any new worms that come into contact with the tree. After you have taken care of the worm problem, spray the solution onto plant leaves every few weeks to keep worms from reinfesting the lemon tree.
Garlic is another acidic herb that will both kill and repel worms. Make a similar solution by mixing two cups of water with three teaspoons of either garlic powder or fresh garlic that has been blended into liquid form. Spray onto worms, along with plant leaves, and repeat as needed to keep worms at bay.
Crush a handful of peppermints into powder form or use peppermint essential oil. Add two cups of warm water to a spray bottle along with three spoonfuls of either the peppermint oil or the crushed peppermint. Shake to dissolve ingredients and spray the mixture onto worms and the leaves of the lemon tree.