Dill is susceptible to powdery mildew. Aphids can be a problem at the time dill starts to flower and the seeds ripen. Dill often attracts more beneficial insects than it has problems with insects. Dill attracts bees butterflies wasps lady beetles lacewings hoverflies tachinid flies and parsley worms. Parsley worms a tiny bright green caterpillar with black stripes is the larva of swallowtail butterflies so make sure to leave them on the plants.