This time of year is a busy time for home horticulturists. Now that we have finished fertilizing landscape and fruit trees and increased irrigations as temperatures warm, we turn to pest problems. Curling of leaf edges on plants like plum is a pretty positive sign of aphids this time of year.             Spring growth attracts overwintering insects. Soft, succulent new growth is easy to feed on. Insects like aphids move to new spring growth to feed and have their young. Expect aphids to begin feeding and multiplying on the undersides of leaves now and through cool weather. Aphids like to spend the winter on weeds close to the ground, particularly just below loose mulch. This protects them from cold and still allows them to feed through the winter. They leave weeds and migrate to spring growth when temperatures warm.             If your landscape is a healthy one, you will see an explosion of ladybird beetles or ladybugs and green lacewings. The young of these insects are voracious feeders upon small, soft-bodied insects like aphids. These adult predators lay eggs in areas where their young can easily feed.             Signs that aphids are present and feeding are the curled edges of new leaf growth. However, what might attract your attention more are ants. When the leaf is turned over and the leaf edge uncurled you will see adult aphids and their young feeding. Their feeding creates a sugary sap that ants relish. Aphids prefer the undersides of leaves like on this apricot leaf. This gives them more protection. If you are planning to spray, you must spray the undersides of leaves, not just the tops.             Soap and water sprays directed on them and spaced several days apart are usually enough to control aphids. Most people will spray the top sides of the leaves to control insects. But when aphids are inside the curls on the underside of the leaf, they can be a challenge to control with just soap and water.             If you an adherent to organic methods of pest control then multiple sprays directed toward the tops and bottoms of leaves will be necessary. Most organic methods do not persist. Multiple applications may be needed a few days apart for good control.