Question: I think my peach tree has aphids, but how can I be sure?

A: Green peach aphids are the most common aphids on peach trees. They are small and can be difficult to detect, but their damage is very noticeable.

Some of the telltale signs of aphids are curling leaves at the tips of branches and twigs or a sticky coating called honeydew on the leaves. The sticky coating can attract nuisance pests or cause sooty black mold growth. Although these symptoms look distressing, aphids don’t really harm healthy trees. Very high aphid populations can also cause wilting, yellow leaves, stunted growth, premature leaf drop, deformed fruit, or staining on fruit in peach trees.

Aphids reproduce quickly, with two to three generations each season. A generation of winged aphids migrate to garden vegetables and weeds by mid-summer. Aphids can carry and transmit certain viruses to vegetable plants when they feed.

Q: My peach tree is covered with aphids. Will they kill my tree? What can I do?

A: Aphids don’t usually affect the health of most fruit trees. Even though they make your peach tree look terrible, a conservative approach to treating aphids is best because it can help preserve the balance in your garden’s ecosystem. Try the following steps for good aphid control.

1. Spray a delayed dormant spray in early spring

Observe the buds on your peach tree in the spring. At the swollen bud stage, apply a delayed dormant spray with a 2 percent horticultural oil solution. Aphids reproduce quickly after hatching. Applying this dormant spray at bud swell suffocates many aphid eggs, making subsequent population more manageable.

2: Scout for aphids twice a week Turn over leaves to check the underside, looking for the first signs of aphids. It’s time to spray when you first notice more than two or three on several leaves. Leaf curl is a common symptom of aphid feeding, but don’t wait for leaves to curl; sprays are not effective where leaves curl significantly.

3: Spray water, insecticidal soap or 1 percent horticultural oil A strong spray of water can often wash off many aphids, quickly reducing the population. There will still be aphids left behind on the tree and insecticidal soap or horticultural oil can be used to kill them.

Insecticidal soaps and horticultural oils are not poisons. Insecticidal soap works by disrupting the cell membranes of soft-bodied insects and mites. Horticultural oils work by suffocating them. Either spray must make direct contact with aphids to be effective. Soaps and oils are less harmful to beneficial insects such as ladybugs, lacewings, and syrphid flies that help protect your peach trees. Read the product label carefully and dilute and apply the spray according to the label directions. Thorough coverage is needed for good results. These products can damage the leaves while daytime temperatures are hot and the sprays are wet. Apply in the evening to allow the spray to slowly dry before the next day.

Conventional insecticides are a poison and kill many beneficial insects. It’s easy to end up in a repeating cycle of spraying to kill aphids that have returned more quickly than beneficial predators can. Since aphids reproduce so quickly, there is also a risk they will develop resistance to insecticides, reducing their effectiveness.

4: Observe and re-spray throughout the growing season Aphids fly back to peach trees to lay eggs by September or October. These eggs can overwinter and become next year’s first generation. Good aphid control in the fall may reduce aphid populations in the spring. Check your peach trees weekly. Watch for aphids and curled leaves and repeat the sprays of soap or oil as needed.