Beginning in late spring through summer,we are often asked to investigate and treat high value trees with aphid problems.
Symptoms and signs of aphid infestation include:
- Leaves which are unnaturally curled inward
- black sooty mold on leaf surfaces
- Sticky substances on sidewalks, driveways, or vehicles
- Ant trails on tree trunks and limbs
- Numerous yellow jackets hovering around tree canopies in late summer
By mid summer, when honeydew production is at its highest, copious amounts of the sticky substance may accumulate on vehicle and sidewalk surfaces causing great annoyance.
Aphids have natural enemies. The most well known predator is the lady beetle. Adult and larvae alike are voracious consumers of aphids and can eat up to 50 aphids per day. Dense groups of aphids provide a generous food supply for these predators.
Fertilizer application-High levels of nitrogen fertilizer favor aphid reproduction. The University of California Extension recommends that we do not apply high rates of Nitrogen fertilizer throughout the growing season. Excessive applications of high Nitrogen (N) fertilizer may cause a burst of new leaf growth, which encourages reproduction of aphids and other plant juice feeding insects. They recommend low Nitrogen rates, applied throughout the season rather than high rates applied all at once. The industry standard calls for spring and fall applications. Tree Solutions Soil Restore fertilizer program uses the guidelines suggested by the University of California Integrated Pest Management program by applying low nitrogen content applications several times per year.
Leaf growth response to high rates of fertilizer can actually cause more harm than good. Your tree or shrub may initially show a vigorous response, but ensuing pest outbreaks may lead to expensive pest management treatments to control them. Applicators generally will blame the pest not the practice of over fertilization.
You do not always have to treat for aphids. If infestations are extremely high, treatment may be warranted. We recommend treatment if the sticky honeydew droppings lead to the production of sooty mold, on leaf surfaces. This condition may interfere with photosynthesis. We recommend treatment of stressed trees.
Pesticide application-If treatment is necessary, we strongly recommend against using canopy sprays using full spectrum insecticides. Many of the chemicals used persist in the environment and have a very detrimental effect to the beneficial insect population, birds, fish and humans. The availability of sub-surface soil applications and stem injection, and trunk drench options make tree canopy sprays unnecessary if using the chemical pesticide option.
For more in-depth information about aphids, use the following link which will guide you to the UC IPM web site.