Ash whitefly (2015)

Michael R. Bush, Christopher Adams, and Sven Spichiger

Siphoninus phillyreae

Ash whitefly was detected in California in 1988 and continues to spread to neighboring states to the south. By 2014, it was found in Oregon. Clouds of whiteflies are seen in the late summer and autumn in the Willamette Valley. This whitefly has wide range of ornamental, native and fruit tree hosts. For now, it is limited in its distribution. Early detection in new locations presents an opportunity to introduce natural enemies so that they increase along with the pest.

Pest description and damage Ash whitefly adults have translucent white wings through which the yellow body may be visible. The pale-yellow eggs are covered by waxy deposits. Translucent nymphs are covered with tufts of white wax and become more opaque and as they mature. The puparia are covered with white wax and surrounded by tubercles that exude sticky honeydew. Infested leaves have a sticky mess of eggs, waxy nymphs, puparia and honeydew. Both adults and nymphs feed on the host plants. Excessive whitefly feeding can defoliate trees, cause premature fruit drop and may lead to the death of the host plant in severe whitefly infestations.

Biology and life cycle Female whiteflies lay eggs on the undersides of the leaves on host plants. Nymphs emerge from the eggs and settle onto the leaves where they remain and feed on the plant sap. They then pupate and later emerge as winged adults. Adults live 30-60 days with several generations in a year. Adults leave preferred summer hosts such as ash, pear and hawthorn to overwinter and breed on evergreen hosts. It is not uncommon for whiteflies to linger on evergreens without developing other life stages. However, for the nursery industry they may be a contaminant the customer does not want any whitefly species introduced into their landscape.

Pest monitoring Watch for clouds of tiny whiteflies, or sticky honeydew and sooty mold under infested leaves.

Management—cultural and physical control

There are no lists of resistant cultivars of plants at this time. Strong streams of water directed to the undersides of plants may dislodge or injure the various life stages. Sticky traps and screening provide some protection.

Management—biological control

In other states, several biological control agents were released to manage populations of ash whitefly including a parasitic wasp Encarsia inaron and a lady beetle, Clitostethus arcuatus. In California and in Florida, E. inaron was the most successful agent limiting the populations of ash whitefly. In California, between 80 to 98% of ash whitefly nymphs were parasitized by the wasp. Encarsia inaron. This parasitic wasp is so effective in parasitizing ash whitefly that pesticide use was avoided to allow the natural enemy to build up to effective numbers.

For biology, life history, monitoring and management

See “Whitefly” in:

Management—chemical control

See “Whitefly” in Table 1:

For further information:

Paine, T., Bellows, T. and M. Hoddle. 2016. Ash whitefly. Center for Invasive Species Research. https://cisr.ucr.edu/ash_whitefly.html

Rosetta, R. 2016. Ash whitefly. Oregon State University Extension. http://oregonstate.edu/dept/nurspest/Ash_whitefly.html