Last week, someone called our helpline about a strange phenomenon happening on her backyard plants. She described the symptoms as “big, white, masses of fluffy cotton.” I asked her to email some photos our helpline address (ucmgstanislaus@ucanr.edu).

Waxy deposits left behind by giant whiteflies. (Linda Schultz)

When I opened her email, I was surprised to see images of what appeared to be giant whiteflies. This pest invaded California in the early 1990's and was until recently only found in Southern California and along the coast. The Stanislaus County Agricultural Commissioner's Office confirmed that giant whiteflies are present in our County.

If you've heard of whiteflies or dealt with them in your landscape, you may wonder how giant whiteflies are different, aside from being larger. Both pests suck plant juices and weaken plants. The main difference is that giant whiteflies tend to feed together in large groups. This large population creates waxy looking deposits that create a “bearded appearance” or what the caller described as “fluffy cotton” on plants. If you look closely at the infestation, you may see the pests living on the undersides of the leaves.

Giant whiteflies on a leaf. (Linda Schultz)

If you find giant whiteflies in your landscape, there are a few things you can do. For small infestations, pull off affected leaves, place them in a sealed bag, and discard them. For larger ones, direct a strong stream of water at the undersides of the leaves to knock giant whiteflies off and kill them.

Visit the UC IPM publication Pest Notes: Giant Whitefly for more information about this pest, or call our helpline at (209) 525-6802 to speak with a UCCE Master Gardener.