White egg sacks on Japanese maple

Asked August 18, 2019, 6:32 PM EDT

I have had a worsening spread of white cottony deposits on undersized of Japanese maple leaves. What causes this and how is it treated?

Linn County Oregon insect issues insect identification

1 Response

Hi There,

These are the sacs of the adult cottony cushion scale (Icerya purchasi). Once the females are beneath their cottony 'sac', insecticides will not work well against them. The scales are literally protected by the sac, from insecticide sprays.

Natural enemies, including beetles and parasitic insects, are your best control. If you see evidence of natural enemies eating your cottony cushion scales, you may want to wait and see if the enemies give you good control, on their own. Note that ants are not natural enemies of the scales. If you see ants, they are 'farming' the scales for honeydew, and help to protect the scales from natural enemies that might otherwise control them. Ants should be removed or excluded, using ant baits or tanglefoot. I personally hate tanglefoot (it's like taffy . . .sticky, pliable, messy). If you do use tanglefoot, do not apply directly to the tree. Wrap the tree with duct tape or tree fabric, and apply the tanglefoot to this material.

If you do not see evidence of natural enemy control on your scales,monitor your maple for evidence of the crawling stage of this pest. The crawlers look like tiny, red dots. This is the vulnerable stage of the pest. Low-toxicity insecticides to consider include the horticultural oils. Make sure to test a portion of your maple, before spraying the entire tree. Hort oils can sometimes 'burn' the foliage of tender plants.

Great information on scale control can be found here: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html

Specifically, this passage gives good infomration on the non-residual, low toxicity insecticides:
Nonresidual, Contact Insecticides

"Where plants can be sprayed, complete spray coverage of infested plant parts with horticultural oil at the proper time provides good control of most scales. Horticultural oils (e.g., Bonide Horticultural Oil and Monterey Horticultural Oil) are specially refined petroleum products, often called narrow-range, superior, or supreme oils. Other nonpersistent, contact sprays for garden and landscape plants include insecticidal soap (Safer Brand Insect Killing Soap Concentrate II), neem oil (Bayer Advanced Natria Neem Oil Concentrate, Green Light Neem, Garden Safe Brand Neem), canola oil (Bayer Advanced Natria Multi-Insect Control), and other botanical (plant-derived) oils.

These insecticides have low toxicity to people and pets and relatively little adverse impact on the populations of pollinators and natural enemies and the benefits they provide. To obtain adequate control, thoroughly wet the infested plant parts with spray, typically shoot terminals and the underside of leaves. More than one application per growing season may be needed, especially if the targeted pest has more than one generation a year. Thorough spray coverage is especially critical when treating armored scales and oak pit scales as these scales are generally less susceptible to pesticides than soft scales."

This section tells you how to make and use a tape trap:

"Tape Traps

Transparent double-sided sticky tape can be used to effectively time a foliar insecticide application. During the spring before crawlers begin to emerge, tightly encircle each of several scale-infested twigs or branches with transparent tape that is sticky on both sides, available at fabric or craft stores. Double over the loose end of the tape several times to make it easier to remove. Place a tag or flagging near each tape so you can readily find it. Change the tapes at weekly intervals. After removing the old tape, wrap the twig at the same location with fresh tape. Preserve the old sticky tapes by sandwiching them between a sheet of white paper and clear plastic. Label the tapes with the date, location, and host plant from which they were collected.

Scale crawlers get stuck on the tape and appear as yellow or orange specks. Examine the tape with a hand lens to distinguish the crawlers (which are round or oblong and have very short appendages) from pollen and dust. Use a hand lens to examine the crawlers beneath mature female scales on bark or foliage to be certain of crawler appearance. Other tiny creatures, including mites, may also be caught in the tape.

Visually compare the tapes collected on each sample date. If a spring or summer foliar insecticide application is planned, unless another time is recommended for that species, spray after crawler production (abundance in traps) has peaked and definitely begun to decline, which is soon after most crawlers have settled."

This page gives specific information on cottony cushion scale control :http://ipm.ucanr.edu/PMG/PESTNOTES/pn7410.html

Good luck! Please let me know if I can be of further assistance.