Garden dectective: My apple tree developed a weird web

Published: Saturday, Sep. 15, 2012 - 12:00 am | Page 10CALIFORNIA LIFE

My apple tree developed a weird web on one branch only that is full of caterpillar-type worms. The branch has died, but the rest of the tree is fine.

Since I discovered my "webbed branch," I have seen others just like it throughout my area on other people's property. I am attaching photos for you to view. Can you tell me what it is and why did I get it?

Thank you very much for any help that you can provide me.

– Jeannine Esposito, Somerset

It would be necessary to get more information from you about the caterpillar-type worms to accurately identify them, according to UC Master Gardener Cindy Gause. However, based on the information you have provided, you may have one of these pests: fall webworm (Hyphantria cunea) or western tent caterpillar (Malacosoma californicum pluviale).

The larvae of the fall webworm are pale brown or gray caterpillars with long white hairs on the sides of the body arising from black and orange spots. They feed inside webbed colonies on ends of branches typically from August to September. Larvae eat leaf material between petioles or veins, which result in leaves appearing "skeletonized."

The western tent caterpillar larvae are hairy and yellowish-brown with a broken blue line down their backs. Overwintering eggs hatch with new foliage around March. The larvae aggregate together and construct and enlarge communal silken tents while consuming adjacent foliage.

These tents are usually formed in the crotches of smaller branches. Young larvae do not venture far from the tent and usually feed on the foliage of a single branch.

As larvae mature, the caterpillars become more solitary, feeding by themselves or in smaller groups. In June, the mature larvae leaves the host tree to pupate by forming a white, puffy cocoon.

Both of these pests have a single generation per year and are generally considered more of a nuisance than a pest. If nothing is done to control them, they both have natural predators and the populations should collapse within one or two years for the fall webworm and two or three years for the western tent caterpillar.

It is best to prune off and dispose of branches containing tents and caterpillars as soon as the infestation is apparent. Western tent caterpillars tend to congregate in their nest at night, so it is best to prune in the early morning or evening.

If necessary, Bacillus thuringiensis or Spinosad – two natural pest killers – can be applied to individual trees with a high-pressure spray when evidence of caterpillars is first observed. Remember, when using pesticides always read and follow the label's directions.

Photos of both caterpillars can be viewed at www.ipm.ucdavis.edu.


GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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