Juniper is the main sustenance for the larvae of several Lepidopterans species. These include: Bucculatrix inusitata, Juniper Carpet, Juniper Pug, Juniper Webworm (Dichomeris marginella), Chionodes electella, Chionodes viduella, and Pine Beauty.
Most common in Europe is the Juniper Carpet. The Juniper Carpet (Thera juniperata) is a moth of the family Geometridae and it is also found throughout the Near East. It is active at night during the months of September, October, and November. While it prefers the dark, the Juniper Carpet will occasionally fly around in the light. In its adult stage, the Juniper Carpet has a wingspan of 26-29 mm. The wings are light brown with a dark shaded band, and black apical streak. The moth’s back wings are buff and pale. This moth and its larva feed exclusively on Junipers.
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Also found in Europe, as well as in northern Asia and in the United States is the Juniper Webworm (Dichomeris marginella). The Juniper Webworm feeds on all types of Juniper, including but not limited to:
·Irish juniper (preferred host)
·Juniperus communis varieties such as: aurea, depressa, hibernica, horizontalis, squamata meyeri, and suecia
Adult Juniper Webworms are brown in color and small in size. They are roughly 5/8 of an inch long, with white wing margins. Juniper Webworms are easy to overlook as they lay still and fly only when disturbed. Adult female Juniper Webworms moths lay tiny white or pinkish eggs that become darker as they age. The Juniper Webworm caterpillar or worm is very small — only around 3/4 inches long. It is whitish or light brown with prominent reddish-brown stripes. The pupa is a light to dark reddish brown measuring roughly 1/4 inch long.
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Once the eggs hatch, the newly hatched larvae begin leaf mining. The damage the Juniper leaves, however is minimal. Larger worms, however, can do serious damage – especially to ornamental Junipers. Evidence of damage included: large quantities of dead needles, ragged looking shrubs, and shrubs that are completely webbed.
One generation of Juniper Webworms occur per year. Adult worms emerge from May to July and they peak in June. If you notice wasps flying around during this time, leave them. They are natural predators and can help control populations. Braconid wasps and ichneumonid wasps parasitize both the pupal stage and the larval stage of Juniper Webworms.
A number of pesticides are available to help control Juniper infestations. Some are suitable for home use as well, as indicated in italics.
Pesticide (Trade Name)
Formulation and Amount
75% soluble powder: 1/3 to 2/3 pound per 100 gallons of water (homeowner formulations are available)
Azadirachtin (BioNeem, Margosan-O)
0.3% emulsifiable concentrate: 2 1/2 to 5 teaspoons per gallon of water
3% emulsifiable concentrate: 1/2 teaspoon per gallon of water
10% Wettable powder: 1 to 1.5 teaspoons per gallon of water
50% wettable powder: 1 tablespoon per gallon of water
Cyfluthrin (Decathlon, others)
20% wettable powder: 1/4 teaspoon per gallon of water (homeowner garden formulations are available)
23% flowable: 1/6 to 1/3 teaspoon per gallon of water
Pyrethrins (Pyrenone, others)
6% emulsifiable concentrate: 1/8 to 1 1/2 teaspoons per gallon of water
Trichlorfon (Dylox, Proxol)
40% emulsifiable concentrate: 2 to 3 pints per 100 gallons of water