Pine tip moths—Rhyacionia spp.
Larvae of this group of moths (family Tortricidae) chew and feed inside of and on pine needles and terminals. Rhyacionia species are pests primarily in Southern California and on Monterey pine, especially when the pine is planted away from the coast. Nantucket pine tip moth (R. frustrana) and near the coast the Monterey pine tip moth (R. pasadenana) are the major pests, attacking most pine species with two or three needles per bundle. Ponderosa pine tip moth (R. zozana) mostly damages young, planted pines grown away from the coast.
Identification
Dead brown or reddish shoots noticeable from a distance are the most obvious symptom of infestation. Silk webbing and boring frass (insect excrement) are visible during close inspection of discolored terminals. Because other causes can produce similar damage, see the table in Pest Notes: Pitch Canker to help you discriminate among the insects and pathogens that cause shoot dieback of pines.
Adults, mature larvae, and pupae are about 2/5 inch long. The adults are reddish brown moths with silver-gray markings. Eggs are spherical, orange or yellow, and occur on needles of hosts. Young larvae are whitish with a dark head. Older larvae are yellow to pale brown with a dark head.
Life cycle
Tip moths develop through four life stages: egg, larva, pupa, and adult. Adults (moths) begin emerging in January in Southern California. The female lays tiny eggs singly on the new growth tips where the young larvae occur on or inside of buds, needles, and shoot terminals. Summer-generation larvae pupate in the tips. Overwinter pupae commonly occur in litter on the ground.
The Nantucket pine tip moth has about four generations per year in Southern California. Monterey pine tip moth and Ponderosa pine tip moth have one or two generations per year.
Damage
Larvae chew in and on pine buds, needles, and terminals and cover infested shoot tips with fine silk. Their boring in shoots causes pitch to exude. Infested terminals discolor and die. Larval damage to the central growing terminal (leader) can significantly alter tree shape, causing regrowth of stems to be bunchy, crooked, or forked. The aesthetic quality of infested pines is marred, for example making them unsuitable for marketing as Christmas trees. However, tip moth feeding does not threaten tree survival, and pines appear to be less affected as they age.
Solutions
If little or no damage can be tolerated, do not plant pine species particularly susceptible to tip moth damage. Consider replacing susceptible species like Monterey pine if their performance is unacceptable. Alternatively, tolerate the damage.
Provide proper cultural care, especially appropriate irrigation, to increase tree tolerance to damage. The introduced ichneumonid wasp Campoplex frustranae parasitizes Nantucket pine tip moth larvae and pupae. This natural enemy has reduced moth populations in many locations, resulting in improved vigor and healthier appearance of pines. Adults are 1/4 inch long and blackish to dark brownish wasps with long antennae and orange legs. Other parasites of pine tip moths include Habrobracon cushmani. See Natural Enemy Promises Control of Nantucket Pine Tip Moth from UC Riverside for more information.
Prune off and dispose of infested tips from October through January to prevent overwintering moths from emerging. If high-value pines must be pruned during other times, monitor adults with sticky traps baited with the Rhyacionia pheromone (sex attractant). Destroy larvae and pupae by pruning infested shoots between the peak moth catches representing each generation of adult flights.
Alternatively, to kill young larvae apply a systemic insecticide (e.g., acephate, dinotefuran, imidacloprid) or spray foliage with a broad-spectrum, residual (persistent) insecticide such as carbaryl, permethrin, or another pyrethroid (insecticides ending in "-thrin") soon after moths are observed flying during each generation. However, insecticide usually is not justified unless trees are of especially high aesthetic value. Insecticide spray can cause spider mite outbreaks and wash off and pollute surface waters. Spraying also kills natural enemies such as Campoplex frustranae, which can provide substantial biological control of this pest.
Some of these insecticides including carbaryl, dinotefuran, and pyrethroids potentially effective for this pest are not available to home gardeners. A professional applicator must be hired to make these applications. For how to get the services you want, see Pest Notes: Hiring a Pest Control Company.
Monitoring and treating high-value pines. Insect activity varies with temperature, and foliar spraying and pruning are more effective if they are performed between the peak moth flight periods. To monitor flights, hang one sticky trap baited with tip moth pheromone at chest height in the outer canopy of each of two trees at least 50 feet apart from January through September. On properties with extensive pine plantings deploy additional traps at approximately 500-foot intervals. Inspect each trap daily. Remove any debris, count the Rhyacionia moths caught, record their numbers, and remove any moths in the traps. Replace traps when the sticky surface becomes dirty or clogged with moths and replace the pheromone lure about every 4 weeks or as recommended by suppliers.
If pruning or spraying of a residual foliar insecticide are performed, do so 10 to 14 days after the beginning of an overall decline in the number of first-generation moths caught and again about 1 week after the peak number of each subsequent generation of moths. If spraying foliage, thorough coverage of all branch tips and the treetop is important for providing control.
For the most effective control timing use degree-day (temperature) monitoring and moth traps. Spray foliage or prune at about 1,233 degree-days after the beginning of each moth generation, using a lower development threshold temperature of 42°F and an upper threshold of 99°F. The first generation begins in the spring when the first moth is caught. Subsequent generations start when moth catches first begin increasing after a dramatic decline in numbers from the previous peak. Enter the threshold temperatures above in the UC IPM degree-day calculator and select the weather station nearest your pine trees to most effectively time control actions.
For more information see The Nantucket Pine Tip Moth: Old Problems, New Research (PDF) from the U.S. Department of Agriculture.
Adapted from the publications above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
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