The production of Virginia pine trees for use as Christmas trees in the Texas upper coast area is a pest management challenge. There are a number of important insect pests which affect production. The primary pest is the Nantucket pine tip moth. Unfortunately, attempts to suppress this pest often aggravate problems with tortoise scale insects and aphids. The Southern pine coneworm is a minor pest of Virginia pine, along with the pine sawyer. In poor planting sites, the deodar weevil can devastate young pine plantings.
Monitoring for Pests
A major consideration for Virginia pine tree production is the ability to carefully monitor for pests. Producers who infrequently visit their production site are at a disadvantage to detect pest outbreaks early. In these instances, a preventive program for pest suppression is often attempted, with erratic results. Optimally, pests should be monitored visually or with commercially available devices such as pheromone traps or frequent inspection.
A number of production practices can influence pest outbreaks. Site selection is an important consideration. Plants grown in poor soil or in moisture stress conditions become more vulnerable to outbreaks of pests such as the deodar weevil. Pruning practices can eliminate undesirable pest damage such as that caused by the Nantucket pine tip moth.
Prior to sale of trees, careful inspection can detect and eliminate trees of poor quality and those with obvious pest damage. Aphid and scale outbreaks cause trees to darken. These insects produce a large amount of honeydew, a sugary substance eliminated during the feeding activities. Honeydew is an energy-rich substance (sugar water) that is colonized by a fungus called “sooty mold.” This organism is black in color and can reduce the aesthetic value of the Christmas tree. Furthermore, mobile aphids will occasionally leave the tree after harvest, causing concern on the part of the consumer. Suppression of these pests prior to harvest is necessary to avoid this consumer problem.
There is No Holiday!
Aphids often become numerous during the winter months. Following the harvest of trees for Christmas sale, trees should continue to be monitored for insect outbreaks to avoid serious production problems for the following year.
Major Virginia Pine Insect Problems in Texas
Nantucket pine tip moth. Caterpillars of this species tunnel through the new growth (candles) of Virginia pine. Several generations occur annually. The first and second generations occur in February-March and April-May. Subsequent generations are overlapping and intensify during the fall.
Pheromone traps can be used to monitor the activity or flight periods of the adult moths. These traps collect male moths only. Wing-type traps are more efficient at collecting moths than are triangular-type traps. Traps should be placed throughout the planting and monitored on a weekly basis. Collection of adult male moths is an indication of moth activity (mating) that is soon followed by egg laying and hatching of caterpillars. Plantings should be monitored more closely following the collection of moths in pheromone traps. Look for an accumulation of resin on the new growth. Dissection of these branch and twig tips should reveal the presence of small, orange-colored caterpillars with black heads. Insecticide treatments should coincide with early detection of larval activity. Fully-grown larvae are about 1/2 inch in length. After development, they pupate in the terminals of the twigs they infest, and just prior to adult moth emergence, the pupae wriggle out of the terminal. Afterwards, the pupal skins are visible at the ends of the damaged twigs and branches.
Occasionally, preventive treatments are made for Nantucket pine tip moths using systemic insecticides applied to the drip line of the tree before larval populations develop. Although these treatments may be effective in suppressing damage for the first two (spring) generations, they may be less effective for controlling summer and fall generations.
Pine aphids are a serious problem all year. During the winter months they can build up in large numbers and cause trees to become unsightly. During the production season, they may also be present. Use of broad-spectrum insecticides such as pyrethroids (cyfluthrin, es-fenvalerate, fluvalinate, permethrin) is thought to aggravate aphid and scale problems in Virginia pine plantings. Careful monitoring for outbreaks is needed after the use of these products. Inspect for aphids, particularly a month or so before anticipated harvest. Several treatments may be necessary to suppress outbreaks. Aphids can be monitored by visual inspection, but also by beating plant parts on a piece of stiff paper to dislodge the critters. During early spring, aphids are commonly encountered on the new growth. However, during other times of the year, and following insecticide applications, aphids may reside close to the trunk of the tree where insecticide coverage was poor.
Tortoise scale insects are brown and globular. Occasionally, white-colored pine needle scales also are encountered. The tortoise scale infests twigs and branches. Like aphids, their presence often results in blackened trees due to the buildup of sooty mold. Severely infested trees are probably best culled from production. Even when scale insects are killed with insecticides, the unsightly dead scales will remain on the tree. Broad spectrum insecticides should be used with care as discussed above for aphids.
Scale insects are best managed by inspecting for crawler stages. Mature, mated female scales lay eggs underneath their scales. When these eggs hatch, six-legged mobile nymphs called, crawlers, emerge. These can be detected by beating plant parts on a stiff card or notebook, or by cutting a piece of infested terminal and placing is in a clear plastic bag. If this bag is stored in a frequently-inspected location at room temperature, the crawlers can easily be observed. When this happens, verify the egg hatch in the field by inspecting for crawlers in the production area. Insecticide treatments are timed to coincide with egg hatch or appearance of crawlers. Treatments need to be repeated, however, at 7 to 10 day intervals, following the initial treatment until the remainder of the eggs have hatched. This practice will prevent the infestation from spreading. Often, just a few trees are severely infested and spot spraying can be practiced.
Southern pine coneworm. Caterpillars of this species can tunnel in terminals and branches of Virginia pine. They also tunnel beneath the bark of young trees at or slightly above ground level. As opposed to Nantucket pine tip moths, these caterpillars are grayish-brown and may reach about an inch in length. Occasionally, up to 5 percent of the trunks in a planting may be infested with coneworms. Infestated trees are easily detected because of the large amount of resin or pitch at the damage site. Some trees may be killed by the larvae when the caterpillars tunnel all the way around the diameter of the trunk, girdling the tree.
Rarely is the severity of Southern pine coneworm infestations sufficient to justify insecticidal treatment of an entire planting. No insecticide is specifically registered for this use. Furthermore, insecticide treatments do not often kill larvae underneath the bark. Spot spraying or attempting to remove larvae from infested trunks with a knife are alternatives to large scale treatments.
Pine sawyer. Adult pine sawyer beetles are mottled brown and nearly an inch in length. They are a member of the long-horned beetles (Cerambycidae). Adults maintain their energy by feeding on tender tree parts such as the crotches of terminals and branches. Although they may disfigure a few trees, their damage is usually limited. Adult females lay eggs in the bark of stressed, dying or dead trees. The larvae hatching from these trees are creamy white and are called round-headed borers. Detection of these larvae under the bark of dead or dying trees should indicate that the infested tree should be removed. Insecticide treatments to prevent pine sawyer damage or eliminate active infestations are rarely justified. See related publication Wood-boring Insects of Trees and Shrubs, B-5086.
Deodar weevil. Problems with this pest are not common, but when they occur, an entire planting may be affected. This weevil lays eggs in the bark at the base of stressed Virginia pine trunks. Larvae hatching from the eggs tunnel beneath the bark during the winter months, often causing infested trees to die during January or February. Removal of bark will reveal cream-colored legless C-shaped grubs. Mature larvae pupate in chambers which appear oval in shape and are lined with wood shavings. Upon hatching, the beetles exit the trees through holes (about 1/8 inch in diameter) in the bark.
Red imported fire ants are a potential medical threat to field workers and to customers in “cut-your-own” operations. The Two-Step Do-It-Yourself Fire Ant Control program advocated by Texas AgriLife Extension Service can be an effective method for suppressing fire ant populations.
This approach uses an annual or biannual broadcast application of an effective fire ant bait such as Ascend®, Amdro®, Award®, Logic® followed by the use of individual mound treatments to clean up “escape” or “nuisance” mounds later on (prior to harvest, in this case). Broadcast bait applications are best applied in September in Christmas tree operations, so that their maximum level of suppression can be attained in November. Nevertheless, it is advisable to place warning signs and disclaimers at the entrance of the planting if potentially sensitive consumers are to cut their own trees.
Chemical Insecticides for Christmas Tree IPM
- Pesticides and Wildlilfe Christmas Trees
- Pesticides Used in Christmas Tree Production
- Christmas Tree Pest Manual [Note: this is a large PDF]
Tips for Proper Insecticide Selection and Use
Justify the need for insecticide use through monitoring efforts. Unfortunately, augmentive biological control agents have not been developed to suppress many of the pests of Virginia pine. However, a number of naturally occurring predators, parasites and pathogens often keep certain pest populations at tolerable levels. Frequent use of broad-spectrum insecticides can result in the outbreaks of normally minor pests by eliminating their natural enemies.
Insecticides are poisonous and should be used in strict accordance to directions printed on the product label. Whenever possible, select the product(s) that is effective specifically for the pest to be controlled, and one which is least toxic to the user and to non-target organisms. Timing of insecticide applications and coverage of the areas where pests are active is the key to control.
For example, difubenzuron is target-specific in its mode of action in that it affects only caterpillars. Conversely, diflubenzuron and other insecticides such as pyrethroids are particularly toxic to non-target organisms in neighboring bodies of water such as crawfish and shrimp. The least toxic materials registered for use on pine trees include the insecticidal soap and horticultural oil products. These are not nerve-acting insecticides and are registered for the suppression of small, soft-bodied insects. Some products have systemic activity, such as acephate, dimethoate, disulfoton or imidacloprid. Once in the plant, these insecticides may spare some predator and parasite species that do not feed directly on the plant. However, care should be taken to avoid groundwater contamination when applying insecticides directly into the soil.
When using a new product for the first time, spray a few trees and observe for possible phytotoxic reactions such as tip burn or deformed new growth. Some products, such as insecticidal soap may affect the waxy coating of foliage, temporarily causing a color change.
- Wood-boring Insects of Trees and Shrubs (AgriLife Extension Publication B-5086)
- Two-Step Do-It-Yourself Fire Ant Control (AgriLife Extension Publication L-5070)
- Christmas Tree IPM in Texas: Insect Pests of Virginia Pine Plantations (PDF)
Bastiaan M. Drees, Professor and Extension Entomologist, Texas Agrilife Extension Service, Texas A&M System. This article is a 2007 revision of Publication UC-027, Pest Management for Texas-grown Virginia Pine Production