The accumulation of heat units (Growing Degree Days (GDD)) is increasing rapidly across many areas of New Jersey as we soon enter into the early weeks of April. If past histories or present-day monitoring indicate the need for interventions, then the best control windows for an increasing number of insect/mite pests are beginning to occur. The following is an incomplete listing of a handful of some of our early season landscape pests that may need to be scouted & possibly controlled. The insect/mite pests included here are: Hemlock Rust Mites; White Pine Weevils; Native Holly Leafminers; European Pine Sawflies; Honeylocust Spider Mites; White Pine Aphids; and Eastern Spruce Gall Adelgids.
As our landscapes start to “wake-up” with warming temperatures, the insect & mite pests will begin activity. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
When monitoring indicates controls are warranted, then pesticides can prevent early spring pests from building-up. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Hemlock Rust Mites: (7-22 = active mites emerge)
Hemlock Rust Mites cause the needles to turn a light yellowish green color. They can feed on both sides of the needles. Numerous cast skins can give the needles a dusty appearance. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Hemlock rust mites are a cool or even cold season mite that has been active for a week or more already. These mites are difficult to see without magnification. Use at least a 10X magnification (20X is better) to identify their light yellow, spindle-shaped forms. The mites are only 0.25 mm or 1/100th of an inch in size. Adults overwinter in bark cracks of hemlocks and start feeding on the needles during warm periods in March. They continue to feed into the months of April, May, and June. Needles turn off-color to a light yellowish green and may drop by midsummer. The mites numerous thin, white, shed skins may be noticed scattered around both sides of the hemlock needles. This gives the needles a dusty or dirty appearance.
The light yellow, spindle shaped Hemlock Rust Mites can build-up into huge populations. (Photo Credit: Ohio State Coop. Ext.)
Although hemlock rust mites may be active up to early summer, most of the damage usually occurs in the spring. A useful monitoring technique is to inspect the sunny, south-sides of hemlocks in April and May for the light-yellow foliage. The mites can feed along the entire surface area of the needles. When mite populations are high, control with horticultural oil at the first sign of activity. There can be several generations per year. Although this eriophyid mite prefers to feed on hemlocks, they can sometimes be found infesting yews, firs, spruce & larch.
White Pine Weevils (7-58 GDD = adult treatment):
Many arborists and landscapers often find it difficult to prevent this pest, because they are typically pruning, applying mulch, fertilizers and dormant oil treatments during the control window. The growing degree-day (GDD) control window begins early in the season (March) & extends for a few weeks. Eastern white pine & Norway spruce are two commonly infested species, although a number of other conifer species are susceptible.
Adult White Pine Weevils initially feed within the terminal leader in early spring. Adult feeding cause resin flow which then turns white after drying. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Treatment timing is critical with this pest and it is necessary to control the adult female prior to egg lying. Adults overwinter in the duff beneath trees. Eggs are laid beginning in mid to late March (sometimes earlier) and continues into April. Before egg lying, adults will chew holes near the terminal bud of the central leader and cause a characteristic resin pitch flow that becomes white in color after drying. Eggs are then laid in the protected holes usually within the top 12 inches of the terminal leader. Control treatments target the adults before they lay eggs. Long residual materials such as pyrethroids & carbaryl (Sevin) can be successful. Only the terminal leaders need to be treated with insecticides. Multiple applications may be required.
Often by July, an infested terminal will brown & die as the weevil larvae have destroyed the vascular tissues. Most adults emerge in July. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
If the control window is missed, then prune out any infested terminals (2020 leader growth included) before the end of June, when the next generation of adults begin emergence (only one feeding generation per year). The white pine weevil larvae will cause a “shepherd’s crook” before killing the main terminal leader. The new central terminal candle growth can extend during the spring months, but by early summer the feeding larvae will have destroyed much of the water conducting tissues in the previous year’s leader. Smaller trees may lose their Christmas-tree shape and/or develop multiple leaders. Side laterals can sometimes be staked and trained to regain single leader dominance. When possible, select the northern most lateral to be the new terminal leader. This new terminal will “reach” & grow toward the southern sun. Once white pines reach a height of 20 feet or more, they become more tolerant of this pest since this pine species naturally develops multiple leaders.
Native Holly Leafminers (active larvae):
Adult female Native Holly Leafminers will use their ovipositor to puncture new leaves to feed or lay eggs. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Most of the feeding damage from these yellow, immature flies that tunnel through the leaves, occurs during the early spring weeks. Although this native leaf miner will initially feed within both American & English hollies, the larvae only complete development in the American holly. Often, the new leaves will show symptoms from numerous ovipositor puncture wounds done by emerged female adults as they feed & lay eggs later during the spring.
Native Holly Leafminers create serpentine leaf mines as they feed. Non-native holly leafminers create more oval shaped blotched mines. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
During the fall, the typical serpentine mines are narrow, but are often greatly expanded during the spring by the overwintering larvae. (The non-native holly leafminer will only feed within English hollies & create blotched as opposed to serpentine mines.) Therefore, late March & April can be an important time to apply controls to prevent the most damaging stage by this leaf miner. Two other possible control window opportunities are against the adults in May and smaller larvae in the fall season. Obviously, the IPM approach dictates that no pesticides will be applied unless significant leaf miner populations are present. With light infestations on small hollies, pull off and destroy mined leaves before adults emerge in May.
Pesticide products include the translaminar materials acephate (Orthene) and spinosad (Conserve) to control the larvae. Imidacloprid (Merit) can be applied during early spring as a soil drench to control developing larvae. Place sticky traps out to monitor for adults. Contact insecticides such as carbaryl (Sevin) or any of the pyrethroids generally may only suppress the adults.
European Pine Sawflies (35-145 GDD = egg hatch):
The most common sawflies on pines are the European pine sawfly (EPS) and the redheaded pine sawfly (RPS). They commonly attack the two-needle pines (mugo pine, Scotch pine, and Japanese black pine). EPS overwinters as eggs in the needles, while RPS overwinters as pupae. EPS may soon begin to hatch, so monitor for the young larvae feeding on the needles. RPS larvae will not be active until May since it must emerge as an adult and then lay eggs.
European Pine Sawflies will feed in groups & the very young larvae will cause pine needles to twist and turn brown like straw. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
When sawfly larvae are young, their mouthparts are small so they cannot initially eat the entire needle. Partial eating of the needles results in the remaining part turning brown and curling. This appearance provides a highly effective monitoring tool, particularly on larger trees. The brown curled needles are easy to spot from a distance and indicate the presence of a population of sawflies feeding near that spot. Remember, sawfly larvae are wasps within the order hymenoptera & are not caterpillars.
Since sawflies are not caterpillars, B.t. (Bacillus thuringiensis) will not control them. A 1-2% horticultural oil spray may control young larvae (however, not larger, older larvae). The uses of sinosad (Conserve), acephate (Orthene), carbaryl (Sevin), or any of the pyrethroids are some choices for the control of older larvae.
The tiny mouth-parts of a group of young European Pine Sawfly larvae having black colored head capsules, strip the outer epidermis of pine needles. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Red-Headed Pine Sawfly are the other primary sawfly species that feed on pines. They do not become active until May, after most European Pine Sawflies have concluded their activity. They can feed on the same pine species as the European Pine Sawfly. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Honeylocust Locust Spider Mites (overwintering adults):
Honeylocust Spider Mites will primarily feed on leaf undersides & concentrate at the base of the leaflets. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
This native spider mite feeds only on the leaves of honeylocust. The orange, overwintering adults are only 0.5 mm or 1/50 of an inch and can presently be found congregating in bud scars and bark cracks. Although this mite is typically classified as a warm season mite, the eggs from the overwintering adults are laid in early spring and hatch shortly after bud break & begin to feed on foliage. There are multiple generations per year and by the beginning of summer, all stages can be seen on the plant. Generally, the honeylocust spider mite can be found feeding on this tree all season long, although the greatest damaging populations will accumulate during the late spring weeks & again during the late summer weeks.
Examine trees with a history of this pest with a 10x to 15x hand-lens during early spring. Look in bud scars and bark cracks to estimate future potential mite populations. During the later spring weeks, monitor the leaves for increasing amounts of stippling damage. Heavy infestations may cause foliage to brown and die. Re-foliation is common if damage occurs early in the season.
This mite species can have multiple generations during the year & peak infestations often take place in late spring & and again in late summer. (Photo Credit: Steven K. Rettke, Rutgers Coop. Ext.)
Dormant oil sprays (3%) can still be used if the leaf buds have not yet opened. Later in the spring, if the mite populations are showing signs of building up on the foliage, use a summer oil (1-2%) or soap. Hexythiazox (Hexygon), a biorational miticide is a mite growth regulator and is effective against only eggs and immature nymphs. Although it does not control adults, any eggs laid by adult females will be sterile. Therefore, if populations have reached high levels, then this material will not give rapid results. Other miticides that may be necessary during large population outbreaks include abamectin (Avid), acequinocyl (Shuttle), fluvalinate (Mavrik), and spiromesifen (Forbid).
White Pine Aphid: (22-91 GDD = egg hatch):
This native aphid feeds only on Eastern white pine. Overwintering oval, shiny black eggs laid in rows along the needle length are easily visible when monitoring. Adult aphids are large (3/16 inch) and brownish-black in color with long legs. Adults also have a central white stripe and white spots on each side of the abdomen. They suck phloem sap through the bark of branches and may cause some branch dieback if populations are high. Their presence is most likely discovered when aphid honeydew excrement turns the needles black with the sooty mold fungus growth. The sugary honeydew may also attract ants and swarms of hornets and yellowjackets (the latter two are more of a nuisance with the generations in the early fall). Feeding aphids live in dense clusters on white pine twigs.
If heavy populations warrant controls, then horticultural oils can be used to treat both overwintering eggs as well as the active aphids. Insecticidal soaps will typically only provide suppression against aphids & may require multiple treatments to achieve satisfactory results.
Feeding White Pine Aphids exude a lot of honeydew which promotes the growth of black sooty mold. (Photo Credit: Unknown)
White Pine Aphids overwinter as black eggs lined-up as a string of beads along a pine needle. They are usually easy to spot. Oils but not soaps will kill eggs. (Photo Credit: North Carolina Coop. Ext.)
Eastern Spruce Gall Adelgids: (25-100 GDD = overwintering nymphs):
The Eastern Spruce Gall Adelgid (ESGA) has galls that form at the base of current year’s growth. Typically, the ESGA is found on Norway spruce. Often the ESGA has the potential to cause aesthetic damage on highly infested trees, but can also cause branch thinning & dieback. The other common spruce gall is the native Cooley spruce gall adelgid & it forms at the twig terminals. It primarily infests Colorado blue spruce, although the galls can also be found on Oriental spruce.
The overwintering immature nymphs of the Eastern Spruce Gall Adelgids. Control them with dormant oils or insecticidal soaps before the lateral buds swell & the stems elongate. (Photo Credit: Bartlett Tree Experts, Bugwood.org.)
With ESGA, the whitish, wax-covered overwintering nymphs are present at the base of lateral buds. Scout for these small, white webbings by using a 10X hand-lens. This will be your target site when directing control sprays.
Apply horticultural oil or insecticidal soap in April before the new bud shoots begin to swell and expand. Good results can be achieved by targeting the nymphs with these materials. Insecticidal soaps have dynamic controls against adelgids if good coverage is achieved.
Once the galls of the Eastern Spruce Gall Adelgids have formed, there are limited chemical controls available. (Phot Credit: Steven K. Rettke, Rutgers Coop. Ext.)
As new twig growth begins, the feeding nymphs introduce a toxin that eventually stimulates abnormal plant cell division and the formation of the protective galls. Once the green, pineapple-like galls have formed at the base of new shoots during May, the only available control is to prune out and destroy the galls. Not even systemic insecticides will negatively impact the nymphs within the galls.
