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Timing Control Actions for Landscape Insect Pests Using Flowering Plants as Indicators

G.J. Mussey, D.A. Potter, and M.F. Potter: Department of Entomology

Landscape managers in Kentucky contend with a wide vari- ety of plants and associated pest problems. In any given landscape, there may be hundreds of species and cultivars of native and exotic trees, shrubs, and garden plants. Throughout the growing season, these plants may be attacked by a similarly diverse assortment of insects, including wood borers, leafminers, scale insects, plant bugs, and leaf-feeding caterpillars.

Timing is everything when managing landscape pests. To be effective, insecticides or biological controls must be applied when pests are present and at their most vulnerable life stage. For example, scale insects are best controlled after the eggs have hatched but before the crawlers have formed a protective cover. Controlling wood borers requires treating host trees with insecticides to intercept the newly hatched larvae before they have penetrated the bark. Leaf-feeding caterpillars such as bagworms and tent caterpillars are easiest to control when the larvae are small. Timing is especially important when using short-lived materials such as summer oils, soaps, and Bacillus thuringiensis (BT).

Frequent in-field inspection is the most reliable means to detect insect problems and time control efforts. Unfortunately, regular monitoring is too time-consuming for many landscape managers. Field workers may not know when or where to look for vulnerable life stages or may not recognize them when encountered. Pests such as the holly leafminer, honeylocust plant bug, and potato leafhopper feed in advance of any recognizable damage. Pheromone traps are available for monitoring certain insects (e.g., clearwing borers) but require time and expertise to use effectively.

Forecasting Using Plant Phenology

Phenology is the science dealing with the effects of climate on seasonal biological events, including plant flowering and insect emergence. Insects are cold-blooded, and like plants, their development will be earlier or later depending on spring temperatures. Since both plant and insect development are temperature-dependent, seasonal appearance of particular insect pests should follow a predictable sequence correlated with the flowering of particular landscape plants. In a three-year research project, the seasonal development and emergence of 33 important insect pests were systematically monitored and tracked resulting in the creation of the timetable below. This information will help landscape managers and lay persons anticipate the appearance of important insect pests and effectively schedule control measures.

Using the Table

Beginning in early spring, the table predicts the sequence and date of emergence of particular insect pests of woody plants or turf (in bold type). Seasonal emergence of each pest is correlated with the flowering of 34 familiar landscape plants. First bloom (when a plant produces its first flower), 50 percent bloom, and 95 percent bloom (essentially full flower) are included to delineate distinct stages of flowering in the landscape. The table also lists average calendar dates of pest emergence during the three-year study, along with the range. Flowering tended to be a more reliable indicator of insect emergence than calendar date due to year-to-year temperature fluctuations.

Locate the pest you wish to monitor in the first column of the table. Flowering events that coincide with that pest's emergence appear in the same vicinity (above and below) of the table.

Phenological sequence of woody plant flowering and insect events in Lexington, Kentucky.
InsectsPhenological Indicator plantsDates of pest emergence
Event3-year avg.Range
Acer saccharinum (silver maple)1st bloom18 Feb12-23 Feb
Cornus mas (cornelian cherry dogwood)1st bloom21 Feb10 Feb-04 Mar
Acer saccharinum (silver maple)50% bloom24 Feb17 Feb-01 Mar
Cornus mas (cornelian cherry dogwood)50% bloom03 Mar26 Feb-13 Mar
Acer saccharinum (silver maple)95% bloom10 Mar03-22 Mar
Forsythia x intermedia (border forsythia)1st bloom12 Mar27 Feb-27 Mar
Cornus mas (cornelian cherry dogwood)95% bloom13 Mar29 Feb-23 Mar
Eastern tent caterpillarEgg hatch16 Mar03-29 Mar
Forsythia x intermedia (border forsythia)50% bloom17 Mar05-29 Mar
Magnolia stellata (star magnolia)1st bloom19 Mar05-29 Mar
Rhododendron 'PJM' (P.J.M. rhododendron)1st bloom22 Mar07 Mar-02 Apr
Magnolia x soulangiana (saucer magnolia)1st bloom22 Mar04 Mar-04 Apr
Forsythia x intermedia (border forsythia)95% bloom23 Mar09 Mar-01 Apr
Pyrus calleryana 'Bradford' (Bradford pear)1st bloom23 Mar09 Mar-04 Apr
Magnolia stellata (star magnolia)50% bloom25 Mar09 Mar-07 Apr
Magnolia x soulangiana (saucer magnolia)50% bloom29 Mar09 Mar-11 Apr
Inkberry leafminerEmergence01 Apr25 Mar-08 Apr
Pyrus calleryana 'Bradford' (Bradford pear)50% bloom01 Apr21 Mar-08 Apr
Pyrus calleryana 'Bradford' (Bradford pear)95% bloom03 Apr24 Mar-10 Apr
Rhododendron 'PJM' (P.J.M. rhododendron)50% bloom03 Apr31 Mar-07 Apr
Amelanchier arborea (serviceberry)1st bloom05 Apr30 Mar-11 Apr
Rhododendron 'PJM' (P.J.M. rhododendron)95% bloom06 Apr02-10 Apr
Berberis x mentorensis (mentor barberry)1st bloom06 Apr30 Mar-12 Apr
Acer platanoides (Norway maple)1st bloom06 Apr04-10 Apr
Magnolia stellata (star magnolia)95% bloom07 Apr04-11 Apr
Cornus florida (flowering dogwood)1st bloom08 Apr01-14 Apr
Boxwood psyllidEmergence09 Apr04-16 Apr
Berberis x mentorensis (mentor barberry)50% bloom09 Apr30 Mar-18 Apr
Amelanchier arborea (serviceberry)50% bloom09 Apr08-12 Apr
Viburnum x juddii (Judd viburnum)1st bloom10 Apr08-13 Apr
Magnolia x soulangiana (saucer magnolia)95% bloom11 Apr08-14 Apr
Acer platanoides (Norway maple)50% bloom11 Apr08-14 Apr
Amelanchier arborea (serviceberry)95% bloom11 Apr08-14 Apr
Malus floribunda (flowering crabapple)1st bloom11 Apr08-15 Apr
Berberis x mentorensis (mentor barberry)95% bloom13 Apr02-22 Apr
Viburnum x juddii (Judd viburnum)50% bloom13 Apr11-17 Apr
Cercis canadensis (eastern redbud)1st bloom14 Apr11-17 Apr
Malus floribunda (flowering crabapple)50% bloom15 Apr13-20 Apr
Syringa vulgaris (common lilac)1st bloom15 Apr14-18 Apr
Acer platanoides (Norway maple)95% bloom15 Apr12-20 Apr
Aesculus x carnea (red horsechestnut)1st bloom16 Apr03-30 Apr
Malus sargentii (Sargent crabapple)1st bloom16 Apr13-22 Apr
Cornus florida (flowering dogwood)50% bloom17 Apr15-19 Apr
Cercis canadensis (eastern redbud)50% bloom17 Apr13-21 Apr
Viburnum x juddii (Judd viburnum)95% bloom17 Apr13-19 Apr
Prunus serrulata 'Kwansan' (Kwansan cherry)1st bloom19 Apr14-25 Apr
Prunus serrulata 'Kwansan' (Kwansan cherry)50% bloom19 Apr17-21 Apr
San Jose scale Egg hatch20 Apr20 Apr
Honeylocust plant bug Emergence20 Apr13-29 Apr
Syringa vulgaris (common lilac)50% bloom20 Apr18-24 Apr
Malus sargentii (Sargent crabapple)50% bloom20 Apr16-26 Apr
Prunus serrulata 'Kwansan' (Kwansan cherry)95% bloom20 Apr18-23 Apr
Birch leafminer Emergence21 Apr20-23 Apr
Malus floribunda (flowering crabapple)95% bloom21 Apr18-25 Apr
Cercis canadensis (eastern redbud)95% bloom21 Apr18-24 Apr
Cornus florida (flowering dogwood)95% bloom22 Apr20-24 Apr
Hawthorn lace bugEmergence22 Apr19-27 Apr
Malus sargentii (Sargent crabapple)95% bloom23 Apr20-28 Apr
Oystershell scale Egg hatch23 Apr20-30 Apr
Magnolia weevil Emergence23 Apr18 Apr-01 May
Viburnum plicatum var. tomentosum

(doublefile viburum)

1st bloom23 Apr22-27 Apr
Black cutworm 1st flight24 Apr22-26 Apr
Syringa vulgaris (common lilac)95% bloom24 Apr20-29 Apr
Lilac borer1st flight24 Apr18-30 Apr
Lonicera tatarica (tatarian honeysuckle)1st bloom25 Apr20 Apr-03 May
Viburnum plicatum var. tomentosum

(doublefile viburnum)

50% bloom26 Apr23-30 Apr
American plum borer 1st flight26 Apr20 Apr-03 May
Holly leafminer Emergence27 Apr24 Apr-01 May
Crataegus viridis 'Winter King'

(Winter King hawthorn)

1st bloom27 Apr23 Apr-04 May
Cornus kousa (flowering dogwood)1st bloom28 Apr18 Apr-10 May
Chionanthus virginicus (white fringe tree)1st bloom28 Apr22 Apr-06 May
Aesculus carnea (red horsechesnut)50% bloom29 Apr26 Apr-03 May
Lesser peachtree borer 1st flight29 Apr24 Apr-07 May
Pine needle scale Egg hatch30 Apr25 Apr-07 May
Viburnum plicatum var. tomentosum
(doublefile viburnum)95% bloom01 May29 Apr-03 May
Chionanthus virginicus (white fringe tree)50% bloom01 May27 Apr-09 May
Crataegus viridis 'Winter King'

(Winter King hawthorn)

50% bloom02 May27 Apr-08 May
Redbud leafhopper (E. aclys) Emergence02 May28 Apr-04 May
Redbud leafhopper (E. bistrata) Emergence02 May28 Apr-04 May
Pyracantha coccinea (scarlet firethorn)1st bloom02 May01-07 May
Lonicera tatarica (tatarian honeysuckle)50% bloom02 May27 Apr-07 May
Boxwood leafminer Emergence03 May02-04 May
Euonymus scale Egg hatch04 May01-07 May
Aesculus carnea (red horsechestnut)95% bloom04 May02-06 May
Cornus kousa (kousa dogwood)50% bloom04 May26 Apr-15 May
Chionanthus virginicus (white fringe tree)95% bloom05 May30 Apr-11 May
Crataegus viridus 'Winter King'

(Winter King hawthorn)

95% bloom06 May04-12 May
Potato leafhopper 1st activity07 May03-14 May
Pyracantha coccinea (scarlet firethorn)50% bloom08 May06-10 May
Cladrastris kentukea (yellowwood)1st bloom08 May05-11 May
Ilex opaca (American holly)1st bloom08 May05-11 May
Lonicera tatarica (tatarian honeysuckle)95% bloom11 May02-21 May
Ilex opaca (American holly)50% bloom11 May08-14 May
Cladrastris kentukea (yellowwood)50% bloom12 May10-15 May
Cornus kousa (kousa dogwood)95% bloom13 May05-24 May
Pyracantha coccinea (scarlet firethorn)95% bloom14 May13-16 May
Juniper scale Egg hatch15 May13-18 May
Ilex opaca (American holly)95% bloom17 May17-18 May
Cladrastris kentukea (yellowwood)95% bloom17 May17-18 May
BagwormEgg hatch18 May18-20 May
Dogwood borer 1st flight20 May19-23 May
Crataegus phaenopyrum

(Washington hawthorn)

1st bloom21 May18-26 May
Bronze birch borer Emergence22 May18-25 May
Tilia cordata (littleleaf linden)1st bloom23 May02 May-07 Jun
Syringa reticulata (tree lilac)1st bloom23 May19-30 May
Catalpa speciosa (northern catalpa)1st bloom24 May21-26 May
Calico scale Egg hatch24 May24-26 May
Crataegus phaenopyrum
(Washington hawthorn)50% bloom24 May21-28 May
Hydrangea quercifolia (oakleaf hydrangea)1st bloom27 May23 May-02 Jun
Catalpa speciosa (northern catalpa)50% bloom27 May26-29 May
Flatheaded appletree borer Emergence28 May20 May-06 Jun
Crataegus phaenopyrum
(Washington hawthorn)95% bloom28 May26 May-01 Jun
Syringa reticulata (tree lilac)50% bloom29 May24 May-05 Jun
Peachtree borer 1st flight29 May26 May-05 Jun
Twolined chestnut borer Emergence29 May26 May-01 Jun
Magnolia grandiflora (southern magnolia)1st bloom30 May23 May-12 Jun
Catalpa speciosa (northern catalpa)95% bloom31 May30-31 May
Syringa reticulata (tree lilac)95% bloom02 Jun28 May-07 Jun
Hydrangea quercifolia (oakleaf hydrangea)50% bloom02 Jun31 May-06 Jun
Japanese beetle 1st flight04 Jun03-08 Jun
Tilia cordata (littleleaf linden)50% bloom07 Jun04-09 Jun
Honeylocust borer Emergence07 Jun26 May-15 Jun
Hydrangea quercifolia (oakleaf hydrangea)95% bloom07 Jun05-11 Jun
Magnolia grandiflora (southern magnolia)50% bloom08 Jun26 May-20 Jun
Walnut scale Egg hatch09 Jun08-11 Jun
Tilia cordata (littleleaf linden)95% bloom09 Jun06-13 Jun
Cottony maple leaf scale Egg hatch11 Jun08-14 Jun
Koelreuteria paniculata (golden-rain tree)1st bloom16 Jun13-18 Jun
Abelia x grandiflora (glossy abelia)1st bloom23 Jun14 Jun-09 Jul
Koelreuteria paniculata (golden-rain tree)50% bloom24 Jun21 Jun-01 Jul
Koelreuteria paniculata (golden-rain tree)95% bloom26 Jun23 Jun-01 Jul
Obscure scale Egg hatch06 Jul05-08 Jul

Determining Treatment Date

For most insects listed in the table, the ideal time to begin insecticide treatment is at or shortly after pest emergence. For bagworms, delay treatment one to two weeks after eggs hatch to ensure all young larvae have emerged from the old bags. For clearwing borers (dogwood, lilac, peachtree, lesser peachtree) and American plum borer, apply a bark spray 10 to 14 days after first flight. Apply a second bark spray one month later for better control of dogwood, peachtree, and lesser peachtree borers. For flatheaded borers (bronze birch borer, flatheaded appletree, honeylocust, twolined chestnut borer), apply a bark spray at or shortly after emergence and repeat after three weeks.

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