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Plant Stress & Insect Pests
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
1 Widely held belief that stressed plants are better food for insects and mite pests than healthy plants.
2 Plant stress is one of the mechanisms often cited for pest outbreaks following adverse environmental conditions such as drought or pollution.
Plant Stress Hypothesis
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Plant Stress & Diversity with Impacts on Insects
1. 70 experimental studies of plant stress response were reviewed
2. Stresses included: drought water logging shading pollution
Test of the previous hypothesis
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
3. 66 insects spp and 40 plant species were involved.
4. Insects organized into 5 feeding guilds:– chewers– suckers– leaf miners– gall makers– borers
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
a. Overall, plant stress had no significant effect on growth rate, survival, or plant density.
b. Variation in insect response did exist and was mostly related to insect guilds.
c. Boring and sucking insects performed better on stressed plants.
d. Gall making and chewing insects were affected adversely by plant stress.
e. Leaf miners were generally unaffected by stress.f. Plant age and growth rate affect outcome of plant stress
on insects.
Results:
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• They can directly affect insect pests.
Elevated temperatures may:* Advance emergence dates of pests
* Inc. the # of generations each growing season
* Allow spp adapted to warm climates to expand there ranges northward
* Unbalance predator-prey interactions in favor of the pest
Environmental factors
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Drought may:
Reduce the infection rates of pests by pathogenic fungi
Reduce survival rates of certain soil dwelling pests such as weevils and white grubs
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
1. No natural enemies found in hot stressed areas!
2. These conditions can be found in disturbed landscapes.
3. Restoration can take place by:• Use of trees to increase shade• Addition of natives to restore natural systems• Accumulation of organic matter
The Role of Diversity:
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Lack of Diversity
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Lack of Diversity
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Lack of Diversity- It’s Everywhere
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Every Neighborhood!
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
More Problems
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
What We Need to be Striving For:
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Diversity Mean “Binding” Things Together
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Turf & Tree Roots Don’t Co-exist
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Therefore: Create Zones of Plantings
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Diverse systems bring in more different kinds of pests but…. Less numbers of each pest!
• Diverse systems have more predators in the landscape.
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Diverse Systems
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Therefore, diverse landscapes with many potential pests provide many food sources for these predators.
Predators Are Generalists
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Plant Stress & Diversity with Impacts on Insects
Diversity can be Geographical
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
1. Lack stability and sensitive to destruction.
2. They have peaks and valleys of pests.
e.g. Pest arrives, predators come in, predator population drops due to a lack of food source, then the pest resurges.
Monocultures
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Plant Stress & Diversity with Impacts on Insects
Trees vs. Turf
They are mutually exclusive in nature.
Trees are not found in the mid-west prairies.
Grasses are not found growing on forest floors.
There is competition between the two plant types.
Unbalanced Landscapes
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Trees vs. Turf
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Impossible to separate fertilizer applications in this system.
• Turf takes up the majority of fertilizer but, trees near turf can still receive enough fertilizer to trigger over-abundant growth and a reduction in defense and storage capabilities.
Fertilizer Interactions
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Plant Stress & Diversity with Impacts on Insects
• Over fertilized trees are pre-disposed to other problems such as insect attack.
Fertilizer Interactions
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Plant Stress & Diversity with Impacts on Insects
Fertilizer Interactions
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Broadleaf herbicides placed on turf can have an adverse affect on trees
• Incidence this past year of a Dupont phenoxy herbicide had dramatic impact where used on nearby trees and shrubs
Herbicides
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Plant Stress & Diversity with Impacts on Insects
• The # of different types or species of organisms in a defined space.
• The # of species that dwell in a habitat.• Native plant communities can maximize the diversity of
animals verse exotic species.• These environments are more stable and less prone to
disruption.
How Do We Define a Diverse Landscape?
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Plant Stress & Diversity with Impacts on Insects
• If you count all the terrestrial bird spp in North America that rely on insects & other Arthropods to feed their young, it would be around 96%.
• These insects would also be among those harmful to ornamental plants.
Why Insects are Essential
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Most insects have very specific and restricted diets and won’t develop relationships with exotics.
• Therefore, these exotics won’t serve as sources of food within the food chain.
• e.g. Tent Caterpillars feed within Rosales.
Why the Need for Natives?
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Eastern Tent Caterpillars
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Complex habitats contain more natural enemies because these plant species varied in Size, Shape, and Structure. This verses simple habitats.
• e.g. Azalea Lace Bug controlled in complex systems.
Conclusions?
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Plant Stress & Diversity with Impacts on Insects
Azalea Lace Bug
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
• Buddleia only attracts adults.
• Asclepia tuberosa, syriaca, incarnata all allow larval stages to
develop.
• Approx 11 Lepidoptera reproduce on Milkweed.
Gardening for Butterflies
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Plant Stress & Diversity with Impacts on Insects
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Gardening for Butterflies
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Plant Stress & Diversity with Impacts on Insects
• Echinacea• Rudbeckia• Cephalanthus• Eupatorium fistulosum• Quercus• Cornus florida• Liquidambar styraciflua• Magnolia species
Other Lepidoptera agents in the Landscape
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Those specialized at eating aphids:
• Ladybird Beetles• Syrphid Flower Flies• Chrysopid Lacewings• Bats & Dragonflies
Aphids as Specialized Predators
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Plant Stress & Diversity with Impacts on Insects
Monocultures
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Plant Stress & Diversity with Impacts on Insects
• Use of Shade Trees• Use of Small Flowering Trees• Use of a Shrub Layer• Groundcovers • Native Ornamental Grasses• Perennials• Add “Structure” like boulders, etc
How Can We Create Diversity?
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Plant Stress & Diversity with Impacts on Insects
• Woodland Landscapes• Meadow Landscapes• Bird and Butterfly Gardens• Rain Gardens• Water Gardens
Landscape Models
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Plant Stress & Diversity with Impacts on Insects
• Architecture of the Property:
– Create a layered approach to create a more suitable environment for natural predators to flourish.
Principles for the Home Landscape
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Plant Stress & Diversity with Impacts on Insects
• Canopy• Mid-level or Understory Trees• Shrub Layer• Herbaceous Layer• Ground Layer• Vines
Layers in the Landscape
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Plant Stress & Diversity with Impacts on Insects
Canopy Layer
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Plant Stress & Diversity with Impacts on Insects
• Liriodendron tulipifera• Fagus grandifloia• Quercus prinus• Acer saccharum• Acer rubrum• Nyssa sylvatica
Canopy Layer
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Canopy Layer
Office of Continuing Professional Education
Plant Stress & Diversity with Impacts on Insects
Canopy Trees
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Plant Stress & Diversity with Impacts on Insects
• Cornus florida• Carpinus caroliniana• Amelanchier species• Cornus alternifolia• Asimina triloba
Understory Trees
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Plant Stress & Diversity with Impacts on Insects
Understory Trees
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Plant Stress & Diversity with Impacts on Insects
Cornus florida
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Plant Stress & Diversity with Impacts on Insects
Asimina triloba
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Plant Stress & Diversity with Impacts on Insects
• Lindera benzoin• Viburnum acerifolium• Calycanthus floridus• Kalmia latifolia• Rhododendron spp
Shrub Layer
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Plant Stress & Diversity with Impacts on Insects
Shrub Layer
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Plant Stress & Diversity with Impacts on Insects
• Mertensia virginica• Carex pensylvanica• Fern spp• Asarum canadense• Aster divaricatus
Herbaceous Layer
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Plant Stress & Diversity with Impacts on Insects
Herbaceous Layer
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Plant Stress & Diversity with Impacts on Insects
• Mosses• Rotting wood and debris• Organic matter• Leaf litter
Ground Layer
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Plant Stress & Diversity with Impacts on Insects
Varying the types of inflorescences will attract a wider range of insect pollinators which may also double as predators:
– Spikes– Raceme– Panicle– Umbel– Composite
Types of Inflorescences
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Plant Stress & Diversity with Impacts on Insects
Spike Inflorescence
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Plant Stress & Diversity with Impacts on Insects
Raceme Inflorescence
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Plant Stress & Diversity with Impacts on Insects
Panicle Inflorescence
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Plant Stress & Diversity with Impacts on Insects
Umbel Inflorescence
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Plant Stress & Diversity with Impacts on Insects
Composite Heads
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Plant Stress & Diversity with Impacts on Insects
• Create layers in the landscape incorporating regional natives
when possible. These regional natives are more likely to
develop natural soil partners.
• Use varying types of inflorescences.
• Reduce stresses by planting trees to produce shade.
Summary
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