1. Ornamental Pest Management (Category 3B)

    2. Non-Pest Disorders and Landscape Weeds

    Chapter 5

  2. The majority of landscape plant injury is caused by poor growing conditions. Landscape plants are weakened by environmental and cultural disorders. Stressed plants are more susceptible to attack and damage by pests.
  3. Ornamental plants are stressed by poor growing conditions, such as:

    4. -Construction -drought

    -salt -flooding

    -desiccation -improper planting

    -mechanical damage -improper cultural practices

    -pesticides -poor plant selection

    -soil compaction

  4. Poor plant selection is all too common. Arborvitae is not the best choice of plants for this dry, unirrigated site.
  5. Some sites are quite wet. Only "flood plain" species like willow and poplar will thrive in such a site. Spruce is evidently not a species tolerant to wet soil.
  6. Any tree expected to grow in this site must be tolerant to heat, compaction, and salt.
  7. Incorrect transplanting ruined this tree’s chance of long-term survival. The synthetic rope and burlap holding the root ball together will not rot away, and must be completely removed to prevent girdling the trunk and roots.
  8. Weed control is an important, but tricky, cultural practice in the landscape. The roots of this pine took up the non-selective herbicide applied to "clean up" the gravel driveway.
  9. The pines in the background of this slide have been stunted by the chemical juglone released by the roots of black walnut trees. Juglone reduces competition by suppressing the growth of other plants. Juglone-susceptible plants should not be used near walnut trees.
  10. This oak was doomed from the beginning of construction. Too many roots were lost during excavation.
  11. But roots left in tact during construction often die from compaction, and changes in exposure or drainage.
  12. A plugged drain created a flood that suffocated the roots of these small trees.
  13. Desiccation is a common winter disorder of landscape plants in Michigan. On sunny, warmer winter days, these euonymus leaves lost more water than could be replaced by roots in frozen ground.
  14. The distortion of these leaves resembles herbicide injury, but weather records confirm developing leaves were exposed to cold temperatures in the spring.
  15. Many types of environmental stresses occur in summer. Lightening damaged trees, like the oak shown here, may die immediately or decline over time.
  16. Be familiar with the most common cultural and environmental problems in your area. The symptoms can be confused with those resulting from pest activity. Pesticides will not help plants suffering from non-pest disorders.
  17. A weed is any plant that grows where it is not wanted. Whether a plant is considered a weed, depends more upon where the weed is growing than its species.
  18. For example, bluegrass is a valuable turf plant, but is an undesirable weed when growing in flowering beds.
  19. Weeds directly compete with ornamentals for growing space, water, nutrients and sunlight. Weeds readily spread to newly disturbed areas and are aggressive growers.
  20. Knotweed is common along walks and drives. This annual is tolerant of compacted soil.
  21. Many weeds thrive in poor growing conditions and are indicators of such sites. Weeds are often a result, not a cause, of poor ornamental plant performance or care.
  22. Weeds significantly increase labor and cost of landscape maintenance. Ragweed, poison ivy and other noxious plants are a source of discomfort for people. Some weeds indirectly harm ornamentals by harboring pests.
  23. Weeds can crowd out or girdle established shrubs and trees, as well as new plants. This aggressive vine is as detrimental to people as it is to plants (poison ivy).
  24. Grassy weeds are monocots. These weeds belong to the grass, sedge, and lily families. All have narrow leaves, parallel leaf veins and single seed leaf after germination. In Michigan, all monocots are herbaceous-they die to the ground each winter.
  25. Dicot weeds have broad leaves, net-like leaf veins and two seed leaves after germination. Some die back to the ground each winter, but some have woody stems (poison ivy) and grow larger each year. Dicots belong to many families such as:

    26. Composite (dandelion) Parsley (wild carrot)

    Mustard (shepard’s purse) Morning glory (field bindweed)

  26. After germinating or sprouting, all plants have four stages of development:
  1. Seedling stage – The plant is new, tender, and vulnerable to all stresses.
  2. Vegetative stage – Period of rapid growth and uptake of water and nutrients.
  3. Seed production – Plant’s energy is directed to flowering, fruit, and seed.
  4. Maturity – Very little movement of water and nutrients or growth.

The developmental stage affects how the weed responds to wed controls. Weeds take up herbicide most quickly when in the vegetative stage. Seedlings are easily killed with cultural or chemical controls.
  1. Weeds are also categorized by the number of years required to complete their life cycle.

    2. Annual weeds: live for one year and may be either grassy or broadleaved.

    Summer annuals: germinate in the spring, mature and die by winter (pigweed, lambsquarter, crabgrass).

    Winter annuals: germinate in late summer, overwinter, and produce seed the following spring. (chickweed, pennycress).

  2. Lambsquarter is a summer annual, but still a large plant. Is this a dicot or monocot plant?
  3. All biennial weeds are broadleaf plants with a two-year life cycle. Biennials typically form a thick, fleshy root and compact cluster of leaves called a rosette the first summer. During the second year, biennials flower, produce seed and die.
  4. Next time you are out and about, take the time to examine a one-year-old wild carrot (Queen Anne’s lace). Locate and study the rosette structure.
  5. Perennial weds live for three or more years and are the most persistent and difficult weeds to manage. Seed production begins the first or second year. Many perennials also reproduce by means of underground structures called propagules. Perennials overwinter by moving stored food from the dying leaves into roots and propagules. There are many monocot and dicot perennial species including quackgrass, dandelions, and poison ivy.
  6. Anyone experienced with pulling these perennial weeds knows their efforts are wasted unless they get the entire root.
  7. As with any pest, you must correctly identify weed species. An inventory of landscape weed problems is useful when monitoring and scheduling management activities.
  8. There are five strategies used to manage landscape weeds. Most weed problems require the coordinated use of multiple techniques.
  1. Create vigorous ornamental plants. Healthy plants are better able to compete with weeds. A vigorous, dense ornamental planting is the first step in weed management. Sound species selection, and planting and maintenance practices will provide an environment in which ornamentals thrive.
  2. Prevent seed production. Weed plants produce a lot of seeds. One pigweed plant can release 100,000 seeds in one season! Eliminate weeds before the seed production stage.
  3. Prevent seed germination. Prevent seed germination two ways: avoid bringing dormant seeds dormant seeds in deeper soil to the surface, and apply preemergent herbicide.
  4. Limit emerged weeds early. Every type of weed is most susceptible to management tactics when young. Small plants are easily removed or destroyed mechanically or chemically.
  5. Target susceptible stages of mature weeds. Coordinate control efforts with periods when weed food reserves are depleted. Woody perennials are most vulnerable just after leaf production. Herbaceous perennials are weakest during the bud-to-bloom stage. Create physical stress in perennials by repeatedly removing top growth.
  1. Because ornamentals and weds are in close proximity in the landscape, and because weeds are persistent pests, successful weed management programs incorporate both non-chemical and herbicide tactics.

    2. Alternative Weeds Control Measures

    Sanitation: Limit weed seeds by maintaining seed-free mulches, tools and planting stock.

    Tillage: Working the soil will kill annual and most biennial weeds, but is not effective against established perennials, tillage cannot be used near ornamental plant root.

    Cutting: Cutting will effectively limit weed height and flowering. Repeated cutting changes the species composition by encouraging low-growing weed species.

    Mulching: mulching is useful weed management tool for many areas of the landscape. Landscape fabric, stone, and shredded bark are commonly used. Black plastic film effectively controls weeds, but also blocks air and water from ornamental plant roots. Also be wary of straw and hay mulches as they often contain weed seeds.

  2. There are many uses in the landscape for herbicides. Plant, soil, and weather conditions influence herbicidal action, and must be considered when choosing a herbicide. Remember that the label defines the legal uses and applications of the product.
  3. Herbicides are developed to manage specific types of weds. For instance, contact herbicides are used on annual and biennial weeds. Since only the portion of the plant that the herbicide directly contacts is killed, perennials are only temporarily suppressed. Systemic herbicides move throughout the plant and are therefore used to manage perennial weeds.
  4. Persistent herbicides remain active in the environment for an extended period of time. They are useful for keeping established beds "clean", but nonpersistent herbicides would be used to free a new planting bed of weeds.
  5. Nonselective herbicides kill most or all vegetation. They must be used with great care around ornamentals. Selective herbicides work on only specific species of weeds and have many landscape uses. Be sure to check the label not only for weed species controlled, but also for susceptible ornamental plants.
  6. Herbicides can be categorized by when in the plant life cycle they are used.

    7. Preplant herbicides are chemicals applied or injected into the soil. They are commonly used in nurseries or the landscape to re new planting areas of weeds.

    Preemergence herbicide is the most common type of herbicide used in the landscape. Preemergence herbicide is applied to the site as a preplant treatment to kill germinating seedlings. Selective preemergence herbicides are useful for eliminating weeds beginning to grow among ornamental plants.

    Postemergence herbicides are applied directly to the weed. Contact postemergence herbicides are used on annuals an biennials. Perennials are best managed with systemic postemergence herbicides.

  7. Knowledge of plant characteristics and life cycles will help you understand how plant characteristics impact the action of herbicides.

    8. Growing points: Growing points that are sheathed or located below the soil surface will not be reached by contact herbicide sprays.

    Leaf shape: Herbicides tend to bounce or runoff narrow, upright leaves. Broad, flat leaves tend to hold the herbicide longest.

    Wax and cuticle: Foliar sprays may be prevented from entering plant leaves by a thick wax and cuticle layer.

  8. Leaf hairs: A dense layer of leaf hairs hold herbicide droplets away from the leaf surface, allowing less chemical to be absorbed into the plant. In contrast, a thin layer of hairs holds the chemical onto the leaf surface, allowing for more absorption.

    9. Deactivation: Certain plants can deactivate herbicides and are therefore less susceptible to chemical injury.

    Life cycle stage: Seedlings are most vulnerable to weed management practices, including herbicides.

  9. As the graph shows, plants in the vegetative and early bud stages take up herbicie readily, while mature plants are least affected.
  10. The climate has considerable impact on the action of herbicides. Relative humidity: A foliar-applied herbicide enters leaves more easily and rapidly at higher relative humidity.

Light: Light breaks down some herbicides, and con otherwise effect how fast the herbicide acts.

Precipitation: Soil moisture and rain impact how long herbicides work an stay on target. Heavy rain can cause soluble herbicides to leach or run-off, but light rain can help root-absorbed herbicides move into root zones.

Temperature: Some soil-applied herbicides become volatile at high temperatures. Incorporate them into the soil if applied in hot weather to reduce the chance of volatilization. Always follow label directions. Further, if temperatures are high, plant processes may shut down and your herbicide will have little activity on the plant.