Plants and Pathogens


Disease to ornamental plants and turfgrass is caused by various agents such as pathogens, insects and vertebrate species. Weeds also interfere with plant growth. Other causes of plant damage relate to inadequate planting, soil makeup, improper fertilization, mechanical damage, pollution, and poor irrigation. These agents are discussed here.

Ornamental plants thrive in the absence of insects and other pathogens.

  • Aphids and spider mites are managed with biological controls, while armored scales are pesticide-resistant, thus horticulture oils are recommended for these pests.
  • Leaf spots are treated with drip (or overhead) irrigation, fungicides or copper-based bactericides; spacing of ornamental plants allow for good air circulation. Likewise, scab and powdery mildew of turf, which are both caused by fungus, are controlled by fungicides.  Fungicides and bactericides are ineffective for root rots and vascular wilt.
  • Bacterial blights are controlled by bacteriostats, by cultural controls, such as the planting of resistant cultivars, pruning (4” to 6” below decayed parts; and about a foot below decayed parts in growing season.
  • Pruning controls some insects and protects against bacterial fireblight. Pruning is best done in the winter when the plant is dormant and growth is stimulated in the spring versus pruning in the summer where this is less growth. In this process, a solution of 1 part bleach to 9 parts water (1:9) is used to disinefect cutting shears between cuts.  The tree is pruned distal to the branch collar where the bark intersects with the branch.  Three cuts  are made for branches larger than 2 inches.  Dressing of the remaining branch is not performed because this favors infection.
Turfgrass is susceptible to fungal diseases, insects, and nematodes.
  • Mulching at a height of 2-4” is recommended any time of the year, but especially in late spring, to retain water, reduce erosion, as well as to provide insulation, prevent weed seed development, and for aesthetic purposes. Organic mulch should be kept inches away from the trunk to prevent crown rot and vole feeding.  Mulch materials include pine bark, straw, and a compost.  Pine straw is more stationery of these.  Geo textiles and landscape fabrics are also available. Rock and rubber mulches increase evaporation by increasing heat transfer down into the soil. Plastic mulch beds stifle the oxygen and water content of the soil, which stresses the plant, and is not recommended.
  • Eco-friendly solutions such as Bacilius thuringensis (Bti) can be used to control young caterpillars, especially of eastern tent caterpillar.
  • Primitive worms called nematodes, which can be detected by soil tests, are best managed with resistant cultivars, solarization (heating of soil to a high temperature to kill worms), nematicides, good watering habits, and proper drainage.
  • Fertilization is recommended in spring or fall and not after mid-August.
  • Irrigation is accomplished best between 9 pm to 9 am--once a week for younger plants and every 7 to 10 days for older plants during periods of drought and less often when evaporation is less during cooler seasons.
  • Plants should be matched to their hardiness zones, which are areas based on average minimum temperatures.   Microclimates are discrete smaller areas that differ in weather conditions.

Ornamentals are susceptible to insect and microbial pathogens, which is the need for pest control.

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