Diagnosing and Managing Plant Problems
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A client of yours is describing several different types of plants in his landscape, all exhibiting leaf yellowing, leaf distortion and a white covering on leaf surfaces. What is the likely diagnosis?
Fire blight is a bacterial infection that causes susceptible plants, typically members of the Rosaceae, to die back quickly from the tip, imparting a blackened, shephard's hook appearance, as if the stem tip had been scorched by fire.
Dutch elm disease
Dutch elm disease is a fungal disease that results in wilting of several Elm species, and it is especially problematic on American Elm (Ulmus americana).
Botrytis is a water mold, causing cellular breakdown and browning of tissue. It can affect leaves, stems, flowers, and fruits.
Question 1 Explanation:
Powdery mildew is a fungal disease that causes leaf yellowing and distortion, and its mycelia give a powdery, white appearance to the effected tissues.
Which of the following is a symptom of over-watering a plant?
Etiolation occurs when a plant part is grown in the absence of light; it has nothing to do with over-watering.
Blanching is depletion of chlorophyll in part of a plant by exclusion of light; it has nothing to do with over-watering.
Stratification is a method to satisfy physiological dormancy of seed; it has nothing to do with over-watering.
Question 2 Explanation:
When plant roots are deprived of oxygen through over-watering, they die and, then, the plant is not able to transport enough water to avoid wilting.
Cool season turfgrasses are susceptible to many leaf blade, crown and root diseases. What cultural conditions encourage fungal infestations?
excess thatch accumulation and under-irrigated sites
Although stressed turfgrasses will be more susceptible to disease, lack of moisture will inhibit fungal infestation and likely cause the turfgrasses to become dormant.
excess N fertilizer and over-irrigated sites
excess thatch accumulation and higher than desired height of cut
Grass clippings do not contribute to thatch accumulation, and a higher cut is recommended, especially on cool-season turfgrasses that are being stressed by high temperature.
excess K fertilizer and dull mower blades
Although providing excess potassium is wasteful and environmentally irresponsible, it will not make turfgrasses more susceptible to disease, nor will dull mower blades.
Question 3 Explanation:
Excess nitrogen fertilizer promotes lush vegetative growth and increases the prevalence of disease in cool-season turfgrasses.
What can be expected as the LD50 of a chemical increases?
the toxicity of the chemical increases
As LD50 increases, toxicity decreases.
the solubility of the chemical in organic solvents decreases
LD50 has no reference to the solubility of a chemical.
the toxicity of the chemical decreases
the water solubility of the chemical increases
LD50 has no reference to the solubility of a chemical.
Question 4 Explanation:
LD50 is the lethal dose where 50% of the test animals died. Thus if a higher dosage of a chemical is required to reach LD50, the toxicity of that chemical is less than one with a lower LD50.
How should you examine a leaf for abnormalities?
Inspect both tops and undersides of leaves for pubescence.
Pubescence is the presence of trichomes. It is not an abnormality in itself; however, some pests can cause an increase in pubescence, e.g. mites on African violets.
Check the upper and lower sides of leaf for signs and symptoms using a hand lens.
Smell the leaf for odor and use a hand lens to view dead or irregular flecks.
Odor would not indicate leaf abnormality. Some plants have fragrant or pungent foliage, others do not.
Inspect the adaxial surface for damping-off using a hand lens.
Damping-off is a disease of seedlings associated with the stem.
Question 5 Explanation:
It is important to inspect both adaxial (upper) and abaxial (lower) leaf surfaces, as some pests and diseases are typically found on one surface before symptoms of their presence are exhibited on the other.
Where on a plant should you look for fungus gnat larvae?
Adult fungus gnats tend to hover just above the soil surface and may be seen among the lower foliage, but their larvae are in the soil.
Adult fungus gnats tend to hover just above the soil surface and rarely would be seen in flowers, but their larvae are in the soil.
Adult fungus gnats tend to hover just above the soil surface and may temporarily light on the stem, but their larvae are in the soil.
Question 6 Explanation:
Fungus gnat larvae are in the soil, feeding on plant roots.
Who needs to keep records required by the Environmental Protection Agency (EPA)?
Produce retailers are not applying pesticides, thus they are not required to keep records for the EPA.
turf pesticide applicators
OSHA (Occupational Safety and Health Administration) assures safe and healthful working conditions and requires that information about the hazard of chemicals in the workplace be readily available to employers and employees.
growers’ rights advocate
Only commercial pesticide applicators need to keep pesticide application records.
Question 7 Explanation:
Commercial pesticide applicators need to keep records.
The herbicide, Millennium Ultra 2, is labeled “for selective broadleaf control.” Which of the following would be an effective application for this product?
crabgrass in lawn and turf
Crabgrass is not a broadleaf weed. Crabgrass is best controlled with a pre-emergent herbicide.
crabgrass in an ornamental plant bed
Crabgrass is not a broadleaf weed. This herbicide would not be appropriate for use in an ornamental plant bed, as drift of the herbicide would likely damage the desirable ornamentals. Also, use in an ornamental plant bed would be contrary to the label; it is not labeled for this application.
dandelion and clover in lawn and turf
dandelion and clover in an ornamental plant bed
Although dandelion and clover are broad-leaved weeds, this herbicide would not be appropriate for use in an ornamental plant bed, as drift of the herbicide would likely damage the desirable ornamentals. Also, use in an ornamental plant bed would be contrary to the label; it is not labeled for this application.
Question 8 Explanation:
Dandelion and clover are broad-leaved weeds and can be controlled in non-residential turfgrass with this herbicide.
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