Cooperative Extension Service

Diagnosing Greenhouse Crop Problems

By Wayne Vandre, Horticulture Specialist

HGA-00433

A checklist to be used in combination with information available from the grower.

I. Look for pattern in symptom development.

  1. Location - portion of bench, house or range, proximity to gutters, shade cloth, CO2 burners, heaters, etc. (may indicate pathogenic, environmental, or cultural)
  2. Greenhouse Operations - time of planting, water and fertilizer regimes, pinching, disbudding, transplanting, changes in employee activities, etc. (cultural problems)
  3. Weather - extreme fluctuation in temperature, light, prolonged periods of unusual conditions such as dark weather (environmental problems)

II. Obtain history of the problem.

  1. Date symptoms first noted
  2. Rate of development and spread or decrease in symptoms
  3. Control measures used and effectiveness - any chemical treatment?
  4. Crop rotation in area
  5. Any problems with previous crops
  6. Soil source, treatment
  7. G. Plant source and original condition (clean starting stock)
  8. H. Uniformity of greenhouse environmental control - temperature, humidity, air circulation

III. Examine plants closely (use hand lens). Is it pathological, entomological, physiological?

  1. Pathological symptoms-(usually not uniform throughout greenhouse, specific for certain crops)
    1. Necrotic (dead) areas on roots, stems, leaves flowers.
    2. Vascular - discoloration of veins, stem conducting tissue
    3. Fungus or bacterial growth above or below soil level
    4. Virus patterns - discoloration or modified growth - symptoms may resemble those caused by 2,4-D, ethylene, etc.
    5. May require laboratory confirmation
    6. Potential problem areas
      1. Faulty (incomplete) soil pasteurization
      2. Reinnoculation of soil through carelessness
      3. End of hoses not hung up
  2. Entomological symptoms
    1. Presence of insects on foliage, stems or roots
    2. Presence of caste skins
    3. Evidence of feeding (chewing, sucking, leaf mining, accumulation of honeydew)
    4. Potential Pest Problems
      1. Ineffective insecticides or faulty application schedules
      2. Weeds under benches and outside air intake areas harboring insects
  3. Physiological and cultural symptoms
    1. Nutrient deficiencies (may differ by plant species)
      1. Nitrogen - light green or yellow foliage, more acute on lower leaves
      2. Phosphorus - darkened, dull foliage color, sometimes purpling with yellowing in later stage, reduced growth
      3. Potassium - chlorosis and or necrosis between veins working in from leaf margin, browning on margins
      4. Magnesium - similar to potassium but leaf margins remain green
      5. Iron - chlorosis of new growth with main veins remaining green for a while
      6. Manganese - foliar chlorosis but veins remain green forming a checkered pattern
      7. Boron - new growth hardens, becomes distorted and lateral growth develops
    2. Nutrient Toxicities
      1. Soluble salt accumulation - plants wilt even when soil is moist, marginal leaf burn, chlorotic new growth, browning of roots
      2. Ammonium nitrogen - wilting, chlorosis, root injury
      3. Nitrate nitrogen - excessive vegetative growth followed by restricted growth at higher levels
      4. Potassium, boron, manganese, zinc - necrotic leaf margins
  4. Possible causes of physiological problems
    1. Soil Problems
      1. Poor drainage
      2. Poor structure - heavy soil
      3. Unfavorable pH
      4. Too frequent or too infrequent watering
      5. Insufficient water applied to thoroughly wet the soil
      6. Cold soil
    2. Chemical - insecticide, fungicide, other
      1. Excessive rates used
      2. Fumigation of greenhouse when foliage was wet
      3. Application at temperatures above 80°F to 85°F (especially fumigants)
      4. Application during prolonged dark periods when plants are soft
      5. Particular species or cultivars sensitive to chemical product
      6. Concentration of solvent used - can occur from combining EC spray materials
      7. Herbicide residue in soil or volatile fumes from nearby application.
      8. Soil fumigant residue in soil
    3. Climatic
      1. High or low temperature (including freezing injury - use temperature recorders or minimum - maximum thermometers)
      2. Wrong photoperiod - light interference - burned out light bulbs -faulty controls - holes in black cloth
    4. Miscellaneous
      1. Penta, creosote (wood treatment) injury
      2. Fertilizer injector faulty
      3. Faulty calculations of materials applied
      4. Gas fumes from faulty burners, fresh manure, other pollution sources -mechanical projects (welding, gas engines)
      5. Nematodes - plants grow to limited extent at intervals, may wilt, may develop lumps on roots
For further information contact:

Horticulture Specialist

Cooperative Extension Service

2221 E. Northern Lights Suite 118

Anchorage, AK 99508-4143

Phone: (907) 279-6575

CES Communications-02/19/99

The University of Alaska Fairbanks Cooperative Extension Service programs are available to all, without regard to race, color, age, sex, creed, national origin, or disability and in accordance with all applicable federal laws. Provided in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Anthony T. Nakazawa, Director, Cooperative Extension Service, University of Alaska Fairbanks.


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