Growers must constantly solve crop-related problems. Some problems are caused by pests, others by diseases and yet others are caused by a variety of noninfectious disorders. These disorders are also called physiological or environmental diseases. Some noninfectious disorders are easy to diagnose while others are difficult or even impossible to diagnose. Identifying the causes of noninfectious disorders is like solving a puzzle and challenges growers to stretch their imaginations, make keen observations and put it all together with the help of their experience. Some noninfectious disorders are beyond help once symptoms are visible. Nevertheless, it is extremely important to reach the right diagnosis in order to avoid the problem in the future. It is important for growers to know that:
What to do when facing noninfectious disorders? The cure, if possible once symptoms are visible, requires:
1. removing or neutralizing the causing agent from the plant's growing environment or
2. supplying the substances whose lack caused the problem.
Identifying the cause of a noninfectious disorder can take time, effort and patience. It is not uncommon to find disorders whose cause cannot be identified. The impossibility of reconstructing past events or high cost of tests or analyses can make identification very difficult.
Some examples of factors causing noninfectious disorders follow:
Something so innocuous as the water we drink can be the source of numerous problems in floriculture. Water related problems fall in three categories:
Too much water is very common in container grown plants. Too much water leads to a lack of oxygen; anaerobic microorganisms (those which grow without oxygen) produce nitrites that are toxic to roots; roots loose selective permeability; etc.
Over-watered plants:
The problem with this list is that many other diseases and/or disorders can cause similar symptoms. Ultimately, questioning the grower and finding out what happened, for example, with the irrigation system will lead towards the cause.
Too little water is even more of a problem on a global scale and very common with container grown plants. Water stress can be categorized in four different subcategories shown in Table 1.
As with water excess stress, these symptoms are, for the most part, common to other problems and ultimately they have to complemented with more evidence obtained by questioning the growers, studying environmental records, or inspecting irrigation systems.
Poor water quality is a common problem in arid areas of the country and with crops grown in containers. The water characteristic that cause problems are:
Each species/cultivar has an optimum range of temperatures. Moving farther from that optimum causes problems. These problems are more severe the farther temperature deviates from the optimum. Temperature problems can be divided into either being too high or too low:
Temperature too high is usually associated with high light, low relative humidity, and/or insufficient water.
Usually high temperature and lack of water have similar symptoms: dead dry tissue that remains on the plant that can be easily broken (it does not bend). Usually young tissue is affected earlier than old tissue.
Table 1. |
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| Single Severe Stress | Periodic Stress | Continual Stress | Low To High Stress |
This stress is sometimes referred as "weekend syndrome." |
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(High EC can cause similar symptoms.) |
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High temperature affects plants by inactivating certain enzyme systems and accelerating others; or by coagulating proteins.
Temperature too low. Depending on the species, low-temperature damage can be caused by chilling temperature or frost.
The injury varies depending on the degree of temperature drop or the duration of the low temperature period. Low temperatures injure plants by inducing ice formation between or within the cells.
Low Oxygen is a consequence of water logging. It can be aggravated by high temperatures. Low oxygen also occurs in the interior of fruits and tubers when the temperature is high. This situation is more common in storage.
Lack of light produces etiolated (pigment deficient) plants. Stretching can be the consequence of low light levels.
Excess light is rare but may occur with indoor plants exposed to sun light or plants grown in the shade and suddenly exposed to sun.
DATA COLLECTION
TEST FOR PESTS AND DISEASES
TEST FOR FERTILITY PROBLEMS
OTHER REASONS(Non infectious disorders)
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Most pollutants are gases. Ethylene, ammonia, chlorine, and mercury vapors are all possible problems in closed areas like greenhouses and storage facilities. Sulfur dioxide, ozone, fluorides, and peroxyacetil nitrate are associated with "smog" and can cause problems with plants outdoors.
Un-vented heaters and problems with the heater's exhaust are very common in the greenhouse industry. These problems are more noticeable in poly houses (because they are more air tight) than in glass houses.
Symptoms of fume injury:
Gas injury. Plants can be injured and killed by gases in the soil. Gases may be directly toxic or reduce oxygen to critically low levels.
Herbicide injury can occur either when herbicides are applied in the greenhouses where the crops are located or outside the greenhouses (green space between greenhouses or crops in the vicinity). Herbicide injury can be caused by:
The "Sherlock Holmes" approach is necessary. Pretend you are solving a criminal case. Like many crimes in real life, they can take a long time to be solved; some never are. It is extremely important to:
The first step is to do an exhaustive collection of data. If the information collected does not give clear indications of noninfectious disorders, then test for pest or diseases. If pests and diseases can be ruled out, test for fertility problems. After ruling out fertility problems, start considering a more complicated noninfectious disorder. The following flowchart summarized the different steps:
Some of the following information is commonly requested when you submit plant samples for diagnosis. Complete information will help to an accurate and speedy analysis and solution to the problem. Not only that, but once you have answered these questions, you will often determine what the problem is yourself, or at least narrow the possibilities. The following list of questions was prepared by Dr. D. J. Wolnick from Penn State and it is reproduced with permission.
If growers are not able to find the problem by themselves after going through these questions, at the very least they will be more prepared to discuss the problem with their Extension Agent or State Specialist. A final thought: cash outlay for testing (e.g sending growing mix to the Research Extension Analitical Laboratory in Wooster or plant material to the Plant and Pest Diagnostic Clinic in Columbus) is not an expense, it is an investment!
1. Describe the plant
What type of plant is it (genus, species, cultivar)? How old is the plant; when was it planted? Did you grow it or purchase it from someone else? If purchased, who did you buy it from (clues to the plant's culture)? Did you purchase cuttings, seed or seedlings, or a potted plant?
2. Describe the plant symptoms
Are there any obvious symptoms of insects or disease such as webs, chewed leaves, honeydew, larvae, shed skins, mold, rust, blackened areas on stems or leaves, root rot, or wilting? Are the symptoms restricted to certain varieties? Does the problem occur in particular locations in the bench or in the greenhouse, or is it scattered throughout the crop? Is the problem mild or severe? How was the crop grown?
3. Outline the case history
On what date did you first observe symptoms? Did the symptoms appear all of a sudden or gradually? Did you apply any treatments to the problem? Did they work? Have you had previous problems of any kind with this crop? Is what you see now a recurring problem?
4. Describe the plant environment
Is the plant in a container or planted in a bench? Are the benches raised or on the ground? What is the location, age, and condition of greenhouse benches? What is the potting or bench mix used? Did you make it or buy it? Was it pasteurized? How was it pasteurized (steam, chemicals)? Did the mix contain any starter fertilizer? What kinds and how much? What were the day and night temperatures, light level, and humidity in the greenhouse?
What chemicals were used during crop production - fertilizer (types, amounts) - pest controls (sprays, fumigants, granular materials, etc.) - growth regulars - weed control (herbicides)? Were label instructions followed carefully? Did you use spreader stickers? If so, which ones? What is the age and conditions of equipment you use in crop production? How accurate is the fertilizer injection system? When was it last calibrated? How about the heating system and the water supply? What is the type, age, and condition of greenhouse covering? Are there any septic tanks or gas lines near the greenhouse which could have caused air pollution problems? Have herbicides been applied around the greenhouse or under the benches?
5. Consider the general details of plant culture as well as any SPECIAL EVENTS
A failed heating system or an improperly adjusted space heater that may have caused a problem. Can you associate the symptoms with any particular age or stage of crop development? Can the symptoms be associated with weather conditions or season? Do the symptoms get worse over time or stay the same once established? Describe in detail the condition of the roots, stems, foliage, and flowers.
NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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