ABSTRACT
Plants are similar to us humans and animals in that when under stress from poor nutrition; our bodies suffer in growth, development, and general health� Animals show these disorders in the form of weak bones, skin discoloration, and poor weight� Plants show nutritional defects in vigor, strength of stems, color of leaves, and poor yields�
Whenever plants undergo any type of stress from environmental conditions to lack or excess of nutrients, they will express signs of disorders� Pests and diseases also cause stress and disorders within the plant� Pest and disease causes and their control are discussed later in Chapter 25� Focus now is on plant symptoms from nutrient stress� By recognizing and segregating out what is the cause of a symptom, adjustments can be made in the environment or nutrient solution to remedy the stress and bring the plant back to healthy growth� In my book, Hydroponic Food Production, there is detailed information on nutritional and environmental effects on plants, how to determine the specific disorder, and the function of elements within the plant� Presented here is a brief summary of symptoms that assist the gardener to discover the causal agent(s)�
Symptoms of disorders within the plant may be expressed as leaf yellowing (chlorosis), browning (necrosis), burning (white coloration due to loss of chlorophyll in leaves), deformation of leaves and growing tips, and stunting of overall growth� The first thing to observe with a nutrient disorder is the location of the affected tissue� Leaves will in general show the symptoms first� If it is a root problem due to disease or lack of oxygen, examination of the roots will reveal that they are not turgid and white, but, slimy and brown (Figure 10�1)� The plant will wilt during high light periods as the water loss by transpiration is greater than the roots’ ability to take up sufficient water�
The location on the plant of symptoms is the first clue as to the cause of the disorder� Focusing on leaf symptoms, if the lower leaves are expressing yellowing, browning, or spots first (Figure 10�2), then the group of nutrients responsible for the disorder would be those of “mobile” elements� Mobile elements can be retranslocated within the plant from the lower older tissue to the younger tissues in the top of the plant� These elements include N, P, K, Mg, Zn, and Mo� Initial symptoms will be a yellowing (chlorosis) followed by browning or drying (necrosis) of leaf tissue� If the
symptoms appear in the young leaves at the tip of the plant this disorder is a result of a lack of “immobile” elements that cannot move from the older plant parts to the growing tip� These immobile elements are Ca, B, Cu, Mn, S, and Fe� To determine which of these is the cause of the disorder there are “keys” composed of a dichotomous table allowing you to make a number of alternative choices (Figure 10�3)� Each selection narrows the possible causes until in the final step there is a single element identified�
It is critical to recognize any symptoms occurring at an early stage of the plants’ expression of these stress clues because as the disorder goes on without correction, the symptoms expand progressing from simple yellowing spots to complete yellowing and necrosis� At that stage, it is very difficult to know the first form of symptoms as they spread throughout the plant giving it an overall chlorosis, necrosis, and deformations of tissues� In addition, as the stress becomes more severe, it will be difficult, taking a lot of time to correct it once identified� The loss of the plant’s health may become permanent or even result in its death� Yields will be greatly reduced as the stress is not corrected� The stress may begin as a cause from a single element and then as it progresses, other element uptake is slowed or blocked and the plant suffers from multiple disorders�
A very useful procedure when a symptom first appears is to immediately change the nutrient solution� That is, make up a new batch� At the same time, to determine the exact cause send a nutrient and/or tissue sample to a laboratory for analysis� Similar to soil analysis, the laboratory will give you guidelines as to what the normal levels of each nutrient should be in the solution or in the plant and direct you to make adjustments in the nutrient solution formulation�
Here is a summary of deficiencies of mobile elements (first symptoms on older leaves) (Figure 10�3) and possible remedies�
Lower leaves become yellowish green and growth is stunted�
Remedies Add calcium nitrate or potassium nitrate to the nutrient solution�
Stunted growth of plant, a purple color of the undersides of the leaves is very distinct and leaves fall off prematurely�
Remedies Add monopotassium phosphate to the nutrient solution�
The leaflets on older leaves of tomatoes become scorched, curled margins, chlorosis between veins in the leaf tissue with small dry spots� Plant growth is restricted and stunted� Tomato fruits become blotchy and unevenly ripen�
Remedies Apply a foliar spray of 2% potassium sulfate and add potassium sulfate to the nutrient solution�
The older leaves have interveinal (between veins) chlorosis from the leaf margins inward, necrotic spots appear�
Remedies Apply a foliar spray of 2% magnesium sulfate� Add magnesium sulfate to the nutrient solution�
Note: When applying foliar sprays, if in a greenhouse, avoid doing so during high sunlight conditions as that can cause burning of the leaves� Apply in the early morning while the sun and temperatures are low�
Older and terminal leaves are abnormally small� The plant may get a “bushy” appearance due to the slowing of growth at the top�
Remedies Use a foliar spray with 0�1%–0�5% solution of zinc sulfate� Add zinc sulfate to the nutrient solution�
The following is a summary of deficiencies of immobile elements (first symptoms appear on the younger leaves at the top of the plant) (Figure 10�3) with suggested remedies�
The upper leaves show marginal yellowing progressing to leaf tips, margins wither, and petioles curl and die back� The growing point stops growing and the smaller leaves turn purple-brown color on the margins, the leaflets remain tiny and deformed� Fruit of tomatoes show blossom-end rot (BER) (leathery appearance at blossom ends of the fruit)�
Remedies Apply a foliar spray of 1�0% calcium nitrate solution� Add calcium nitrate to the nutrient solution�
Upper leaves become stiff and curl down, leaves turn yellow� The stems, veins, and petioles turn purple and plant growth is restricted�
Remedies Add potassium sulfate or other sulfate compound to the nutrient solution� A sulfur deficiency is usually rare because it is added to the nutrient solution by use of potassium, magnesium, and other sulfate salts�
The terminal leaves start turning yellow at the margins and progress through the entire leaf leading eventually to necrosis� Initially the smallest veins remain green giving a reticulate pattern� Flowers abort and fall off, growth is stunted and spindly in appearance�
Remedies Apply a foliar spray with 0�02%–0�05% solution of iron chelate every 3-4 days� Add iron chelate to the nutrient solution�
The growing point withers and dies� Upper leaves curl inward and are deformed having interveinal mottling (blotchy pattern of yellowing)� The upper smaller leaves become very brittle and break easily�
Remedies Apply a foliar spray of 0�1%–0�25% borax solution� Add borax or boric acid to the nutrient solution�
Young leaves remain small, margins turn into a tube toward the midribs in tomatoes, petioles bend downward, and growth is stunted to get a “bushy” appearance of the plant at the top�
Remedies Use a foliar spray of 0�1%–0�2% solution of copper sulfate� Add copper sulfate to the nutrient solution� Note: Whenever applying a foliar nutrient spray, apply it first to a few plants and wait to apply it to all plants for about a day to be sure that no burn occurs from the spray�
Middle and younger leaves turn pale and develop a characteristic checkered pattern of green veins with yellowish interveinal areas� Later small necrotic spots form in the pale areas� Shoots will become stunted�
Remedies Apply foliar spray of 0�1% manganese sulfate solution� Add manganese sulfate to the nutrient solution�
All leaves show a pale green to yellowish interveinal mottling, usually progresses from the older to the younger leaves�
Remedies Apply a foliar spray of 0�07%–0�1% solution of ammonium or sodium molybdate� Add ammonium or sodium molybdate to the nutrient solution�
You will note that distinguishing among the symptom differences, especially with copper and molybdenum is difficult� The differences among iron, boron, and manganese are very prominent with the effects on the growing points and the distinct checkering coloration of manganese�
A deficiency in calcium is very similar to that of boron in the growing point; however, calcium will cause the BER on the fruit of especially tomatoes and peppers� Nonetheless, always remember to check the moisture level in the substrate and adjust irrigation cycles to give adequate watering so that wilting of the plant does not occur, as such water stress would be the first cause of the BER symptom�
These disorders occur from environmental stresses such as high relative humidity, excessive temperatures (either high or low), very high light intensity, and incorrect irrigation� Often unfavorable environmental conditions cause upsets in nutrient uptake and therefore will also appear as a nutrient disorder� These disorders, including the entire nutrient disorders described in this chapter, are not encountered only in hydroponics, but are very common in soil growing also�
A brown, leathery tissue forms at the blossom end of the fruit (Figure 10�4)�
Causes and Remedies Calcium deficiency, water stress due to insufficient irrigation frequency or too much on compact clay soils that causes poor root aeration� In hydroponics, it is a lack of irrigation cycles, especially under high temperatures and light intensity� It is often a calcium deficiency induced by poor irrigation practices� Adding calcium will not rectify the problem if the irrigation frequency is not corrected�
Cracks radiate from the stem end, especially on maturing fruit (Figure 10�5)�
Causes and Remedies Poor irrigation is the cause of water deficit, especially under high temperatures, when an irrigation cycle is initiated the water is taken up very rapidly by the plant that directs it to the fruit where the sudden expansion is too fast for the skin to expand and it cracks� This can be prevented by avoiding high temperatures with shading and maintaining uniform soil moisture levels� Start irrigation cycles 1-2 hours after sunrise and the last one no later than 1 hour before sunset�
Fruit color is uneven with brown vascular tissue inside the fruit�
Causes and Remedies There are a number of environmental and possible induced nutritional disorders� Low light intensity, cool temperatures, high medium moisture levels, high nitrogen and low potassium are all potential causes� Avoid this condition by adding
supplementary lighting, or using less irrigation cycles under low light conditions and lower nitrogen levels in the nutrient solution�
The top shoulder area of the fruit remains a blotchy green while the rest of the fruit is colored� This is particularly common in some tomato varieties� A lot of varieties have resistance to this disorder� With peppers and eggplants, a blackened leathery spot appears on the fruit as a result of sunscald�
Causes and Remedies The cause is high temperatures combined with direct sunlight striking the fruit� This can be prevented by keeping good leaf growth above the ripening fruit and in a greenhouse provide shading in the hot, summer months� Also, if peppers have a lot of fruit developing at a given time, this high production slows the plant growth and fruit forms near the tops of the plants where few, or small developing leaves cannot shade the fruit sufficiently� You can add nitrogen to the nutrient solution to promote more vegetative growth in the plant� In addition, with peppers, do not permit more than five to six fruits to form on each stem of the plant� Thin, if necessary, to reduce the fruit load and this will also give you larger fruit�
This is fruit distortion with protuberances and indentations (Figure 10�6)�
Causes and Remedies High relative humidity and low light levels cause poor pollination� Avoid these environmental conditions with ventilation and addition of supplementary lights, especially with indoor growing to increase light intensity�
This is the bending of the fruit as it expands (Figure 10�7)�
Causes and Remedies The causes include any poor temperatures that cause slowing of growth, fruit hanging up on leaves, tendrils (long stringy appendages of the cucumber) attaching to the fruit, mechanical damage, or pest injury during the rapid fruit expansion� The cure is to keep good temperatures and avoid the other causes by proper training of the plant as described in Chapter 24�
The fruit gets soft, yellows, and shrivels when very small�
Causes and Remedies This condition can be caused by poor nutrition, too heavy of fruit load, low light, and improper training of the plant� Keep the plant pruned and thin the fruit set if necessary�
Note: Proper training of the plants is presented in detail in Section VI, Chapter 24�
In summary, it is essential for good production to recognize any nutritional and/or environmental-induced disorders in plants early from symptoms they express when under stress� Their early correction will prevent losses in yields and their decline in vigor� There are many books available with photos describing these symptoms and keys to assist in identifying nutritional disorders such as in my book, Hydroponic Food Production�
