Water is designated as the most important factor for plant growth and not the fertilizers nor other synthetic chemicals-- as evident from the wild/natural plants habitats in forests or river/lakes sides.
They (wild plants-crops) also experience pest and microbes attacks but how often a forest got devastated completely by so. On contrary, this is common and a major problem in agronomy sector for major crops constituting a billion dollars loss annually.
Is biodiversity the answer?
Extensive monocultures are more prone to attack by pest insects due to the ecological imbalance that occurs when broad-spectrum insecticides are applied to control a pest species. With the elimination of natural enemies, populations of pest insects increase considerably causing economic damage to the crop. In natural forests due to the diversity of plants and ecological niches insects are in ecological balance with their natural enemies.
The devastation by diseases and pests of cultivated crops are due mainly to high level of intensification and uniformity at the expense of diversity. While in the forests; we have nearly balanced and stable ecosystem with high level of diversity .
Excellent question. We have to trace back the answer by examining the rhizosphere ecology of two contrasting ecosystem s, natural ecosystem versus domesticated ecosystem....
@ Ali, yes diversity is one of the major factor to reduce the pest and diseases of cultivated crops as not all crops are infested by similar pest and diseases moreover the rhizosphere environment may change due to diversity and we have found that more beneficial enzymes plays the role for native nutrient mobilization under diversified cropping pattern.
Extensive monocultures are more prone to attack by pest insects due to the ecological imbalance that occurs when broad-spectrum insecticides are applied to control a pest species. With the elimination of natural enemies, populations of pest insects increase considerably causing economic damage to the crop. In natural forests due to the diversity of plants and ecological niches insects are in ecological balance with their natural enemies.
Man made agricultural systems are intensified monocultural systems that need time to build up natural enemeis to have natural balance in the ecosystem, while in the forests there is a natural balance, no need for the man intervention, no chemicals are sprayed in forest to control pests, and no disturbance of the natural balance, while in man made systems or agricultural systems chemical sprayed disturb the nutural balance even after it has been established after a long period of time. In addition to the diverseity of the plant ecosystem that affects the diversity of the other organisms diversity.
Biodiversity is the main issue. You could also invoke r versus K selection and climax communities. A part of that would also be disturbance. Just making trails so that people can pass through to gather food will change the system dynamics and make available open spots where r species can invade.
Genetic diversity also play an important role. Monoculture crop has very less /no genetic diversity as compared to genetic diversity of natural forests. Hence, easily susceptible to diseases. Other reason is that natural balance in forest but no balance in Agri crops.
Excellent answers. I like to add a bit: agricultural crops are "improved" breeds or varieties; they may have bigger and more succulent leaves but shorter in height making conditions (shady and moist) ideal for pests. The "improved" plant structure requires more nutrients (fertilizers) to realize its potential of higher yield/production.
Very nice answers. I would like to add that with agricultural systems, application of agrochemicals may play a role in making plants more susceptible to diseases and pest infestation because some fertilizers for example (N) makes plants more succulent and pesticides can eliminate some pests hence imbalance the natural balance exists in the wild.
A.M.R. Abdel-Mawgoud Marilou Montemayor Dr. Purushottam Khetri Ramteke Timothy A Ebert Hanna M. Madanat Luis Miguel Constantino Yahya Shakhatreh Anoop Kumar Srivastava J. C. Tarafdar
I thank you all for your scholarly insights.
Dwelling on the this, I have some further thoughts;
- If mono-culturing amends the risk of pests infestation then why the biodiversity models are not in common practice?
- By supporting progressive farmers to obtain uniformity in harvest (usually of a single crop specie), why do the big firms intend to avail?
- Are we not helping in the evolution of better adapted genomes of pests by application of pesticides etc.
Thanking in anticipation.
While some breeding may reduce host plant resistance, one needs to be careful about breeding plants that are highly resistant. Sometimes what kills pests kills us too. There was a story of a plant breeder making a potato resistant to Colorado Potato Beetle. When he ate the potato, he got sick too.
Some agrichemicals might disrupt plant defense, but there is also systemic acquired resistance (SAR) that can be activated by some chemicals.
Sometimes the natural areas are devastated: or at least greatly affected. Gypsy moth, bark beetles, water hyacinth, prickly pear, Emerald ash borer, wooly hemlock adelgid, Dutch Elm Disease. The list is quite long especially for islands. Rats in Hawaii for example. One might include Zebra mussel and flying Asian carp.
The short answer is "its complicated."
Nice question and excellent answers. I would like to mention the role of faulty plant protection measures which are adopted by nonjudicious use of chemicals in crop field and ultimately these are killing the beneficial organisms. Thus pest population is increased.
More over, crop ideotypes and hybrids which are high yielders also, are of different morphological type with luxuriant growth and foliage are prone to pest attack.
On the other hand (as all agreed), diversity is saving the forest ecosystem from the threat of pests.
The monoculture and use of pesticides are responsible for diseases mainly. As mot of the crops/genotypes are not native part of that microclimate/environment, therefore more prone to diseases and lack of natural immunity, the wild plants have.
I think where nature maintain the ecosystem very efficiently and perfectly while people manage ecosystem with a lots of errors or harmful decision. Finally, nature is the best scientist.
Because crops are heavily grown in a small area, the pathogen will find an environment conducive to its growth and increasing numbers due to the availability of sufficient food and as a result of the presence of host plants, while wild plants are formed in smaller numbers and spaced and therefore are less likely to be infected
the micro climate around plant canopies are different between the two environment being in favor more for bests in intensive agriculture.
Alexander and José Walter, you don't have to go far to find out, the question formulated by Ali is very clear, why do crops are devastated by pests even utilizing pesticides. The reason is the development of pesticide resistance in insects when the same insecticide is used in a generalized and continuous way. On the issue of insect resistance to pesticides there are many examples in the entomological literature that can serve as an example.
Alexander Pfaff
, What do you mean when you say I have to read the question again? The question asked by Ali is very clear, although he does not say what is the cause of the devastation, but he gives the examples for pests and diseases "even using pesticides", This implicitly indicates that pesticides have already been applied and had no effect on pest control. We must know how to interpret the question in order to answer. Your interpretation of the question is different: "the application of an insecticide happens in consequence of pest occurrence or pest density reaching a specific level, " The problem is that Ali does not mention which variety or crop they have or how many pesticide applications have been made in the crop, or maybe they applied the wrong insecticide or the wrong dose, who knows, only Ali should know that, therefore there is a lack of information on the type of management and agronomic practices that are carried out in the crop to give a definitive diagnosis. Everything is based on speculation, the evidence is missing. Under this premise any answer is valid, which can be refuted with scientific evidence, not under speculation or hypothesis as you are posing.- Badges
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