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118 Frutas del trópico
galls or cankers. Lichen growth on tree trunks and large branches can be common and are not
harmful to plants. Some trees have peeling bark or heavy pubescence (hairiness) that is nor-
mal for the species. Variegation in leaves can be normal in some plant species. The presence
of sooty mold does not normally affect plant health, however, it can be an indication of the
presence of insects.
Generally speaking, plants grow within defined environmental units such as temperature, mois-
ture, soil pH, air quality, light, and nutrition. If any of these factors goes below or above the optimum
range, injury may result. Diagnosis of these types of symptoms can be difficult. For example, frost
or freeze injury may cause areas of necrotic tissue, especially at the leaf tips or margins. Excessive
temperature may cause plant tissues to desiccate and die. Moisture extremes may also cause wilting
due to lack of water and lesions (edema) due to excessive water. Proper nutrition is important
in plant growth and the important elements (nitrogen, phosphorous, and potassium) as well
as some of the micronutrients must be available in certain levels to avoid deficiency or excess
problems. Some of these symptoms can cause yellowing, chlorosis, distorted shoot growth,
and marginal necrosis.
Another type of injury that may be observed is phytotoxicity from pesticides which may
be from directly spraying on plants or drift from nearby applications. Phytotoxicity can be
easily confused with virus diseases or mineral imbalance. Pesticides can sometimes cause blea-
ched spots, marginal necrosis and chlorosis, stunting, or shoot dieback.
II. Integrated pest management
Integrated pest management (IPM) means that you use the best, most effective and safest ways
to manage pests. Generally, you cannot get rid of pests entirely and that should not be the goal.
You should manage the pests to keep the pest numbers or level of damage at an acceptable
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