Yami No Matsuei's Hangout

Weed Classification

2008-02-01T01:46:00.000-08:00

Weeds are classified according to their similarities and differences which are effective in formulating an effective control program. These are according to their: a) Life Cycle, b) Gross Morphological Features, c) Body Texture, d) Habit-Manner of Growth, and e) Habitat.

According to their Life Cycle, weeds are classified as annual, or perennial. Annual weeds complete their life cycle in one season and reproduce mainly by seeds while perennial weeds live for more that one season and reproduce vegetatively and by seeds. They can either be simple perennials that reproduce only by seeds or creeping perennials that reproduce by seeds and by vegetative propagules.

Weeds are classified according to their Morphological Features can be grass, sedge, or broadleaf. Grasses have stems called culms that are cylindrical and has has a well defined nodes and internodes. Their leaves arise alternately in two rows. Ligules can be observed in grasses. Sedges on the other hand have triangular culms and does not have ligules. Their nodes and internodes are indistinct which are located at the basal part of the culm. Broadleaved weeds are characterized as having expanded leaves. They can either be monocots or dicots.

We classify weeds as herbaceous, woody, or vine according to the general appearance of their stems. Their habit of growth can be erect-those that have an upwight growth, prostrate-lying flat on the ground, or twining-those that are climbing or clinging for support.

Weeds can be aquatic-those living in water, terrestrial-grows on land, or aerial-or epiphytes growing in air or attached to trees or other support, according to their habitat.

Insect Characteristics

2008-01-28T10:57:00.000-08:00

There are 725,000 insect species recorded in 1954. This is three times more that all other animals combined. The recent number of insect species known today is close to a million. Insects have lived on earth for about 350 million years compared to a less that 2 million years for man. They evolved and developed unusual morphological features, habit or behavior and unique characteristics to survive in any type of habitat.

Here are some insect characteristics that made them a successful group of arthropods:

1. Insects have hard and impervious body cover which is called the exoskeleton.

2. Insects possess wings that help them avoid predatory enemies, unfavorable conditions, and in finding food and mate.

3. Insects have high rate of reproduction. They have short developmental period and have high fecundity, meaning, several eggs are being laid by the mother.

4. Insects have a small size. This made them capable to complete development and reproduction with small amount of food.

5. Insects have varied developmental stages and habits.

6. Insects have a great capability of adaptation which allowed them to survive for a very long period of time.

7. Insects have highly varied habits and behavior.

These characteristics have made the insects of today survive millions of years ago.

Weeds

2008-01-25T06:20:00.000-08:00

Weeds are important component of the agroecosystem. They always grow with crops and its economic impact is greatest in agriculture. It is an important factor to consider in the management of land and water resources and dictate many of the crop production practices and management decision in growing crops.

We can defined a weed as a plant unwanted at a particular time and place and can do more harm than good under such time and place. The concept of a weed is man-made. One man's crop may be another man's weed. Of the 300,000 species of angiosperms, 10% 30,000 species behave as weed 99% of the time.

Weeds can be characterized to have a rapid vegetative growth, reproduce rapidly and mature early, be very prolific and produce plenty of seeds, have the ability to survive and adapt to adverse conditions, be adapted to crop competition, and whose propagules possess dormancy or can be induced to become dormant under favorable conditions.

The last characteristic of the weed is the reason why most of the empty lots we see today are populated with weeds. One year of planting would equal to seven years of weeding.

Global Warming

2008-01-24T09:51:00.000-08:00

Global warming is the increase in the average temperature of the earth. This is due to the increase in the amount of green house gases in the earth's atmosphere. Carbon dioxide is one of the green house gases that contributes to the present temperature of earth today. The degree of hotness that you feel right now is highly due to global warming or the green house effect.

Global warming operates due to the earth reaction to reflect radiation coming from the sun. The earth reflects the radiation to the atmosphere and into space. This is the mechanism where the earth can maintain its temperature. The amount of green house gases present in the atmosphere has a great impact on the efficiency of earth to reflect back this radiation. What happens is that, the green house gases like carbon dioxide traps the sun radiations within the earth making it difficult for the radiation to escape into space. The radiation accumulates inside the earth's atmosphere causing an inefficiency in the dissipation of heat. This consequently results to the increase in the average temperature of earth today.

The air today is composed of 350ppm and other gases. Such low carbon dioxide concentration in the air has caused this temperature today. What will happen if it continues to rise? More and more carbon dioxide in the atmosphere means more and more green houses to trap the radiation and more and more radiation to cause heat accumulation, thus the advent of global warming.

Pest Sampling

2008-01-23T19:15:00.001-08:00

Sampling is the process of selecting units from a population. The sample is studied and generalization is made to the population based on the results of the sample. The characteristics of a good sample are
(a) it should be large enough to cover or represent the population;

(b) it should be reliable. It is important because of the following reasons:
(a) population of pest is too large (b) low cost

(c) time consideration and

(d) area covered is too large.

In developing a sound crop protection program, the proper pest sampling and damage assessment is essential and also some important information about the components of agroecosystem. The implementation of a management tactics relates to the prevention of commodity loss since the management tactic was implemented at the appropriate time based on good estimates of pest damage potential and as well as pest densities. There are two general methods of sampling in the field; the first one is direct sampling, the direct sampling of pest from the host plant on in the environment and the second method is the indirect wherein the account of the damage of the pest is considered.

Giant Colocasia esculenta

2008-01-23T09:38:00.000-08:00

This is a picture of a Colocasia esculenta i took at our backyard. It grew so big that i have to cut it down and feast on its edible part, its root! We call it "gabi" in our native language and it is hig in carbohydrates. It is an ingredient in what is popularly known here in the Philippines as "nilaga".

This plant stayed in our backyard for almost 5 months already so it grew this big. As you can see, the place where it is planted is composed of dried leaves and the like. This caused an increase in the Organic Matter content of the soil, thus favoring the growth of the gabi.

Since high Organic Matter in the soil can promote favorable growth for plants, this is likely to happen. Without any addition of inorganic or commercial fertilizers, this plant was able to grow this big. If we are to look at it, it is really possible to grow healthy plants without the addition of inorganic fertilizer.

Pyrethrins

2008-01-23T09:01:00.000-08:00

Pyrethrins are natural organic compounds (Pyrethrin-I, pyrethrin-II) that can be used for insect control. They are found in daisy-like Chrysanthemum (Chrysanthemum cinerariaefolium) flowers grown and harvested in Kenya, Africa and Australia. They are viscous liquids that oxidize readily to become inactivate. The insecticidal properties of pyrethrins are derived form ketoalcoholic esters and pyrethroic acids which are strongly lipophilic and rapidly penetrate many insects and paralyze the insects’ nervous system (Reigart et al., 1999).

Pyrethrins, as neurotoxins, attack the nervous systems insects. If in minimal amount not fatal to insects, they serve as insect repellants, thus, they are also applied to prolong the viability of storage grains and protect it from storage insect pests. They are far less toxic to warm-blooded animals but harmful to fish. It affects the skin touch receptors and balance organs of fish and tadpoles. Toxicity increases with higher water temperatures and acidity. Pyrethrins are also toxic to beneficial insects such as honeybees and toxic to other aquatic invertebrates. In humans, pyrethrins are known to irritate the eyes, the skin, and respiratory system. But they are less toxic compared to many synthetic insecticides. Pyrethrins have been considered to be one of the safest insecticides and may be used with safety in plants used as food, at homes and around animals. It has a long history of satisfactory use around mammals and birds. Pyrethrins interfere with the ionic conductance of nerve membranes by prolonging the sodium content and stimulate the nerves to discharge repeatedly causing hyper-excit-ability in poisoned animals (WHO, 1999).

A derivative from pyrethrins is pyrethroids. Pyrethroids are synthetic forms of pyrethrins. They are more stable and are less affected by sunlight and oxygen. They also tend to be more effective compared to natural pyrethrins and are less toxic to mammals. A common pyrethroid is allethrin. Pyrethroids are neuropoisons acting on the central nervous systems by interacting with sodium channels in mammals and/or insects. The main systems for metabolism include breakage of the ester bond by esterase action and oxidation at warious parts of the molecule. Induction of liver microsomal enzymes has also been observed (WHO, 1999)

Pyrethrins are biodegradable, hence non-persistent, and break down easily when exposed to light or oxygen. This means that there will be no excessive build-up of insecticides in the treated area. Natural pyrethrins are highly fat soluble, but are easily degraded; thus, do not accumulate in the body. Pyrethrin-I, pyrethrin-II, and allethrin have multiple sites in their structures which can be readily attacked in biological systems, it is unlikely that they will concentrate in the food chain

Many pyrethroids have also been linked to disruption of the endocrine system, which can adversely affect reproduction and sexual development; interfere with the immune system and increase chances of breast cancer. Pyrethroids contain human-made, or xenoestrogen, which can increase the amount of estrogen in the body (Garey et al., 1998). When tested, certain pyrethroids demonstrate significant estrogenecity and increase the levels of estrogen in breast cancer cells (Go et al., 1999). Because increased cell division enhances the chances for the formation of a malignant tumor in the breast, artificial hormones, like those found in pyrethroids, may increase breast cancer risk (PCBR, 1996). Some pyrethroids are classified by EPA as possible human carcinogen.

While the development of the synthetic pyrethroids was heralded with claims of selective toxicity to insects, both pyrethroids and pyrethrins are extremely toxic to aquatic organisms, including fish such as the bluegill and lake trout, with LC39 values less than 1.0 ppb. These levels are similar to those for mosquito, backfly and tsetse fly larvae, and the actual target of the pyrethroid application. Lobster , shrimp, mayfly nymphs and zooplanktons are the most susceptible non-target aquatic organisms (Muller-Beilschmdt, 1990) The nonlethal effects of pyrethroids on fish include damage to the gills and behavioral changes.

Natural pyrethrins and synthetic pyrethroid compounds vary in their toxicity. Inhaling high levels of pyrethrum, pyrethrins or pyrethroids, may bring about asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, lose of coordination, tremors, convulsions, facial flushing and swelling, and burning and itching sensations. Infants are severely affected due to their inability to efficiently break down pyrethrums. Animals exposed to toxic amounts may exhibit tongue and lip numbness, diarrhea, and nausea or even death. But rapid recovery can be observed from serious intoxication of mammals. Rats and rabbits are not affected by large dermal applications. Pyrethrum produces irritation and sensitization when touches broken skin and is further aggravated by sun exposure.

Pyrethrum absorption through the stomach and intestines and through the skin is slow. However, humans can quickly absorb pyrethrum through the lungs during respiration. Response depends on the pyrethrum compound used. Overall, pyrethrins and pyrethroids have low chronic toxicity and the most common problems in humans resulted from the allergenic properties of pyrethrum. Many of the natural and synthetic compounds can produce skin irritation, itching, pricking sensations and local burning sensations which may last for about two days. At high doses, pyrethrum can be damaging both to the central nervous system and the immune system which can worsen allergies. Animals fed large doses of pyrethrins may experience liver damage.

REFERENCES:

http://www.doyourownpestcontrol.com/pyrethrin.htm

http://en.wikipedia.org/wiki/Pyrethrin

http://npic.orst.edu/factsheets/pyrethrins.pdf

http://extoxnet.orst.edu/pips/pyrethri.htm

http://www.beyondpesticides.org/pesticides/factsheets/Synthetic%20Pyrethroids.pdf