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Introduction

Nematodes are inoculated in plants to evaluate plant-nematode relationships and to establish nematode association, nematode involvement, or the role of the nematode in the disease development. Inoculation varies depending on the experimental purpose it will serve.

The first stage in studying plant-nematode relationships is a strong evidence of the suspected nematode involvement in the disease. Observing nematodes feeding or on in the host is useful at association stage and this can be done through general field observations, nematode surveys, soil fumigation studies and preliminary greenhouse inoculation experiments.

The second stage is to establish that the nematode is involved in the disease development. This is achieved by conducting inoculation experiments under controlled conditions. Observations and experiments may involve other microorganisms other than the nematodes which is the reason why graded series of nematode inocula may be added to the non-infested soil to establish a treated and non-treated check for comparison and correlation of the differences due to nematode population.

Experiments should be done under asceptic condition to establish the role of the nematodes in the disease or its activity in the plant. A microbiologically sterile single population of nematode should be used.

For the purpose of this experiment, Meloidogyne incognita, a root-knot nematode, is used to determine if it is responsible for the development of root-knots in Lycopersicum esculentum (tomato).

Methodology

A gram of infected roots were placed near the base of a set of tomato plants. Another set were prepared this time placing 20 grams of infested soil. The plants were arranged in the greenhouse following a randomized block manner. Initial plant heights were gathered and data were collected every week for four weeks. After four weeks, the final heights of the tomato plants were recorded. The tomato plants were removed from the pots carefully so as not to leave any plant roots on the soil. Afterwhich, the roots were washed to remove excess soil particles followed by the counting of the root-knot formations on the roots. The data were recorded.

Results and Discussion

The initial and final plant heights were recorded and the height differences were calculated.  Galls were also counted and were evaluated using the following index:  (RGI-Root Galling Index*) 1 - no gall, 2 - trace galling (1-25% galling), 3 - slight galling (26-50%), 4 - moderate galling (51-75%) and 5 - severe (76-100%).

Height differences were calculated so as to have a simple basis of comparison for the effects of the root-knot formation caused by Meloidogyne incognita on Lycopersicum esculemtum while the counting of the number of nematodes can be used for analyzing how the nematode population can affect the growth of the plant.

Below are the data gathered during the experiment:

Table 1. Data gathered for Lycopersicum esculentum with no inoculation to serve as control

Control
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10.2	46	35.8	0	1
Rep2	13.5	59.6	46.1	0	1
Rep3	9	57.1	48.1	0	1
Rep4	11.5	53.4	41.9	0	1
Average	11.05	54.03	43	0	1

Table 2. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using an infested soil as source of inoculum.

Infested Soil
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10	46	36	149	5
Rep2	11	55	44	50	3
Rep3	11	52	41	31	3
Rep4	8.5	52	43.5	15	2
Average	10.13	51.25	41.13	61.25	3

Table 3. Data gathered for Lycopersicum esculentum inoculated with Meloidogyne incognita using galled roots as source of inoculum.

Galled Tomato Roots
	Initial Plant Height (cm)	Final Plant Height (cm)	Height Difference (cm)	Number of Galls	Index*
Rep1	10	41.5	31.5	102	5
Rep2	9	wilted	n/a	n/a	n/a
Rep3	10.5	61.2	50.7	284	5
Rep4	10	56	46	43	3
Average	9.88	52.9	42.7	143	4

Table 4. Average height differences, number of galls and index of the three treatments.

Source of Inoculum	Average Height Difference (cm)	Average Number of Galls	Average Index *
Control	43	0	1
Infested Soil	41.13	61.25	3
Galled Tomato Roots	42.7	143	4

Data has shown us that of number of galls is highest on plants whose source of inoculum was the galled tomato roots giving it a moderate galling (4) in the RGI while the control treatment showed no signs of galling, hence an index value of 1. The average growth of the plants has negligible differences so we look at the number of galls that were formed from t plants respectively and it can be noted that many galls were formed especially in the plants inoculated with nematodes from galled tomato roots. Hence, more nematodes came from the galled tomato roots. This means that between the two sources of inoculum, the use of galled tomato roots will yield more disease formation. It can also be noted that since the same galls from the inoculum were formed in the test plants, it can be concluded that the same nematodes were the cause of both the diseases observed.

Conclusion

Since the same gall formation were observed from the source of the inoculum and the test plants, it is confirmed that the presence of the nematode is indeed the cause of the disease since no galls were observed from the control set-up and galls were also observed from the roots of test plants inoculated with infested soil.

Tags: Nematodes, Plat Disease Diagnosis

These are the elements that plants need to survive. Essential elements, whether in large amounts or in minute quantities, are chemical elements that plants need in order to complete their normal life cycle . The functions of these elements in the plant cannot be fulfilled by another. Thus making the element essential for the plant growth and development.

Elements that are needed in large quantities are called macronutrients while those in minute or trace quantities are called micronutrients.

Below is a table of the essential elements of plants.

Name	Symbol	Atomic number	Atomic weight	Classification	Importance to plants
Nitrogen	N	7	14.01	Macronutrient	Constituent of chlorophyll, amino acids and nucleic acids
Potassium	K	19	39.10	Macronutrient	Stimulates a number of enzymatic activities; involved in opening of stomata
Calcium	Ca	20	40.08	Macronutrient	Contributes to cell membrane stability, cell wall rigidity, and cell division
Magnesium	Mg	12	24.31	Macronutrient	A major component of chlorophyll; activates enzymes for respiration, photosynthesis, and DNA synthesis
Phosphorus	P	15	30.97	Macronutrient	Component of membrane phospholipids, nucleic acids, sugar phosphates, ATP, & ADP
Sulfur	S	16	32.07	Macronutrient	Component of some amino acids and some coenzymes for the plant’s metabolic and synthetic processes
Chlorine	Cl	17	35.45	Micronutrient	Involved in water-splitting reaction in photosynthesis, cell division, osmoregulation, and closure of stomata
Iron	Fe	26	55.85	Micronutrient	Component of proteins involved in photosynthesis, respiration, & nitrogen fixation; required for chlorophyll synthesis
Boron	B	5	10.81	Micronutrient	Involved in sugar transport, cell wall synthesis, carbohydrate metabolism, & pollen tube growth
Manganese	Mn	25	54.94	Micronutrient	Required for photosynthetic evolution of oxygen; cofactor in many enzymes
Zinc	Zn	30	65.39	Micronutrient	Component of many enzymes; involved in gene regulation
Copper	Cu	29	63.55	Micronutrient	Cofactor of enzymes involved in redox reactions; involved in cell wall lignifications
Molybdenum	Mo	42	95.94	Micronutrient	Catalyst for nitrogen metabolism
Nickel	Ni	28	58.69	Micronutrient	Component of urease and hydrogenase; involved in mobilization of nitrogenous compounds

Reference:  Alejar, A.M.A. and Sese, M.L.D.(1999).Fundamentals of plant physiology. Philippines: Plant Physiology Society of the Philippines, pp. 77-90

Tags: Essential Elements, macronutrients, micronutrients

Harvesting immature farm products can lead to more loses than gains since these goods might not be appealing to the market. There are two types of maturity, the physiological maturity and the economical maturity. What is important if you are a seller of fresh produce is the economical maturity. The produce is economically mature if it has reached the stage when it appeals to the market. Physiological maturity is the stage of the plant it is capable of reproducing. An physiologically mature crop may be economically mature but not all economically mature produce are physiologically mature.
Below are maturity indices of some fruits, vegetables, root crops, oil crops and cut-flowers. I hope you will find them useful.
Fruits:

Durian

The fruit is a large (1.5 to 2.5 kg), spiny capsule that opens into five segments containing seeds covered with a pulpy, edible aril. External color changes with maturation from dull olive-green to light yellowish-green. When mature, the fruit drops to the ground, but it can be carefully harvested before this occurs and ripened in 4 to 6 days. Ease of fruit abscission can be used as a maturity index. Fruit is picked with peduncle attached.

Avocado

Percent of dry matter is highly correlated with oil content and is used as a maturity index in California and most other avocado production areas; minimum dry matter required ranges from 19 to 25%, depending on cultivar (19.0% for ‘Fuerte’, 20.8% for ‘Hass’, and 24.2% for ‘Gwen’).

Florida-grown avocado cultivars have lower oil content and are harvested on the basis of a calendar date (days after full bloom).

Caimito

Fruit are harvested when the flesh begins to turn red and mature when the newly exposed layer is turned from green to pinkish-brown, orange, or red. Immature fruit will fail to soften, and their pulp will turn dark-brown and inedible. Harvesting must be done carefully to avoid mechanical damage. Twist the fruit until it breaks from the stem. Poles with knifes at the end are also used to harvest fruit. Fruit should not be allowed to fall on the ground.

Vegetables:

Squash

Summer squashes (soft-rind) are consumed at a range of physiological maturities but are defined as immature fruits of the diverse Cucurbitaceae family. Depending on cultivar and temperature, the time from flowering to harvest may be 45 to 60 days for zucchini, yellow straightneck or crookneck, and scallop (Patty Pan-type) squash and 75 days or more for many of the Sponge squash (immature gourds) such as Luffa. Fruit may be harvested at a very immature stage, at the desired fruit size, before seeds begin to enlarge and harden. A thin, soft external rind and external glossiness are also indicators of a pre-maturity condition. The entire fruit is edible, either raw or cooked, without removal of seeds and seed cavity tissue. Small, young fruit are tender and generally have a slightly sweet taste.

Ampalaya

Desirable size reached but still tender (overmature if color dulls or changes and seeds are tough)

Sitao

Well-filled pods that snap readily

Okra

Desirable size reached and the tips of which can be snapped readily

Onion

Indicated when approximately 10 to 20 percent of tops have fallen over

· Conversion from active growth to dormancy accelerated by undercutting bulbs 1 to 2 inches

· “Field-dry” maturity is indicated when bulb neck is completely dry to the touch and not slippery. Typically reached at 5-8% weight loss following harvest.

Cutflower:

Rose

Roses are harvested at different levels of maturity, depending on marketing and cultivar. For long-distance transport or storage, roses should usually be harvested with some of the sepals reflexed. Flowers harvested before the sepals reflex may fail to open, or may be more susceptible to bent neck. Fast-opening roses, like some yellows and whites, should be harvested just before the sepals start to separate from the bud. The marketing life of roses harvested later will be reduced unless extra care is taken with their postharvest handling. Harvesting is most convenient using shears provided with auxiliary jaws to hold the bloom after harvest. The cut is normally made so as to leave 2 five-foliate leaves below the cut. When stem length is an important consideration, the cut may be made ‘below Roses should be purchased and sold by cultivar name. Avoid blooms that are already open – flowers should normally have some or all of their sepals (the green protective ‘leaves’ at the base of the flower) folded back, but the petals should not have started unfolding. Brown spots or patches on the outer petals may be an indication of Botrytis infection.

Orchids

Orchid flowers are usually harvested 3 to 4 days after opening, because flowers cut prematurely will fail to develop normally off the plant. Early and late in the season, individual flowers are cut from the spike as they develop, because prices are high at these times. In mid-season, the whole spike is cut. Virus diseases can be spread from plant to plant during harvest, so cutting tools should be sterilized before being used on the next plant or disposable razor blades should be used. As individual flowers, purchase when fully opens. Spikes should be purchased when at least two flowers per spike are open.

Carnation

The maturity at which carnations are harvested depends on the proposed marketing procedure. Star-stage buds are too immature for most purposes except long-term storage. Buds at the ‘paint-brush’ stage, with petals straight up, will open quickly. Flowers for immediate use are normally harvested with the outer petals between vertical and horizontal. To minimize spread of disease, avoid harvesting from plants with obvious disease symptoms. Many pickers place cut flowers on the top of wires for later collection into bunches. Flowers collected into canvas slings can be taken to the shed by mechanical devices ranging from overhead cables to tractor-hauled trailers designed to hold the slings. Standard carnations ship better and last longer if purchased in the bud stage while miniature carnations should be purchased when at least one flower per stem is open. Fragrant cultivars have more consumer appeal.

Oil Crops:

Sunflower

Sprouts, plant seedlings consumed shortly after germination, are produced from many vegetable and agronomic plant seeds. Harvest maturity is highly regulated by germination (sprouting) conditions. The desired sprout length is the primary maturity index and harvesting is done at a relatively fixed number of days following radicle (root) emergence. Depending on seed type, harvest generally occurs 3 to 8 days after germination (Ex. alfalfa and sunflower, respectively). Examples of typical desired sprout lengths are given below;

Coconut

Young coconuts are harvested 6 to 9 mo after flowering, as the nut approaches full size and the skin is still green (Consignado et al., 1976; Srivichai, 1997) and the short stem (rachillae) on the top of individual coconuts that originally held the male flowers (in Thai called ‘rat-tail’) becomes half green and brown. In immature nuts, the skin surface around the calyx (cap) on the top of coconuts is creamy-white or a whitish-yellow. When the area surrounding the cap is green the coconut is regarded as mature and is 10 to 12 mo old. At maturity the skin begins to change from green to yellow then brown and the ‘rat-tail’ is entirely brown.

Sugar Crops

Sugarcane

* Ripening and maturation phase in a twelve-month crop lasts for about three months starting from 270-360 days.
* Sugar synthesis and rapid accumulation of sugar takes place during this phase and vegetative growth is reduced.
* As ripening advances, simple sugars (monosaccharide viz., fructose and glucose) are converted into cane sugar (sucrose, a disaccharide).
* Cane ripening proceeds from bottom to the top and hence bottom portion contains more sugars than the top portions.
* Ample sunshine, clear skies cool nights and warm days (i.e., more diurnal variation in temperature) and dry weather are highly conducive for ripening.

Root and Tuber crops:

Carrots

* In practice, harvest decisions for carrots are based on several criteria depending on the market outlet or sales endpoint.
* Typically carrots are harvested at an immature state when the roots have achieved sufficient size to fill in the tip and develop a uniform taper.
* Length may be used as a maturity index for harvest timing of ‘cut and peel’ carrots to achieve a desired processing efficiency.

Maturity standards

Maturity standards have been determined for many fruit, vegetable and floral crops. Harvesting crops at the proper maturity allows handlers to begin their work with the best possible quality produce. Produce harvested too early may lack flavor and may not ripen properly, while produce harvested too late may be fibrous or overripe. Pickers can be trained in methods of identifying produce that is ready for harvest.

Other information

Root, bulb and tuber crops

Radish and carrot

Large enough and crispy (overmature if pithy)

Potato, onion, and garlic

Tops beginning to dry out and topple down

Yam bean and ginger

Large enough (overmature if tough and fibrous)

Green onion

Leaves at their broadest and longest

Fruit vegetables

Cowpea, yard-long bean, snap bean, batao, sweet pea, and winged bean

Well-filled pods that snap readily

Lima bean and pigeon pea

Well-filled pods that are beginning to lose their greenness

Okra

Desirable size reached and the tips of which can be snapped readily

Fruit vegetables

Upo, snake gourd, and dishrag gourd

Desirable size reached and thumbnail can still penetrate flesh readily (overmature if thumbnail cannot penetrate flesh readily)

Eggplant, bitter gourd, chayote or slicing cucumber

Desirable size reached but still tender (overmature if color dulls or changes and seeds are tough)

Sweet corn

Exudes milky sap when thumbnail penetrates kernel

Tomato

Seeds slipping when fruit is cut, or green color turning pink

Sweet pepper

Deep green color turning dull or red

Muskmelon

Easily separated from vine with a slight twist leaving clean cavity

Honeydew melon

Change in fruit color from a slight greenish white to cream; aroma noticeable

Watermelon

Color of lower part turning creamy yelow, dull hollow sound when thumped

Flower vegetables

Cauliflower

Curd compact (overmature if flower cluster elongates and become loose)

Broccoli

Bud cluster compact (overmature if loose)

Leafy vegetables

Lettuce

Big enough before flowering

Cabbage

Head compact (overmature if head cracks)

Celery

Big enough before it becomes pithy

References:

http://postharvest.ucdavis.edu/Produce/ProduceFacts/

usna.usda.gov/hb66/126sapodilla.pdf

http://www.sugarcanecrops.com/crop_growth_phases/ripening_maturation_phase/

http://www.fao.org/Wairdocs/X5403E/x5403e03.htm#maturity%20standards

Tags: Maturity indices

This is a summary report about an article our professor in Plant Pathology 141-Plant Disease Epidemiology asked us to read. The article was about the beginning of Plant Disease Epidemiology and how the field of study continues to develop. The summary is as follows:

The development of plant disease epidemiology can be attributed to the disease outbreaks that occurred in the past and have changed the course of history of man. The defeat of Peter the Great, the discovery of the Bordeaux mixture, the conversion of the British from a nation of coffee to tea drinkers, the destruction of chestnut trees in the Americas, and the great loss in the corn industry of the USA in the past were due to several disease outbreaks caused by different plant pathogenic organisms.

The defeat of Peter the great of Russia in his fight to gain control of certain warm-water ports on the Black Sea in 1972 was due to the ergotism. Ergotism was due to the ergot of rye caused by Claviceps purpurea. This fungus invading the grain produces an ergot that contains many alkaloids including a hallucinogenic drug, LSD. When grains with ergot are ground and baked to bread, the problem begins.

Small amounts of alkaloids can induce abortion in cattle and in man. Larger amounts can cause can fingers and toes to tingle, and high fever that can result to derangement and even death if the fever persists. The patient may also experience hallucinations and even gangrene of the extremities after ingesting contaminated rye bread.

Sacer ignis-the holy fire was also an epidemic of ergotism during the 857 AD in the Rhine Valley in Europe killing thousands of people. The monks of St. Anthony were able to relieve the symptoms of the disease in 1039 AD in France and the disease was known as St. Anthony’s fire. The monks fed the patients with ergot-free bread together with spiritual administrations. An epidemic of ergot of rye has also lead to the accusations of witchcraft in Salem Village, Massachusetts and in Fairfield Country, Connecticut in 1962 as shown by some evidences. In 1951, weather conditions have allowed ergot to develop in rye in France. By fall, 200 cases of severe illness, insanity and four cases of deaths have been reported in Pont-St.Esprit.

Bordeaux mixture-a mixture of copper sulphate and lime was proven to effectively control potato late blight that caused the Irish famine in the early 1840’s. The potato late blight disease is caused by Phythopthora infestans favoured by cool, wet weather. The full effects of the disease was felt by 1846, thus the Irish famine.

The disease, however, was not limited to Ireland. There were reports of the occurrence of the disease in the northern United States and northern Europe. By 1855, the Irish population dropped by 3 million-1 million dead due to starvation and associated maladies, and 2 million as emigrants to the United States, Canada, and other countries.

In 1882, Bordeaux mixture was discovered in France during the World War I. But due to the war needs, military leaders did not release the copper since potato and grains were supplied for the army in 1916 and 1917. Military collapse of Germany in 1918 was due to the decline of morale of the army because although they were not hungry but their family were starving.

The British in Ceylon, now Sri Lanka, who were coffee drinkers, became a nation of tea drinkers when Hemileia vastatrix, the causal agent of the devastating coffee rust came to existence.

By 1870, 200,000 ha of coffee were planted by the British in Ceylon with 50 million kg of coffee beans for export per year. A year ago, Reverend M.J. Berkeley was able to describe and name Hemileia vastatrix, the disease results to the premature falling of leaves in about a hectare of land and suggested that sulfur be immediately applied to prevent further spread of the fungi. No one took heed on Berkeley’s suggestions and by 1874; the disease has become widespread on the island and has reduced 55% of the total yield four years after. In 1880, Henry Marshall Ward arrived in Ceylon and studied the fungi, Hemileia vastatrix, and showed an effective way of controlling the disease but due to the high costs of the control method, farmers started to plant tea bushes. Tea became popular in Britain with the demise of coffee in Ceylon. Coffee rust also destroyed coffee plantations all over Southeast Asia and India and destroyed the whole continent’s coffee industry in ten years.

The destruction of chestnut trees in the Americas was caused by Cryphonectria parasitica, formerly known as Endothia parasitica responsible for the chestnut blight epidemic that has caused a major effect in their industries. Chestnut was a major forest species in the United States contributing 25% of the 100 commercial hardwood species in the southern Appalachian region. The nuts were good sources of food for humans and wild life while the wood was used in furniture, home and fences, as firewood, as decay-resistant poles, and as railroad tiles. The highly successful leather tanning industry was also a product of chestnut since chestnut was the major source tannin during that time.

In 1904, H.W. Merkel observed that the chestnut trees in the Bronx Zoological Park in New York City were dying caused by an exotic fungus, then Endothia parasitica. The fungus was brought to the United States and by 1911, the blight had spread over New Jersey and parts of New York, Connecticut, Massachusetts, Rhode Island, Delaware, Virginia and West Virginia and the pathogen continued to spread. As a result, entire communities of the Appalachians turned to other enterprises since their major source of tannin has disappeared. Thirty billion board ft was estimated to be the loss of their lumber.

Epidemic leaf blight hit throughout the corn-producing areas of the eastern United States in the summer of 1970. February of the same year, the southern corn leaf blight, caused by Bipolaris maydis, was found in hybrids that have exhibited previous resistance. This was alarming since 85% of the total corn planted acreage the US were planted with this hybrid.

Hypersusceptibility to Bipolaris maydis by the hybrids was attributed to the use of the Texas cytoplasmic male sterility technique in producing the hybrids. The hypersusceptibility of Tcms hybrid was first discovered in the Philippines by Mercado and Lantican in 1961. In 1969, Race T, a new race, of B. Maydis invaded the Corn Belt. Race T was highly virulent on corn with Tcms but mild on corns with normal cytoplasm.

By May 1970, Southern Corn Leaf Blight has invaded the southern United States and was moving northward due to weather conditions by June. Since 85% of the corn planted was susceptible, losses ranged from 10-30% resulting to 15% of the U.S. corn crop or about 20 million metric tons of corn (about $1 billion) was lost.

These five plant diseases are examples only of epidemics caused by plant pathogens. Understanding of the multitude of biological and environmental factors and the historical and sociological lessons that can be derived from these epidemics should help us better in managing plant diseases in the field.

Plant disease epidemiology was not recognized as a discipline of plant pathology until the 1960’s. The appearance of J.E. Vanderplank’s Plant Diseases: Epidemics and Control served as the catalyst for the development of plant disease epidemiology. The book provided the first comprehensive treatment of the description and quantification of plant disease epidemics.

Phytopathology became a discipline only in the late 1800’s and trends that would lead to epidemiology were not evident until the twentieth century.

Duhamel’s work in the eighteenth century discussed the epidemiology of the Death, a disease of saffron crocus, caused by now Rhizoctonia violacea and causes epidemics on plants and provided control recommendations for the disease. This was the first known published work of plant disease epidemiology but received little attention in the scientific world.

In 1850’s, the dawn of the science of plant pathology, the concept of an epidemic was exemplified in the writings of Julius Kühn. In 1901, H. Marshall Ward’s Diseases in Plants displays high perception in epidemics.

It was Ernst Gäumann’s Pflanliche infektionslehre (Principles of Plant Infection), the first comprehensive work in plant pathology concentrating in botanical epidemiology that emphasized the uniqueness of each plant disease epidemic. He also discussed the concept of “infection chain” providing the foundation for the analysis and understanding the components of an epidemic.

With Gäumann’s book together with the development of modern computers, and the growing awareness of plant pathologists in mathematics, statistics, and ecology in the 1950’s, the epidemiology of plant disease as a quantitative discipline took shape. The “birth” of modern botanical epidemiology occurred in 1960 when J.E. Vanderplank, in the chapter “Analysis of Epidemics” of his Plant Pathology, Vol. 3. Edited by J.G. Horshall and A.E. Dimond, took the quantitative approach and the logistic equation was first systematically applied in plant disease epidemics.

In 1963, a NATO Advance Study Institute in Pau, France, “Epidemiology of Plant Diseases” was held. Several international conferences, symposia and workshops soon followed over the years and were hosted by different organizations all over the world. Since then, an increasing number of scientists have made significant contributions to plant disease epidemiology.

Plant disease epidemiology is now a vital and growing discipline that will continue to play a role in understanding plant diseases and providing strategies for successful management of plant diseases.

Tags: Coffee Rust, Epidemiology, Plant Disease Epidemiology, Plant Pathogenic Fungi, Southern Leaf Blight

In every field, weeds are always present. But what exactly are weeds? Well, some people define weeds as an unwanted, undesirable and useless plant. But no plant is completely useless. We may then define weeds as plants that are unwanted at a particular time and place and whose economic use has not yet been discovered. A plant species can only be called as weed if humans have not yet found a use for it. “One man’s crop maybe another’s weed.”

Some plant species though occur 99% as weeds in some fields. Echinochloa spp. and Monochoria vaginalis in rice fields for example. R. cochinchinensis and Cyperus rotundus in corn and vegetable fields respectively are considered as weeds. 10% of the 300,000 angiosperm species behave as weeds 99% of the time.

The unique characteristics of weeds have made them difficult to control in the field. They have excellent adaptations to disturbed environment and occupy the ecological spaces left open in agroecosystems. Other characteristics of weeds include their rapid vegetative growth, reproduce rapidly and mature early, very prolific and produce plenty of seeds, can survive and adapt to adverse conditions, dormancy of propagules or can be induced to dormancy under favorable environments, and are adapted to crop competition.

Rapid Vegetative Growth and Reproduce Rapidly and Mature Early

Weeds have numerous tillers for grasses, rapid tuber and shoot formation for sedges, and faster stem elongation and branching for broad leaves. Also, weeds are able to reproduce sexual and asexually. These have allowed the weeds to be able to maintain high population densities if not managed effectively. They also mature early so they are able to reach their reproductive period at a lesser time, hence more plants capable of to reproducing.

Very Prolific and Produce Plenty of Seeds

R. cochinchinensis can produce more than 700 tillers and branches and can produce inflorescence. Perennial weeds can reproduce rapidly through vegetative means through tubers, rhizomes, and stolon. Scirpus maritimus, a perennial sedge, can produce more than 100 dormant and non-dormant tubers in one cropping season in irrigated rice paddies.

Ability to Survive and Adapt to Adverse Conditions

Weeds are capable of resisting drought and excessive moisture stress. Large crabgrass (Digitaria sanguinalis) form contractile roots and arrests its growth during extremely dry conditions and resumes their normal conditions until a favorable condition is met. The common purslane (Portulaca oleracea) incline their leaflets upward to reduce exposure to sun during dry conditions thus reducing excessive moisture loss due to transpiration.

Propagules Possess Dormancy or Can be Induced to Dormancy

Dormancy is a mechanism that enables the species to survive under unfavorable conditions. This mechanism is common to weed species and until a favorable condition for growth is observed.

Adapted to Crop Competition

Weeds have proper synchronized germination. They are able to germinate at the right time in favorable environments. Their seedlings are fast growing and can be rapidly established. Their quick response to moisture and nutrient availability make them well adapted to crop competition in the agroecosystem.

It is very important to know the characteristics of weeds so that proper and effective weed management measures can be design to solve weed issues. What even makes it difficult is that weeds are also plants, like the crop planted in the field, anything that can harm them can possibly harm the crop as well. The soil too is a seed bank of thousands of weeds so it is expected that a weed can grow in empty spaces in the agroecosystem. Weeds are also are important in disease development because some weed species are alternate hosts of some pathogens. Weeds also provide a niche for other insect pests in the field, hence, controlling them is a very important management practice in the field.