Pesticides And Grey Leaf Spot Biology Essay

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Pesticides are chemical compounds sprayed onto crops to target specific pests or disease that have invaded a plant and is causing harm to the plant .They are categorized into three main types according to what they specific pest they target; Herbicides, Fungicides and Insecticides. Herbicides target and kill weeds by using chemically manufactured synthetic plant hormones to interfere with the growth of the specific weed, therefore killing the weed. Fungicides target fungal growth on a specific plant. It kills fungal growths by inhibiting the fungal spores of the fungus affecting the respective plant. Insecticides target any insects of the plant that may be considered a pest. To do this they target the eggs and larvae of the insect which is inhibiting and causing detrimental affects of the plant. Therefore is preventing the insects from increasing and spreading to other plants by killing its larvae and eggs. However it may also kill useful pollinators of the plant which can cause a reduction of yield, as the plant is no longer as productive without the pollinators. Pesticides have three different methods in which to be absorbed by the plant to kill the respective pest: by contact (these pesticides only protect the plant where the pesticide is applied to and does not absorb into the plant),translaminic (where the pesticides is redistributed from a sprayed surface to other non sprayed surfaces on the plant) or systemically(where the pesticide enters the plant by secret manufactured leaf barriers and is then redistributed through the Xylem vessels which is within the stem to the upper parts of the plant). Pesticides are a great asset in agricultural and garden communities in that it kills any unwanted pests or diseases that may affect the plants yield, production and also improve the health of the plant by killing the specific pests. Without the pests the plant will greatly increase in health as due to the decreasing of pest. The project will be focusing on pesticides in agricultural or farming communities. Pesticides in farming communities are applied to crops once or twice every season to decrease specific pests or diseases that may affect the plant. They are applied to the crop by either soaking the respective crop (before planting) seed in the pesticide by the recommend dosage or they are sprayed onto the crop by special airplanes in a recommend dosage and environmental conditions such as lack of wind and heat .300ml to 4litres per hectare is applied once or twice each season. However certain pesticides are known to be absorbed into a variety of water sources, soil and affect certain animals within the surrounding area. Therefore each pesticide safety to humans and the environment is controlled by a specific period known as a withholding period. A withholding period is a period between after the application of the pesticide and until the pesticide is considered safe to the environment because it has been broken down by the plant and is no longer present in the plant and therefore can no longer be absorbed into the soil or underground water sources or directly affect any surrounding wildlife. This period ranges from 3 days to 60days from the application of the pesticide. It is determined by experts by how long the pesticide takes to be broken down by the plant. The toxicity of each pesticide depends on how lethal the pesticide is in the environment and to what extreme it affects surrounding biodiversity of the area. Each RSA approved Agricultural Pesticide is divided into five toxicity groups which focus on the toxicity of the formulation and is expressed as the "LD50" value (Lethal Dosage).The toxicity groups range from Extremely Hazardous (5mg/kg) to unlikely hazardous (3000mg/kg). The extremely hazardous pesticides include Dichlorodiphenyltrichloroethane (DDT) and Atrazine which have been recently banned or severely controlled and restricted in countries around the world. Dichlorodiphenyltrichloroethane (DDT) is a persistent fungicide insecticide that poisons the central and peripheral nerve system of respective insects and mammals and copies the insects' hormones which disrupts the endocrine system. It has been used since World War 2 to control agricultural pests of farming communities. But later certain insects developed resistance to the pesticide. Also it was found to be a fat soluble, this caused the DDT to remain in plant and any food it may produce and was found to remain in certain food such as meat of a mammal that may have eaten the plant or accumulated it through the food chain. It has therefore since been banned in 26 countries and severely restricted in 12 countries. It was first banned in 1970 (Cuba) to 1986 (Switzerland). Atrazine a strongly persistent herbicide that greatly affects varies water sources and aquatic life has also been banned in certain countries. Atrazine besides from killing a certain fungal disease also inhibits photosynthesis and interferes with enzyme processes of a plant it is applied to, therefore reducing the plants yield and overall health. It also modifies the steroid balance within certain aquatic life such as many species of frog interfering with reproduction. It remains in the water leading to water poisoning and becoming unsafe for drinking purposes. The above concerns of the plant has lead to the herbicide being severely controlled or banned in varies countries. Other pesticides used today also have negative effects of the environment and the respective plant. However this is greatly prevented by certain measures and control instructions given to the person applying the pesticide. These include favourable weather conditions such as lack of wind and humidity that will prevent any affect of the pesticide on the plant, location in which it may be applied i.e. Not near any water source or residential areas and concentrations it must be applied in and all pesticides are usually mixed with other pesticide to ensure the pest becoming resistant to the pesticide .The instruction and control measure above will prevent minimum effect on the surrounding environment. Therefore this project focus on how present pesticides do not affect the environment, if used in controlled measures as mentioned above.

Type of Pesticide

Active Ingredient

LD50 mg/kg body mass

Target Pest

When it is applied

Withholding Period(days)

Amistar

Fungicide.

Azoxytrobin  

5000

Cercospora zeae-maydis (Grey leaf spot )

Sprayed 45 Days after germination

14

Punch C/Punch Extra            

Fungicide

Carbendazim Fluilazole

5000

Cercospora zeae-maydis (Grey leaf spot )

Sprayed 40 days after application of AmiStar

21Table showing Basic Information of Pesticides used in Investigation on Maize

AmiStar targets Cercospora zeae-maydis (Grey leaf spot.) Amistar is a non persistent fungicide used on varies crops such as cereals, vines, fruits, vegetables, rice and maize. It inhibits the mitochondrial respiration of Grey Leaf Spot. It is most toxic to water sources but after a specific period will remain stable in the water. It also may be absorbed into soil and underground water sources but does not cause damage as it is non persistent in soil. However if applied in humid conditions toxic vapors may be produced by the fungicide and cause varies effects both on people and the surrounding environment. It is most toxic to aquatic life and may cause long term undesirable effects such deformities.

Punch C / Punch Extra. Carbendazim is an active ingredient in Punch C/Punch Extra. The ingredient is absorbed systematically (absorbed internally within the plant).It interferes and inhibits mitosis of the fungal disease therefore interfering with the growth of the ovules. In the environment it may cause increased tumours in mammals, disrupt their endocrine system (hormones) and damage growing foetus in the womb of mammals, which have ingested the pesticide. It is highly toxic to both aquatic life and soil animals which live close to the surface. It is ultimately decomposed be micro-organisms of the environment.

Grey Leaf Spot

Figure 2 Showing Grey Leaf spot in its beginning stages

Source: http://agriculture.kzntl.gov.za/portal/AgricPublications/TechnicalInformation/GreyLeafSpotofMaize/tabid/280/Default.aspx Is a fungus that invades the maize plant .It is caused by the fungus Cercospora zeae-maydis It greatly limits yield of the maize .The leaves are the first to be affected: small irregular tan spots along the veins of the leaves will start to develop(Figure 2). Under favourable conditions (Humidity and warm temperatures) the Cercospora zeae-maydis Fungus will progress and move towards the stem and other parts of the maize plant (Figure 3). The results of this may cause the stem to rot and cause the plant to die (Figure 4).

Figure 3 Showing Grey Leaf spot after favourable conditions

Source: http://agriculture.kzntl.gov.za/portal/AgricPublications/TechnicalInformation/GreyLeafSpotofMaize/tabid/280/Default.aspx

Figure 3: Showing Maize Plant affected by Grey Leaf Spot

Source: http://agriculture.kzntl.gov.za/portal/AgricPublications/TechnicalInformation/GreyLeafSpotofMaize/tabid/280/Default.aspx

Pesticide Effects

The maize plant

The Fungicide used in the test below(full results Figure 2 of appendix) was AmiStar mixed with Punch Extra and was used to treat Grey Leaf Spot on Maize .AmiStar is absorbed translaminar (spread along surface of plant )and Punch Extra Systemically(absorbed internally within the plant). They were mixed to prevent, Cercospora zeae-maydis the fungal disease that causes Grey Leaf Spot to become resistant to the Fungicide. They were sprayed over the maize plant. The yield in the maize plant has increased in both maize types SC206 and PAN6568 after AmiStar and Punch Extra where a applied. This shows the fungicides were effective in eradicating the, Cercospora zeae-maydis fungus as Cercospora zeae-maydis mainly influences and decreases crop yield .The increase in yield shows the maize plants health was not affected by the pesticide if it were affected the yield would decrease as the plant is not effective when damaged.

The test and Data shown below was gained from Cedara in which they tested fungicides AmiStar and Punch Extra on 3 maize varieties.

Table2Table Showing effect of Pesticides AmiStar +Punch Extra on Maize Yield

Type of Maize

Average Yield per hectare

 

 

No Spray

After Spray

 

SC 206

7.9

9.98

 

Figure 5

Figure 5

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to itPAN 6568

9.3

10.02

 

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to itSC 627

8.87

8.15

 

Figure 5

SC206 is the most susceptible to the Fungicide

PAN6568 is of medium tolerance

SC627 is the least susceptible to the Fungicide

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

Figure 5

Figure 5

Figure 5

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

SC206 most susceptible and will have the highest response to the fungicide

PAN6568 is of medium tolerance to the fungicide

SC627 is the most tolerant to the fungicide and will have the lowest response to it

Affect on Biodiversity

Wildlife can absorb pesticides through water sources, by eating the affected crop before the withholding period is finished or by eating another animal which was severely poisoned by the specific pesticide. Wildlife can only absorb pesticides if they (the pesticide) do not reach their target area. Pesticides (especially ones that are sprayed) can enter the environment through run-off from fields into surface waters, leaching directly into the soil and drifting by air currents away from the targeted crop. They therefore can enter the environment through soil, water sources, food (food chain) and air. When observing the effect on the environment one must observe the effect on Biodiversity (plant life and animal life).To access the extent of health defects caused to animals and plant life it depends on the LD50 value (Lethal Dose), the volume of pesticide that is orally (mouth) or dermally (skin) absorbed, the amount of time (duration) it is exposed to the animal, and if the animal ate the crop product that was sprayed with pesticide during the withholding period or not. AmiStar mainly affects various aquatic life forms, as it is sprayed by airplane over the crop and if not spayed in the correct condition (lack of wind) the pesticide can easily drift to nearby water sources and leach into soils. The pesticide is absorbed into water sources where aquatic life is affected at a hazardous toxic level and can causes long terms aquatic effects. However when examining the LD50 Value, the fungicide is Unlikely Hazardous. However when it is absorbed into the biological food chain either through exposed insects that are eaten by secondary consumers or an animal that may have accidentally been exposed to the pesticide within the withholding period of the pesticide. As it is ingested further and further along the food chain the pesticide becomes more concentrated (ingests larger quantities) and also the insect or primary consumer ingests the pesticide at a much higher concentration that is found in the water or soil. And because of this the insect dies and a secondary consumer that eats the insect absorbs the pesticide is subsequently affected. Plants in the surrounding area are also affected if the pesticide accidentally drifts by wind. Plants will begin to decrease. This is because pollinators may be killed in error when applying the pesticide. With a decrease in pollinators the plants will be unable to reproduce effectively and die as a result. This will reduce plant diversity and abundance in the area. However animals and plants in the surrounding area will only be affected and /or killed if the control measures and instructions aren't adhered to. Animal and plants are affected when the pesticide is not applied in the correct conditions (lack of wind will prevent the pesticide drifting into any water source and onto nearby plant life). Also if the withholding period is strictly controlled animals are unlikely to be exposed to the pesticide

Analysis

Pesticides AmiStar and Punch Extra from the data displayed above proved not to harm the maize plant and instead increase its overall yield ,after spraying ,which results in more food products of the plant being produced. Grey leaf spot (pg4/pg5) mainly affects the yield of maize and killing the pathogen of the disease increases the plants yield Also the plants health does increase because of the effectiveness of the pesticide and killing of the fungal disease ( Grey leaf spot). AmiStar however can heavily affect the aquatic life of the area where as Punch Extra does not. It is not likely to poison any wildlife that may eat the pesticide crop and will not be heavily affected by it.SC206 being the most susceptible of the maize types to the fungicide showed the greatest increase in its yield compared to the other types of maize. The other types of maize were not as affected by the fungicide .And SC627 maize type the least susceptible decreased it yield after the pesticide was used.

Problems and solutions

Problems that can occur: Problems can however occur if the pesticide is not used in a controlled and Preventive manner i.e. The Control instructions (below) of the pesticide are not followed. The control and preventive methods are: The pesticide must not be applied in humid weather as toxic vapors may be produced and effect the surrounding environment (especially bird life which may fly over the crop area). There must be a lack of wind when applying the pesticide (to avoid drifting and polluting of the natural environment). Also it must not be applied near any water source, to prevent poisoning of aquatic life and water sources. The correct dosage must be strictly followed by the applier if not the pesticide will be ineffective if the dosage is too high the pesticide will burn the leaves and /or the pest will not be affected by pesticide if the dosage is too low. The instructions of method of application must be followed and the withholding period adhered to. However certain pests may become resistant to the pesticide applied, even if the correct dosage is followed. To solve this all pesticides are mixed commercially, if the pest becomes resistant to one pesticide the other pesticide (mixed with that pesticide) will kill the disease and/or pest that is affecting the plant. Also a minority of virus or pests will not be affected at all by any pesticide e.g. Phaerla Leaf Spot. This is however not a growing concern among agricultural communities as the disease or virus can be killed by natural methods.

Constraints

No data was collected on the effect of pesticides on biodiversity therefore could have been analyzed in more detail if results were obtained

Conclusion

Therefore one can conclude that pesticides increase the maize yield and its health because of the eradication of the fungal disease (Grey leaf spot). Pesticides are harmful to wildlife and surrounding plants because of pesticides chemical properties .However if the control and preventive methods and instructions are followed by the applier strictly there will be no effect on the environment

(Word Count (2569 words))

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