20. Agricultural Chemistry supplementary (mostly) not in text, but see Chapt 14 sections: 14.14, 14.15. Protect the (Food Producing) Plants !.
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supplementary (mostly) not in text, but see Chapt 14 sections: 14.14, 14.15
Natural 'enemies': 80,000diseases(viruses, bacteria, fungi, algae 30,000 species of weeds(a plant growing in the wrong place) 10,000 species of plant-eating insects
Food crop losses: ~30% world wide(>40% in developing countries) Estimated costs in US(2000): $15 billion ($4 billion to insects alone)
Pest = any organism that in some way reduces crop yields, or endangers human health, eg. malaria mosquitoes, tape worms, lice, cockroaches, rats(?) Pesticides = chemicals(?) used to control(kill, scare away) pests. Classified by 'pest', ie. Insecticide - kills insects Herbicide - kills weeds Fungicide - kills fungi
There are ~1500 'active' ingredients (down from ~2500 in 1980), in ~50,0000 different 'formulations' divided into 18 categories.
Some numbers: 1995(world): 500 billion lbs pesticides(~$7.5 billion), 80% for agriculture 2007(USA): 700 million kg(400 million as herbicides)
Many pesticides have LD50s(rats) = 1-100mg/kg.
Cons: effects of biomagnification, esp. persistents since 1945 a 30X increase in pesticide use and slight increase(31- 37%) in crop loss USA(2007) - 45,000 'poisonings’, 200 fatalities Worldwide(1995) - 1 million & 20,000
Pros: probably 'saves' ~35% of food crops yearly WHO estimates DDT has saved 25 million lives from malaria we consume ~1.5 g/day of 'natural' pesticides (49 in cabbage, 23 in lima beans); 10,000 x 'synthetics'
We're surrounded! aphid, gypsy moth, corn borer, locust, spruce budworm, potato beetle, cotton weevil ….. plus ……. lice (typhus), mosquito(malaria), mites, ticks(Rocky Mtn. fever), tse tse fly(sleeping sickness).
Most common insecticides are non-selective (broad spectrum) and rated by 'reactivity'/ rate of breakdown from persistent (bioaccumulate!) non-persistent.
Many have LD50 of 1-300mg/kg(rat) but 'bugs' are much smaller than humans
DichloroDiphenylTrichloroethane = 1st chlorinated HC
Discovered in 1938(Paul Muller, Swiss, >Nobel '48). Inexpensive, broad spectrum, 'low' toxicity = ideal.
Used extensively worldwide 1943-1965: (US -76 million kg/yr in '62) by '46 first 'problems' (resistance, bioaccumulation); Silent Spring by Rachel Carson) by 1975 banned in most developed countries.
Unreactivepersistent; fat solublebioaccumulates.
Hydrocarbon skeleton with many chlorines, eg. aldrin, chlordane, toxaphene, heptachlor, methoxychlor
DDT = first 'endocrine disruptor', eg. 3-eyed fish, 1-leg frogs, thin bird's eggs. Probably saved more lives than any other chemical; still used for malaria but at 'a cost'(birds, fish, shrimp, plankton)
Function as 'neurotoxins'(wrt. acetylcholine); broad spectrum; somewhat 'fat-soluble'; decompose in days/weeks; rarely found in foods.(LD50, rats)
Produced by plants to kill/deter insect predators; still commonly used but not 'industrial'-scale 1) Nicotine - since 1700 in France(Black Leaf 40) 2) Rotenone(tropical legumes) – used since 1850 as insecticide 3)Pyrethrum*(chrysanthemums) - Chinese in 0 AD; from Iran/Persia in 1800; commercial crop in Kenya; particularly for flying insects; degraded by air/sunlight, very low mammalian toxicity(in household aerosols); now 'synthetics',eg. permethrin, dimethrin, allethrin * distinctive odour antifeedant(repels insects) eg. citronellal, marigolds/nasturtiums in gardens
Native to Africa/Asia the oil from seeds of the neem tree have been used in India for centuries to deter(antifeedant) or kill insects, eg. locusts, aphids, cockroaches.
Azadirachtin, the major 'active ingredient, interferes with molting, reproduction,digestion and is 'non-toxic' to 'predators' and mammals. Effective against ~200 species. Somewhat unstable but looks good! Already on the shelves as Azatin/Margosan.
Organisms that feed on 'pesty' insects but 'do no harm' to the 'crop'. 1)Cane toads - introduced to Australia(1930) to control sugar-cane beetle; now 'invade' most of NE Australia
2)Lady bugs - for aphids in many parts of world
3)Bacillus thuringensis(Bt) - soil bacteria that releases a toxin that kills many insects(powder form), eg. against cotton weevil, gypsy moth; already 'resistance' is developing.
“BIOCONTROL” approach-sounds good,but………
Lady bugs introduced to “solve” the aphid and leafhopper problem in Ontario vineyards
Weed = plant in the wrong place, eg. grass in canola, mustard in potatoes, poison ivy/ragweed/dandelions in urban setting, 'baddies' in cereal crops
Eliminate how? - manually, cultivate/till(erosion), spray
Species selective or non-selective, eg. inhibit essential a.a. production or photosynthesis. Contact or systemic; often defoliants(broad leaf) Exploit: different metabolism, timing, young vs mature
? Inorganics, eg. NaCl, urea(NH3)- fertilizer/ice melter Usually 'organics' acting as 'plant hormones'
1) 2,4D (2,4-Dichlorophenoxy- acetic acid), aka Killex Systemic(broad leaf) - plant grows to death (can't get enough nutrients)
also 2,4,5T = Agent Orange(defoliant in Vietnam) and Mecoprop(MCPP)
2) Atrazine - shuts down photosynthesis Corn can deactivate, weeds do not. 'Persistent' - now 'polluting' lakes /ground water, eg. in eastern Ontario & US midwest
1) Pheromones - chemicals secreted by insects to 'send a signal' eg. mark a trail, signal alarm, attract a mate. Sex pheromones(mostly synthetic analogs) can limit reproduction by attracting males to kill/ sterilize (radiation) or to confuse. expensive; some success with gypsy moth. 2) Juvenile Hormones(and 'synthetics') - interrupt the maturation cyclecan't reproduce; expensive; some success with malarial mosquitoes & fleas. Limited application; clearly no use if caterpillar is the 'enemy' not moth. 3) Growth Hormones – for animals(natural peptides or synthetic) and plants (gibberellins)
Keep alive - use antibiotics on the factory farms; in USA 4.5 million kgs/yr used in agriculture (= 50% of annual production) Bigger(& better?) - use growth hormones for animals, plants(gibberellins) or milk(up 20% with BGH) Control/delay ripening - N2 in shipping containers to dilute ethylene buildup
Modern farming is specialized, energy intensive(13% of all energy consumption in NA), causes serious soil erosion/damage and increasing water pollution.
'New' changes: 1) crop rotations, 2) multiple crops in a field, 3) 'natural' fertilizer, 4) increasing 'biological' pest control, 5) soil and water conservation.
Organic farming: ~50% less 'non-renewable energy', ~25% more labour, ~20% less production
30% of food costs in NA are for transport, eg. $6 x106 & 3.6 x106L of fuel per year to supply NY city with California broccoli!
Insect resistance (Bt gene) Herbicide resistance (“RoundUp ready”) Virus resistance (tobaco mosaic virus) Specialty oils (less sat’d. fatty acids) Controlled ripening
corn, cotton, potato, rice
canola, soybean, cotton, squash squash
flavr savr tomato
(18 months old)
Carotenoids in (golden)rice. Disease resistance in papayas(Hawaii), bananas (Kenya) and sweet potatoes(Africa). Grapes + ‘antifreeze genes’ from salmon = ‘cool climate’ wines. ‘Kinder/gentler’ chickens (then pigs) for factory farms. New ‘drugs’ and polymers from ‘cloned’ sheep/goats raised on ‘pharms’.