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Adding surfactants to pesticides reduces the surface tensions of the spray droplets and ultimately enhances the contact of the pesticide active ingredient with the surface of the plant cuticle-Hydrophilic molecules penetrate best during warm humid conditions-Hydrophobic molecules penetrate best during dry conditions-Final barrier to chemicals entering the living cells of plant leaves is the plasmalemmaRoot uptake-Chemicals dissolved in soil water can diffuse readily into the spaces between root epidermal and cortical cells-Some debate on next steps of how water or solutes cross the endodermis (the next barrier)-After this, the chemical is either transferred through the plant by phloem or xylemUptake through stem-Water-soluble chemicals must be injected directly into the xylem or water-carrying tissues of the stem with devices that can mechanically penetrate the bark-Oil soluble chemicals can penetrate the woody stem if applied to the bark as a highly concentrated spray (may not move readily through the bark, but may move through lenticels, pores, or natural breaks in the bark)
Symplastic movement-Main function of the phloem is the movement of sugars from sites of photosynthesis to sites of storage or active growth (direction most often downward except during periods ofvery rapid shoot growth)-Symplast is “total mass of living cells in the plant”-Symplastic pesticides are moved from cell-to-cell via the interconnecting plasmodesmata-These chemicals are often toxic to plant routes (due to movement in phloem)-First visible effects are on new growth areasApoplastic movement-Apoplast is “non-living cell wall continuum that surrounds the symplast”-Main function of xylem is the upward movement of water and dissolved ions from the roots to the leaves-Toxic symptoms of xylem-mobile pesticides are first seen in leaf margins (where rate of water loss is greatest)Animals as Target SystemsOral consumption-Can be formulated as pesticide treated food or as a growing plant that has been treated with insecticide to make it toxic-Rodenticides, avicides, and mammalian poisons are usually formulated as baits (b/c of their lack of selectivity, the must be placed selectively to avoid non-target exposureSkin penetration-Ex. Contact insecticide that is sprayed on insect itself, or on a surface that the insect mustmove on in which it’ll pick up a lethal dose of pesticide-Insect cuticles are very similar to plant cuticles (waxy layer that has a main purpose of not letting the organism desiccate)-Skin of mammals is more easily penetrated by oleophobic pesticides and hair follicle is an additional route of penetrationFungi as Target SystemsProtectant fungicides-Most fungicides are surface protectants (coating the surface to prevent spore germination or pathogen growth)-Multi-site activity and are toxic at many different sites of action (& non-specific)-Often selectively toxic by virtue of location, not b/c of a unique sensitivity of the fungal target