Lecture 13 - Herbicide Uptake and Translocation

Question 1

how do herbicides work

Answer 1

1. penetrate waxy leaf or root hair
2. move through watery space around the cell
3. enter cell by passing through oily membrane
4. reach the target site
5. inhibit the target

Question 2

what is uptake and translocation affected by

Answer 2

• the physiochemical properties of the herbicide (lipophilic or hydrophilic)
• weed biology
• environmental factors prior to and following application

Question 3

foliar uptake

Answer 3

herbicide applied to the shoots that need to bypass certain barriers to entry into the plant

Question 4

barriers to herbicide penetration into the plant

Answer 4

1. surface roughness of leaves (trichomes)
2. epicuticular waxes (cuticle)
3. Cell wall
4. cell membrane

Question 5

herbicides move through cuticle by _______

Answer 5

diffusion

Question 6

the cuticle is ____ permeable if plant is under stress, but ____ permeable to lipid soluble comounds

Answer 6

less, more

Question 7

t/f: the cuticle is very hydrophobic and very lipophilic

Answer 7

t

Question 8

herbicides move through cell wall via ______

Answer 8

diffusion

Question 9

lipophobic compounds diffuse _______ through cuticle and _____ through cell wall

Answer 9

slowly, rapidly

Question 10

hydrophobic compounds diffuse _______ through the cuticle and __________ through the cell wall

Answer 10

quickly, slowly

Question 11

what is the most difficult uptake barrier to get through and why

Answer 11

the cell membrane, because it requires active transport to move herbicide through

Question 12

how do roots take up herbicides

Answer 12

move into plant through roots or hypocotyl of emerging seedling by mass flow with water

Question 13

barriers to root uptake

Answer 13

1. casparian strip
2. cell membrane (active transport needed)

Question 14

ambimobile

Answer 14

move in either phloem or xylem

Question 15

immobile

Answer 15

very lipophilic herbicides that are unable to be translocated (contact herbicides)

Question 16

factors affecting uptake and translocation of herbicides

Answer 16

• soil pH can affect root uptake
• environmental conditions affect foliar absorption

Question 17

why does pH affect root uptake

Answer 17

it can affect the water solubility (ex: sulfentrazone is more soluble at high pH)

Question 18

herbicides are _____ likely to have control in acidic soils

Answer 18

less

Question 19

how does environmental conditions affect foliar absorbtion

Answer 19

adequate temp and moisture optimize plant growth, metabolic pathways are active, and sugar is translocated from source to sink