Midterm 2

Question 1

What is the difference between theory and application when referring to cultural practices and cultural weed control?

Answer 1

Theory is the options and techniques for management, application is the manipulation of cropping practices to suppress weeds and promote desired plant growth.

Question 2

Give several techniques that are part of cultural weed control?

Answer 2

Sanitation, planting and harvesting dates, crop rotation, soil solarization.

Question 3

Define mechanical weed control

Answer 3

Use of a physical activity or barrier to remove or inhibit the growth of weeds.

Question 4

List several examples of mechanical weed control and how they work.

Answer 4

hand-pulling, mowing, mulching, tillage, and thermal methods. They work by removing/damaging the plant, removing access to sunlight.

Question 5

What is the difference between cultivation and tillage?

Answer 5

Cultivation mixes soil post planting, tillage breaks soil up and disturbs it.

Question 6

What are some advantages/disadvantages of mechanical weed control?

Answer 6

Advantages: Herbicide use reduced, can be highly selective or non selective, effective on herbicide-resistant weeds.
Disadvantages: May affect soil OM, erosion, and compaction (tillage), less flexibility since effectiveness depends on timing, often slow or inefficient, can damage crops.

Question 7

Explain primary and secondary tillage.

Answer 7

Primary: breaking up the soil. Secondary: process of burying, cutting up, pulling up weeds.

Question 8

What are the optimum conditions for tillage and why?

Answer 8

Younger weeds = weaker.
Dry and level soil = effective equipment operation.
Warm temps, wind, sunshine = less chance of disturbed weed reestablishment.

Question 9

Define biological control.

Answer 9

Use of naturally occurring organisms to maintain a target weed’s population at a lower density than would naturally occur.

Question 10

List different agents used in biological control.

Answer 10

Insects, pathogens, grazing animals

Question 11

What are some of the challenges/disadvantages with biological control?

Answer 11

BC must self disperse, have the same life cycle as weed, survive in a new environment, be raised in captivity, and cannot be recalled.

Question 12

What are the ideal properties of an herbicide?

Answer 12

Easy to apply, works in small amounts, can be applied in many different ways, not cancer causing, high selectivity, low mammal toxicity.

Question 13

What are some advantages/disadvantages to herbicides?

Answer 13

Advantages: Can control weeds when nothing else is possible/works effectively, costs less than manual weeding, can control weeds before emergence or well into the season.
Disadvantages: Requires licensing, training, technical knowledge, health risks to humans and environment, injury to off target plants, eg crops, development of herbicide resistance.

Question 14

What is the a.i. and how does it compare to inerts in chemical applications?

Answer 14

Active ingredient, toxicity to target plants, inerts have little to no effect on target plants.

Question 15

List examples of organic weed control.

Answer 15

Biodegradable mulch, mowing, livestock grazing, handweeding or mechanical weeding, flame, heat, or electrical methods.

Question 16

Explain different herbicide classifications and the different examples of these.

Answer 16

Pre-emergence: After planting, before crop emergence.
Post-emergence: After crop/weed emergence.
Broadcast: Overlapping nozzles on boom, full field sprayed.
Band: Strip application centered over crop row.
Spot treatment: To save money in situations where only specific areas need to be sprayed.
Selectivity: Ability for an herbicide to kill one plant and not others. Selectivity varies between products.

Question 17

What is carbon seeding and how does it work?

Answer 17

Slurry of activated carbon and water is applied over the seed, then a non-selective herbicide is applied over seedbed. Carbon protects crop seed from herbicide, all other seeds are defenseless.

Question 18

Explain how systemic herbicides work versus contacts

Answer 18

Contact: kill tissue on contact, do not move within plant. Need good coverage.
Systemic: Moves within plant via symplast, apoplast, or both.

Question 19

Define Herbicide persistence

Answer 19

Half life of a herbicide, too much limits crop rotation or results in crop injury.

Question 20

What is the mode of action and what is site of action?

Answer 20

Mode of action is the complete sequence of events of how a herbicide affects a target plant,
site of action is the major effects that an herbicide has.

Question 21

List all 8 sites of action and associated groups

Answer 21

Inhibitors of Lipid Synthesis (Group 1)
Inhibitors of Amino Acid Synthesis (Groups 2 and 9)
Growth Regulators (Groups 4 and 19)
Photosynthesis Inhibitors (Groups 5, 6 and 7)
Pigment Inhibitors (Groups 12, 13 and 27)
Cell Membrane Disruptors (Groups 14 and 22)
Root and Shoot Growth Inhibitors (Groups 3, 8, 15 and 16)
Undefined (Group 17)

Question 22

What is herbicide metabolism?

Answer 22

Degradation/molecular modification of an herbicide into a non-toxic form.

Question 23

Explain/draw the action of Herbicide Metabolism in terms of Phase 1, 2, 3a, 3b, 3c.

Answer 23

Phase 1. Metabolism via oxidation, reduction or hydrolysis.
Phase 2. Conjugation to glucose, glutathione or amino acid.
Phase 3a. Transport to a vacuole or cell wall
Phase 3b. Further conjugation
Phase 3c. Formation of insoluble salts

Question 24

How do different soil types impact how herbicides interact with soil colloids?

Answer 24

Sandier soils have a lower OM and a lower CEC, which means more of the herbicide will bind with soil colloids and less herbicide will be available in the soil solution. Vice versa with more clayey soils.

Question 25

Draw the 7 different fates (8 if you include plant uptake) of herbicides applied to soil.

Answer 25

Plant uptake, volatilization, photodecomposition, runoff, adsorption, leaching, chemical degradation, microbial degradation.