Herbicide Activity and Selectivity

Question 1

On which type of weeds are contact herbicides most effective?

Answer 1

Annual weeds are more likely to be controlled by contact herbicides. Biennials and perennials
may be controlled by contact herbicides if they are sprayed in the seedling stage. Complete
coverage is required for best results when applying contact herbicides to any type of weeds.

Question 2

Are most herbicides contact or translocated?

Answer 2

translocated

Question 3

How are translocated herbicides able to control weeds that regrow from underground parts such
as rhizomes or tubers?

Answer 3

In translocated herbicides, the herbicide enters the plant through the foliage or roots and is
transported to other parts of the plant.

Question 4

Why do contact herbicides sometimes fail to kill, especially biannual and perennial weeds?

Answer 4

contact herbicides never reach these areas of

the plant, and the plant can resprout at a later date.

Question 5

Describe the basic way growth regulators work to kill plants (mode of action).

Answer 5

Growth regulators change the hormone balance and protein synthesis in plants, thus causing the
plant to grow abnormally.

Question 6

Roundup (glyphosate) is in which major mode-of-action group?

Answer 6

Amino acid synthesis inhibitors.

Question 7

What property of 2,4-D makes it dangerous to apply on hot days?

Answer 7

2,4-D has a high volatility. On hot days, the chemical can turn into vapor and damage nearby
sensitive vegetation.

Question 8

Casoron is in which major mode-of-action group?

Answer 8

Seedling growth inhibitor.

Question 9

Name three active ingredients that are among those most likely to leach into groundwater.

Answer 9

tebuthiuron, picloram, bromacil

Question 10

When an herbicide kills one species of plant while not affecting another species, it is called
_________.

Answer 10

Selective

Question 11

Name four factors that might affect herbicide selectivity.

Answer 11

Application rate, formulation, timing, and placement.

Question 12

What is the general mode of action for contact herbicides?

Answer 12

Disruption of cell membranes

Question 13

What are 9 common modes of action of herbicides?

Answer 13

growth regulators, lipid inhibitors, seedling growth inhibitors, photosynthesis inhibitors, cell membrane disruptors, pigment inhibitors, plant growth regulators

Question 14

Complete the following information for Fosamine: Trade name___
Application ____
Symptomology___

Answer 14

Fosamine, or Krenite (trade name), is a postemergence pesticide that causes plants to fail to refoliate in the spring following application.

Question 15

Name 4 commonly used Rights-of-Way premixed products and their trade names and applications.

Answer 15

Bromacil + diuron (Krovar IDF, preemergence)
2,4-D + triclopyr (Crossbow, postemergence)
Chlorsulfuron + sulfometuron methyl (Landmark, pre/post emergence)
Diuron + imazapyr (Sahara, pre/post emergence

Question 16

Broadleaf plants are tolerant of ____, a group of herbicides effective against most annual and perennial grasses.

Answer 16

Lipid inhibitors

Question 17

What are some factors of plant structure that may limit effectiveness of herbicides.

Answer 17

Leaf angle, size, hairiness, and thickness of wax and cuticle are structural factors to consider. Plants with upright leaves, hairy leaves, or hard-to-wet (waxy) leaves are less likely to retain sprays

Question 18

What’s the trade name of right-of-way premix Bromacil + diuron?

Answer 18

Krovar IDF (preemergence)

Question 19

What’s the trade name of right-of-way premix 2,4D + triclopyr?

Answer 19

Crossbow (postemergence)

Question 20

What’s the trade name of right-of-way premix Chlorsulfuron + sulfometuron methyl?

Answer 20

Landmark (pre/postemergence)

Question 21

What’s the trade name of right-of-way premix Diuron + imazapyr?

Answer 21

Sahara (pre/postemergence)