Northeast Region Certified Crop Adviser (NRCCA) Study Resources

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In This Section

• PO 10 Weed life cycles
• PO 11 Weed survival mechanisms
• PO 12 Common weed identification
• PO 13 Dichotomous key
• PO 14 Timing of control
• PO 15 Mechanical weed control
• PO 16 Cultural weed control
• PO 17 Biological weed control
• PO 18 Chemical weed control
• PO 19 Herbicide site of action
• PO 20 Environmental affects herbicides performance
• PO 21 Problems associated with herbicide use

Competency Area 2: Weed Management

PO 19.Chemical – Know example herbicides (product names), types of weeds they control, and weed/crop injury symptoms caused by each of the following herbicide site of action groups:
A. Growth regulators (synthetic auxins)
B. Amino acid synthesis inhibitors
C. Lipid synthesis inhibitors
D. Seedling root and shoot inhibitors
E. Photosynthesis inhibitors
F. Cell membrane disruptors
G. Pigment Inhibitors
H. Glutamine synthetase inhibitors

A. Growth regulators (synthetic auxins)
Growth regulators or synthetic auxins (GROUP 4) – act at multiple sites in plants to disrupt hormone balance and protein synthesis resulting in growth abnormalities.

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
Phenoxy acetic acids	2,4-D, MCPA, 2,4-DB	Butyrac 200
Benzoic acids	dicamba	Banvel, Clarity, Distinct, Status
Carboxylic acids	clopyralid, triclopyr	Stinger, Garlon
Injury: Corn shows onion-leafing, fused brace roots, bent and brittle stalks. Broadleaf plants show epinasty, callus tissue and leaf malformations.

B. Amino acid synthesis inhibitors
Amino acid synthesis inhibitors - act on enzymes to prevent amino acid production.

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
ALS (acetolactate synthase) inhibitors (GROUP 2)
Imidazolinones	imazethapyr, imazamox	Pursuit, Raptor
Sulfonylureas	halosulfuron, nicosulfuron, primisulfuron, rimsulfuron	Permit Accent Beacon Matrix
Triazolopyrimidines	chloransulam-methy,l flumetsulam	FirstRate, Python
EPSP synthase inhibitors (GROUP 9)
Glycines- (amino acid derivatives)	glyphosate	Roundup, Touchdown, etc.
Injury: Grass plants stunted with interveinal chlorosis or purpling.  Broadleaf plants are stunted and chlorotic or purple.

C. Lipid synthesis inhibitors
Lipid synthesis inhibitors or ACCase inhibitors (GROUP 1) - affect grasses only by preventing formation of fatty acids essential for plant lipids which are vital to integrity of cell membranes and growth.

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
Aryloxyphenoxypropionates	fluazifop quizalofop	Fusilade Assure II, Targa	grasses
Cyclohexanediones	sethoxydim clethodim	Poast Plus Select	grasses
Injury: Seen on grass plants only.  New leaf tissue chlorotic or necrotic and leaves in whorl easily are separated from the plant.

D. Seedling root and shoot inhibitors
Seedling growth inhibitors – inhibit root and/or shoot growth in developing seedlings.

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
Root inhibitors or microtubule assembly inhibitors (GROUP 3) interfere with cell division
Dinitroanilines	pendimethalin trifluralin	Prowl, Pendimax Treflan
Shoot inhibitors – interfere with lipid and protein synthesis.
Thiocarbamates or lipid synthesis inhibitors – not ACCase (GROUP 8)
Thiocarbamates	EPTC	Eptam
Acetamides or long–chain fatty acid inhibitors (GROUP 15)
Acetamides	acetochlor alachlor dimethenamid-P S-Metolachlor	Surpass, Harness, etc. Micro-Tech Outlook Dual II, Magnum, Cinch
Injury for Root Inhibitors: Stunted plants with short, thick lateral roots.  Grass shoots may be red or purple.  Broadleaf plants have swollen/cracked hypocotyls.
Injury for Shoot Inhibitors: Grasses leaf out underground, leaves do not unfurl. Broadleaf plants have crinkled or puckered leaves and/or shortened mid-vein.

E. Photosynthesis inhibitors
Photosynthesis inhibitors – bind to specific sites within plant chloroplasts and stop carbohydrate production.

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
Mobile (translocated) photosynthesis inhibitors
Photo System II – site A (GROUP 5)
Triazines	atrazine simazine prometone	AAtrex Princep Pramitol
Triazinones	hexazinone metribuzin	Velpar Sencor
Uracils	bromacil	Hyvar X
Photo System II – site A, but different binding (GROUP 7)
Ureas	linuron tebuthiuron	Lorox Spike
Nonmobile photosynthesis inhibitors
Photo System II – site B (GROUP 6)
Nitriles	bromoxynil	Buctril
Benzothiadiazoles	bentazon	Basagran
Injury for Mobile Photosynthesis Inhibitors: Symptoms occur after leaves emerge. Chlorosis of older leaf margins or tips initially. Interveinal chlorosis in broadleaf plants. Tissue will turn brown and die.
Injury for Non-mobile Photosynthesis Inhibitors: Leaves turn yellow or bronze and then turn brown and die.  Symptoms are similar to those of cell membrane disruptors although less patterned though because there is no movement.

F. Cell Membrane Disruptors
Cell membrane disrupters – are activated by sunlight to form oxygen compounds such as hydrogen peroxide which rupture plant cell membranes

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
PPO inhibitors (GROUP 14)
Diphenylethers	fomesafen lactofen	Reflex Cobra
N-phenylphthalimides	flumiclorac	Resource
Triazolinones	carfentrazone sulfentrazone	Aim Authority
Photosystem I – electron diversion (GROUP 22)
Bipyridiliums	paraquat	Gramoxone Inteon
Injury: With Gramoxone Inteo, a water soaked appearance followed by necrosis.  With the others, leaves turn yellow then bronze/brown and die.

G.Pigment inhibitors
Pigment inhibitors – prevent formation of photosynthetic pigments

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
DOXP synthase inhibitors (GROUP 13)
Isoxazolidinones	clomazone	Command
4-HPPD inhibitors (GROUP 27)
Triketones	mesotrione	Callisto
Pyrazoles	topramezone	Impact
Injury:  Plants turn white, often becoming translucent at the leaf tips.

H.Glutamine Synthetase inhibitor
Glutamine synthetase inhibitors (GROUP 10) – inhibit the enzyme that converts glutamate plus ammonia to glutamine. The accumulation of ammonia in plants destroys cell walls and directly inhibits Photosystem I and Photosystem II reactions. Theree is no accepted chemical family, however sometimes referred to as phosphorylated amino acids or amino acid derivatives –

Herbicide Family	Chemical Name(s)	Trade Name(s)	Control
See statement above	glufosinate	Liberty, Ignite, etc.
Injury: causes chlorosis and wilting within 3-5 days after application, followed by necrosis in 1-2 weeks. Translocation in plants is quite limited.