1. Original Power Point Created by Danny Silva
Weeds: Friends or Foes?
Original Power Point Created by
Danny Silva
Modified by the GA Agricultural Education Curriculum Office
July 2002

2. Weeds: Benefits
Weeds are controversial plants that are neither all good nor all bad, depending on one’s outlook.
1. Many weeds can be enjoyed for their attractive flowers and interesting seed pods.
2. Weeds quickly grow
to cover unsightly scars
on the landscape made
by man or by nature.

3. Harmful Weeds
1. Weeds reduce crop yield and increase the cost of production.
2. Some weeds are poisonous and others may cause allergies.

4. Don’t Let Weeds Ruin Your Day!
For a farmer or gardener to do an effective job of controlling troublesome weeds, exact identification of the weed is important.
The selection of the most effective control method depends on one’s ability to properly identify the problem species.

5. Identification Is The Key
The purpose of a weed collection is to help the person making the collection more adept at identifying weeds:
1. A simple way to begin identifying common weeds is to compare your specimens against drawings and colored photographs from references.

6. Identification Is The Key (cont.)
a. The use of weed keys, such as those found in field guides and references, do require a specialized knowledge of weeds.
b. Specialists like farm advisors, agricultural commissioners, or college/university faculty can be contacted for help with identifying plant species.

7. Weed Classification
II. The classification of weeds is achieved by grouping together those weeds whose similarities are greater than their differences.
a. Most weeds can be placed into two convenient groups: narrow-leafed or broad-leafed.
1) Narrow-leafed weeds include: grasses, sedges, rushes and cattails. All have parallel veins running throughout their leaves.
2) Broad-leafed weeds include: most others, such as mustards, dock, pigweed, purslane, and morning glory. All have a net-like pattern of veins running throughout the leaves.

8. Weed Classification (cont.)
b. Like other plants, weeds have varying types of life cycles:
1) Annual weeds live for one year or less.
2) Biannual weeds live for two growing seasons.
3) Perennial weeds live for 3 or more years.

9. What’s Your Name?
c. Weeds have unique physical features which can be used for identification.
1) Flowers and certain sexual reproductive organs vary among species:
a) Flowers can appear singly or as a compound inflorescence.
b) Different names such as catkin, head, panicle, raceme, spike, and umbel describe how flowers are arranged in an inflorescence.
c) The arrangement, shape, vein patterns, or presence of hairs/spines on leaves may vary between species.

10. What’s Your Name? (cont.)
d) Stem variations such as rhizomes, stolons, and tubers are helpful in identification.
e) Taproots of the broad-leafed weeds differentiate them from the fibrous roots of grasses.
f) The fruits and seeds of weeds are all unique in their shape, size, markings, and color.

11. The Cotyledon Stage
III. It is especially helpful to identify weeds while they are in the cotyledon stage because:
a. The weed can be controlled before it competes with the crops.
b. Control measures are more effective and less costly when the weeds are treated during this immature stage of their life cycle.

12. A Chance To Practice
IV. The following 25 slides are examples of several common weeds:
The first line is the common name.
The second line is the scientific name.
The third line gives the life cycle.
The fourth line is the growing season.

13. Annual Bluegrass
Poa Annua
Annual
Cool season

14. Bermuda Grass
Cynodon dactylon
Perennial
Dormant in
the cool season

15. Bristly Oxtongue
Picris echioides
Biennial

16. Broadleaf Plantain
Plantago major
Perennial

17. Bur Clover
Medicago
polymorpha
Annual
Cool season

18. Cheeseweed or
Mallow
Malva parviflora
Biennel

19. Common Goundsel
Senecio vulgaris
Annual
Cool season

20. Crabgrass
Digitaria ischaemum
Annual
Warm season

21. Cudweed or
Cotton Batting
Gnaphalium chilense
Biennial

22. Curly Dock
Rumex crispus
Perennial

23. Dandelion
Taraxacum officinale
Perennial

24. Fennel
Foeniculum vulgare
Perennial

25. Filaree
Erodium spp.
Annual
Cool season

26. Knotweed
Polygonum aviculare
Annual
Warm season

27. Lambsquarters
Chenopodium album
Annual
Warm season

28. Narrowleaf Plantain
Plantago lanceolata
Perennial

29. Oxalis
Oxalis spp.
Perennial

30. Petty Spurge
Euphorbia peplus
Annual
Cool season

31. Prostrate Spurge
Euphorbia maculata
Annual
Warm season

32. Purslane
Portulaca oleraceae
Annual
Warm season

33. Scarlet Pimpernel
Anagallis arvensis
Annual
Cool season

34. Shepherd’s Purse
Capsella bursa-paston’s
Annual
Cool Season

35. Sow Thistle
Sonchus oleraceus
Annual
Cool season

36. Yellow Mustard
Brassica species
Annual
Cool season

37. Yellow Nutsedge
Cyperus esculentus
Perennial