1. Ed Peachey and Chal Landgren, OSU
CHRISTMAS TREE WEED
IDENTIFICATION AND
CONTROL

2. Outline for today
§ 3:45-Weed biology and implications for
control
§ 4:00 Weed ID
ú 1st step to successful control
§ 4:15 Herbicides: site of action and efficacy
§ 4:45 Sprayer calibration
§ 5:00 Finding weed control info on the web

3. Weed Biology and Control

4. Weed Seedbanks
(ie seeds living in the soil)
Source: vric.ucdavis.edu/issues/vegnotes-tomato/weedseed.gif

5. Weed seed predation videos

6. Weed Seed Lifespan in Soil
§ Many seeds are shorter lived if on the soil
surface
ú Seed predation
ú Desiccation
§ Grass weeds 1-3 yr seed survival
§ Broadleaved 3-7 yr seed survival

7. Depth of Emergence
§ Typically ½ to ¾ inch
§ Occasionally up to 2 inches for large seeds
§ Many seeds may germinate but not
emerge=fatal germination

8. Seed dormancy
Seasonal periodicity of germination

9. Factors that influence germination
and weed shifts
§ Water
§ Temperature
§ Oxygen
ú Tillage provides oxygen to seeds
§ Light
ú Light flash during tillage may cause germination
ú Weeds sense light quality changes caused by
§ Proximity to surface
§ Moves seed from deep in the soil where it is preserved
§

10. Herbicides and weed seeds
§ Herbicides generally do not effect weed
seeds
§ Only seeds that are germinating
§ Exception is fumigant metam

11. Successful use of Preemergence
Herbicides
§ Apply before seeds germinate
§ Activate
§ Protect the barrier

12. Preemergence Herbicides
Rainfall/tillage
½ to 1
inch thick
Too much
rain/ water/or
tillage

13. Seedbanks are a black box
What goes in, might come out

14. Plant Characteristics + Selection Pressure
= Weed Shifts
Plant Characteristics Selection pressure or
methods of control
Growth habit 1. Prevention
ú Perennial
ú Annual 2. Cultural
ú Biennial
3. Chemical
Plant family
Grass, broadleaf, sedge 4. Mechanical
Season of emergence or 5. Biological
growth
Root system: tap root vs
surface roots
Seed dispersal: short vs long
distance

16. Weed Identification
First step to effective control

17. Dirty Dozen
Horseweed (marestail) 1
Annual Lettuce, prickly 2
broadleaves Sowthistle, annual 3
Northern willow herb 4
Bindweed, field 5
Perennial
Thistle, Canada 6
broadleaves
Blackberry
Biennials Queen Anne’s lace 7
Barnyardgrass 8
Annual Grasses Witchgrass 9
Bentgrass 10
Perennial grasses Fescue, rattail 11