Irrigation Water 
25 
f SUMMARY 
] 1. Irrigation water is a most important factor in the dis- 
I semination of weed seeds in the irrigated sections of the west- 
[ ern states, conveying tremendous quantities of weed seeds. 
I 2. In 156 weed seed catches from three different ditches, 
a total of 81 different species of weeds were found, those most 
L frequently met with being prostrate pigvmed, tall pigweed, 
! sedge. Iambus quarters, tall marsh elder, door weed, black 
r bindweed, curled dock, and dandelion. The number of weed 
j^. seeds passing a given point on a 12-foot ditch during a period 
j of 24 hours may reach several millions. 
f 3. Our ditch banks are more to be feared than roadsides 
li as sources of weed infestation. 
, 4. The early irrigation waters are most heavily loaded 
with weed seeds. 
j 5. Many weed seeds rest during the non-irrigating season 
. in the mud of the ditch. 
I 6. Weed seeds differ in the readiness with which they 
sink or float and this is determined somewhat by the condition 
of the water surface and b}^ the manner in which the seeds 
! alight upon it. 
I 7. Some seeds float for days no matter how they strike 
i the water surface or how it is agitated; some float if laid on the 
, water carefully and the surface is not disturbed, but sink 
readily if the surface is agitated, or sink almost immediately 
if they strike the surface with some force. 
8. Ordinarily, grazing is one of the most effective and 
( economical ways of keeping weeds down along large irriga- 
tion ditches. 
f . . ' * 
! 9. In some instances, the seeding of ditch banks to brome- 
, grass (Bromus inermis) is to be encouraged. 
