None of the fumigation treatments tested have eliminated weeds. Some hand weeding 

 has been required to control deep-rooted perennials, weeds from windblown seed, and, 

 no doubt, weed seed which escaped fumigation due to imperfect application techniques. 

 Much of the effort spent in fumigation can be lost if weeds, which become established 

 in spite of the best fumigation efforts, are not removed or killed prior to their seed 

 maturation and dispersal. 



Hand-weeding time studies were made during the 1963 spring and fall fumigation 

 trials at Coeur d'Alene. A range of weed densities provided by fumigation treatments 

 were correlated with weeding time and cost. Figure 1 shows the relationship between 

 number of weeds, weeding time, and fumigant treatment for a total of four hand weedings 

 during the first growing season in the 1963 spring fumigation trials. Unfumigated beds 

 with approximately 22 weeds per square foot required nearly 400 hours of hand-weeding 

 time per acre; weeding time was below 300 hours per acre on fumigated beds. The better 

 fumigants reduced weed populations to less than 10 weeds per square foot and weeding 

 times to under 200 hours per acre. 



For seedbeds fumigated in the fall of 1963, time records were obtained for a 

 single hand weeding in late June of the following year (figure 2) . Weeding time for 

 given weed densities ran higher than those for spring fumigation because the weeds 

 were larger and greater care had to be used in removing them to keep from damaging 

 tree seedlings. Unfumigated beds, and those fumigated with Brozone at 110 pounds per 

 acre and Vapam at 40 gallons per acre (not covered by tarpaulins), had two to three 

 times as many weeds as the more effective fumigants. Weed populations were generally 

 higher in this test than in the 1963 spring tests due to the accumulation of windborne 

 seed during the fall and winter following fumigation. 



These two analyses (figures 1 and 2) indicate that, on the average, 10 fewer weeds 

 per square foot should result in a reduction of 137 to 155 hours per acre in weeding 



EFFECTS ON WEED CONTROL COSTS 



Vapam (40 Ib./acre) 



Figure 2. — Weeding time 

 and weed density 

 relationships, 196S 

 fall fumigation 

 (four blocks, June 24 

 hand weeding) . 



100 











5 



Trizone (200 Ib./acre) 



10 



15 



20 



25 



30 



35 



WEEDS (Number/square foot) 



7 



