10 MISC. PUBLICATION 4 6, U. S. DEPT. OF AGRICULTURE 



Christie, J. R. (Division of Nematology, Bureau of Plant Industry. 1939) : 

 Weeds are sometimes useless as indicator plants. During a field survey 

 in Caroline County, Virginia, the notably susceptible weeds such as 

 amaranth and lambsquarters were not found growing, but buffalo-bur, 

 goldenrod, and ragweed predominated. 



Cunningham 1936 (51) : All of the more common weeds, e. g., lambsquarters, 

 wild mustard, purslane, ragweed, and smartweed, were found infested 

 at some time during the season. New York (Long Island). 



Fikry 1939 (64) • Weeds are attacked throughout the Nile Valley. Egypt. 



Georgia Coastal Plain Experiment Station 1935 (81): The' growth of 

 weeds for 2 successive years has shown satisfactory though not complete 

 prevention of root knot; beggarweed and Florida pursley (Richardia 

 scabra) are more resistant than crabgrass. High-quality tobacco can be 

 grown after certain weeds. 



1936 (83) : In various experimental 3-year rotations infestation on 



tobacco, the third year has averaged between 12 and 15 percent after 

 velvetbeans or native weeds (beggarweed, crabgrass, and Florida 

 pursley) compared with 2 percent after harvested peanuts or after 2 

 years of bare fallow and 45 percent after less resistant crops; 2-year 

 rotations with weeds have been unsuccessful; 3-year rotations with 

 oats and weeds were successful and practical when susceptible grasses 

 were less numerous than beggarweed and Florida pursley, but much less 

 effective where bull grass (Paspalum boscianum) and crabgrass predom- 

 inated. [See also Cassia and Gramineae.] 



■ 1938 (85) : Successful control for one tobacco crop by two or more 



successive crops of oats followed by weeds. [The Nematology report (84) 

 in the same bulletin states: "In most places in this vicinity a nearly pure 

 stand of Florida pursley will spring upon plowed ground'."] 



Le Roux and Stofberg 1935 (13?) : Infestation high in experimental plot 

 following weeds, though less than in plot following beans and tobacco. 

 Transvaal. 



Ltjxx and Mattison 1938 (14-3) : A crop of volunteer weeds reduces the root 

 knot population of the soil to the extent that a normal crop of quality 

 tobacco may be expected. Percentage of severe infestation was rela- 

 tively low on tobacco following horseweed 7 and ragweed 8 planted 

 separately as experimental crops, compared with a high percentage of 

 infestation following corn or cotton. The above weed rotations pro- 

 duce a yield and quality of tobacco superior to that following corn or 

 cotton. Following partridge-pea, "a native wild legume," tobacco 

 showed very little evidence of root knot, with relatively high yield but 

 poor quality. Lambsquarters 9 not only builds up the nematode popu- 

 lation but apparently leaves the soil in a somewhat toxic condition 

 (3-year tests). South Carolina. 



Naude 1939 (175): Weeds "heavily affected" included Amaranthus panicu- 

 latus, Atriplex spp., castor-oil plant, Chenopodium ambrosioides, mallow 

 (Malva parviflara). nightshade (Solarium nigrum), thornapple, and wild 

 tobacco. South Africa (Oudtshoorn). 



Scott, Lindsay, and Harrison 1939 (209): Root knot present on all weeds 

 and grasses in certain districts. California (San Joaquin Valley). 



Shaw 1940 (213a): Tobacco in enclosure units showed less than 10 percent 

 severe infestation following bare fallow or certain highly resistant crops, 

 75.8 percent following weeds (with crabgrass), 77.5 percent following 

 oats and weeds, and 100 percent following tobacco or other susceptible 

 crops. In field plots, tobacco showed 11 percent severe infestation 

 following peanuts, 35.5 percent following weeds, 43.5 percent following 

 oats and weeds, and 93.3 percent following tobacco (2-year averages) ; 

 in 3-year rotations, tobacco showed less than 10 percent severe infesta- 

 tion following 2 years' weeds, the same following oats and weeds after 

 peanuts, less than 25 percent following oats and weeds after corn. 45 

 percent following weeds after cotton, and 93 percent following continuous 

 tobacco (1 year's results). [North Carolina.] 



United States' Department of Agriculture, Office of Information 

 1935: "Native weeds . . . practically immune." [A misleading state- 

 ment based on a misunderstanding of results reported from the Georgia 

 Coastal Plain Experiment Station or those of Lunn and Mattison.] 



7 Erigeron canadensis, according to Mandelson (155). 



8 Ambrosia elatior (A. a r temi<iaefolia), according to Mandelson (165). 

 4 Chenopcdium album, according to Mandelson (155). 



