The effects of Pseudomonas putida ATH2-1RI/9 and Acidovorax delafieldii ATH2-2RS/1 on rhizosphere colonization, cyanide production, and growth of velvetleaf and corn was examined. When formulated in alginate beads and inoculated onto velvetleaf and corn plants (10(9) CFU/plant), only P. putida ATH2-1RI/9 consistently reduced velvetleaf growth. Neither isolate inhibited corn growth. Interestingly the levels of P. putida ATH2-IRl/9 in the velvetleaf rhizosphere were 1000-fold higher (7 x 10(7) CFU/g root) than the A. delafieldii ATH2-2RS/1 Populations. Cyanide (53-68 mM/g, root) was recovered from the P. putida ATH2-1RI/9-inoculated velvetleaf plants. In contrast both A. delafieldii ATH2-2RS/1 and P. putida ATH2-IRI/9 colonized the corn rhizosphere to the same extent (1-5 x 10(7) CFU/g, root), producing 1 mM and 14 mM/g root respectively. These results suggest that bacterial C, formulation methods can influence the effectiveness of deleterious rhizobacteria in reducing weed growth.