Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/29/2004
Publication Date: 6/1/2004
Citation: Abbas, H.K., Johnson, B.J., Pantone, D.J., Hines, R. 2004. Biological control and use of adjuvants against multiple seeded cocklebur (xanthium strumarium l.) in comparison with several other cocklebur types. Biocontrol Science and Technology. 14:855-860. Interpretive Summary: Multiple seeded cocklebur (MSC) is a recently discovered type of this noxious weed. Little has been known about this type of cocklebur. We did this study to determine if the fungus Alternaria helianthi can be used to control this weed with or without the wetting agents, Silwet L-77 or microemulsion of unrefined corn oil (MESUCO). The use of certain dew periods was also investigated. MSC can easily be controlled by this fungus in MESUCO or Silwet with reasonable dew period (~ 6 hrs). This information should be useful to farmers and companies that manufacture biological control agents.
Technical Abstract: Multiple seeded cocklebur (MSC) was recently found in Texas and described as a biotype having up to 25 seeds per bur, usually producing more than two seedlings. Mortality occurred on all three biotypes MSC, NCC-TX and NCC-MS with 8 hr dew periods. At 2.5 x 10**4 conidia/ml 0.2% SW and 50% microemulsion solution of unrefined corn oil (MESUCO), A. helianthi caused 60 to 75% mortality on 6 to 8 leaf stage of NCC-TX and 8 to 12 leaf stage of MSC, respectively. However, at this rate A. helianthi did not cause dramatic mortality (15% to 20%) on NCC-MS. At 5 x 10**4 conidia/ml 0.2% SW and 50% MESUCO of A. helianthi caused 100% mortality on all previous three biotypes. No mortality occurred on all three biotypes rates of 2.5 x 10**4, 5 x 10**4, and 1 x 10**5 conidia/ml H20 sprayed, to run-off with 8 hr dew periods, except 5 and 10% mortality measured at the highest rate on NCC-TX and MSC-TX plants, respectively. Alternaria helianthi caused severe damage and mortality on 8 to 12 leaf stage of MSC plants, when sprayed to run-off with a > 6 hr dew period at 2.5 x 10**4 conidia/ml. Mortality occurred on treated plants at 8 leaf stage of MSC with a 6 hr dew period but mortality increased to 100% with increase in the dew period up to 20 or 24 hr. However, fungal efficacy on MSC was enhanced when the fungal conidia were formulated in 0.2% Silwet (SW) L-77 or in 50% MESUCO. Mortality occurred on treated plants with 2.5 x 10**4 conidia/ml 0.2% SW or 50% MESUCO compared to zero percent mortality when MSC plants were sprayed with 2.5 x 10**4 conidia/ml water only and subjected to a 8 hr dew period. MSC was more sensitive to A. helianthi than both normal common cocklebur (NCC) biotypes from Texas (NCC-TX) and Mississippi (NCC-MS). Also, fungal conidia formulated in SW or MESUCO decreased the dew period required by the fungus to practical levels. These results showed that MSC was the most susceptible biotype to the biological agent A. helianthi used in these studies.