Effect of plant stage, <Emphasis Type="Italic">Colletotrichum truncatum</Emphasis> dose,and use of herbicide on control of <Emphasis Type="Italic">Matricaria perforata</Emphasis>

Colletotrichum truncatum (Ct) was examined in a tank mix with the herbicide 2,4-D, clopyralid plus MCPA (Caurtail M^®), or metribuzin (Sencor^®) for control of scentless chamomile at 8- (younger) and 11-leaf stages (older) under controlled conditions. In initial trials, Ct at 7 × 10⁶ spores/ml (200 l/ha) reduced the fresh weight of scentless chamomile only slightly. However, its combinations with herbicides improved the efficacy variably depending on the herbicide used and stage of the weeds. Ct plus 2,4-D reduced the fresh weight by about 50% at both leaf stages of scentless chamomile when compared to untreated controls but no plants were killed. The fungus plus Curtail M consistently killed younger but not older plants, and the efficacy was substantially greater than that of the herbicide alone. The herbicide Sencor was highly effective on younger plants, and adding Ct did not achieve additional benefits. On older plants, however, Ct plus Sencor was substantially more effective than the herbicide alone, causing 76% fresh-weight reduction when compared to controls and killing 9 out of 16 older plants in four trials. Sencor applied alone reduced the fresh weight of older plants by 65%, but no plants were killed. Tested at doses ranging from 2 × 10⁶ to 20 × 10⁶ spores/ml, Ct plus Curtail M was most effective at the highest fungal inoculum dose, consistently killing younger but not older plants. In comparison, Ct at a medium dose (7 × 10⁶ spores/ml) plus Sencor killed the majority of older chamomile plants (7 out of 12), whereas the herbicide alone did not cause plant mortality. Further increasing fungal inoculum dose from this medium level did not enhance the weed control by Ct plus Sencor.