Influence of potential stress factors on anthracnose development on Xanthium spinosum.
Colletotrichum orbiculare is being evaluated for use as a mycoherbicide for biological control of this weed in Australia. Moisture stress to 50% relative leaf water content before spraying with a spore suspension decreased disease development but disease on plants given the same stress up to 3 times after inoculation was not significantly different from that on unstressed controls. Simulated rainfall (15 mm) as soon as 1 h after inoculation had no effect. Exposure to 10°C for 3 or 7 d after inoculation did not significantly affect disease development after 14 d from inoculation compared with plants at 25° for 14 d, but delayed the onset of infection. Disease developed more rapidly in 3-week-old plants than in those at 5 weeks but was not affected by flowering in 5-week-old plants compared with non-flowering plants of the same age. Applications of the fungus in the field before or soon after rain should enhance its effectiveness as a mycoherbicide.