Cause Alternaria dauci and other species have been reported on coriander, including in Florida, Hawaii and in Canada. Alternaria species can be seedborne. Once this fungus is introduced to a field, it survives on non-decomposed plant debris. Spread occurs with wind, water (wind-driven rain, dew drips, irrigation), and by mechanical means (tools or workers).
Symptoms Leaf spots start as small, round brown spots with white centers which can coalesce and blight the leaves.
Cultural control
- Use Alternaria-free seed or hot-water treated seed (127°F for 30 minutes).
- Rotate with unrelated crops, avoid umbelliferous plants. Four (4) year rotations are recommended for diseased fields; 2 to 3 years for nondiseased fields.
- Incorporate crop debris to speed up decomposition.
- Minimize leaf wetness periods.
Chemical control
- Badge SC (Group M1) at 0.75 to 1.5 pints/A on 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
- Dithane F-45 Rainshield (SLN OR-090016, SLN WA-220008) (Group M3) at 1.5 quart/A or Roper DF Rainshield (SLN OR-130003, SLN WA-1300003) at 2 lb/A on 7- to 10-day intervals is labeled for Alternaria leaf spot for Oregon and Washington seed crops only. 24-hr reentry.
- Fontelis (Group 7) at 14 to 24 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7). Preharvest interval is 3 days. 12-hr reentry.
- Topaz (Group 3) at 3 to 4 fl oz/A on 14-day intervals. Preharvest interval is 14 days. 12-hr reentry.
Biological control
- Prestop WG. 4-hr reentry. O
- Stargus at 0.5 to 4 quarts/A on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
References Poudel, B., and Zhang, S. 2018. First report of Alternaria leaf spot of cilantro (Coriandrum sativum) caused by Alternaria dauci in the United States. Plant Dis. 102(4):822-822), https://doi-org.oregonstate.idm.oclc.org/10.1094/PDIS-08-17-1297-PDN.
UMass Extension. Hot water treatment of seeds. At https://Ag.umass.edu/vegetable/news/hot-water-treatment-of-seeds (accessed 5 Dec 2023).