Pest and disease control

Coriander crops usually require no spraying for insect pests as it seems the strong odour of the plants acts as a deterrent. Heavy infestations of red legged earth mite at seedling emergence can affect plant survival. Bees and flies are attracted to the flowers and are most important in the pollination and seedset of the crop. Granary-type weevils can invade seed after it has been stored for more than six months and it can require fumigation prior to sale.

Fenugreek is susceptible to a wide range of insect pests including red legged earth mite, lucerne flea, cutworms, Heliothus, cowpea aphids, thrips and Rutherglen bugs. An active crop monitoring program must be employed over the life of the crop, particulary at seed-pod formation.

Today one particular disease threatens the continued wide-scale production of coriander and in particular the Moroccan type. Commonly referred to as "bacterial blight", this bacterial disease, identified as Pseudomonas syringae pv coriandricola, emerged in the early 1990s and caused destruction of seed fields. Large areas in South Australia stopped growing this crop because of the losses. The slow-bolting lines have shown high tolerance levels to this disease and production has continued to market demand. Research has not yet given us resistant plants nor chemical control methods for this disease in coriander. Tests have been developed to identify certain disease levels in seed and growers should only use seed tested as being negative for this disease.

However, seed testing negative can still carry enough infection so that when frost strikes the crop the disease emerges and multiplies and within days can waste crops. Experience has shown that frost is the main trigger for crop infestation, so production should not be undertaken in areas with regular frost occurrences. Bacterial wilt usually occurs at flowering and seed set, when seed stems seem to wilt and brown, leaving a single main stem that eventually dies. Infection and plant destruction can happen in three to five days after severe frosts. Wind, irrigation, rain and vehicle movements through crops seems to aid the spread.

Chemical control has relied on copper and Mancozeb fungicide sprays to slow the spread but these are not satisfactory. Last season a combination of these sprays with a pre-application of a liquid sterilising agent seemed to arrest the disease in some fields.

The slow-bolting /smaller seeded types seem to show the disease but unless there has been a severe frost spread seems to be slow and does not cause a great yield loss.

Another disease that must be watched is Alternaria alternata, which affects flowering and seed set but has not killed plants. It causes flowers to abort. Again, it appears seed borne. Regular fungicide applications with copper oxychloride or Mancozeb commenced before flowering seem to provide reasonable control of this disease. Septoria has also been recorded in crops.

Fenugreek seems to be reasonably free of disease but can suffer badly from powdery mildew (Erisiphe polyoni). Blight disease (Cercospera traversiana), Rhizoctania solani, Fusarium oxysporum (wilt) and Meloidogyne incognita ( root-rot) have also been recorded in this crop.

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