By Bassam Bayaa, N. El-Hossein and Willie Erskine

ven for a parasite, orobanche (Orobanche crenata) is a particularly nasty weed. No known lentil varieties can withstand its attack, and it has painfully brought lentil growing to a complete halt in many Mediterranean regions.
        Early sowings are particularly at risk from this underground parasite. It attaches its specialized sucking apparatus to the root system of the lentil plant from which it then clandestinely withdraws water, minerals and assimilated nutrients, leaving the plant dry and unproductive. All this takes place before the farmer is able to see the aerial shoots of orobanche in his field.
        The tiny seeds are produced in enormous numbers in capsules, and can be spread by wind, surface water, or from field to field by equipment. They can remain viable in the soil for 12 years or more, so a severe infestation can mean an end to lentil growing for long periods.
        Even after extensive screening of lentil germplasm, ICARDA has not yet been able to identify sources of resistance to this flowering parasitic weed. Farmers in south and east Europe, North Africa and West Asia, therefore, tackle it using different practices:
• Hand weeding--a time-consuming and labor-intensive
  process
• Delayed sowing--can negatively affect straw and seed
  yields, especially in dry seasons
• Inclusion of cumin (Cuminum cyminum) in the rotation for
  its apparently adverse effects on seeds of the weed in
  the soil
        Now ICARDA has put together an integrated weed management package for testing under field conditions in collaboration with the Syrian national program. Two sites were chosen at Idlib (wet) and Tel Hadya (relatively dry).
        The package includes two sowing dates (early and normal); three cultivars--Hourani, a Syrian local large, and an early-maturing cultivar adapted to late sowing; and foliar sprays with one of three chemicals. These were imazethapyr, applied either as pre-emergence treatment at a 30 milliliters active ingredient per hectare rate, or as two post-emergence treatments, each at 15 ml ai/ha; imazaquin as two post-emergence treatments each at 7.5 ml ai/ha; or imazapic as two post-emergence treatments, each at a rate of 5 ml ai/ha. Controls were either untreated or weeded twice by hand.

        In general, orobanche infestation was higher at the wetter Idlib site than at Tel Hadya. Compared with the first sowing at Idlib and Tel Hadya, the second sowing reduced infestation by 35% and 75%, respectively, at these sites. Best results from the herbicides were from imazapic and imazethapyr. Orobanche shoots were reduced by 80% and 84%, respectively, in the first sowing and by 99% and 100% in the second sowing, at the two sites.
        These two herbicide treatments also increased the biological yield from the first sowing by 52% and 39%, and by 32% and 38% for the second sowing. This was also associated with a seed yield of between 113 and 224% from the first sowing and 181 and 113% in the second sowing over non-treated plots. Over the two seasons of trials, imazaquin was the least effective treatment.
        Not only did imazapic reduce the number of orobanche shoots, it rendered the inflorescence infertile, thereby contributing to the reduction of the parasite's seed bank in the soil.
        The herbicide sprays did not affect Phytomyza orobanchiae,one of the few natural enemies of orobanche.
        Different concentrations of the two successful herbicides are being tried out in the laboratory as seed dressings to control the pest. Since the herbicides allow an earlier sowing date--to take advantage of moisture--the trials are being repeated at field-scale at ICARDA's main station. Next step will be to try the package out with farmers with a view to transfer the techniques to lentil production areas where orobanche is a major problem.


Dr Bassam Bayaa is a Consultant Pathologist with ICARDA's Germplasm Program, Mr Naim El-Hossein is an MSc student at the University of Aleppo, and Dr Willie Erskine is Acting Assistant Director General of Research at ICARDA.