Orobanche cernua

Hand-weeding of emerged stems of O. cernua is often too late to prevent crop damage but may be worthwhile where infestations are still light, to prevent or reduce future infestations. The stems should immediately be removed from the field to preclude seed shed after pulling.
Trap crops may be used to promote germination of Orobanche seeds in soil, without themselves supporting parasitism, in order to deplete the seed reserve. Examples of trap crops for O. cernua include species of Sorghum, Vigna unguiculata (cowpea), Capsicum annuum (chilli), Cannabis sativa (hemp), Linum usitatissimum (linseed), Medicago sativa (lucerne), Glycine max (soybean), Cicer arietinum (chickpea) (Parker and Riches, 1993), Crotalaria juncea (sunn hemp) and Vigna radiata (mung bean) (Dhanapal and Struik, 1996). While trap crops rarely provide high levels of control, they should be considered in any integrated control approach.
Soil solarisation, based on mulching moist soil with polyethylene sheets for several weeks under solar irradiation, can provide excellent levels of control of Orobanche seeds in the upper soil layers where temperatures are high enough (Jacobsohn et al., 1980) and this has been confirmed in a number of studies involving O. cernua (Parker and Riches, 1993;Meti and Hosmani, 1994).
Host-Plant Resistance
There has been little progress on enhancing resistance in crops attacked by O. cernua however, resistant varieties of Helianthus annuus (sunflower) has been developed for the closely related species O. cumana. Some variation in the susceptibility towards O. cernua has been reported in both Solanum lycopersicum (tomato) and Nicotiana tabacum (tobacco) (Alonso, 1998;Cubero, 1991;Parker and Riches, 1993;Cubero, 1994), but there has been little evidence that resistance in these crops is proving of practical usefulness. Nagarajan and Reddy (2001) screened over 100 varieties of tobacco and failed to find any that were resistant.
A mutant of tomato, SI-ORT1, produced by fast-neutron mutagenesis from the standard processing variety M82 shows resistance to O.cernua and related species characterised by its inability to secrete strigolactones. This character is controlled by a single recessive gene and is of potential value for further breeding work (Dor et al., 2010). Subsequently, the same group used ethyl methane sulfonate to cause more refined point mutations in M82 tomato and have 8 lines highly resistant to Orobanche species, again lacking strigolactone secretion. Although these yield equally with M82, there are problems of fruit quality (Dor et al., 2013).
Induced Resistance
A recent development has been the demonstration of induced resistance in Helianthus annuus (sunflower) resulting from seed treatment with the benzothiadiazole compound known as 'BTH'. This treatment greatly reduces subsequent attack by O. cernua, apparently due to the enhanced production of the phytoalexin scopoletin and/or hydrogen peroxide in the crop roots (Sauerborn et al., 2002).
Chemical Control
In Iran, sulfosulforon directed to the soil 20 days after transplanting proved partially selective for control of O. cernua and of other weeds in tomato (Bazgir et al., 2013). In India, Prabhakaran et al. (2009) achieved good control with post emergence application of imazethapyr 55 days after transplanting. For N. tabacum, the use of glyphosate applying at 40 and 60 days after planting has been reported to reduce the levels of O. cernua (Jinga et al., 2006).
More recently it has also been shown that post-emergence application of maleic hydrazide can provide selective control of O. aegyptiaca in S. lycopersicum (Herschenhorn et al., 2015). Dor et al. (2015) report on the use of chemical mutagenesis to create a tomato line HRT-1 that is resistant to several groups of ALS inhibiting herbicides, including imidazolinones. Thus imazapic and imazapyr can be safely used to cause complete suppression of Orobanche seeds Field tests at very high doses of herbicide have caused no yield reduction.