Orobanche cumana (sunflower broomrape)

O. cumana, like many other Orobanche species is listed and restricted under the phytosanitary regulations of most countries.

In Spain, late sowings (from the end of March until the beginning of April) favour the enhanced expression of resistance of sunflower to O. cumana race F irrespective of seedbank and can be therefore recommended, under irrigation and together with the use of moderately resistant sunflower hybrids, as part of an efficient strategy on the control of C. cumana (Akhtouch et al., 2013). Similarly, in Israel, resistance of the sunflower cv. Sunbred-254 to O. cumana was enhanced when sown from January onwards than when sown before January (Ish-Shalom-Gordon et al., 1994). Conversely, in Romania, Grenz et al., (2008) found that delayed sowing combined with improved water and nitrogen supply were associated with increases in parasite number that neutralised the yield-boosting effects of irrigation and fertilisation at the highest infestation level.

Trap crops could help stimulate germination of O. cumana seeds and contribute to the reduction of the soil seed bank. Species identified in pot studies as possible trap crops include Panicum virgatum (An Yu et al., 2015), various species of Sorghum and Sudan grass varieties (Antonova et al., 2015), Secale cereale (rye) (Cimmino et al., 2015), Cannabis sativa (hemp) (Yu and Ma, 2014) and Zea mays (maize) (Ma et al., 2013) but this has not been reported in the field.

The shoots of O. cumana can be hand-pulled but the benefit is limited and often too late as most of the damage will already have been done.

Bedi et al. (1994) investigated the potential of Fusarium oxysporum f. sp. orthoceras isolated from diseases inflorescences of O. cumana in Bulgaria as a potential biocontrol agent. This pathogen has been studied further and has proven to be efficacious under greenhouse conditions when formulated as wheat-kaolin granules (Shabana et al., 2003; Dor et al., 2007). A combination with F. solani (a weak pathogen of O. cumana) isolated in Israel from O. aegyptiaca was found to be synergistic providing more effective control of O. cumana than either agent alone (Dor et al., 2006).

Other potential biocontrol candidates have included Aspergillus alliaceus (Aybeke et al., 2014) and Ulocladium botrytis [Alternaria botrytis] (Müller-Stöver et al., 2005). In spite of this there are no reports of the current use of fungi for biological control in the field.

The one insect to have been extensively studied as a possible biocontrol agent is the dipteran Phyomyza orobanchia which feeds on a number of species of Orobanche (Kroschel and Klein, 1999). In one study in Russia, P. orobanchia was exploited on over 30,000 ha, involving the release of 5-600 adults per ha and was estimated to have reduced seed production by 82-88%. Studies on other species of Orobanche achieved over 90% reduction but only when repeated for 3-4 years. However, since seed production is not completely prevented, the benefits of this agent are dubious. In addition to this P. orobanchia itself is severely affected by the hymenopterous parasites Chalcidoidea and Braconidae (particularly Opius occulisus) and also by Cladosporium cladosporioides and various species of Fusarium (Horváth, 1987).

Louarn et al. (2012) have demonstrated that the arbuscular mychorrhizal fungus Rhizophagus irregularis can significantly reduce infestation of sunflower by O. cumana, by directly and indirectly reducing its germination.

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: