Dissipation of metham-sodium from soil and its effect on the control of Orobanche aegyptiaca

The effect of metham-sodium on Orobanche aegyptiaca Pers. was tested in the laboratory and in soil columns. The laboratory experiment was carried out on O. aegyptiaca seeds placed in Petri dishes and germinated with GR₂₄, a synthetic strigol analogue. In soil columns, metham-sodium was applied by application of the chemical through the irrigation water to three different soils and its dissipation determined in three soil layers by gas chromatography, by a lettuce bio-assay to check the herbicide's phytotoxicity, and with a flax bioassay to check its effect on O. aegyptiaca. Results of the germination experiments showed an exponential decrease in O. aegyptiaca germination, parallel with the increase of metham-sodium concentration, with an average effective concentration (EC₅₀) of 18 mg L^?1. In a soil column, methylisothiocyanate (MIT, the metham active product) rapidly disappeared from the upper soil level (0–10 cm) within 24 h. Seven days after application only traces of MIT remained in all soil layers in all soils, except for the sandy Rehovot soil that contained low concentrations in the lower soil layer (20–30 cm). Flax bioassay confirmed the chemical analysis, showing that O. aegyptiaca tubercles developed only on plants grown in the upper soil layer of all three soils.     

The effects of flax (Linum usitatissimum L.) and other crops as trap and catch crops for control of Egyptian broomrape (Orobanche aegyptiaca Pers.)*

Growing trap and catch crops to decrease infestation of Egyptian broomrape (Orobanche aegyptiaca Pers.) was tested in a 2-year field experiment supported by two pot experiments. Growing flax (Linum usitatissimum L.) in two successive winter seasons or one summer cropping with mung beans (Phaseolus aureus Roxbg.) reduced early infestation of the parasite and significantly increased tomato (Lycopersicum esculentum Mill.) vigour and production. However, the efficacy of using trap and catch crops for broomrape control in a heavily infested field was limited. Orobanche aegyptiaca attacked clover (Trifolium alexandrinum L.), flax and mung bean and developed inflorescences. Various sources of the parasite showed different degrees of virulence to flax, from heavy attack and severe damage, to sparse attachment with no production of flowering shoots. The virulent subspecies attacked flax all year round, causing severe damage. Vetch (Vicia saliva L.) var. Sadot was not parasitized by O. aegyptiaca. Effets du lin (Linum usitatissimum L.)et d'autres plantes cultivées comme plantes pièges et hôtes pour lutter contre l'orobanche égyptienne (Orobanche aegyptiaca Pers.) L'utilisation de plantes cultivées comme pièges et hôtes pour diminuer l'infestation par l'orobanche égyptienne (Orobanche aegyptiaca Pers.) a fait l'objet d'une expérimentation au champ sur deux ans ainsi que de deux expériences en pots. Si du lin (Linum usitatissimum L.) était cultivé sur deux saisons hivernales successives ou lors d'une saison estivale avec de l'ambérique (Phaseolus aureus Roxbg.), l'infestation précoce de la tomate (Lycopersicum esculentum Mill.) par le parasite était réduite, et sa vigueur ainsi que sa production étaient significativement augmentées. Cependant, l'efficacité des plantes cultivées pièges et hôtes pour lutter contre l'orobanche égyptienne dans des champs fortement infestés était limitée. Orobanche aegyptiaca attaquait le trèfle (Trifolium alexandrinum L.), le lin et l'ambérique, et développait des inflorescences. Différentes sources du parasite montraient des degrés variés de virulence à l'égard du lin, allant d'attaques importantes qui occasionnaient de sévères dommages, jusqu'à des infestations éparses qui ne produisaient pas de tiges florales. Les espèces virulentes attaquaient le lin tout au long de l'année et causaient des dommages importants. La vesce (Vicia sauva L.) variété Sadot n'était pas parasitée par O. aegyptiaca. Saat-Lein (Linum usitatissimum L.) und andere Kulturen als Fangpflanzen und Zwischenfrüchte zur Bekämpfung von Orobanche aegyptica Pers. In einem 2 ährigen Freiland- und 2 Gefäßversuchen wurden Fangpflanzen und Zwischenfrüchte zur Minderung der Verunkrautung mit Orobanche aegyptica untersucht. Nach dem Anbau von Saat-Lein (Linum usitatissimum L.) in 2 aufeinanderfolgenden Wintern oder einer Sommerkultur der Mungo-Bohne (Phaseolus aureus Roxbg.) war bei der Tomate (Lycopersicum esculentum Mill.) der frühe Befall durch den Parasiten herabgesetzt und Wachstum und Ertrag signifikant erhöht. Die Wirksamkeit des Anbaus von Fangpflanzen und Zwischenfrüchten zur Bekämpfung der Sommerwurz war jedoch auf stark verseuchten Feldern begrenzt. Orobanche aegyptica befiel Trifolium alexandrinum L., Saat-Lein und Mungo-Bohne und entwickelte Blüten. Die Virulenz verschiedener Herkünfte des Parasiten variierte von schwerem Befall und starkem Schaden bis schwachem Befall ohne Blütenbildung. Die virulente Unterart befiel den Lein das ganze Jahr über und führte zu schwerem Schaden. Die Sorte ‘Sadot’ der Saat-Wicke (Vicia sativa L.) wurde von O. aegyptica nicht befallen.     

Orobanche aegyptiaca control in tomato fields with sulfonylurea herbicides

Field experiments were conducted from 1994 to 1997 at two locations to study the effectiveness of chlorsulfuron and triasulfuron applied through different irrigation methods (chemigation) for control of Orobanche aegyptiaca Pers. in tomato ( Lycopersicon esculentum Mill). Three split applications of chlorsulfuron at 2.5 g a.i. ha⁻¹ and of triasulfuron at 7.5 g a.i. ha⁻¹, through conventional sprinkler irrigation systems, 10–14 days apart followed immediately by sprinkling with water, controlled O. aegyptiaca by about 90% and 80% and increased crop yield 25–47% and 30%, respectively, without any crop injury symptoms. Repeated applications of the same herbicides at half rates resulted in slightly higher O. aegyptiaca control and crop yield than only one herbicide application at double rate. Chemigation by the sprinkler systems (microsprinklers, 60 m³ ha⁻¹) slightly increased the herbicide efficiency as compared with the high volume spray (800 m³ ha⁻¹). O. aegyptiaca control from sulfonylureas applied by drip chemigation was poor, as this probably requires very accurate timing and the herbicide distribution in the soil was not uniform.