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Field and laboratory studies were conducted from 1993 to 1997 to determine the feasibility of controlling nodding broomrape in sunflower by treating crop seeds with pronamide. Soaking sunflower seeds for 5 min in 50% pronamide solution or coating at the equivalent of 2 kg/ha with pronamide did not impair seed germination or seedling growth, and controlled nodding broomrape 49 to 68% and 51 to 77%, respectively, up to 105 d after planting. Studies of the effect of treated sunflower seeds on germination and seedling growth, at several time intervals after the herbicide application (0, 30, 60, and 90 d after treatment [DAT]), were conducted. Soaking with 50% solution or coating at 2 kg/ha reduced seedling growth by 20 and 24% 60 DAT, respectively, compared with the control. Nomenclature: Pronamide; nodding broomrape, Orobanche cumana Wallr. #3 ORACU; sunflower, Helianthus annuus L. Additional index words: Herbicide seed treatment, parasitic weed. Abbreviations: DAP, days after planting; DAT, days after treat...

Summary: Resume: Zusammenfassung Field experiments were conducted from 1989 to 1992 to determine the effects of pre-emergence herbicides in sunflower (Helianthus armuus L.) on: (1) the control of Orobanche cemua Loefl. (broomrape) and (2) crop damage and crop yield. Herbicides tested belong to the imidazolinone, sulfonylurea and substituted amide families. Imazethapy r (20–40 g ha−1), imazapy r (12.5–25 gha−1) and chlorsulfuron (4–6 gha−1) controlled broomrape efficiently without crop injury. With good O. cernua control and good crop tolerance, sunflower seed yield from these treatments were generally similar to the non-infested checks and higher than the infestedchecks. Imazaquin (20–40 gha−1), triasulfuron(4gha−1), pdmisulfuron(3g ha−1), acetochlor (4–4 kg ha−1) and metazachlor (2 kg ha−1) were less effective. Imazamethabenz (200–600 g ha−1) and metolachlor (3–3 kg ha−1) were ineffective. Wetconditions aftercropsowing considerably decreased O. cemua control with pre-emergence herbicides probably caused by enhanced degradation. Des herbicides de prelevee pour la lutte contre Vorobanche (Orobanche cemua Loefl.) dans le toumesol (Helianthus annuus L.) Des experimentations au champ ont ete conduites de 1989 a 1992 pour determiner les effets d'herbicides de pre1evee du toumesol sun (a) la destruction de l'orobanche (Orobanche cernua Loefl.) et (b) la phytotoxcite sur la culture. Les herbicides testes appartenaient aux imidazolinones, aux sulfonylurdes et aux amides substituees. L'imazethapyr (20 a 40 gha−1), l'imazapyr (12,5 a25gha−1)et le chlorsulfuron (4 a 6 gha−1) detruisaient efficacement l'orobanche sans occasionner de phytotoxidt6 sur la culture. Dans ces conditions, les rendements etaient generalement semblables a ceux des temoins non infestes et superieurs a ceux des temoins infestes. L'imazaquin (20 a 40 g ha−1), le triasulfuron (4 gha−1), le primisulfuron (3 g ha−1), lacetolachlor (4,4 kg ha−1) et le metazachlor (2 kg ha−1) etaient moins efficaces. L'imazamethabenz (200 a 600 g ha−1) et le metolachlor (3,3 kg ha−1) etaient inefficaces. Des conditions humides aprfes le semis diminuaient considerablement la destruction de O. cemua par les herbicides de prelevee, probablement a cause d'une degradation plus elevee. Vorauflaufherbigide zur Bekdmpfung der Sommerwurz Orobanche cemua Loefl. in Sonnenblume (Helianthus annuus L.) Zwischen 1989 und 1992 wurden in Sonnenblume Feldversuche zur Wirkung von Vorauflaufherbiziden aus den Gruppen der Imidazolinone, Sulfonylharnstoffe und substitutierten Amide auf die Sommerwurz Orobanche cernua und auf Kulturpflanzenschaden sowie den Ertrag durchgefuhrt. Mit Imazethapyr (20 bis 40 g ha−1), Imazapyr (12,5 bis 25 g ha−1) und Chlorsulfuron (4 bis 6 g ha−1) lieβ sich die Sommerwurz wirksam bekampfen, ohne daβ Schaden an der Sonnenblume auftraten, und die Ertrage waren allgemein ahnlich oder hoher als bei der nichtparasitierten Kontrolle. Imazaquin (20 bis 40 ha−1), Triasulfuron (4 g ha−1).Primisulfuron (3 g ha −1). Acetochlor (4,4 kg ha −1 und Metazachlor (2 kg ha −1) waren weniger wirksam. Imazamethabenz (200 bis 600 g ha−1) und Metolachlor (3,3 kg ha−1) hatten keine Wirkung. Bei Niederschlagen nach der Saat der Sonnenblume war die Bekampfung der Sommerwurz mit Vorauflaufherbiziden vermutlich wegen verstarkten Abbaus erheblich schwacher.

The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua-resistant and O. cernua-susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host-tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7-hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR(24) and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection.

8 pages, 2 tables, 2 figures, [14C]-Imazethapyr was applied as a seed treatment and at plant pre-emergence and post-emergence to peas (Pisum sativum L.) parasitized by Orobanche crenata Forsk. Herbicide uptake increased with time regardless of the application method. Uptake reached about 98%, 89%, 81% and 94% of the total herbicide applied for the seed coating, seed soaking, pre-emergence and post-emergence treatments respectively. Herbicide translocation within the host plants consistently differed between O. crenata-infected and non-infected plants. High levels of 14C activity were accumulated by parasitic plants from the host. In non-infected pea plants, pods were stronger sinks for imazethapyr than the other parts of the plant, regardless of the application method. The herbicide distribution in the pea plant: O. crenata complex showed the same pattern regardless of the application methods. However, accumulation of radioactivity in the parasite was lower with pre-emergence and post-emergence application than with the seed treatments. In addition, radioactivity concentration in O. crenata plants was slightly higher when [14C]-imazethapyr was applied to pea seeds by coating than by soaking.

5 pages, 2 figures, 4 tables, Field studies were conducted at nine locations in southern Spain during 2 yr to develop models of nodding broomrape competition with sunflower and to establish economic thresholds. At each location, 30 to 35 small plots, each consisting of three sunflower plants, were chosen at random. The infection severity (BIS, no. of emerged broomrapes per sunflower plant) varied from 0 to 35. Plots were harvested at maturity to assess several sunflower and broomrape population variables. The percent sunflower yield reduction averaged over locations due to broomrape was estimated by the equation: % SYR= 1.7 × BIS (r² = 0.92). Crop yield loss per BIS unit increased with the expected yield and was estimated to be about 25, 50, and 75 kg ha-¹ for yields of 1000, 2000, and 3000 kg ha⁻¹, respectively. A consistent relationship could be established between broomrape-infected sunflower yield, crop and broomrape biomass, and BIS parameters: SSY1 = 0.2259 x PoBio/(1 + 0.0687 x BIS) (r2 = 0.7820). The BIS economic threshold was about 1.5 and 3.5 for control treatment cost of $ 40 ha-1 and potential yields of 2000 and 1000 kg ha-1, respectively., Europen Union (EEC XII-TS2*0124-C) and the Spanish Scientific and Technological Commission (CICYT Agro-Petri 0057/92).

Despite the tremendous economic impact of broomrapes (Orobanche spp.) on agriculture in many countries little is known of the pattern of genetic variation within this group of parasitic weeds. The present paper describes the use of RAPD markers for the study of five Orobanche species in agricultural fields in Israel. Pronounced genetic differentiation was found between the species, and RAPD markers were raised for the identification of each of them. Southern-hybridization patterns of RAPD products of the various species were used to confirm the interpretation. The same markers were valid both for broomrapes collected in agricultural fields and for those collected in natural habitats. The validity of the markers found for O. cumana and O. crenata was confirmed on plants of the same species that were collected in Spain. Parsimony analysis of 86 RAPD characters produced a tree that clearly distinguishes between the five studied Orobanche species, separates the two Orobanche species belonging to sect. Trionychon from those belonging to sect. Osproleon, and supports the separation of O. cumana from O. cernua and of O. aegyptiaca from O. ramosa.