Broomrape species (Orobanche spp. and Phelipanche spp.) pose a tremendous threat to economically important crops in Iran; however, there is little information on the country’s major broomrape species, their distribution and host ranges, and the subsequent crop losses they cause. The literature from Iran describes Egyptian broomrape (Orobanche aegyptiaca Pers.), hemp broomrape (Orobanche ramosa L.), Phelipanche nana (Reut.) Beck, and Orobanche cumana Wallr. as the major species of broomrape infesting agricultural fields. Solanaceae crops are among the most susceptible crops to infestation by broomrape in the country, and farmers are either shifting production to crops with lesser value or abandoning crop production entirely. Among infested crops, tomato (Solanum lycopersicum L.) is the most susceptible and widely infested, resulting in annual crop yield reductions of up to 40%. Chick pea (Cicer arietinum L.) and canola (Brassica napus L.) are also highly susceptible to broomrape infestation. Current control methods (physical, agronomical, biological, and chemical) have not proven to be effective or economic. The microscopic size of broomrape seeds and the presence of a wide range of host plants (weeds and crops) have promoted the spread of broomrape to new areas of Iran. Hence, the familiarization of farmers with the biology of broomrape would be highly effective in finding suitable control measures and in preventing its further distribution.

Egyptian broomrape (Phelipanche aegyptiaca Pers.) is a root-parasitic weed that severely damages many crops worldwide, including tomato (Solanum lycopersicum L.). In Israel, the management protocol used for P. aegyptiaca in open-field tomato includes PPI sulfosulfuron at 37.5 g ai ha−1 to the top 10-cm soil layer. The objective of this study was to investigate the co-effect of sulfosulfuron application timing and variable degradation rate in soil on the control efficacy of P. aegyptiaca in tomato. Degradation of sulfosulfuron (80ng g−1 soil) at a temperature of 15C, measured in soil samples from three farms using liquid chromatography–tandem mass spectrometry, followed a first-order kinetics with variable degradation rate constant among sites (0.008 to 0.012 d−1). Incubation at 25 C increased sulfosulfuron degradation rate constant by a factor of 2 to 2.7 in soils from the different sites, with a similar degradation rate order among soils. A higher degradation rate in the soil resulted in a shorter period of residual activity, measured using a sorghum [Sorghum bicolor (L.) Moench.] bioassay. Phelipanche aegyptiaca management in open-field tomatoes was investigated in five independent field experiments. Sulfosulfuron soil concentration throughout the growing season (following preplant incorporation of 37.5 g ha−1) was calculated from laboratory-measured degradation rates, which were corrected to represent the effect of recorded temperatures at each field. At the end of the tomato growing season, control efficacy of P. aegyptiaca varied among experiments (70.4% to 100%) and positively correlated with predicted sulfosulfuron concentration at the critical period for seedling control (R2=0.67). The current study confirms that sulfosulfuron is degraded in soil to nonphytotoxic metabolites and that rapid degradation rates would result in reduced injury to P. aegyptiaca seedling and, consequently, lower control efficacy.

Field studies were conducted from 1991 through 1994 in several locations of Southern Spain to determine the efficacy of imazapyr as late postemergence application in sunflower for broomrape control and the crop response to this herbicide under weed-free conditions. Single applications of imazapyr at 10 to 15 g/ha on sunflower plants at about the V12 (12 leaves) to V19 (19 leaves) growth stages, infected with broomrape plants at the predominant growth stages “c” (small nodule with shoot bud visible) and “d” (shoot bud and roots well developed), resulted in effective control without damaging the crop. Double applications of imazapyr at 10 + 10 g/ha at about the same crop growth stages V12 to V19, at a time interval of 12 to 14 d between single applications, were also efficacious and well tolerated by the crop. The same herbicide treatments applied to weed-free sunflower did not adversely affect the biomass, head diameter or yield of the crop as compared with the nontreated check. As a result of the low rate of imazapyr required for broomrape control, the herbicide treatments are economical (about $3 to $6/ha), non-residual and not affected by the type of soil texture and rainfall conditions.

Broomrape is a severe problem in the continuous cropping of bidi tobacco in India. Fifteen herbicides were evaluated for postemergence control, at different dates and rates, in field experiments in Nipani, Karnataka State. The effects of the herbicides on Orobanche control and growth and yield of tobacco were compared to the effects of handweeding and an untreated check. Following this screening experiment, four herbicides were selected for further testing. Glyphosate at 500 g ai/ha applied at 60 days after transplanting (DAT) and imazaquin at 10 g ai/ha applied at 30 DAT reduced the number of aboveground broomrape spikes by 75 to 80% and increased the tobacco yields by 80 to > 100% compared to the untreated plots. Imazethapyr and EPTC were found to be less effective for broomrape control, but they still led to substantially higher tobacco yield. None of the herbicide treatments resulted in yields higher than those in the hand-weeded plots. These plots probably did not yet reflect the potential yield of tobacco under broomrape-free conditions, due to nonemerged spikes. Toxicity to tobacco of all herbicides was higher for the higher rates tested. It was lowest with imazaquin.

Trifluralin selectively controls dodder in alfalfa. However, its soil activity dissipates allowing some late season dodder germination. Thiazopyr applied PRE was also found to control dodder selectively in alfalfa. Thiazopyr was more effective when applied in February than in November. Thiazopyr did not control dodder longer into the season than trifluralin in field tests, however it was more effective in greenhouse experiments. The effect of thiazopyr on dodder shoot tips was similar to that of trifluralin, in that both herbicides produced bulbous cells with thickened, globular nuclei, typical of cells treated with herbicides affecting microtubules.

Glyphosate and SC-0224 at 75 or 150 g ae/ha, applied to alfalfa foliage after field dodder and largeseed dodder were parasitically well established, controlled dodder selectively. Glyphosate applied at any time over a range of developmental stages stopped the growth of dodder. Control was best when the herbicides were applied when alfalfa was 20 to 30 cm tall, when maximum length of dodder shoots was 30 to 60 cm, and while host and parasite were both vegetative and growing vigorously. Later application allowed dodder to injure alfalfa before being controlled, and earlier application sometimes allowed dodder to recover and suppress alfalfa before the hay was cut.

A soilless unit was devised in which host plant (carrot, tomato) roots can be readily infected with broomrape. The simple, inexpensive and reusable unit consists of two glass plates, synthetic cloth, and foam rubber. The host plants are placed (or grown) between the glass plates, being held against one of the plates by foam rubber. The unit provides proper growing conditions, convenient visibility of host roots and parasite from an early stage of infection, and nondestructive access to the roots and parasite. Exposure of the broomrape seeds to a synthetic germination stimulant (GR 24) prior to their application to the host roots, generally, but not always, caused some increase in the number of parasitic infections and/or the rate of broomrape growth.

The tolerance of broad bean (Vicia faba L. Moruna and Alameda) to glyphosate [N-(phosphonomethyl)glycine] was studied under field conditions. Chlorosis, rolling of apical leaves, and reduced growth were the typical symptoms caused by glyphosate on broad bean plants. Visual phytotoxicity from glyphosate at 60 and 120 g ae/ha was very slight. Moderate or severe crop injury was caused by glyphosate at 360 and 600 g ae/ha, when applied before blooming. Seed yields were 2, 4, 9, 23, and 47% lower than the control after glyphosate applications at 60, 120, 240, 360, and 600 g ae/ha, respectively, when averaged over stages of growth and locations. Broad bean was more susceptible to glyphosate at the vegetative stage, when the plants had five to seven nodes, and less susceptible at the late-flowering and pod-bearing stage. Double applications of glyphosate at 120 g ae/ha reduced seed yield more than 10% compared with similar treatments at 60 g ae/ha, regardless of growth stage. Glyphosate decreased seed yields mainly by reducing the number of pods per plant, but germination, fiber content, and gross energy of the seeds were not altered.

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 x 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: SSYI = 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.

Progression of crenate broomrape population density (PD, number of emerged plants m-2) in faba bean was studied over 8 yr in Spain. Spatial dispersion and effect of climatic conditions on parasite population growth rate (PGR) also were studied. With repeated cropping of faba bean, infestations of crenate broomrape increased from an initial PD of 0.15 to an average of 26, with a maximum of about 40 to 45. The average population growth rate (PGR, ratio between the PD of any 2 consecutive years) was approximately 3. However, this figure varied widely among localities and years, from 0.8 to 7.7. A highly significant relationship (P = 0.01) was found between PGR and rainfall and soil temperatures during December to February, months of crop vegetative growth. Dispersion of crenate broomrape infestations mainly followed direction of crop rows, most likely due to the effect of tillage and harvesting operations, which were the same direction as sowing.

The effectiveness of soil solarization with black (BPE) and clear polyethylene mulches (CPE), 0.04 and 0.06 mm thick, respectively, was tested during the 1986 to 1990 growing seasons for controlling Egyptian broomrape, hemp broomrape and nodding broomrape in heavily infested fields. Solarization for 6 wk reduced or eliminated broomrape infestation and improved crop yields. The CPE started to show splitting and deterioration after 4 to 5 wk of solarization. The BPE lasted in usable conditions throughout the growing season. Deep soil tillage with the hand hoe, after solarization, caused broomrape to reappear. Crops grew best in plots after solarization with BPE if they were planted through the same mulch after it was perforated. Soil solarization with BPE or CPE in large tomato field trials, completely eliminated both nodding and hemp broomrapes during the growing season. However, greenhouse pot experiments indicated that solarization significantly reduced weed seedling numbers, but did not significantly reduce the dry weights of the broomrape plants that emerged in the soil samples taken from solarized plots.

Olive jift is a solid by-product of olive (Olea europea) oil processing. Greenhouse experiments were conducted to evaluate olive jift effect on broomrape (Orobanche spp.) infections on three crops. Soil—jift mixtures were used as potting medium in ratios of 1:0, 1:1, and 3:1 soil to jift. Broomrape seeds were evenly incorporated in the potting media at 0, 150, 300, 450, 600, 750, and 900 seeds/kg. Pots planted with faba bean or pea were inoculated with seeds of O. crenata Forsk., whereas pots planted with tomato were inoculated with seeds of O. lavandulacea Reichenb. Jift in soil reduced broomrape germination and infection on all three hosts regardless of inoculation densities. Pea was not infected with broomrape in jift-containing media at any inoculation density, whereas only sporadic broomrape infections were observed in faba bean and tomato grown in jift-mixed soils. Fresh and dry weights of all crops were not adversely affected by mixing jift with soil. These results suggest a possible use of jift as an inexpensive organic material for broomrape control.

Parasitic witchweeds inflict most of their damage while still underground and attached to crop roots. Most selective translocated herbicides are detoxified by crops such as corn and thus cannot reach the attached parasites. Corn with target site resistance to acetolactate synthase (ALS)-inhibiting herbicides was tested to ascertain whether these herbicides could control witchweeds, assuming that witchweeds do not obtain amino acids from the crop. Postemergence directed sprays of 27 g ae ha−1 imazapyr 54 d after planting (DAP) delayed Striga asiatica emergence on corn in South Carolina from 3 wk (control) to 7 wk and to 11 wk when mixed with 45 g ae ha−1 AC 263 222. Treatments with up to 71 g ae ha−1 imazamox, and up to 71 g ae ha−1 AC 263 222 only delayed Striga emergence by 1 wk, and 71 g ae ha−1 imazethapyr was ineffective. ALS-inhibiting herbicides were far more effective when applied in 1-ml drenches above the seed at planting. Chlorsulfuron (10 g ai ha−1) and sulfometuron (50 g ai ha−1) were somewhat phytotoxic to Pioneer 3245IR. Rimsulfuron (30 g ai ha−1), metsulfuron (10 g ai ha−1), halosulfuron (120 g ai ha−1), and imazethapyr (140 g ae ha−1) were marginally active in Kenya, with some mature Striga hermonthica seed-bearing capsules appearing at harvest (12 wk). Imazapyr at 15 g ae ha−1 gave 70 to 95% suppression of capsule formation, whereas no capsules appeared at 30 g ae ha−1. The use of imazapyr in Kenya increased the harvest index by 17% when corn plants in Striga-infested soils were kept insect and disease free by using insecticides and fungicides. Thus, complete control can be achieved at affordable cost by farmers in subsistence conditions.

The effect of the sulfonylurea herbicides, bensulfuron, chlorsulfuron, nicosulfuron, primisulfuron, rimsulfuron, thifensulfuron, and triasulfuron, on seed germination and radicle elongation of the parasitic plant, Egyptian broomrape, was tested in vitro without a host plant. These herbicides applied to the seeds at the preconditioning and germination stages significantly reduced radicle elongation of the parasite. Chlorsulfuron, rimsulfuron, and triasulfuron were further tested in polyethylene bags, where the parasite was able to parasitize tomato roots. Chlorsulfuron and triasulfuron applied at 2.5 and 25 μM ai and rimsulfuron at 5.0 μM ai, at the preconditioning and germination stages, almost completely inhibited parasite development, but at lower concentrations the parasite partially recovered 26 days after application. Chlorsulfuron inhibited parasite development for 34 d. Chlorsulfuron, triasulfuron, and rimsulfuron damaged parasite organs and caused rapid death of Egyptian broomrape tubercles when applied after the parasite had completed attachment to host roots. However, chlorsulfuron and triasulfuron at 25 μM ai were toxic to the tomato plants.

Studies were conducted from 1993 through 1995 to determine broomrape control from imazethapyr applied to pea seeds. Soaking seeds for 1 to 10 min in 0.0001% to 1% imazethapyr (Pursuit-10) solutions or coating seeds with imazethapyr at 0.025 to 0.30 mg/g (herbicide/seed, equivalent to 5 to 60 g/ha for a seeding rate of 200 kg/ha) did not affect seed germination or crop emergence and growth. Broomrape control with imazethapyr applied by coating seed at 0.1 to 0.2 mg/g (herbicide/seed, 20 to 40 g/ha) or by soaking seeds for 5 min in 0.1% to 1% imazethapyr solution was from 75 to 80% and 50 to 70%, respectively. Pea biomass and seed yield increased, compared to broomrape-infested nontreated control, when pea seeds were treated with imazethapyr and imazapyr at 5 g/ha was applied late postemergence, as a result of the excellent broomrape control.

Field experiments were conducted to study the phenology and growth of broadbean (Vicia faba L. ‘Alameda’) and crenate broomrape (Orobanche crenata Forsk. # ORACR) in relation to planting date. The establishment of crenate broomrape on broadbean planted between mid-December and mid-January coincided with the flower initiation on the crop. Establishment occurred during the vegetative phase, several weeks before flowering from a mid-November and mid-October planting. In general, no consistent relationships were observed between growth of the host and attachment or subsequent growth stage of the parasite. The maximum number of crenate broomrape plants successfully attached to the host as well as the duration of the underground stage of crenate broomrape decreased as broadbean planting was delayed. Broadbean dry weight decreased as infection rate increased. This effect was more intense in early than late plantings.

Striga hermonthica is a major threat to cereal production in western Kenya and other parts of the world. In laboratory experiments, maize and sorghum showed some resistance to late Striga attachment and parasitism. Field experiments were conducted in 1996 and 1997 in western Kenya to assess the effect of transplanting maize and sorghum, under rain-fed field conditions, on grain yield and Striga parasitism. In transplanted sorghum, Striga emergence was not reduced and sorghum failed to produce grain yield in three out of four seasons. Transplanting maize in all experiments significantly increased grain yield compared to direct seeding. The improved productivity was largely associated with less Striga attachment. Striga densities were considerably lower if maize seedlings were more than 17 d old at transplanting, with decreasing levels of Striga with increasing age of the maize seedlings. Seedlings transplanted before they were 15 d old did not reduce Striga attachment. Transplanting maize under rain-fed conditions is probably only suitable for small areas that are highly infested with Striga, due to its high labor requirements. Under these conditions, crop yield can be more than doubled. An incentive to using this method by small-scale farmers would be that the main input at risk is their own labor. However, the establishment of nurseries and the timing of the transplanting operation require a certain level of farm management that could constrain the adoption of this technique.

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions.

A botanical survey conducted from 2003 to 2007 showed the occurrence of the acacia strap flower and the Oriental mistletoe plant in different regions in Jordan. Acacia strap flower was found parasitizing 26 plant species belonging to 12 families. Oriental mistletoe attacked 14 plant species from eight families. Parasitized species ranged from wild shrubs to fruit and forest trees. Eleven Fabaceae species were parasitized by acacia strap flower, whereas Oriental mistletoe parasitized six Rosaceae species. Caper, pomegranate, white weeping broom, and white willow were attacked by both parasites. Infection by both parasites resulted in mortality of host plants in many cases. Hosts severely attacked by acacia strap flower were African jujube, Australian pine, chinaberry, Christ thorn jujube, common jujube, oleander, poinciana, sumac, tamarisk, terebinth, and white weeping broom. Oriental mistletoe heavily parasitized almond, mosphilla, olive, Palestine buckthorn, pomegranate, and white weeping broom. Results indicated the high potential of both parasites to spread and attack new hosts in the absence of control measures.

The Parasitic Plant Genome Project has sequenced transcripts from three parasitic species and a nonparasitic relative in the Orobanchaceae with the goal of understanding genetic changes associated with parasitism. The species studied span the trophic spectrum from free-living nonparasite to obligate holoparasite. Parasitic species used were Triphysaria versicolor, a photosynthetically competent species that opportunistically parasitizes roots of neighboring plants; Striga hermonthica, a hemiparasite that has an obligate need for a host; and Orobanche aegyptiaca, a holoparasite with absolute nutritional dependence on a host. Lindenbergia philippensis represents the closest nonparasite sister group to the parasitic Orobanchaceae and was included for comparative purposes. Tissues for transcriptome sequencing from each plant were gathered to identify expressed genes for key life stages from seed conditioning through anthesis. Two of the species studied, S. hermonthica and O. aegyptiaca, are economically important weeds and the data generated by this project are expected to aid in research and control of these species and their relatives. The sequences generated through this project will provide an abundant resource of molecular markers for understanding population dynamics, as well as provide insight into the biology of parasitism and advance progress toward understanding parasite virulence and host resistance mechanisms. In addition, the sequences provide important information on target sites for herbicide action or other novel control strategies such as trans-specific gene silencing.