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Mature broomrape plant bearing numerous black seed capsules which split open when ripe, releasing tiny seed. Broomrape matures seed during the entire tomato harvest.
COVER
Broomrape as it appears in tomato fields in midsummer. Bright yellow shoots of the parasite contrast sha rply with the green tomato plant. Below ground, broomrape roots fuse with tomato roots, and all nutrition of the broomrape is supplied by the tomato.
Any individual who has seen tJ1e broomrape p est or who has knowledge of its presence is ur gently re BRANCHED quested to notify the Agricultural Commissioner of his county. Help s1.amp ou t broomrape. BROOMRAPE THE AUTHORS: (Orobanche ramosa) Stephen Wilhelm is Professor of Plant Pathology and Plant Pathologist in the Experiment Station, Berkeley; Ja mes E. Sagen is Laboratory Technician in the Department of A THREAT TO CALIFORNIA CROPS Plant Pathology, Berkeley; D. H. Hall is Extension Plant Pathologist, Davis; Dan Y. Rosenberg, Carl W. Nichols, and A. Schlocker a re Plant Pathologists, California State Depart ment of Agriculture, Sacramento.
JUNE, 1965 -w -···~-,,,
('.(l~!ln n,i,-<: E11:1cn~ion wcHl: in A,:riculiurc- a.th.I Hon'I~ [ conomio . Collrc r (ll Apirul1ur(', Uni~tt~hy al Cali. f1>rnin, 1111d Unil
@ "' - The branched broomrape, Orobanche ramosa L., is be can-ied in trouser cuffs, in tire treads holding wet a flowering plant parasitic on the roots of tomato, soil or squashed tomato fruit, on tomato boxes, and lettuce, safflower, and other crops, and is a serious pest by farm machinery. Seed can also be spread long· in several areas of California. First recognized in and distances by surface water, as the rough structure of confined to one field in Alameda County in 1929, the the seed surface traps air in depressions, and causes pest has spread o,ver many acres between Centerville the seed to float. 'i.Yater also deposits seed below the and Alvarado. In San Joaquin and Sacramento soil surface where roots may contact it and where it counties, broomrape still has a limited distribution is protected against drying. Spread by wind un but the heavy concentrations on certain farms on doubtedly occurs, but the importance of wind d"is Grand and Roberts islands suggest infestations of long semination is not presently known. standing. The branched broomrape is not known to On perennial hosts, such as poison hemlock, Conium · occur in any other areas of California at this writing. rnaculatum L., .the broomrape grows as a perennial DESCRIPTION AND HABITS and may send shoots aboveground at any time of the year. Perennial weed hosts also may perpetuate the , Shoots are yellow-they lack chlorophyll-smooth pest in pastures, along railroads, canals, etc., where or hairy, and arise as branches from a central shoot. cultivation is not possible and where inspection is Roots are short, non-branched, and fleshy. Certain difficult. This creates a particular hazard. roots attach to tomato or other host roots and with Seeds of broomrape lie dormant in soil for many draw nutrients through the attachments. Flowers, years (12 according to a Kentucky study, 7 thus far in borne in spikes on the upper portions of the branches, our studies), and germinate only in the close presence are tubular - resembling small snapdragons - and of roots of susceptible plants. Thus, broomrape seed range in color from white to faint yellow, violet to may lie dormant for years while land is planted to non blue. host crops such as alfalfa, corn, sorghum, sugar beets, Seeds are produced in capsules which split open at or potatoes, then germinate when the land is planted the top when mature. They are about the size of to tomatoes. Also, during one year, a crop such as ground pepper and one plant may produce 5,000 to tomatoes starts germination of only a portion of the 50,000 or more. broomrape seed in t11e soil. In our studies, five suc 'il\Then the branched broomrape attacks annual crops cessive plantings of tomatoes grovm in large pots were such as tomato, it grows as an annual, appearing above required to deplete the soil of viable broornrape seed. ground in June or July, flowering from July through November, maturing seed from August to December. ECONOMIC IMPORTANCE AND T HREAT The long flowering season, coupled with the fact that Broomrape reduces tomato yields in direct propor seed matures during the entire tomato harvest, con tion to the number of parasites attached to a plant, tributes to the ease of spread of this pest. Seed may and to the earliness of the attack. In heavily infested
Left. Tomato plants abundantly parasitized by broomrape yield nothing at all. At least 50 parasites were counted on this one pla nt. Right. Branched broomrape attacks lettuce; if lettuce is young when attocked a head does not form. Lettuce appears to be attacked only in the summer and fall. areas as many as 50 broomrape plants attached to a Though preferring the semi-arid climate where it is single tomato plant have been counted. Such plants most destructive, the branched broomrape occurs in yield nothing at all. (See photo.) every country of Europe, in England and in several eastern states of the U.S. WORLD DISTRIBUTION The present distribution of 0. ramosa shows it HOSTS well adapted to many different climatic regions of The primary hosts of the brandied broomrape are the world, but thriving in countries where rain falls hemp, tobacco, and tomato, but melons, safflower, let-· primarily during the winter and spring, and where the tuce, crucifers, and grapes may also be attacked. (See summer and are dry. The Caucasus, western and fall photo.) 0. ramosa also attacks many different kinds of central Siberia, the Middle East, Turkey, Greece, North ornam,ental plants and weeds. On some weeds it grows and South Africa are among the semi-arid countries luxuriously, on others feebly. But in all instances where the branched broomrape thrives. Thus, there is weeds serve to perpetuate, increase, and disseminate little doubt that O. could become established ramosa the pest either during years when the susceptible crop and destructive in any part of California. The pest is has not been planted, or even after the crop has been a potential threat to the tomato industry, to lettuce, safflower, and possibly to other crops. (<.;ontinued on back)
HOSTS OF BRANCHED BROOl\ffiAPE Tropaeolum majus L. nasturtium Veronica sp. This list has been gathered from observations on plants speedwell Vicia faba L. in California and from the world literature on broomrape, broadbean and contains the most complete information available to Weeds or crop hosts not grown in California date. In some instances the literature includes under the designation "branched broomrape" species to which other Amaranthus retrofiexus L. rough pigweed investigators have given different botanical names. Dif Angelica archangelica L. garden angelica ferences between species are often so slight that they are Brassica napus L. rnpe felt to be of questionable importance. Cannabis sativa L. hemp Capsella bursa---pastoris (L.) Medic. shepherd's-purse Crops or ornamentals grown in California Conium maculatum L. poison-hemlock Fagopyrum escu/entum Moench buckwheat "' Armoracia rusticana Gaertn. horseradish Gnaphalium sp. cudweed Begonia semperftorens Link & Otto perpetual begonia Lactuca perennis L. perennial lettuce Brassica caulorapa Pasq. kohlrabi Lamium album L. white deadnettle Brassica oleracea var. capitata L. cabbage Lamium maculatum L. . spotted deadnettle Brassica rapa L. turnip Lamium purpureum L. purple deadnettle Calceolaria integrifolia Murr. shrubby calceolaria Lepidium virginicum L. pepper-grass Carthamus tinctorius L. safflower Leucas martinicensis R. Br. West Indian leucas Coleus sp. coleus Nicotilma glauca Grah. tree''tobacco Cuphea ignea A. DC. cigarflower Nicotiana tabacum L. common tobacco Eupatorium ligustrinium DC. Mexican eupatorium Perilla frutescens Britt. var. crispa Deane Fuchsia speciosa Hort. Fuchsia hybrida Voss. purple common perilla Helianthus an-nuus L. sunflower Plantago lagopodus L. round-headed plantain Heliotropium arborescens L . common heliotrope Rumex acetosa L. garden sorrel Lactuca sativa L. lettuce Solanum sarachoides Sendt. hairy nightshade Lycopersicon esculentum Mill tomato Taraxacum lwk-saghyz Rodin Russian dandelion Me/ilotus alba white sweet clover Triganella Foenum-Graecum L. fenugreek Melilotus ofjicinalis yellow sweet clover Xanthium strumarium L. cocklebur Pelargonium domesticum Bailey Martha Washington geranium Questionable hosts-reported only once or Pelargonium zonale Willd. horseshoe pelargonium identity uncertain Penstemon hartwegii (Mc Lind!.) Benth. penstemon A nthyllis tetraphyl/a kidney vetch Petunia hybrida Vilm. co=on petunia Chrysanthemum coronarium L. garland chrysanthemum Salvia coccinea Juss. Texas salvia Cucumis melo L. melon Salvia splendens Sello scarlet salvia Gossypium spp. Sea Island and Egyptian cottons Solanum pseudocapsicum L . Jerusalem cherry Pisum sativum L. garden pea Trifolium sp. clover Vitis vinifera L. European grape A. Prior to fumigotion, heavy soil must often be rotovated. The roller compacts the soil to conserve moisture. B. Simultaneous iniection of methyl bromide and chloropicrin and covering of the soil with polyethylene sheeting, Men on the back inspect for rips, riding on small platform. C. Close view of fumigant distribution system. A polyethylene tube leads to each chisel. D. Soil remains covered for 48 hours. Soil between the polyethylene strips is fumigated after the polyethylene has been removed . .. han-ested. vVeeds may be abundantly parasitized if taneously covering the soil ·with polyethylene sheeting. allowed to gTow in fields after the crop has been (See photos.) harvested. Prompt destruction of the old crop residue The chemicals most effective against broomrape are after harvest, and an occasional disking to discourage methyl bromide and ch.loropicrin used in proportions volunteer weeds_ help to control broomrape. of 2: I by weight. These chemicals are amoqg the oldest known soil fumigants, and the mixture at rates ·of-325- SUPPRESSION AND ERADICATION 425 lbs. per acre has proved effective in eradicating Three general methods of suppression have been broomrape. In addition, other soil-borne pests such as employed against broomrape since ancient times: insects, nematodes, mites, injurious fungi, and weeds I) rogueing the pest before seed is produced; 2) rigolen are controlled. Confining the fumigant under th e poly plowing, that is, burying the seed deep by inverting ethylene sheeting, which must be a minimum of 0.75 the upper foot of soil with the second foot; 3) planting to I mil in thickness, assures control of broomrapc - a trap crop before the commercial crop and plowing throughout the soil volume from beyond the injection it under before the broomrape flowers. These me_thods depth, to the surface soil. Soil for fumigation must be are costly, only relatively effective, and have served in seed bed tilth, moist, and preferably above 60°F only to_ slow intensification and spread of the pest. in temperature. ·wet, cold, or cloddy soil, or soil con Under modern farming systems these methods of con taining· trash from the previous crop should not be trol hold 1ittle attraction. fumigated. Under some circumstances, it is possible to Soil fumigation properly done offers the promise of successfully fumigate at lower soil temperatures, but eradicating broomrape. The method of fumigating soil adjustments in dosage, proportions of the chemicals, now widely used for many different crops and nurseries and length of time that the soil remains covered must consists of injecting the fumigant into and simul- be rnade.