was apparent on both Cal 7 and DSL by mid-season of 1960. But Cal 7 gave a Tarweed higher lint yield than A4-42 and the DSL yield was below that of A4-42. The 1961 planting was made on a field where an a nuisance plant on California ranges observational block of DSL was grown in 1960. Following the wilted cotton of 1960, it was easy to detect wilt symptoms S. S. WINANS ’ C. M. MCKELL in mid-summer throughout the Ca17 and DSL plots, and minor symptoms were evi- dent even in A4-42 plots. Yields from this forms dense patches among and above location were considerably lower for all the dry annual forage species-obscuring varieties in 1961 than in 1960. Never- and limiting use of desirable species as theless, the grower allowed the test to dry feed by livestock. remain on the same plots in 1962. Some observations of tarweed seed However, the grower did switch the production, germination, and hard seed planting scheme from “solid” cotton to percentage were made to help show how “2-in, 2-out.” Significant yield differ- tarweed persists even though a seed crop ences were obtained among the varieties might fail to mature. Clipping and fall in 1962. A442 was outstanding for its application of nitrogen were studied as wilt tolerance even though the low sum- possible means of minimizing tarweed mer temperatures in 1962 were ideal for stands during the seedling stage. the wilt organism to operate. Heavy wilt Three tarweed-infested rangeland areas damage was evident in the Ca17 plots and located in the Sierra Nevada foothills in lint yield was 19% lower than A4-42, as Sacramento, Tuolumne, and Madera shown in the graph. DSL was severely counties were chosen in the fall of 1956 damaged by Verticillium wilt. In fact, the as study sites. An additional study of ni- wilt attacks occurred so early in the sum- Tarweed seedling (Holocarpha virgata) as it trogen fertilization was initiated in the mer that the “2-in, 2-out” planting scheme appears in early annual range forage. fall of 1958 and carried on through 1960 offered no advantage. With both the di- at the Shaubach Ranch, Madera County. Old tarweed plants from the previous rect wilt damage and the indirect loss of Tarweed is well adapted for survival as a growing season were used as a basis to growth advantage due to the earliness of nuisance plant on California ranges. While the wilt attack, the yield of DSL was 5770 choose specific sites for these studies. expensive control measures may not be lower than that of A4-42. Tarweed seeds were harvested by hand justified, effective methods are needed for in the fall from mature plants growing Woodville minimizing the use of soil’ moisture by tar- on a foothill range area in Madera It was necessary to relocate the test weed seedlngs in the spring. Clipping or County. Seeds were germinated for 28 plots at Woodville with a different grower heavy grazing and nitrogen fertilization days with temperatures alternating from each year since farm units are smaller offer possibilities for reduction in density 5, 15, 20, and 2O-3O0C. and the growers cannot afford to absorb of tarweed seedlings in favor of the more Treatments the loss from Verticillium wilt continu- desirable forage species. A series of 10x20 ft. plots were ously. clipped at three-week intervals through Verticillium wilt was evident by mid- ARWEED, Holocarpha virgata (A. the spring months. A different set of plots season on both Cal 7 and DSL in 1960 Gray, Keck) , is a nuisance plant that was clipped at a height of 1% inches and 1961. The land used in 1962 gave growsT on California foothill rangelands with a scythette mower at each location less wilt damage. Data for the three years, and is generally distributed in the Sierra each time. Tarweed density estimates as shown in the graph, shows higher foothills, Central Valley and inner coast were made on June 27, 1957. Soil mois- yields were obtained from A4-42. The ranges. At times it dominates some of ture percentage was determined at 5 to 7- growth of both Cal 7 and DSL’was visi- the better forage-producing sites. This inch and 18 to 20-inch depths. bly reduced on the 1960 and 1961 plots annual forb germinates in the fall, but Fertilized plots, .2 acre in size, were as a result of wilt attacks. The Woodville has its greatest growth in the late spring established at each county location in area plots showed a more drastic yield re- and summer. The tarweed stand is per- 1957. Treatments consisted of 60, 120, duction for Ca17 than at any of the three sistent but may be dominant one year and 180 pounds of nitrogen applied as other areas. and of only minor proportions in a fol- 16-20-0 for comparison with an unferti- Merrill Lehman is Assistant Agrono- lowing year. Grazing use of tarweed has lized check plot. A strip through each plot mist; R. J. Miravalle is Geneticist; and been observed during winter and early was harvested June 27, 1958, with a John H. Turner is Agronomist-in-Charge, spring. Tarweed growth is most rapid in scythette mower. The percentage of tar- CRD, Agricultural Research Service, the late spring when the plants compete weed was obtained by hand separation. USDA Cotton Research Station, Shafter. with desirable forage species for the At the Shaubach Ranch the rates of Miravalle and Turner are also Research diminishing soil moisture. Tarweed be- nitrogen applied were 0, 40, 80, 120, and Associates in the Agricultural Experi- comes most noticeable and particularly 160 pounds per acre using 16-20-0. Fer- ment Station, Department of Agronomy, objectionable in the summer season when tilizer treatments were replicated four University of California, Davis. its bushy-stemmed, ill-scented growth times using 20x20-ft. plots. The total plot CALIFORNIA AGRICULTURE, APRIL, 1963 11 TABLE 1. MEAN SEED GERMINATION AND HARD SEED TABLE 2. RESULTS OF CLIPPING ON TARWEED none at the other. In April all forage PERCENTAGE OF TARWEED DENSITY ON JUNE* 27 AT THREE FIELD LOCATIONS plants were growing rapidly and tarweed Germination* Time of Sacramento Tuolumne Modero Hord Seed foroge plants per plonts per plonts per seedlings were from 4 to 6 inches in Ya (%I (C) 14 days 28 days removal sq. ft. sq. ft. sq. ft. height. In contrast, soft chess was 8 to 14 5" 1 1 89 March 6 . .. .. 18.5 3.5 8.9 inches tall, and in the early flowering 15" 2 2 94 March 27 ...... 14.8 6.3 17.2 20" 2 3 84 April 15 . .._.._4.4 4.5 6.9 stage. Clipping during the final weeks of 20-30" 0 3 90 May 10 ........ 0.7 2.5 4.5 the spring growing season substantially *Germination tests by Seed Laboratory, State of June 10 ____....0.0 0.0 8.9 reduced the density of tarweed. California Deportment of Agriculture. Non-cbped . 14.2 4.4 12.6 'Meon of three replications. Plots clipped on May 10 when tarweed seedling height was from four to sixteen area was fenced during winter and inches had 95% less tarweed than non- spring, but dry feed was removed by to produce fifty to several hundred yel- clipped plots at Sacramento, 43% less at grazing during the summer. The plot area low-flowered, composite-type heads. Four Sonora, and 64% less at Madera. Tar- was again fenced the second growing sea- or five glistening black seeds, 1 mm in weed density was reduced to zero at both son following fertilization. Moisture de- diameter, are usually produced in each Sacramento and Tuolumne locations pletion was recorded for 12-inch and 36- seed head. Maximum seed germination when clipped in early June just after inch soil depths by using gypsum electri- was 1% to 3% for one-year-old seed, forage maturity. In the Madera plots, tar- cal-resistance blocks. Following fertilizer regardless of temperature (table 1). No weed density increased after forage ma- application in the second year, forage differences resulted from an additional turity, probably because of a late rain. yield, tarweed density and tarweed height 14 days in the seed germinator. Hard Forage composition were recorded from all treatments near seed content ranged from 84% to 94% forage maturity. Three random square- under all temperature conditions. Species composition of forage one year foot samples were harvested and oven- Results from time of clipping varied later, in each location, appeared to be dryed from each plot. The number of from no reduction to almost complete re- unaffected by the clipping treatments ex- tarweed plants per square foot was duction of the current stand of tarweed cept on plots clipped late in the previous counted and measured for height. Plant (table 2). Early clipping generally re- growing season. On these plots, bur clo\er material from one replication was hand- sulted in an increase in the number of appeared to replace soft chess in domi- separated by forage class to determine tarweed plants present in June as com- nance. species composition. pared to unclipped plots. In March, tar- The effectiveness of clipping tarweed weed seedlings were small, averaging l?hz in the late spring is attributed to the in- Seed yield inches tall, and the two major forage creased height of tarweed and limited Tarweed seed yield per plant is high, species, soft chess and broadleaf filaree, availability of soil moisture. In March hut the seed germination percenatge is averaged 43" inches in height.