M. LEHMAN - R. J. MIRAVALLE J. H. TURNER because of its wilt susceptibility) ; and (3) Deltapine Smooth Leaf (DSL), a Mississippi variety which has yielded well in the Imperial Valley, but has lower fiber quality and is wilt susceptible. Tests were located at Firehaugh, Fi\e Wilt Tolerance Points, Huron, and Woodville and a ran- domized complete lhck design was used at each site. Firebaugh in Cotton Varieties Most soils in the Firc.l)augh area art’ wilt-infested, but the land rhosen for thi- test had been in rice production tht. tHo previous years. No wilt symptoms were diq~layvdI)\ Results of this three-year testing program 42), the standard planting seed for the either of the three varietiw in 1960 at in the indicate that San Joaquin Valley One-Variety district ; Firebaugh in thc initial year of the ex- Verticillium wilt damage to cotton may (2) Cal 7, an experimental strain, devel- periment (sre graph). Both Cal 7 and vary from one area to another-but when oped at Shafter for its early maturity and DSI, gave higher yields than A4-42 ur1dt.r superior fiber quality (but not released wilt symptoms appear by mid-season, the conditions that year. Wilt symptoms were wilt-tolerant Acala 4-42 variety will signifi- noted by September, 1961, and the DSL yield fell below that of A4-42. Verticil- cantly outyield the two susceptible varie- lium wilt was common in Cal 7 and DST, ties, Cal 7 and Deltapine Smooth Leaf. plots during 1962 and both these varie- When cotton is grown continuously on the ties gave lower lint yields than A.1’-4*2. same plots, more drastic declines in yield The much higher yield level in 1962 occur with wilt-susceptible varieties than over the 1960 and 1961 seasons can be at- for Acala 4-42. tributed basically to a change in the planting scheme. The 1960 and 1961 plantings were made in the normal solid- E RTI c I LLI u M w I LT ( Verticillium planted, 40-inch row bed\. Then the V albo-atrum R. & B.) is the most seri- grower switched to the “2-in, 2-oat” ous cotton disease in the San Joaquin scheme of planting in 1962, which re- Valley of . This disease is also sulted in each row of cotton having an an important factor in certain rotton- adjacent unplanted row. This spacing al- producing areas of Arizona and New lows the cotton to utilize extra sun- Mexico but is of only minor importance light, moisture, and nutrients-and has in the soils of rain-belt states. The most been found to increase yields by 50 to satisfactory means of minimizing wilt 100% as compared with normal solid- damage is by growing a variety that is planted cotton. resistant or highly tolerant of the wilt fungus. Complete resistance has not been Five Points developed in any variety, but Acala 4-42, At Five Points, this experiment &a< the variety grown in the San Joaquin located at the newly established Univer- Valley, has shown a high degree of re- sity of California West Side Field Station. sistance since 1954. All other varieties Solid plantings were made on the plot. tested are either susceptible to Verticil- each of the three years. Lint yields ob- lium wilt or display less, tolerance than tained for the three varieties were prac- 4-42 when tested in the San Joaquin tically the same. This was the only Valley. location at which the effects of Verticil- Observations at the [J. S. Cotton Re- lium wilt were not apparent. It was late search Station, Shafter, have indicated summer of the third year of the experi- that wilt became increasingly severe ment before wilt symptoms were noted when susceptible varieties were grown in Cal 7 and DSL plots. It is not known year after year on the same heeding nur- whether cropping to continuous cotton, sery rows. The main purpose of this ex- internal wilt, or cultural management periment was to determine the effect of contributed to the gradual decline in Verticillium wilt on cotton yield at sev- yield at Five Points from 1960 to 1962. eral San Joaquin Valley locations by as shown in the graph. growing wilt-tolerant and wilt-susceptible varieties continuously for three years. Huron Three varieties of cotton were chosen The test area at Huron was relocated for this experiment: (1) Acala 4-42 (A4 aftrr the 1960 season. A low he1 of wilt

10 CALIFORNIA AGRICULTURE, APRIL, 1963 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 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 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 ( 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