Current recommendations for fruit thinning of processing clingstone peaches in California suggest that growers delay thinning until an assessment of fruit size is made at reference date (10 days after first indications of pit hardening) and then adjust the crop load according to the fruit size attained. Recent research on modelling peach fruit growth indicates that delaying thinning until reference date (usually mid-May) can substantially limit final fruit size potential and crop yield when initial fruit set is heavy. In 1991 we initialed a field study to lest these model predictions and evaluate the yield response and economic feasibility of fruit thinning within 50 days of bloom to a specific crop load. The experiment was conducted in commercial orchards of the extra-early maturing cling peach cultivars Loadel and Carson. Three thinning treatments involved thinning different sets of trees on April 10, April 30, (∼30 and 50 dafb) and May 23 (reference date). Although costs of thinning at the earlier dates were 140-290% of thinning at reference date the increase in yield resulting from early thinning more than compensated for the higher thinning costs. There were no major effects of thinning treatment on the occurrence of split pits or other quality characteristics. This research has stimulated a re-evaluation of commercial fruit thinning practices used for clingstone peaches in California.
T.M. DeJong, K.R. Day, R. Beede, and R.S. Johnson
M. Zahara, S. S. Johnson, and R. E. Garrett
The average time required to harvest a carton of lettuce by hand ground pack was 12.67 minutes in 1960-1963 and 3.57 minutes in 1970-1973. The change in the number of harvests, trimming, packing, and method of pay is the reason for the big difference in the time required. Selecting, cutting, and trimming lettuce heads consumed 45.4 to 46.3% of the total harvest time. Film wrapping lettuce heads increases harvest time to 11.19 minutes per carton. An experimental 1-bed harvester increased the man-hour output to 20 cartons, a 3 carton increase over hand ground pack. Estimated cost of harvest with a mechanical harvester would be $.29 per carton, compared with the present cost of $.45. Labor is the major part of harvest costs regardless of method of harvest.
Theodore M. DeJong, Kevin R. Day, James F. Doyle, and R.S. Johnson
This paper describes a moderately high-density orchard training system (1000 trees/ha) developed at the Univ. of California's Kearney Agricultural Center for peach and nectarine trees grown on standard rootstocks. This two-leader system was developed to increase production during the early years of the orchard while minimizing specialized management operations during orchard maturity. Early selection of two primary scaffolds oriented perpendicular to the tree row is recommended during the first season of growth. During subsequent years, summer and dormant pruning requirements are similar to the standard open-vase system grown in California. Because of the uniform and relatively simple tree structure, individual scaffolds, rather than whole trees, can be used as functional units for crop load management.
C. A. Jaworski, S. M. McCarter, A. W. Johnson, and R. E. Williamson
Six general-purpose fumigants applied by different methods were evaluated for control of the fungal-nematode complex on onion (Allium cepa L.) for transplant production. Most soil treatments improved plant vigor, size, uniformity, and yield, and these positive responses were correlated with reduced populations of soil-borne fungi and nematodes. Growth response and control of pathogens varied with the fumigant used and the method of application. Populations of Pythium spp. and Fusarium spp. were reduced with methyl bromide, methyl bromide-chloropicrin mixture, chloropicrin, DD-MENCS (Vorlex), metham (748 liters/ha, drenched) and Bunema (drenched). Metham (748 liters/ha, drenched or drenched and incorporated) controlled Rhizoctonia solani Kuehn. Complete control of root-knot nematodes was obtained with methyl bromide and methyl bromide-chloropicrin mixture and nearly complete control with chloropicrin and DD-MENCS.
C. R. Johnson, T. A. Nell, S. E. Rosenbaum, and J. A. Lauritis
Water stress reduced dry matter accumulation in Ficus benjamina plants, especially those grown in the sun. Accumulation of carbohydrates and reduction of chlorophyll was associated with water stress in sun plants, but there were no stress related changes of carbohydrate or chlorophyll levels in plants grown under 47% shade. Electron micrographs of chloroplasts showed starch deposits and disruption of thylakoid structures with water stress in sun plants, while disruption due to water stress was less severe in shade-grown plants. Net photosynthesis (Pn) was lower for unstressed shaded plants, but interposure of water stress resulted in similar Pn levels for both light regimes. Photosynthesis was restored to non-stressed levels after irrigation in both sun and shade light treatments. Lowest light compensation points (LCP) occurred in shade plants with no influence due to water stress, but water stress caused high LCP in sun plants.
J. Girona, M. Mata, D.A. Goldhamer, R.S. Johnson, and T.M. DeJong
Seasonal patterns of soil water content and diurnal leaf water potential (LWP), stomatal conductance(gs), and net CO2 assimilation (A) were determined in a high-density peach [Prunus persica(L) Batsch cv. Cal Red] subjected to regulated deficit irrigation scheduling. The regulated deficit irrigation treatment caused clear differences in soil water content and predawn LWP relative to control irrigation treatments. Treatment differences in midday LWP, gs, and A were also significant, but not as distinct as differences in predawn LWP. Leaves on trees subject of the deficit irrigation treatment were photosynthetically more water-use-efficient during the latter part of the stress period than were the nonstressed trees. Midday LWP and gs, on trees that received the regulated deficit irrigation treatment did not recover to control treatment values until more than 3 weeks after full irrigation was resumed at the beginning of state III of fruit growth, because of water infiltration problems in the dry soil caused by the deficit irrigation. The regulated deficit irrigation treatment caused only a 8% reduction in trunk growth relative to the control, but resulted in a 40% savings in irrigation requirements.
T. Auxt Baugher, J. Schupp, K. Ellis, J. Remcheck, E. Winzeler, R. Duncan, S. Johnson, K. Lewis, G. Reighard, G. Henderson, M. Norton, A. Dhaddey, and P. Heinemann
Hand thinning is a necessary and costly management practice in peach (Prunus persica) production. Stone fruit producers are finding it increasingly difficult to find a workforce to manually thin fruit crops, and the cost of farm labor is increasing. A new “hybrid” string thinner prototype designed to adjust crop load in vase or angled tree canopies was evaluated in processing and fresh fruit plantings in varying production systems in four U.S. growing regions in 2009. Data were uniformly collected across regions to determine blossom removal rate, fruit set, labor required for follow-up green fruit hand thinning, fruit size distribution at harvest, yield, and economic impact. String thinner trials with the variable tree forms demonstrated reduced labor costs compared with hand-thinned controls and increased crop value due to a larger distribution of fruit in marketable and higher market value sizes. Blossom removal ranged from 17% to 56%, hand thinning requirement was reduced by 19% to 100%, and fruit yield and size distribution improved in at least one string-thinning treatment per experiment. Net economic impact at optimum tractor and spindle speeds was $462 to $1490 and $264 to $934 per acre for processing and fresh market peaches, respectively. Case study interviews of growers who thinned a total of 154 acres indicated that commercial adoption of string-thinning technology would likely have positive impacts on the work place environment.
C. E. Johnson, J. C. Taylor, W. A. Young, R. S. Woodward, D. W. Newsom, and N. L. Horn
‘Ouachita Gold’ peach (Prunus persica (L.) Batsch) was released by the Louisiana Agricultural Experiment Station to provide a high quality, large freestone fruit that ripens about 20 days after ‘Elberta’ or about August 5 in north Louisiana.