In the last 3 years, ≤50% of the North Carolina sweetpotato crop has been produced with the variety Hernandez. A brown to black discoloration on the epidermis of the `Hernandez' sweetpotato may develop when maintained in storage for several months. The symptoms resemble blister—blister is caused by a boron deficiency. Preliminary studies in 1994 indicated that boron reduced the discoloration on `Hernandez' but did not eliminate the problem. To help confirm these findings and further define the role of boron in defining skin discoloration, boron was applied in 1995 at several rates (0 to 5.6 kg·ha–1) and stages of plant development using two application methods (foliar or soil). Yields and plant analysis data were obtained. Marketable yields ranged from 18.4 to 29.3 mt/ha. Leaf boron concentration ranged from 50 to 100 mg·kg–1 throughout the production season when 1.1 kg·ha–1 boron was soil applied shortly after planting. Excessive levels of boron (200+ mg·kg–1) were measured in plant tissue when application levels exceeded 2.2 kg·ha–1 regardless of timing. Soil application appeared to be an adequate method for boron application. Roots were examined for symptoms of discoloration after 5 months. Results indicated no affect of boron on incidence or severity of the symptoms.
Jonathan R. Schultheis and C. Ray Campbell
Patrick H. Brown, Louise Ferguson, and Geno Picchioni
The uptake and distribution of foliar and soil applied boron has been followed in a seven year old pistachio orchard by utilizing 10B isotope dilution techniques and ICP-MS determination. In conjunction with these uptake studies, in-vivo and in-vitro measurements of pollination and fruit set have been used to determine the role of boron in flowering and fruit set.
Foliar applications of boron (1, 2.5 and 5 kg/400 l) resulted in improved fruit set when compared to control trees receiving no supplemental B even when tissue B levels in these control trees appeared adequate (>60 μg/g dwt). Results indicate that B applied to male trees in the late dormant phase (february) is effective in enhancing in-vitro pollen germination by as much as 50%. Movement of B into flower buds and fruit clusters was verified using 10B techniques thus demonstrating the potential usefulness of this technique in correcting incipient B deficiency. A possible role of B in the flowering and fruiting process is discussed.
Regina P. Bracy, H. Hobbs, and D. Dufresne
Field studies were conducted in 1993, 1994, and 1995 to evaluate chemical and biological agents for control of phytophthora blight in bell peppers grown on polyethylene-mulched raised beds. Treatments included Kocide 606 (foliar applied), Ridomil 2E (soil applied), Ridomil 2E (directed spray), Ridomil/Copper 70W (foliar), Ridomil 2E (soil) + Ridomil/Copper 70W (foliar), fluazinam (soil/foliar), and Actinovate bioconcentrate (seedling media applied). The experimental area was inoculated with Phytophthora 2 weeks after transplanting. All plants were rated for disease incidence (number of plants exhibiting visual symptoms) beginning at inoculation and continuing every week for 5–6 weeks. Disease incidence was severe in 1993 and 1995. None of the chemical or biological agents had an effect on total marketable yields or fruit weights during the three years. Disease ratings were highest in the control, Ridomil 2E (soil), and Actinovate plots. Yields did not reflect the severe disease infestation that occurred in some plots, possibly because greatest disease incidence occurred late in the season. Best Phytophthora control was obtained from chemical treatments containing copper compounds (Kocide and Ridomil/Copper 70W).
Esmaeil Fallahi and Brenda R. Simons
The influence of three rootstocks, various levels of soil-applied nitrogen in fall, and spring spray applications with and without minimum ground nitrogen on tree growth, productivity, leaf and fruit nutrient partitioning, and postharvest quality of fruit at harvest and after storage in `B.C. 2 Fuji' apple was studied over several seasons. Early results showed that trees on M.26 and M.9 were more precocious and had higher yield and yield efficiency. Trees on M.9 had significantly higher leaf Ca and incidence of sunburned fruit than those on other rootstocks. Trees on M.7 had larger fruit and higher leaf N, K, and Cu, but had lower fruit starch degradation pattern (SDP) and leaf Ca. Soluble solids at harvest were lower in fruit from trees on M.26 rootstock. Trees with fall nitrogen application had lower leaf N and better fruit color. Lower quantities of N application had smaller fruit but better fruit color and higher firmness at harvest. Fruit from all rootstocks did not produce ethylene for several days in the ripening chambers. After this period, fruit on M.9 rootstock produced ethylene before those from other rootstocks. Trees established with only nitrogen spray without any ground application had leaf N deficiency after they started bearing fruit. Establishment of a new `Fuji' orchard based on only nitrogen spray produced weak trees with low yield and yield efficiency, while addition of a small quantity of ground-applied N improved tree growth and fruit quality.
S. Gurusiddaiah and M. Ahmedullah
For the control of Reeds Canary grass (Phalaris arundinaceae) and yellow nutsedge (Cyperus esculentus) in blueberry fields, no satisfactory control measures are available. We tried microbially derived aerobic fermentation extracts of Pseudomonas syringae strain 3366 (P. S. 3366) as pre- and -post-emergence applications for the control of Reeds Canary grass and yellow nutsedge. In greenhouse studies using “conetainers,” 2 mg of extract per g of soil applied as preemergence completely inhibited seed germination and aerial growth of Canary grass, but had no effect on nutsedge. In addition, the same level of concentration of P. S. 3366 (2 mg of extract/g of soil) under field conditions also showed 99% inhibition of germination and growth of Canary grass, but had no effect on germination of nutsedge. However, 4-fold increase in concentration of P. S. 3366 extract completely inhibited the sprouting of yellow nutsedge in greenhouse studies. These studies indicate microbially derived extract of P.S. 3366 can be used and has potential for the control of these weeds. Post-emergence foliar sprays of P. S. 3366 extract in blueberry fields failed to inhibit the aerial growth of Reeds canary grass and yellow nutsedge.
Hermen Malik and Douglas D. Archbold
The potential for plant growth regulator (PGR) manipulation of `Chester Thornless' blackberry (fibus spp.) primocane growth was evaluated. PGR treatments included combinations of soil-applied uniconazole at 1, 5, 25, and 125 mg/plant and GA, foliar-applied one or two times at 100 ppm 3 and 4 weeks after a 25-mg/plant uniconazole application. Also, GA and BA were applied at 100 ppm alone or in combination one, two, or three times. Increasing rates of uniconazole reduced primocane length, leaflet count, and leaf, cane, and root dry weights. GA, applications reduced primocane length and increased branch elongation but failed to reverse the effects of uniconazole at 25 mg/plant, except those on branch length, leaflet count, and primocane dry weight. Only applications of BA + GA, increased both branch production and elongation and dry weights of some component tissues, while BA alone generally had no effects. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); gibberellic acid (GA).
Harry L. Andris and Carlos Crisosto
Soil-applied reflective materials significantly improved the red color development, fruit size, and early harvestability of `Fuji' apple grown under hot climate conditions of the the San Joaquin Valley of California. Red surface color was significantly improved from 7.35% in the control to 14.27% where 60-inch-wide silver polypropylene o 48-inch-wide crinkled foil on cloth backing were applied to the soil between rows of `Fuji' apple grown on a Lincoln trellis. The weight per apple was also significantly increase where the reflective materials were used. There was no significant difference in soluble solids, acidity, pH, pounds firmness, or starch content. Packinghouse records showed a 33% increase in first harvest pack-out where the reflective materials were used. Total pack-out in the larger sizes was improved in the extra-fancy and US#1 grades, while the utility-grade fruit was reduced by using these materials. Ground color was shifted from green to yellow where the reflective materials were used.
Timothy K. Broschat and Monica L. Elliott
Foxtail palms (Wodyetia bifurcata Irvine) were grown in 6.2-L containers using a 3 calcitic limestone gravel: 2 coir dust (by volume) substrate to induce Fe chlorosis. Plants were treated initially and 2 and 4 months later with soil applications of FeDTPA, FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeEDTA+FeDTPA on clay, ferric citrate, ferrous ammonium sulfate, ferrous sulfate, ferrous sulfate+sulfur, or iron glucoheptonate at a rate of 0.2 g Fe/container. Similar plants were treated initially and 2 and 4 months later with foliar sprays of FeDTPA, FeEDDHA, ferric citrate, ferrous sulfate, or iron glucoheptonate at a rate of 0.8 g Fe/L. After 6 months, palms receiving soil applications of FeEDDHA, FeEDTA+FeHEDTA on vermiculite, FeDTPA, or FeEDTA+FeDTPA on clay had significantly less chlorosis than plants receiving other soil-applied Fe fertilizers or untreated control plants. Palms treated with foliar Fe fertilizers had chlorosis ratings similar to untreated control plants. Palms with the most severe Fe chlorosis also had the highest levels of leaf spot disease caused by Exserohilum rostratum (Drechs.) K.J. Leonard & E.G. Suggs. Neither chlorosis severity nor leaf spot severity was correlated with total leaf Fe concentration.
Enrique E. Sánchez and Timothy L. Righetti
This study was carried out on mature `Delicious' apple trees (Malus domestica Borkh.) on EM 9 rootstock. Labeled B (99.63 Atom % 10B) was applied as boric acid. Treatments were postharvest foliar B at 375 mg·L–1, postharvest foliar B (375 mg·L–1) plus urea (2.5% wt/vol), and a soil application at the same per-tree rate as the foliar treatments (16 g boric acid/tree). Postharvest foliar B applied with or without urea was efficiently transported from the leaves into storage tissues for the next year's growth. However, soil-applied B remained mostly in the roots while very little was translocated to the above-ground portions of the tree at full bloom. When urea was added to a foliar B spray, the amount of B in the roots and flower clusters increased at full bloom. Although increasing the efficiency of foliar B applications may not be necessary, combining urea and B into a single application is recommended when growers want to apply both N and B. Shoot leaves from all treatments collected late in the season (midsummer) had similar B concentrations, even though treatments altered the amount of added B that was present in different tree tissues early in the season.
James M. Wargo, Ian Merwin, and Christopher Watkins
`Jonagold' apple often has problems of inadequate red blush development at harvest, and loss of firmness and skin “greasiness” after refrigerated storage. During two growing seasons we tested factorial combinations of three preharvest treatments for managing these problems: 1) N fertilization (no applied N, 34 kg N/ha in May, or 1% (w/w) foliar urea sprays in May and June); 2) mid-summer trunk scoring (girdling); and 3) aminoethoxyvinylglycine (AVG) applications 3 weeks prior to harvest. Fruit were harvested at four weekly intervals each year, and evaluated for size, blush, firmness, soluble solids, ethylene, and starch hydrolysis. Nitrogen delayed blush development in 1998, but not 1999, and there was no difference in fruit surface blush coverage between foliar urea and soil applied N. Nitrogen applications increased fruit size, decreased fruit firmness, and increased post-storage flesh breakdown in 1999. Trunk scoring increased blush coverage and intensity both years, and improved market-grade packouts. Blush increase after trunk scoring was not caused by advanced fruit maturity (based on ethylene and starch indices) in either year, although it did increase skin greasiness slightly. AVG treatments delayed maturity and blush development of `Jonagold' by 7 to 10 days both years, relative to untreated fruit. Flesh firmness increased and greasiness decreased in AVG treated fruit harvested on the same dates as controls. However, in AVG fruit harvested at comparable stages of maturity 7 to 10 days later, firmness and greasiness were equivalent to untreated fruit on the previous harvest date. Trunk scoring and no N fertilizer were effective for improving fruit blush coloration, and AVG for delaying harvest maturity.