The influence of B and salinity [3 Na2SO4 : 1 CaCl2, (molar ratio)] on B toxicity and the accumulation of B, sodium, and SO4 in six Prunus rootstocks was evaluated. High salinity reduced B uptake, stem B concentrations, and the severity of toxicity symptoms in five of the six rootstocks. Forward and backward stepwise regression analyses suggested that stem death (the major symptom observed) was related solely to the accumulation of B in the stem tissue in all rootstocks. The accumulation of B and the expression of toxicity symptoms increased with time and affected rootstock survival. No symptoms of B toxicity were observed in leaf tissue. The Prunus rootstocks studied differed greatly in stem B accumulation and sensitivity to B. The plum rootstock `Myrobalan' and the peach-almond hybrid `Bright's Hybrid' were the most tolerant of high B and salinity, whereas the peach rootstock `Nemared' was very sensitive to high B and salinity. In all rootstocks, adding B to the growth medium greatly depressed stem SO4 concentrations. In every rootstock except `Nemared' peach, adding salt significantly depressed tissue B concentrations. A strong negative correlation between tissue SO4 and B was observed. Grafting experiments, in which almond was grafted onto `Nemared' peach or `Bright's Hybrid', demonstrated the ability of rootstocks to influence B accumulation and scion survival.
Rawia El-Motaium, Hening Hu, and Patrick H. Brown
Ariena H.C. van Bruggen, Philip R. Brown, and Art Greathead
In growth chamber experiments with five concentrations of NH4NO3 and inoculation of lettuce (Lactuca sativa L.) cv. Salinas with Rhizomonas suberifaciens, the causal agent of corky root (CR), symptoms of noninfectious corky root induced by high rates of N were distinct from those of infectious corky root (ICR). Nitrogen toxicity was observed at 350 kg·ha-1 and above, and was not affected by inoculation with R. suberifaciens. There was a curvilinear relationship between concentration of NH4NO3 applied and ICR severity with a maximum at 525 kg·ha-1. In a similar growth chamber experiment with NH4NO3 plus urea, ICR severity decreased and N toxicity increased at increasing N levels (N at 160 to 650 kg·ha-1). In microplots at Davis, Calif., sidedressing with NH4NO3 (N at 170 kg·ha-1) increased ICR severity on `Salinas' lettuce over the nonfertilized control. There was a significant interaction between N fertilization and soil-infestation with R. suberifaciens with respect to head fresh weight: sidedressing with NH4NO3 increased head weight in noninfested plots, but decreased head weight in infested plots. In four field experiments at Salinas, Calif., sidedressing with N at 78 to 213 kg·ha-1, with N as (NH4)1SO4, NH4NO3, urea, or Ca(NO3)2, increased ICR over the control, but there were no significant differences between the forms of N. Head fresh and dry weights were either increased or unaffected by sidedressing with N fertilizers, depending on the residual concentrations of N in the soil. The increase in ICR was likely related to concentrations of soil NO3 rather than NH4.
S. Christopher Marble and Stephen H. Brown
Plant invasions pose a serious threat to biodiversity, agricultural production, and land value throughout the world. Due to Florida’s unique climate, population expansion, expansive coastline, and number of seaports, the state is especially vulnerable to non-native plant naturalization and spread. Invasive plant management programs were shown to have higher success rates with fewer resources when invasives were managed soon after non-native plants were observed. However, some newly emerging invasive plants may go undetected due to their resemblance with native species or other invasive plants. The objective of this review is to highlight a few key invasive plants in Florida that have native lookalikes. While morphological differences are discussed, the primary goal is to discuss management implications of misidentification and delayed response times, as well as the need for plant identification guides that include information on how to distinguish problematic invasive plants from similar native species.
A.G. Manganaris, F.H. Alston, N.F. Weeden, H.S. Aldwinckle, H.L. Gustafson, and S.K. Brown
Pgm-1, the gene responsible for variation in the most anodal isozyme of phosphoglucomutase in apple (Malus spp.), is shown to lie ≈8 centiMorgans from the gene Vf, which confers apple-scab resistance. The proximity of the marker and the ease by which allozymic forms can be resolved suggest that Pgm-1 will be useful for following the inheritance of scab resistance conferred by Vf.
Slavko Perica, Patrick H. Brown, Joseph H. Connell, Agnes M.S. Nyomora, Christos Dordas, Hening Hu, and James Stangoulis
A 2-year field study was conducted to determine if foliar B applications prior to flowering increased fruit set in olive (Olea europaea L.) cv. Manzanillo. Boron solutions were applied (935 L·ha-1) at four concentrations (0, 246, 491, and 737 mg·L-1) to trees exhibiting no vegetative symptoms of B deficiency. Foliar B application increased both the percentage of perfect flowers and fruit set, but no effect on pollen germination was observed in either year. The increase in fruit set was not accompanied by a reduction in fruit size. The beneficial effects of foliar B application varied between years and were greater when fruit set was low. The results obtained here are in agreement with those observed in other tree species, in which foliar B applications made immediately prior to flowering or during the period of floral bud initiation significantly increased fruit set and yield. The physiological basis for this effect, however, remains unclear.
T.A. Wheaton, J.D. Whitney, W.S. Castle, R.P. Muraro, H.W. Browning, and D.P.H. Tucker
A factorial experiment begun in 1980 included `Hamlin' and `Valencia' sweet-orange scions [Citrus sinensis (L.) Osb.], and Milam lemon (C. jambhiri Lush) and Rusk citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] rootstocks, tree topping heights of 3.7 and 5.5 m, between-row spacings of 4.5 and 6.0 m, and in-row spacings of 2.5 and 4.5 m. The spacing combinations provided tree densities of 370, 494, 667, and 889 trees ha. Yield increased with increasing tree density during the early years of production. For tree ages 9 to 13 years, however, there was no consistent relationship between yield and tree density. Rusk citrange, a rootstock of moderate vigor, produced smaller trees and better yield, fruit quality, and economic returns than Milam lemon, a vigorous rootstock. After filling their allocated space, yield and fruit quality of trees on Milam rootstock declined with increasing tree density at the lower topping height. Cumulative economic returns at year 13 were not related to tree density.
James E. Brown, Daniel W. Porch, Ronald L. Shumack, Charles H. Gilliam, and Larry Curtis
In sweet corn field plots in Alabama, urea-ammonia nitrogen was applied to the soil through underground and aboveground drip fertigation systems. Dry nitrogen in the form of ammonium nitrate was surface band-applied as a control. Nitrogen rates of 67 kg/ha and 135 kg/ha were applied in either 2 or 4 applications by each of the 3 methods. P and K fertilizers were applied to all treatments in a dry form according to soil test recommendations. The underground drip pipe was placed 23 cm beneath the soil surface in each row. Nitrogen (wet or dry) rate of 135 kg/ha produced greater sweet corn yield than the 67 kg/ha rate with no effect of application number on yield in 1988, when rainfall was less than adequate. In 1987 and 1989, when rainfall was adequate, no differences occurred in yields regardless of number, rate, or method of application of nitrogen.
D.S. Lawson, S.K. Brown, J.P. Nyrop, and W.H. Reissig
A barrier system for pest control consisting of insect-exclusionary cages covered with three types of mesh material was placed over columnar apple (Malus domestica Borkh.) trees. This system has been shown to provide arthropod control equivalent to insecticides. Light intensity, evaporation, and air and soil temperature were reduced inside the cages. Shoot elongation of columnar apple trees grown inside insect-exclusionary cages was significantly greater than that of trees grown outside the cages. However, this increased shoot growth was not due to etiolation. Tree performance was unaffected by insect-exclusionary cages. Fruit set and fruit soluble solids concentration were not reduced by the cages; however, fruit color intensity was reduced as the degree of shading from the mesh increased. These findings, in conjunction with high levels of arthropod control by insect-exclusionary cages, may allow insect-exclusionary cages to be used for evaluating integrated pest management thresholds, predator-prey relationships, and apple production without insecticides.
James E. Brown, Charles H. Gilliam, Ronald L. Shumack, and Daniel W. Porch
Commercial snap bean (Phaseolus vulguris L.) yields in spring were similar when comparing a commercial fertilizer standard based on soil test recommendations to three application rates of broiler litter. Snap bean yields in the fall were higher on plots that received spring-applied broiler litter than on those receiving the commercial fertilizer standard in the fall. Increasing the application rate of broiler litter generally resulted in a linear yield response during both seasons.
Edwin J. Reidel, Patrick H. Brown, Roger A. Duncan, and Steven A. Weinbaum
Almond [Prunus dulcis (Mill.) D.A. Webb] yields have increased substantially since the 1961 publication of the Univ. of California (UC) guidelines for leaf potassium (K). Numerous growers and reputable analytical laboratories are concerned that the recommendations for leaf K are inadequate. A highly productive almond orchard with low leaf K was selected to reassess the leaf K critical value of 1.1% to1.4% and determine the relative sensitivity of various yield determinants to inadequate K availability. Baseline yields for 100 individual trees were measured in 1998 and four rates of potassium sulfate were applied under drip irrigation emitters to establish a range of July leaf K concentrations between 0.5% and 2.1%. No relationship was observed between leaf K and post-treatment yield measurements made in 1999. We also monitored individual limb units on trees from the treatment extremes for effects of low K availability on flower number, percentage fruit set, fruit size, spur mortality, and vegetative growth (potential fruiting sites in subsequent years). Those measurements indicated that although current-year yield determinants (percentage fruit set and fruit size) were not influenced by K deficiency, components of future yield were impacted negatively by low K availability: mortality of existing fruiting spurs was increased by K deficiency and growth of fruiting wood was reduced.