Individual bearing pecan [ Carya illinoinensis (Wangenh.) C. Koch] trees periodically exhibit episodes of substantial shoot and small limb death referred to here as “shoot dieback maladies” (SDMs). These SDMs have received little study and are
Charles C. Reilly, Bruce W. Wood and Katherine L. Stevenson
Michele R. Warmund and Jeanne D. Mihail
, Diplodia , Nectria , Neonectria , and Sphaeropsis spp. are fungi that have been associated with cankers and mortality of the distal end of elderberry canes ( Charlebois et al., 2010 ). The incidence of cane dieback and foliar necrosis symptoms in early
Scott N. White, Nathan S. Boyd and Rene C. Van Acker
growth of these ramets until abortion of the apical meristem (tip dieback) stimulates development of floral buds in late summer and fall ( Aalders and Hall, 1964 ; Barker and Collins, 1963 ; Hall and Ludwig, 1961 ). Ramets generally emerge rapidly from
Sharon Inch, Ed Stover, Randall Driggers and Richard F. Lee
natural freeze events in east–central Florida. Defoliation and dieback were assessed in the winters of 2010 and 2011. Materials and Methods Seeds from Citrus and Citrus hybrids were obtained from the USDA-ARS National Clonal Germplasm Repository for
Aref A. Abdul-Baki, Clyde Wilson, George E. Brown Jr., Lidia M. Carrera, Sam Aslan, Sam Cobb and Tim Burke
The mineral concentration of bearing `Mejhool' date palm (Phoenix dactylifera L.) trees was investigated with the objective of identifying the cause of browning and dieback of distal parts of the fruit-bearing strands. Tissue analyses of leaves, fruits, healthy and dead portions of fruit-bearing strands indicated that tissue browning and dieback appeared to be associated with a high concentration of certain mineral elements. A comparison of mineral concentration between healthy and dead tissue of the fruit-bearing strands showed no significant increase in K, Cu, B, Zn, and Na, but very high increases in the concentrations of P, Ca, Mg, S, Mn, and Fe. The levels of P, Ca, Mg, S, Mn, and Fe in the distal part of the fruit-bearing strand over a 3-year average were 5, 18, 12, 3, 11, and 2 times, respectively, higher than those in the healthy, proximal part of the strand. Mineral concentrations of leaves and mature fruits were determined for comparison with those in fruit-bearing strands.
Patrick H. Brown, Hening Hu and Warren G. Roberts
The phloem mobility of boron (B) in plants varies dramatically among species. Variations in phloem B mobility occur as a consequence of the presence of sugar alcohols (polyols) in some species but not in others, and these differences in phloem B mobility profoundly affect the expression of B toxicity symptoms. Twenty-four species including common ornamental species varying in sugar alcohol content, were selected to test their response to B toxicity. Species that do not produce sugar alcohols exhibited previously described B toxicity symptoms that include accumulation of high concentrations of B in, and burning of, the tip and margin of old leaves. In the sugar-alcohol-producing species these symptoms were absent, and B toxicity was expressed as meristematic dieback and an accumulation of B in apical tissues. These symptoms have not previously been associated with B toxicity in these species and hence may have been frequently misdiagnosed.
Maurus V. Brown, David C. Ferree, David M. Scurlock and Gene Sigel
In the Spring and Summer 1997, severe die back of `Pinot Gris' and `Chambourcin' grape (Vitis vinifera) vines was observed by aerial surveillance in a commercial vineyard adjacent to Lake Erie. Vines grown over the tile lines grew well during 1997-99 following the excessively wet year of 1996. This was not the case for vines that were located betweentile lines. It was postulated that by digging and refilling the trench to insert the tile that either soil compaction or soil pH had been altered and could be responsible for the vine performance. Measurements indicated that these factors were not altered enough to explain the growth differences between vines growing over tile lines and those vines growing between tile lines. It appears that soil oxygen was improved by tiling and likely made the difference in cane dieback during the excessively wet year of 1996. By 1999, vines over tile and between tile had similar yields, and the pattern was no longer visible from the air. This study showed that heavy clay soils with naturally poor internal drainage caused cane dieback and poor growth of vines, especially in very wet years. Thus, it appears prudent on soils of this type, tile drainage is beneficial and spacing of lateral tile lines needs to be closer than 40 ft (12 m) in plateau silt loam soils to adequately protect vines from wet years.
Ivan Simko, Ryan J. Hayes, Krishna V. Subbarao and Rebecca Grube Sideman
SM09A and SM09B are F 8 romaine breeding lines of lettuce ( Lactuca sativa L.) resistant to the dieback disease and with good shelf life. SM09B was selected from a cross between ‘Darkland’ and PI 491224, whereas SM09A was developed from ‘Green
Bijan Dehgan, Joseph E. Durando and Thomas H. Yeager
Cycas revoluta, an important ornamental palm-like plant of warmer regions of the world, often exhibits a foliar chlorotic/necrotic dieback in landscapes. Despite a weak correlation (r2 ≤ 0.28) of percent symptoms with soil nutrient levels or pH, symptom severity was correlated more notably (r2=0.49) with Mn and had even a higher correlation (r2 = 0.61) with the Fe : Mn ratio. Anatomical examination of chlorotic leaflets indicated an accumulation of tanniniferous cells but did not provide direct evidence of Mn deficiency. Although field surveys indicated a link between low Mn levels and Fe : Mn ratio in the plant and appearance of the disorder, the manifestation of symptoms could not be directly correlated with any edaphic factors. However, identical symptoms were induced in young plants by withholding Mn in a solution culture experiment. Application of chelated Mn on expanding leaves alleviated the disorder, but only for the current growth flush. Irrigation frequency in concert with other cultural practices probably are more responsible for development of symptoms than actual soil Mn inadequacy. In consideration of acute susceptibility of cycads to micronutrient deficiencies, plants should be supplied with a complete micronutrient fertilizer during growth in containers and before field planting.
S.M. Southwick, W. Olson, J. Yeager and K.G. Weis
During the fruit growing season, April through August 1990, 1991, and 1992, four sprays of 20-22 liters/tree of KNO3 were applied to `French' prune trees (Prunus domestica L. syn. `Petite d'Agen). Spray applications of KNO3 were compared to single annual soil applications of KCl (1.4-2.3 kg/tree) and sprays of urea + KNO3 with respect to leaf K and N, fruit size, drying ratio, and dry yield. Potassium nitrate sprays were as effective, or better, than soil-applied K in maintaining adequate levels of leaf K throughout the season. Treatment effects were not carried over into the next year. Lowest leaf K was found in trees where no K had been applied. Those values were below the adequate level of 1.3% K and the untreated group developed K deficiency symptoms. Consistent effects on leaf K were not obtained when urea was applied and no negative effect on leaf K was demonstrated. Equivalent dry yields per tree were obtained by foliar and soil K applications. There was no best time for KNO3 sprays. Yield per tree was not enhanced when foliar K-N sprays were applied to trees that had levels of 1.3% K or more as of 15 Apr. 1992. Trees that were below optimum K in April tended toward improved dry yields after four K-N sprays. Trees that had no applied K were lowest yielding. Drying ratios and fruit size (number of fruit per kilogram) were not different among K treatments. Dry yields per tree were increased without a decrease in fruit size or an increase in drying ratio with either soil or foliar K application. These results suggest that foliar KNO3 sprays applied four times throughout the growing season can be used to correct incipient K deficiency in `French' prune and to obtain dry yields equivalent to those obtained with soil applications of KCl.