Influence of Elevating Tree Potassium on Fruit Drop and Yield of Pecan

Abstract

Excessive Stage II fruit drop (i.e., June drop) often limits profitability of certain pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars. Anecdotal evidence indicates that one cause of drop is linked to a nutrient element deficiency. This study examines the consequences of improving tree potassium (K) nutrition on fruit drop, nutmeat yield, and kernel quality (i.e., % kernel) in 'Desirable' orchards in which generally accepted foliar analysis standards indicate satisfactory tree K nutritional status (i.e., 0.75% or greater to 2.5% K/dry weight). Multiyear field studies of two such orchards found that elevating leaf and fruit K concentration through soil banding of potash over drip irrigation emitters: 1) increased fruit retention by reducing Stage II fruit drop; 2) increased in-shell nut yield; and 3) increased nut quality by increasing percentage kernel. Potash applied through soil banding elevated foliar and fruit K concentration by ' ' 0.1% to 0.4% units within a few months post-application depending on the amount applied; however, the beneficial effects of a single potash soil band application diminished after the first year.

Influence of Aminoethoxyvinylglycine (AVG) on Yield and Quality of Nut Crops from a Commercial Pecan Orchard

“…The ReTain-associated %36% increase in marketable meat yield per unit area of orchard observed in a moderate ''off'' year was not replicated in the subsequent heavy ''on'' year when ReTain was again used. Thus, ReTain's efficacy for 'Desirable' is greatly influenced by crop load and possibly by other factors (e.g., status of nutrient element physiology; Wood et al, 2009Wood et al, , 2010. It is important to note that trees receiving ReTain in an ''off'' year produced less in-shell, total kernel, marketable kernels per unit orchard area in the subsequent ''on'' year than did the nontreated control.…”

“…This indicates that besides crop load, there might be one or more additional interacting factors affecting ReTain's efficacy for increasing nut or nutmeat yield. Anecdotal evidence indicates that this might be early-season fruit K status (Wood et al, 2010). The aforementioned preliminary study (Wood et al, 2009) was in an orchard where young fruit were K-deficient (i.e., meeting the K sufficiency threshold for foliage but not meeting a higher K sufficiency threshold for young fruit; Wood et al, 2010) for the first few weeks post-ovule fertilization.…”

“…Anecdotal evidence indicates that this might be early-season fruit K status (Wood et al, 2010). The aforementioned preliminary study (Wood et al, 2009) was in an orchard where young fruit were K-deficient (i.e., meeting the K sufficiency threshold for foliage but not meeting a higher K sufficiency threshold for young fruit; Wood et al, 2010) for the first few weeks post-ovule fertilization. Another possible interacting factor often touted by growers and extension specialists is an excessive number of pollen grains reaching the stigmatic surface of flowers during an ''on'' year, which can in turn trigger fruit abortion.…”

“…The most problematic drop is typically ''Stage II drop,'' occurring %3 to 5 weeks (usually by mid-June; i.e., June drop) after stigmas of pistillate flowers lose receptivity and fruit begin rapid elongation growth (Sparks and Madden, 1985). A primary cause of Stage II drop is associated with abnormal ovule development (i.e., integument, parenchymal nucleolus cell layers, embryo sac; Sparks, 1994, 1995); however, it is also potentially influenced by nutrient element nutrition at anthesis until a few weeks thereafter (Wood et al, 2010). Although Stage II drop is beneficial in excessively heavy crop-load years, it is undesirable when crop load is less than moderate.…”

“…73049-45; Valent BioSciences, Libertyville, IL}, an ethylene inhibitor, can reduce or prevent drop in certain situations (Wood et al, 2009). AVG, formulated as ReTain, possesses potential as a horticultural tool for preventing or reducing unwanted fruit drop in pecan by interfering with endogenous ethylene biosynthesis, presumably by competitively inhibiting 1-aminocyclopropanecarboxylate synthase (Wood et al, 2010;Yu et al, 1979), the rate-limiting enzyme in the apparent primary ethylene anabolic pathway. Wood et al (2009) observed earlier that AVG, or ReTain, conditionally exhibits efficacy for reducing 'Desirable' fruit drop, thus justifying further evaluation in a real-world large commercial orchard environment.…”