Powdery mildew (Golovinomyces spadiceus) is the most common disease of greenhouse cannabis. Most hemp grown for cannabinoid production is propagated by cuttings or started from feminized seed in greenhouses and then moved outdoors, while most marijuana and some hemp are grown entirely indoors. To determine the effects of silicon on powdery mildew in the greenhouse, silicon was applied to hemp roots in a peat-based soilless mix and evaluated for plant uptake and disease suppression over a 6-week period. This study confirmed that there was a negative linear relationship between percent silicon accumulation in leaf tissue and the percent powdery mildew per leaf area. Mildew severity in the upper canopy was significantly reduced at 300 kg/ha of silicon, while 600 kg/ha was needed for the mid canopy. Results confirmed that silicon may be a useful tool for the integrated management of powdery mildew. As the cannabis market expands, silicon can serve as a viable option for greenhouse growers, especially for plants grown in soils or soilless mixes low or limiting in soluble silicon.

Numerous reviews and hundreds of refereed articles have been published on silicon's effects on abiotic and biotic stress as well as overall plant growth and development. The science for silicon is well-documented and comprehensive. However, even with this robust body of information, silicon is still not routinely used for alleviating plant stress and promoting plant growth and development. What is holding producers and growers back from using silicon? There are several possible reasons, which include: (i) lack of consistent information on which soil orders are low or limited in silicon, (ii) no universally accepted soil test for gauging the amounts of soluble silicon have been calibrated for many agronomic or horticultural crops, (iii) most analytical laboratories do not routinely assay plant tissue for silicon and current standard tissue digestion procedures used would render silicon insoluble, (iv) many scientists still state that plants are either silicon accumulators or non-accumulators when in reality all plants accumulate some silicon in their plant tissues, (v) silicon is not recognized as being necessary for plant development, (vi) lack of economic studies to show the benefits of applying silicon, and (vii) lack of extension outreach to present the positive benefits of silicon to producers and growers. Many of these issues mentioned above will need to be resolved if silicon is to become a standard practice to improve agronomic and horticultural crop production and plant health.

Update of the 2015 version with Geoffrey Meru includes new integrated management procedures to reduce the impact of crown and root rot.

Bacterial fruit blotch (BFB) caused by Acidovorax citrulli (Ac) is the most destructive bacterial disease affecting melon production in northeastern Brazil. Silicon (Si), which is widely recognized for suppressing plant diseases, has been proposed as a possible alternative for the control of BFB. Field experiments were conducted to evaluate the effects of slag fertilization on bacterial blotch development, soil chemical properties, plant growth and nutrition, and fruit quality. Melon hybrids AF 4945 and Medellin were grown in slag-fertilized (5.00 t ha-1) and non-fertilized plots, being inoculated with Ac 25 days after emergence. The slag fertilization significantly reduced the area under the disease progress curve (10%), disease index (14%) and disease incidence in fruit (12%) at harvest, regardless of hybrid. Slag fertilization improved the soil fertility, plant growth and nutrition after 55 days of cultivation. Tissue analyses showed no differences in Si accumulation between the melon hybrids. However, AF 4945 accumulated more Ca and Zn than Medellin, which was associated with higher reduction in disease intensity. Also, slag treatment increased fruit flesh thickness (8%) and soluble solids (7%). Our study confirms that the supply of slag to the soil previously assessed under greenhouse studies can reduce the severity and incidence of melon BFB while improving fruit quality under field conditions.

Silicon (Si) is a "quasi-essential" element that helps plants to overcome various abiotic and biotic stresses. This review summarizes research which examined application of Si in turfgrass management and its impact on plant health. Research on inclusion of Si in turfgrass has largely centered upon three areas: plant disease suppression, improvement in wear tolerance, and reductions in drought and salinity stress. Of these, the ability of Si to reduce turf diseases has received the most attention, with applications of Si often reducing various diseases, including gray leaf spot, dollar spot, and brown patch, in creeping bentgrass, bermudagrass, perennial ryegrass, and St. Augustinegrass. One potential constraint to its effectiveness is that Si application rates for disease reduction are often quite high (e.g., rates as high as 400 to 2,000 kg Si ha(-1)). Responses were also variable with turfgrass species, soil type, and soil Si content, and the measured response was often not great enough to produce turf of desirable quality without additional use of fungicides. More research is needed in the area of Si and turf wear, as the use of Si to "harden" turfgrass and improve wear and ball roll is widely marketed in turfgrass maintenance. Further research is also needed to identify best soil extractants for measuring soluble Si and to calibrate this extractable Si for the determination of critical levels of soil Si across soil types and turfgrass species.

While silicon (Si) fertilization is widely practiced in rice production, establishing critical soil Si levels has remained understudied. Field trials were established at 12 sites across Louisiana from 2013 to 2015 to determine critical soil Si for rice cultivation. Five silica slag (14% Si) rates at 0, 1, 2, 4, 6, and 8 Mg ha(-1) and two lime rates (2 and 4 Mg ha(-1)) were arranged in randomized complete block design with four replications. Post harvest soil samples were analyzed for Si using seven extraction procedures. The critical soil Si levels established by the linear plateau model using 0.5 M acetic acid-1 hr (OAc-1) extraction procedure were 36, 41 and 50 mg kg(-1) for plant Si uptake, grain yield, and relative yield as response variables, respectively. Generally, soils having high initial Si and pH had minimal responses to Si fertilization, whereas Si content of soils with low initial Si was significantly increased.

Adequate silicon nutrition in plants has shown positive effects on the growth and yield of the crop and physico-chemical properties of the soil. Hence, this study was initiated to survey the plant-available silicon in the agricultural soils of different parishes of Louisiana. Soil samples were collected from 212 representative agricultural fields of 27 agrarian parishes of Louisiana. Poor correlations between deionized water, calcium chloride, and other extractants suggest that the unbuffered calcium chloride extraction may reflect only a transient status of soil soluble silicon similar to deionized water extraction procedure. Also, acetic acid-2 extraction procedure may reflect the net effects of the sorption/desorption reactions by extracting the readily as well as the slowly releasable silicon that control solubility, thus giving a true measure of current availability. Compared to the previously established critical soil silicon levels, several agricultural fields of Louisiana were deemed to be low in plant-available silicon.

Silicon (Si) plays a pivotal role in the nutritional status of a wide variety of monocot and dicot plant species and helps them, whether directly or indirectly, counteract abiotic and/or biotic stresses. In general, plants with a high root or shoot Si concentration are less prone to pest attack and exhibit enhanced tolerance to abiotic stresses such as drought, low temperature, or metal toxicity. However, the most remarkable effect of Si is the reduction in the intensities of a number of seedborne, soilborne, and foliar diseases in many economically important crops that are caused by biotrophic, hemibiotrophic, and necrotrophic plant pathogens. The reduction in disease symptom expression is due to the effect of Si on some components of host resistance, including incubation period, lesion size, and lesion number. The mechanical barrier formed by the polymerization of Si beneath the cuticle and in the cell walls was the first proposed hypothesis to explain how this element reduced the severity of plant diseases. However, new insights have revealed that many plant species supplied with Si have the phenylpropanoid and terpenoid pathways potentiated and have a faster and stronger transcription of defense genes and higher activities of defense enzymes. Photosynthesis and the antioxidant system are also improved for Si-supplied plants. Although the current understanding of how this overlooked element improves plant reaction against pathogen infections, pest attacks, and abiotic stresses has advanced, the exact mechanism(s) by which it modulates plant physiology through the potentiation of host defense mechanisms still needs further investigation at the genomic, metabolomic, and proteomic levels.

HomeMycologyFusarium Wilts of Greenhouse Vegetable and Ornamental CropsCHAPTER 15: Fusarium Diseases of Tomato PreviousNext CHAPTER 15: Fusarium Diseases of TomatoCheng-Hua Huang, Pamela D. Roberts, and Lawrence E. DatnoffCheng-Hua HuangSearch for more papers by this author, Pamela D. RobertsSearch for more papers by this author, and Lawrence E. DatnoffSearch for more papers by this authorAffiliationsAuthors and Affiliations Cheng-Hua Huang Pamela D. Roberts Lawrence E. Datnoff Published Online:2 Aug 2017https://doi.org/10.1094/9780890544822.018AboutSectionsPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Abstract Fusarium wilt and Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. lycopersici, are two important diseases of tomato. Fusarium wilt, a warm weather disease, was first described in England in 1895 and has since been found in at least 32 countries. In contrast, Fusarium crown and root rot, thriving at cooler temperatures, was first identified in Japan in 1969 and thought to be a new race (J3) of f. sp. lycopersici. In the United States, Fusarium crown and root rot was first noted in California in 1971 and then in Florida in 1975. In 1978, Jarvis and Shoemaker proposed that the causal agent of Fusarium crown and root rot was distinct from F. oxysporum f. sp. lycopersici based on symptomology, disease development, and physiological characteristics. Genetic differences have been proposed between F. oxysporum f. sp. lycopersici and f. sp. radicis-lycopersici because the two formae speciales are vegetatively incompatible. DetailsFiguresLiterature CitedRelated Fusarium Wilts of Greenhouse Vegetable and Ornamental CropsISBN:978-0-89054-482-2 Metrics Pages: 145-158 InformationPDF download

Two diseases of St. Augustinegrass (SAG) [Stenotaphrum secundatum (Walt.). Ktze.] are caused by different anastomosis groups (AGs) of Rhizoctonia solani. Brown patch (BP) is a foliar disease of little economic importance, and large patch (LP) causes leaf sheath rot and death of affected turfgrass shoots and stolons. St. Augustinegrass genotypes were inoculated with an isolate that causes BP and an isolate that causes LP in repeated experiments. Three disease severity parameters were calculated from data recorded from each genotype, including final disease severity (Y), area under the disease progress curve (AUDPC), and the apparent infection rate (r L). The inoculation protocol reliably produced symptoms, and both r L and AUDPC provided statistically significant separations between genotypes for their susceptibility to BP and LP. A significant interaction between isolate and genotype was observed, and some genotypes that were very susceptible to LP were among the least susceptible to BP. These data suggest that differences in resistance to LP can be quantified in SAG genotypes, but genotype response may be isolate dependent.

A series of pot experiments were conducted to: (1) evaluate the effects of different Si sources (soil- and foliar-applied) on grain yield and Si accumulation of rice supplied with varying P rates, and (2) evaluate Si absorption of rice using foliar- and soil-applied Si fertilizers. Three P rates, (0, 112, and 224 kg ha−1) combined with five Si treatments (wollastonite and slag applied at 4.5 ton ha−1 and one foliar Si solution applied at 20, 40 and 80 mg Si L−1) and a check were arranged in a randomized complete block design with four replications. The presence of P and Si in the soil created a synergistic effect on soil Al, Mn, and As (P < 0.01), but not on rice growth and P uptake. Wollastonite and slag application were most effective in raising rice Si content than foliar applied Si (P < 0.001). While there was an improvement in biomass (42%) and tiller production (25%) for rice receiving foliar Si, no supporting evidence was obtained in these experiments to verify leaf surface Si absorption. The application of Si-rich materials to soil still remains the most effective method for enhancing Si uptake by plants.

Field studies were established on the alluvial floodplain soils in Louisiana, from 2013 to 2015, to evaluate the effect of silicate slag applications on productivity of wheat (Triticum aestivum), under sufficient and high nitrogen (N) application rates. Treatments were arranged in a randomized complete block design, with four replications consisting of twelve treatments: a factorial combination of two N (101 and 145 kg N ha−1) and five silicate slag rates (0, 1, 2, 4.5, and 9 Mg ha−1), and two control plots (with and without lime). Nitrogen had a greater impact on wheat productivity than silicate slag application. Wheat grain yield reached over 7000 kg ha−1 with applications of 145 kg N, and 9 Mg silicate slag per ha for soil having Si level <20 mg kg−1. Yield increases due to N or Si were attributed to the increase in number of spike m−2 and grain number spike−1. Silicate slag application effectively raised soil pH, and availability of several plant-essential nutrients, including plant-available N (nitrate, NO3−), demonstrating the benefits of slag application are beyond increasing plant-available Si. The benefits of silicate slag application were clearly observed in wheat supplied with high N, and on soil with low plant-available Si.

The amount of monosilicic acid (H4SiO4), which is the plant-available form of silicon (Si), released from fertilizers can be influenced by Si source and soil properties. A series of laboratory experiments were conducted using six soil series from Louisiana to document the differences in the release characteristics of H4SiO4 from wollastonite and slag. Monosilicic acid in solution released from slag declined with time while wollastonite consistently increased its concentration across all soil suspensions well above 40 mu g mL(-1). Among these soil series, soils high in organic matter and clay were seen to have maximum percent sorption (up to 79%) with minimum polymerization of H4SiO4. The presence of ions like aluminum (Al) and magnesium (Mg) enhanced the process of H4SiO4 polymerization, which led to a decrease in H4SiO4 concentration in solution. Evident relationships were observed between H4SiO4 concentration in solution with added Si sources and sorbed quantity from soil solutions.

Silicon (Si) is the second most abundant element in the earth's crust and plays a number of important roles in the mineral nutrition of plants. In the past 20 years, the scientific documentation on the benefits of Si to crops has helped establish Si fertilization as an agronomic practice in many agricultural lands worldwide. However, very little information has been consolidated on the use of Si specifically for US agriculture. Consequently, the objectives of this review are to provide (1) information on the dynamics of Si in soil, use, and sources; (2) a history and up-to-date documentation on Si-related research in many areas of US production agriculture; and (3) perspectives on Si as a plant beneficial nutrient and the potential of Si fertilization as an agronomic practice in US crop production systems. The Si-driven mechanisms enhancing the productivity of a wide array of crops under stressed conditions are discussed in this review. Based on the recent 10-year average production level and published shoot Si content, the principal crops grown in the United States can collectively take up 9.55 million tons of Si annually, whereas the annual Si removal rate for the entire US cropland area is estimated at 21.1 million tons. On the basis of this projected annual Si removal rate, adoption of continuous intensive farming systems in the country, low solubility of soil Si, and complex chemical dynamics of Si in soil, increasing plant-available Si levels through fertilization is therefore foreseen a logical agronomic practice for US agriculture.

Calibration of crop responses to applied silicon (Si) serves as a basis for developing Si fertilizer recommendation guidelines. A greenhouse experiment was set up in a randomized complete block design with five replications, two sources of Si (wollastonite and slag) and four Si rates (0, 170, 340 and 680kgha(-1)) to calibrate plant-available Si for growing rice in Louisiana soils. Silicon concentrations were determined in soils using seven different extraction procedures. Based on a quadratic model (p<0.05), the estimated soil Si critical level using 0.01M calcium chloride (CaCl2) for Sharkey clay soil was 110mgkg(-1) while for Crowley silt loam and Commerce silt loam, levels were 37 and 43mgkg(-1), respectively. These results suggest that suitability of an extractant that gives the best estimate of plant-available Si could considerably depend on soil type and it is unlikely that there is a universal extractant for all soils.

The health of any ornamental crop is a direct function of the nutritional status of the plant. Disease susceptibility or resistance is often governed by the speed in which the plants can directly react to infection by plant pathogen and/or indirectly by their ability to tolerate predisposing stresses such as drought. Information is presented herein on the role of essential minerals N, P, K, Ca, Mg, S, Cl, Fe, Mn, Cu, Zn, B, Mo, and Ni along with beneficial elements Si and Al for their effects on suppressing diseases in ornamental crops.