Overhead Irrigation Research Articles

Risks for infection of strawberry plants with an aerosolized inoculum of Xanthomonas fragariae

Xanthomonas fragariae is the causative agent of angular leaf spot of strawberry, a quarantine organism in plant propagation material in the European Union. Field experiments were conducted to assess the risks for infection of strawberry plants through dispersal of an aerosolized inoculum. In practice, pathogen aerosols can be formed during mowing of an infected crop or by water splashing on symptomatic plants during overhead irrigation or rain. In our experiments, aerosols were generated by spraying suspensions of X. fragariae with a density of 108 cfu ml−1 or water under pressure vertically up into the air. In strawberry plants (cv Elsanta) placed at 1.3, 5 and 10 m distance downwind from the spray boom, infections were found, as evidenced with a combination of dilution–plating and molecular techniques, but more frequently in plants wetted prior to inoculation than in plants kept dry. A logarithmic decrease in infection incidence was found with the distance to the inoculum source. Symptomatic plants were found up to 5 m distance from the inoculum source. No infected plants were found in plants placed 4 m upwind or treated with water. In glasshouse studies, it was shown that under conditions favorable for disease development, spray-inoculation of strawberry plants with estimated densities of X. fragariae as low as 2000 cfu per plant were able to cause symptoms both in cv Elsanta and cv Sonata. Results indicate that there is a considerable risk on infections of strawberry plants exposed to aerosolized inoculum.

Long-Term Irrigation Affects the Dynamics and Activity of the Wheat Rhizosphere Microbiome.

The Inland Pacific Northwest (IPNW) encompasses 1. 6 million cropland hectares and is a major wheat-producing area in the western United States. The climate throughout the region is semi-arid, making the availability of water a significant challenge for IPNW agriculture. Much attention has been given to uncovering the effects of water stress on the physiology of wheat and the dynamics of its soilborne diseases. In contrast, the impact of soil moisture on the establishment and activity of microbial communities in the rhizosphere of dryland wheat remains poorly understood. We addressed this gap by conducting a three-year field study involving wheat grown in adjacent irrigated and dryland (rainfed) plots established in Lind, Washington State. We used deep amplicon sequencing of the V4 region of the 16S rRNA to characterize the responses of the wheat rhizosphere microbiome to overhead irrigation. We also characterized the population dynamics and activity of indigenous Phz+ rhizobacteria that produce the antibiotic phenazine-1-carboxylic acid (PCA) and contribute to the natural suppression of soilborne pathogens of wheat. Results of the study revealed that irrigation affected the Phz+ rhizobacteria adversely, which was evident from the significantly reduced plant colonization frequency, population size and levels of PCA in the field. The observed differences between irrigated and dryland plots were reproducible and amplified over the course of the study, thus identifying soil moisture as a critical abiotic factor that influences the dynamics, and activity of indigenous Phz+ communities. The three seasons of irrigation had a slight effect on the overall diversity within the rhizosphere microbiome but led to significant differences in the relative abundances of specific OTUs. In particular, irrigation differentially affected multiple groups of Bacteroidetes and Proteobacteria, including taxa with known plant growth-promoting activity. Analysis of environmental variables revealed that the separation between irrigated and dryland treatments was due to changes in the water potential (Ψm) and pH. In contrast, the temporal changes in the composition of the rhizosphere microbiome correlated with temperature and precipitation. In summary, our long-term study provides insights into how the availability of water in a semi-arid agroecosystem shapes the belowground wheat microbiome.

Foodborne pathogens and their risk exposure factors associated with farm vegetables in Rwanda

In this study, we tested farm vegetables and agricultural water for the presence of foodborne pathogens, and evaluated farming practices of vegetable farms in Rwanda. Farm vegetable samples were found to be contaminated with foodborne pathogens at considerably high rate (overall 15/99 = 15%). Specifically, the prevalence of pathogens in farm vegetables varied from 1.0% (1/99) for Listeria monocytogenes, 3.0% (3/99) for thermo-tolerant Campylobacter spp., 5.1% (5/99) for Salmonella spp. to 6.1% (6/99) pathogenic Escherichia coli. In agricultural water from rivers, lakes, lagoons, ground and marshlands, prevalence of DNA from pathogens varied from 3% (1/30) for Enteroinvasive E. coli (EIEC); 7% (2/30) for Enteroaggregative E. coli (EAEC); 13% (4/30) for Enterotoxigenic E. coli. (ETEC) and Vibrio cholera; 20% (6/30) for Yersinia pestis; 27% (8/30) for Francisella tularensis; 40% (12/30) for Cyclospora to 87% (26/30) for thermo-tolerant Campylobacter spp. DNA of the following pathogens was not detected (0/30) in water: entero pathogenic E. coli (EPEC), shiga toxin producing E. coli (STEC), Salmonella spp., L. monocytogenes, Burkholderia, Rickettsia, Toxoplasma gondii, Giardia lamblia, Cryptosporidium, Entamoeba histolytica and Hepatitis E. About farming practices, 60% of the visited vegetable farms practiced irrigation and all the water used was from un-protected sources (from marshlands [70% ], rivers [18% ], lakes [7% ], runoff lagoons [5% ]). Over 80% of the farms applied overhead irrigation methods and none of the farms had implemented measures to restrict the access of domestic and wild animals, while 50% of the farms used untreated manure. The reported high detection rate of foodborne pathogens DNA in agricultural water and the observed risky farming practices, provides a likely explanation of the reported prevalence of pathogens in farm vegetables and presents an important public health concern if these vegetables are to be consumed raw.

Response of Japanese Privet to Plastic Mulch Applied over Nonspaced Containers

Mulches have many positive benefits for the production of plants, ranging from weed suppression to water conservation. In this study, a novel method of using plastic film mulch for container-grown plants was evaluated. Plots of 25 japanese privet (Ligustrum japonicum) in #1 (2.5 qt) nonspaced containers were wrapped with 1.25-mil white or black plastic mulch over the top and sides of containers. Small plants were planted through the plastic and grown for 22 weeks with overhead irrigation. Water application amount was determined by moisture sensors placed in the substrate of each treatment. Plant growth, dry weights (DWs), weed fresh weights, weeding time, substrate electrical conductivity (EC), substrate temperature, total water applied, and mulch costs were determined. Black plastic (BP) and white plastic (WP) mulch reduced water applied by 82% and 91%, respectively, compared with the nontreated control (NT). Nontreated control plants grew faster and had greater DW at the end of the experiment. Mulched containers had fewer weeds and required less labor to remove weeds than the NT treatment. Substrate EC level was greater in BP and WP treatments than for the NT after 20 weeks, and plastic mulch did not result in different substrate temperatures. Plastic mulch added $4.94/1000 containers ($2.24 input cost and $2.70 removal cost) to production costs, not including disposal costs. This novel method of mulching nonspaced plants reduced irrigation water, herbicide applications, and weeding labor, but probably added 2–3 weeks to finish time.

Uptake and Accumulation of Pharmaceuticals in Overhead- and Surface-Irrigated Greenhouse Lettuce.

Understanding the uptake and accumulation of pharmaceuticals in vegetables under typical irrigation practices is critical to risk assessment of crop irrigation with reclaimed water. This study investigated the pharmaceutical residues in greenhouse lettuce under overhead and soil-surface irrigations using pharmaceutical-contaminated water. Compared to soil-surface irrigation, overhead irrigation substantially increased the pharmaceutical residues in lettuce shoots. The increased residue levels persisted even after washing for trimethoprim, monensin sodium, and tylosin, indicating their strong sorption to the shoots. The postwashing concentrations in fresh shoots varied from 0.05 ± 0.04 μg/kg for sulfadiazine to 345 ± 139 μg/kg for carbamazepine. Root concentration factors ranged from 0.04 ± 0.14 for tylosin to 19.2 ± 15.7 for sulfamethoxazole. Translocation factors in surface-irrigated lettuce were low for sulfamethoxalzole, trimethoprim, monensin sodium, and tylosin (0.07-0.15), but high for caffeine (4.28 ± 3.01) and carbamazepine (8.15 ± 2.87). Carbamazepine was persistent in soil and hyperaccumulated in shoots.

Evaluation of Fertigation Applied to Furrow and Overhead Irrigated Cotton Grown in a Black Vertosol in Southern Queensland, Australia

Abstract.Field trials were conducted at gated pipe surface and overhead irrigation sites established to cotton ( L.) to evaluate irrigation and fertigation management using a model-based control system. The control strategies determined the timing and volume of irrigation, and the rate of fertilizer-N to apply through fertigation. For this, nitrogen (N) was applied in-crop season using urea ammonium nitrate (UAN, 30% N solution) at a rate of 40 kg ha-1 N. At the furrows site, the uniformity of distribution of fertilizer-N applied through fertigation was satisfactory, which was achieved both at distance (600 m) and depth (0-600 mm). Applying fertilizer-N through fertigation, at the rate used in this study, showed relatively small (=8%) improvements in cotton yield, which was explained by relatively high N rates (180 kg ha-1 N) applied before planting. Given current price ratios (fertilizer-to-cotton), application of N through fertigation appears to be economical in both systems, but relative agronomic efficiencies and economic return from the fertilizer applied were lower in furrow compared with overhead (P<0.05). Fertigation may be recommended when pre-season N application rates are low (e.g., <100 kg ha-1 N), particularly in overhead irrigation as significantly higher efficiencies both in terms of water and N use can be achieved with this system. This would enable some of the operational constraints associated with application of N in-crop season to be overcome; thereby, reducing the need for high rates of N applied up-front. For the overhead system, there were also advantages compared with the furrow system in terms of reduced potential for N2O emissions after irrigation or fertigation. Overall, short-term (30-day period) soil emissions of N2O were approximately eight times higher in furrow compared with overhead. Emissions from non-fertigated crops were approximately two times higher in furrow compared with overhead. Emissions from the fertigated crop under the overhead system were comparable to the non-fertigated crop of the furrow system (P>0.05). In both systems, fluxes were highest within five days of irrigation or fertigation, but they decreased significantly after that time as soil moisture content (water-filled pore space) and soil nitrate levels decreased due to crop uptake. Nitrous oxide fluxes were similar in furrow and overhead 15 days after the irrigation or fertigation event. Areas that warrant further investigation are presented and discussed, including the need for improved timing of fertilizer delivery during the irrigation cycle to ensure that N losses through leaching or gaseous evolution (e.g., N2O, N2) are not economically or environmentally significant. Keywords: Greenhouse gas emissions, Irrigated cotton, Nitrogen use efficiency, Urea ammonium nitrate, Water-run urea.

Development and Testing of a Variable Rate Nitrogen Application System through an Overhead Irrigation System

Nutrients are injected through overhead irrigation systems at a uniform rate in a process known as fertigation. The highly variable soils in the Southeastern US pose challenges for effective fertigation. Currently, there is no variable-rate fertigation system available to apply the correct amount of N within a field through an overhead irrigation system. Therefore, the objective of this study was to develop and test a variable-rate N application system that works independently of irrigation water flow for site-specific N application. The variable-rate fertigation system (VRFS) was designed to apply different rates N using a pulse width modulation technique. The VRFS utilized the Clemson Lateral Irrigation Control software which controlled the solenoids in each zone by turning the N supply on and off (pulsing) for each zone. In this study, four tests were conducted to determine the uniformity of the VRFS. In test # 1, the pump output showed a linear slope relationship and was the same for water and N. In test # 2, nozzle flow and uniformity were determined using four different irrigation system travel speeds at N application rates of 31, 59, 88, and 113 kg/ha. There was a strong correlation (R2 = 0.9998) between irrigation system speed and N rate. In test # 3, the uniformity across the length of the irrigation system was determined. The nozzles produced an average flow of 31.1, 58.7, 87.6, and 112.7 kg N/ha with an overall average error of 0.1% across all N rates. Results also showed the system was capable of accurately applying N based on prescription maps with an error of less than 1.8%. Test # 4 was conducted to determine the accuracy of the map-based controller system for applying variable rate N. There was a strong correlation between target N and actual N rates (R2 = 0.9999). In summary, the VRFS applied the correct amounts of N within each zone by either manually controlling the pulsing mechanism or utilizing a prescription map to apply different rates throughout the field.

Environment Affects White Drupelet Disorder Expression on Three Blackberry Cultivars in South Mississippi

White drupelet disorder (WDD) is a problem that occurs during the ripening stage in some blackberry (Rubus subgenus Rubus) cultivars. Although berries affected with a few white drupelets may taste fine, they are unpleasant aesthetically, and this may lead to negative consumer perceptions and economic ramifications. During 2 years of observational studies and field trials (2016 and 2017), we evaluated changes in three susceptible cultivars in Mississippi affected by WDD. ‘Chickasaw’, ‘Kiowa’, and ‘Sweetie Pie’ berries were harvested twice per week and assessed for WDD. Weather conditions differed substantially during harvest in 2016 and 2017, with 2017 being cooler and rainier which resulted in a lower incidence of WDD. Compared with 2016, in 2017, the overall percentage of berries exhibiting WDD dropped from 22% to 12% for ‘Sweetie Pie’, 6% to 3% for ‘Chickasaw’, and 8% to 3% for ‘Kiowa’. The soluble solids concentration was highest in ‘Sweetie Pie’, 11.9% and 9.5% for 2016 and 2017, respectively. For all cultivars examined, the soluble solids concentration of extracted white drupelets was substantially lower than regular drupelets. The value for skin break force for white drupelets was higher than that for black drupelets, 0.99 N vs. 0.29 N, respectively. In 2017, an about 30% shadecloth treatment had a significantly positive impact by decreasing WDD symptoms in all cultivars by 63% when compared with non-shaded plants, but soluble solids concentration was lower. Our results indicate that rain and shadecloth decrease symptoms of WDD. Therefore, growers may be able to use overhead irrigation and shade to reduce WDD symptoms.

Nitrogen fertilization of warm‐season turfgrasses irrigated with saline water from varying irrigation systems. 1. Quality, spring green‐up and fall colour retention

AbstractA 3‐year study was conducted at New Mexico State University in Las Cruces, NM, to investigate the effects of different fertilization treatments on turf performance when water conservation strategies are applied. These strategies include the use of non‐potable saline irrigation water and the use of efficient subsurface irrigation systems. Two low water use warm‐season grasses, “Princess 77” bermudagrass (Cynodon dactylon L.) and “Sea Spray” seashore paspalum (Paspalum vaginatum O. Swartz), were irrigated with either potable [Electrical Conductivity (EC) = 0.6 dS/m] or saline (EC = 3.1 dS/m) water from either an overhead or a subsurface drip irrigation (SDI) system. Four different fertilizers, liquid slow release, granular slow release, granular urea and liquid urea, were applied at two rates: 10 and 20 g N m−2 year−1 for “Sea Spray” and 20 and 30 g N m−2 year−1 for “Princess 77.” Spring green‐up, summer quality and fall colour retention were determined using digital image analysis, visual quality ratings and normalized difference vegetation index. Generally, subsurface drip‐irrigated grasses were slower to green‐up than overhead irrigated ones. “Sea Spray” irrigated from the SDI system took 18, 28 and 15 days longer to reach 80% green cover in 2010, 2011 and 2012, respectively, than their sprinkler‐irrigated counterparts. The combination of “Princess 77” and overhead irrigation reached 80% green cover 35 (in 2010), 34 (in 2011) and 12 (in 2012) days faster than SDI‐irrigated “Princess 77.” Fertilization rate and type had no effect on summer turfgrass quality of “Princess 77” irrigated from a sprinkler system throughout the research period reaching ratings of greater than 7 during all 3 years. Similar results were observed for “Princess 77” irrigated from a SDI system during 2010 and 2011. Summer quality of sprinkler‐irrigated “Sea Spray” was negatively affected by liquid fertilization. During two of three summers, visual quality of plots fertilized with either liquid slow release or liquid urea was lower than “Sea Spray” fertilized with granular fertilizer. Further research is needed to investigate the effect of fertilization on bermudagrass and seashore paspalum over a wider nitrogen range including both granular and foliar products.

The frequency of freeze events in subtropical blueberry growing regions in Florida

Freeze events during January and February can result in major crop and economic losses for growers of low-chill, early-ripening cultivars of blueberry (Vaccinium spp.) in Florida. Overhead irrigation for freeze protection is commonly used by growers to protect their crop from freeze events. Freezes are typically categorized as either radiative or advective, each with their own set of risk parameters. The objective of this research was to use historical weather data to provide growers with additional information for their selection of passive and active freeze protection strategies to mitigate risk. Three sites in Florida were chosen as representative of major blueberry growing regions and weather data from 2000-2015 were downloaded from the Florida Automated Weather Network (FAWN) and analyzed. Hourly temperature, wind speed, and relative humidity were used to determine the average of number of days per month with sub-zero temperatures, the average duration of freeze events, and to classify each event as a radiation, advective, or mixed freeze. Radiation freezes were the most common type of freeze event in Alachua County, Florida, whereas Polk County has fewer freeze events including some years without sub-zero temperatures, without a clear prevalent freeze event type. Ultimately, the frequency and severity of freeze events, based on historical data, can be used to further inform grower investments in freeze avoidance and protection.

Characterization of Foliar Web Blight of Spinach, Caused by Pythium aphanidermatum, in the Desert Southwest of the United States.

A unique foliar disease of spinach, determined to be caused by Pythium aphanidermatum, was observed on spinach in Yuma County, AZ and Imperial County, CA desert spinach production areas in both 2015 and 2016. The foliar symptoms of the disease included water-soaked foliage, rapid collapse of young plants, and white, aerial, cottony mycelia. The disease was associated with hot (27 to 42°C) and wet conditions associated with overhead irrigation under high-density plantings (>8.0 million seeds/ha). Isolations were performed on symptomatic tissue, and DNA was recovered from pure culture of the isolates recovered and sequenced using the internal transcribed spacer (ITS) ribosomal DNA (rDNA) primers ITS1/ITS4 and gene cytochrome oxidase I (COXI) primers FM55 and FM59. BLAST searches in GenBank indicated that the isolates were P. aphanidermatum based on 99 to 100% homology of ITS rDNA. Moreover, the DNA sequences of the ITS and COXI were identical for the five representative isolates. The objective of this research was to determine whether P. aphanidermatum recovered from symptomatic spinach tissue was able to cause foliar web blight and damping-off of spinach and other crops. In addition to spinach, other hosts evaluated included cotton, soybean, pepper, tomato, cucumber, melon, squash, lettuce, corn, wheat, and rice in greenhouse trials. Inoculations were performed by either foliar inoculations or infesting the soil with plugs of potato dextrose agar colonized by the P. aphanidermatum. Web blight symptoms were severe on spinach and all other dicotyledonous hosts tested, except lettuce. No web blight symptoms were observed on corn or rice, and only minor symptoms were observed on 10-day-old seedlings of wheat. P. aphanidermatum caused severe preemergence damping-off of all dicotyledonous plant species tested but only caused limited seedling size reduction in corn and wheat. Mefenoxam treatment of spinach seed provided complete protection against preemergence damping-off of spinach at both low (0.15 g a.i./kg of seed) and high (0.70 g a.i./kg of seed) rates of application, and the high rate of the application resulted in complete protection against web blight of spinach for 10 to 20 days after planting.

Effect of Endophyte on Salinity Tolerance in Perennial Ryegrass

Perennial ryegrass (Lolium perenne L.) is an important cool‐season turfgrass species that germinates quickly and is the main species used for overseeding on golf courses in the United States. It will be important to improve salinity tolerance in perennial ryegrass as the use of alternative water sources (with increased salinity levels) increases. The natural Epichloë festucae var. lolii endophyte in perennial ryegrass has been shown to convey resistance to various abiotic and biotic stresses but the role of endophytes in salinity tolerance has not been well studied. The objective of this study was to determine whether endophytes have an overall effect on salinity tolerance in perennial ryegrass or whether salinity tolerance is specific to the genotype–endophyte combination. Four perennial ryegrass clones (two salt susceptible [Brightstar SLT clone 5 and Paragon GLR clone 4], and two salt tolerant [4501‐7 and 4540‐9])), with (E+) and without (E–) their natural endophytes were grown in control (1 dS m−1) and saline water conditions (15 dS m−1) for 10 wk. Treatments were applied using an overhead irrigation chamber in the greenhouse. Visual percent green, digital image analysis, clipping yields, shoot weight, and root weights were collected. In the Paragon GLR clone, the E– clone performed better than the E+ clone for all measurements when averaged across rating dates. For most of the clones, E–clones tended to be more tolerant than E+ clones except for 4540‐9 which exhibited the opposite effect. The natural endophytes in these grasses did not provide a strong positive effect on salinity tolerance among these ryegrass clones, however, there is some evidence for an endophyte–host genotype dependent response in salinity tolerance among specific perennial ryegrass clones.

Chemical control of branched broomrape in processing tomato using sulfonylureas in southern Italy

The present research investigated the efficacy and the selectivity of three sulfonylureas (SUs) rimsulfuron (RS), chlorsulfuron (CS) and triasulfuron (TS) for <em>Phelipanche ramosa</em> control in processing tomato. In 2014 a single dose (D) (75, 15 and 22.5 g ha–1 active ingredient – a.i.– of RS, CS and TS, respectively), split into three applications at equal rate, was delivered into the soil layer interested by the roots using two herbigation methods i) through the drip irrigation system (DH) or ii) by foliar spray followed by overhead irrigation (FH). In 2015 SUs were applied in pre-transplant at one third of D, and in post-transplant at the dose D, at onehalf and at one-fourth of D, delivered in 3 rates by drip herbigation. In both experiments RS gave the best broomrape control and the highest yield increase compared with the untreated crop and CS improved crop yield similarly to RS despite being less effective in contrasting branched broomrape, In 2014, the foliar application of TS and CS resulted in plant injuries which, more significantly with TS, caused lower numbers and fresh weight of fruits as well as a lower crop productivity increase. In the same year the drip herbigation with TS resulted in the lowest broomrape control and tomato yield increase. In 2015, the best parasite control and tomato yield performances were obtained with RS and CS when applied in pre-transplant at 25.0 and 5.0 g ha<sup>–1</sup> a.i., respectively, and in post-transplant at 75.0 and 15.0 g ha<sup>–1</sup> a.i., respectively. With TS, the pre-transplant application a.i. was the most effective among the TS treatments resulting in a yield improvement similar to RS and CS, while it was confirmed the low broomrape control when applied through drip irrigation due to its low mobility in the soil. More research is needed in order to better exploit the combination of pre- and post-transplant applications in the chemical control of <em>P. ramosa</em> of tomato under the conditions in southern Italy.

Automated ebb-and-flow subirrigation for citrus liners production. I. Plant growth

Ebb-and-flow subirrigation is a closed system that applies water to the bottom of the containers, reducing water and nutrient losses due to recirculation of fertilizer solution (FS). The technology can improve plant growth and eliminate the improper disposal of salts into the environment. Subirrigation is widely used in the ornamental industry, and sensor-based ebb-and-flow benches can be used by the citrus nursery industry. There is a need for establishing water and fertilizer guidelines to produce citrus rootstocks. The objectives of this study were: 1) design and build an ebb-and-flow subirrigation equipment, 2) automate the system operation using soil moisture sensors, 3) evaluate the system performance on plant growth, and 4) determine the water and fertilizer guidelines to produce Rangpur lime (Citrus×limonia) liners in 56-cm3 cone-shaped containers. The treatments were four volumetric water content (VWC) to trigger subirrigation (0.12, 0.24, 0.36 and 0.48m3m−3), three FS concentrations (25%, 50% and 75% of the fertilizer recommendation) and a control (nursery manual overhead irrigation using breaker nozzles), arranged in a completely randomized 4×3+1 factorial plus design, with three replications. The system was automated by 39 capacitance sensors connected to a data logger, multiplexer and relay drivers, which controlled independent submersible pumps. Subirrigation was turned on when VWC dropped below the set thresholds. Sensors effectively monitored the substrate moisture and controlled subirrigation. Treatments with highest VWC had higher substrate moisture and number of irrigations over time (p<0.0001). The volume of water applied doubled from treatments 0.12–0.48m3m−3 (p<0.0001). Subirrigation increased shoot height, stem diameter, dry weight, leaf area, physiological parameters (leaf intracellular concentration of CO2, transpiration, stomatal conductance, and net photosynthesis), and water use efficiency in response to increase in VWC and FS (p<0.0001). Subirrigation shortened the crop cycle in 30 days, anticipating the liners transplant for grafting, allowing another cultivation cycle in the nursery during the year. VWC of 0.48m3m−3 and FS concentration of 50% of the recommended value for overhead irrigation are indicated for Rangpur lime liner production in 56-cm3 containers.

Automated ebb-and-flow subirrigation for citrus liners production. II. Pests, diseases and nutrient concentration

Subirrigation has the potential to reduce water and nutrients losses in citrus seedlings production by recirculating fertilizer solution (FS) and eliminating improper disposal of salts into the environment. The objectives of this study were to evaluate the effect of an automated ebb-and-flow system on pest and disease incidence and nutrient concentration of Rangpur lime (Citrus×limonia) liners. Nutrients were determined on plant tissue (shoot and root), substrate, and recirculated FS collected on 121-L water tanks. The treatments were four volumetric water content (VWC) to trigger subirrigation (0.12, 0.24, 0.36 and 0.48m3m−3), three FS concentrations (25%, 50% and 75% of the fertilizer recommendation) and a control (nursery manual overhead irrigation using breaker nozzles), arranged in a completely randomized 4×3+1 factorial plus design, with three replications. The system was automated by 39 capacitance sensors connected to a data logger, multiplexer and relay drivers, which controlled submersible pumps inside 121-L tanks with different FS. Subirrigation was turned on when VWC dropped below the set thresholds. There was occasional appearance of leaf miners (Phyllocnistis citrella, Lepidoptera: Gracillariidae) and fungus gnats (Bradysia sp. nr. coprophila, Diptera: Sciaridae), and no diseases (especially Xanthomonas axonopodis and Phytophthora nicotianae). Different treatments resulted in changes on macro and micronutrients content in shoots and roots, substrate, and FS at 0, 30, 60 and 90days (p<0.0001). Higher FS concentrations increased the nutrient content over time (p<0.0001). There was a decrease in pH and an increase in electric conductivity on treatments with higher VWC and FS (p<0.0001). The substrate electric conductivity reached 5dSm−1 twice, demanding substrate washing by water application on treatments with VWC of 0.36 and 0.48m3m−3 and FS of 75%. Subirrigation is suitable for liner production in 56-cm3 cone-shaped containers.

MANAGEMENT OF SEED BORNE FUNGAL DISEASES OF TOMATO: A REVIEW

Plant diseases caused by different kinds of microorganisms either carried through air, water or present in soil, seeds or propagative planting materials have adverse impact on agriculture production and economy worldwide. Apart from other crops vegetables are also subjected to several seed borne fungal, bacterial and viral pathogens, which cause substantial yield loss upto 10 percent in Pakistan. This article gives vast information regarding significance and prevalence of various kinds of seed borne mycoflora (Alternaria solani, Fusarium oxysporum, F. solani, Botrytis cineria, A. alternata, Chaetomium globosum, Curvularia lunata, Aspergillus niger, Drechslera specifer and Rhizoctonia solani) particularly associated with seeds of tomato. These mycoflora are causative agents of devastating tomato diseases like early blight, fusarium wilt and foot rots, grey mold, root and fruit rots. A range of conventional and modern techniques employed for seed borne fungal detection and different control strategies including chemical and biological methods opted by researchers have been reviewed in present paper. A variety of factors like availability of susceptible plants, favorable environmental conditions and overhead irrigation are serious constraints for plant disease development. Under these conditions, monitoring of plant health and detection of diseases particularly using seed detection assays to screen infested seed lots before planting provide effective disease management strategy.

Automated cycled sprinkler irrigation for spring frost protection of cranberries

Overhead (sprinkler) irrigation is commonly used for spring frost protection of cranberries in southeastern Massachusetts, United States. Historically, conventional forms of irrigation management have been used, generally consisting of running irrigation pumps continuously throughout the night and into the early morning until ambient air temperature reached 1–2°C above the critical temperature of the plant. However, a general paucity of information exists on the horticultural and hydrological effects of on-off “cycling” of irrigation pumps based on pre-programmed temperature setpoints. To fill this gap, three years of monitoring were conducted to quantify the relative effects of cycled and conventional spring frost irrigation on cranberry bud damage, crop yield, and water use. Results showed that cycled irrigation reduced seasonal water use from 33 to 80% compared to conventional frost irrigation, with water savings under cycled frost irrigation ranging from 113 to 198mm (mean±SD: 176±47mm). Despite some variation in type and amount of observed bud damage, values of cranberry yield were similar between the two methods or higher for cycled irrigation. The conventional frost irrigation method always applied more irrigation water, possibly increasing soil saturation and anaerobic conditions that are known to lower crop yield in cranberry. Together, these results point to cycled irrigation as a water management strategy that can enhance cranberry production and reduce agricultural water use in southeastern Massachusetts.

Cane Water Content and Yield Responses of Vitis vinifera L. cv. Sultanina to Overhead Irrigation During the Dormant Period

The possibility to increase grapevine cane water content during the dormant period by applying overhead irrigation, and thereby increasing yield, was investigated in a semi-arid summer rainfall climate. A field trial was carried out with Sultanina grapevines in the Lower Orange River region over two seasons. During the 2000/2001 season control grapevines (Tl) that received no overhead irrigation in winter were compared to ones receiving overhead irrigation applied over a ca. 30-day period, starting either in July (T2), mid-July (T3), August (T4) or mid-August (TS). Overhead irrigation was applied as ten-minute pulses on the hour from 10:00 until 16:00. Due to the lack of winter rainfall, all treatments received normal, under-vine irrigation in winter to avoid severe water deficits. All treatments, except T2, were repeated during the 2001/2002 season. Two additional treatments which received no irrigation during winter were included during the second season. Of these two, T6 received overhead irrigation in August, whereas T7 received no overhead irrigation. Compared to the Tl control, overhead irrigation applied during August 2000 (T4) not only increased cane water content measured before bud break, i.e. early September, but also increased yield. The other overhead irrigation treatments did not affect cane water content or yield. During the second season overhead irrigation started in mid-July (T3) or in the beginning of August (T4) induced higher yields compared to grapevines that received overhead irrigation in the period before bud break (TS). Where available soil water depletion of 90% occurred, overhead irrigation (T6) seemed to negate the adverse effects of dry soil on yield. In contrast, cane water content and yield were considerably lower where neither normal nor overhead irrigation was applied (T7), compared to T3 and T4. These results confirmed that overhead irrigation can increase cane water content and yield, and that soil water deficits during the dormant period should be avoided. Overhead irrigation and/or water deficits during winter did not affect cane mass, as measured at the end of the following growing season.

Productivity of strawberry plants growing under dry and wet conditions in subtropical Queensland

The effect of growing environment on the performance of two strawberry (Fragaria ×ananassa) cultivar/breeding lines ('Festival' and 'Breeding Line 1') was studied in south-eastern Queensland, Australia. Plants were grown under tunnels or outdoors. Supplementary over-head irrigation was given to the plants outdoors to provide a water supply (irrigation + rainfall) about twice that of the long-term average rainfall for the area. Half the plants under the tunnels or outdoors received the standard sprays to control grey mould, while the other half of the plants received none of these sprays. The yields of the plants in the dry environment under the tunnels (without over-head irrigation) were more than double the yields of the plants in the wet environment outdoors (with over-head irrigation). This result indicates that losses that may occur during a wetter than average season. The plants under the tunnels had lower incidences of rain damage and grey mould than the plants outdoors. There were higher incidences of powdery mildew, and of small and misshaped fruit under the tunnels. Only cultivars with some resistance to powdery mildew should be grown under protected cropping. Spraying reduced the incidence of grey mould outdoors but not under the tunnels. Crops growing under protected cropping in Queensland probably do not need to be sprayed for grey mould.

A Laboratory Evaluation of Chemigation to Manage Stink Bugs (Hemiptera: Pentatomidae)

Application of insecticides for stink bug management through overhead irrigation, also called chemigation, could reduce application costs, soil compaction, and applicator exposure, while enabling growers to treat multiple fields simultaneously. The objective of these laboratory experiments was to compare knockdown, survival, and efficacy of insecticides when appropriately diluted for ground sprayer and chemigation applications. Treatments included water, bifenthrin [0.11 kg (AI)/ha] and dicrotophos [0.56 kg (AI)/ha] diluted for a ground sprayer (93.5 liters/ha), bifenthrin and dicrotophos diluted for chemigation (25,396 liters/ha), and bifenthrin and dicrotophos plus adjuvants diluted for ground sprayer or chemigation. Two- to 14-day-old adults of Nezara viridula (L.), Euschistus servus (Say), and Halyomorpha halys (Stål) were briefly submerged in appropriately diluted insecticides and then introduced into a disposable petri dish with or without food. Dishes were placed in a growth chamber provisioned with digital video cameras to monitor knockdown and feeding after insecticide exposure. Knockdown was visually assessed at 24 h after treatment followed by mortality and recovery from knockdown at 48 h after treatment. All stink bugs were knocked down within 1 h and never recovered when exposed at ground sprayer dilutions. However, many bugs survived chemigation dilutions. Less than half of the stink bugs were knocked down when exposed to dicrotophos (with or without adjuvants) and survival ranged from 17 to 77%, compared to 7-90% survival when exposed to bifenthrin at chemigation dilutions. These results strongly suggest that chemigation applications for stink bug management need to be closely examined.