Fungicide efficacy on tar spot and yield of corn in the Midwestern United States

Tar spot of corn caused by Phyllachora maydis has recently led to significant yield losses in the eastern corn belt of the Midwestern United States. Foliar fungicides containing quinone outside inhibitors(QoI), demethylation inhibitors(DMI), and succinate dehydrogenase inhibitors(SDHI) are commonly used to manage foliar diseases in corn. To mitigate the losses from tar spot thirteen foliar fungicides containing single or multiple modes of action (MOA/FRAC groups) were applied at their recommended rates in a single application at the standard tassel/silk growth stage timing to evaluate their efficacy against tar spot in a total of eight field trials in Illinois, Indiana, Michigan, and Wisconsin during 2019 and 2020. The single MOA fungicides included either a QoI or DMI. The dual MOA fungicides included a DMI with either a QoI or SDHI, and fungicides containing three MOAs included a QoI, DMI, and SDHI. Tar spot severity estimated as the percentage of leaf area covered by P. maydis stroma of the non-treated control at dent growth stage ranged from 1.6 to 23.3% on the ear leaf. Averaged across eight field trials all foliar fungicide treatments reduced tar spot severity, but only prothioconazole+trifloxystrobin, mefentrifluconazole+pyraclostrobin+fluxapyroxad, and mefentrifluconazole+pyraclostrobin significantly increased yield over the non-treated control. When comparing fungicide treatments by the number of MOAs foliar fungicide products that had two or three MOAs decreased tar spot severity over not treating and products with one MOA. The fungicide group that contained all three MOAs significantly increased yield over not treating with a fungicide or using a single MOA.

Spatial and temporal population dynamics of Aspergillus flavus in commercial pistachio orchards in Arizona

Aspergillus flavus infects a wide range of crops, including pistachios, and subsequent aflatoxin contamination results in significant economic losses. Application of biocontrol products based on non-aflatoxigenic (atoxigenic) strains of A. flavus is one of the most effective tactics for controlling aflatoxins in crops. Both risk of aflatoxin contamination and effectiveness of biocontrol are influenced by the extent to which A. flavus spores move into pistachio tree canopies during periods of nut development. Thus, the purpose of this study was to evaluate spatial and temporal population dynamics of A. flavus, including the applied biocontrol strain AF36, in canopies of pistachio orchards in Arizona. Propagule densities of A. flavus were quantified on leaf samples collected from lower, middle, and upper canopies from spring through harvest in 2018 and 2019. Aspergillus flavus propagule densities peaked during periods of high temperature and rainfall in 2018 (up to 600 CFU/g) and 2019 (up to 23 CFU/g), which coincided with nut development and maturation. The applied biocontrol strain AF36 was detected at all canopy heights, but overall propagule densities were greater in the upper and middle canopy (mean = 70 CFU/g) compared to the lower canopy (mean = 47 CFU/g). Results suggest June to August is the period during which A. flavus inoculum increases in Arizona pistachio orchards, and to most effectively displace aflatoxin-producing fungi in tree canopies, biocontrol applications should precede this period. In addition, this study demonstrates that soil-applied biocontrol strains can successfully disperse throughout the canopies of commercial tree nut orchards.

Prescreening of biological and biorational fungicides against common hemp pathogens using in vitro analyses

Upon reintroduction of hemp in 2014 and legalization in 2018, labeled pesticides have remained limited. Further, consumer demand has aimed the market toward organic or chemical-free production systems. In efforts to manage diseases and pests in fields and greenhouses, producers turn toward biological and biorational formulations. Efficacy of these fungicides against common aerial diseases of hemp is largely unpublished. Challenges of efficacy testing, however, further delay or discourage research. In this study, we evaluated screening methods against some common biological products. The aim was to test a screening model in order to examine products against fungal pathogens and to identify demonstrable differences under controlled conditions. Thus, in this study, we prescreen 11 biological and biorational fungicides against four common fungal leaf and flower pathogens using three bioassays. Confirmation that the major modes of action for these products have measurable activity against major pathogens of hemp serves as a first step toward more complex field studies.

An integrated pest management program outperforms conventional practices for tomato (Solanum lycopersicum L.) in Cambodia

For several years, pest management in tomato production in Cambodia has generally focused on the use of synthetic pesticides. We compared conventional pest management (farmers’ traditional practices) with an IPM program on 12 farms in the northwestern part of Cambodia. The IPM program combined cultural, biological, and chemical practices. We found that IPM practices reduced aphid damage by 46% and diseases such as Fusarium wilt and damping-off were substantially reduced. Our results indicate that the IPM package increased tomato yield and income by an average of 23% and 34%, respectively, compared to conventional practices during both dry and rainy seasons.

Impacts of row spacing and fungicide timing on foliar disease, greenstem and yield in double cropped soybeans grown in the Chesapeake Bay region of the United States.

Double cropped soybeans are planted on approximately 1/3 of crop acres in the Chesapeake Bay region of the United States. Producers have asked if foliar fungicides are required to optimize yields in this region. We assessed the impacts of foliar fungicide application timing and row spacing on foliar disease, greenstem, and yield from 11 site years spanning 2017-2019. Foliar diseases only developed at rateable levels in one location. Fungicide application, regardless of timing, increased percent greenstem over non-treated controls. Fungicide application did not impact soybean yield. Yield was greater in 38.1 cm rows when compared to 19 cm rows. Our data do not support the use of foliar fungicides in double cropped soybean production in this region.

Evaluation of damping-off tolerance in spinach cultivars in field soils and in a standardized lab assay with Pythium ultimum

Spinach growers face increasing problems of damping off in the production of fresh market (baby-leaf) spinach due to increasing restrictions on chemical treatments. Damping-off tolerant cultivars are increasingly important, requiring proper evaluation methods. From three locations in the Netherlands with a history of spinach cultivation and from one location in France, potential damping-off pathogens were isolated from the soil, identified to species or genus, and tested for their pathogenicity. Pythium ultimum was the most prevalent pathogen in those fields, causing spinach pre- and post-emergence damping off. Eight spinach cultivars with two or three seed lots each, were evaluated at the same field locations and in a greenhouse with soil sampled from one of the Dutch field sites. Pre-emergence damping off was more discriminating for differences among the cultivars than post-emergence damping off. Variation in levels of infection among trials, replicates, and seed lots of same cultivars, emphasized the need for a more standardized phenotyping assay. For such an assay, a cornmeal/sand-based inoculum with a pathogenic P. ultimum isolate was added to a substrate mixture of sand, perlite, and vermiculite, moistened until 50% water holding capacity, in which spinach seeds were incubated for ten days in a dark climate cabinet at 15°C, including a control treatment without P. ultimum inoculum. The assay showed reproducible results for discriminating differences in pre-emergence damping-off tolerance levels among seed lots. However, cultivar differences in pre-emergence damping-off tolerance levels could not be confirmed due to a large variation among seed lots that needs further investigation.

Fusarium Head Blight Epidemics in Soft Red Winter Wheat Fields in Georgia from 2018 to 2019

Fusarium head blight (FHB) epidemics on wheat have caused significant yield and economic penalties in the United States since the early 1990s. This report documents FHB epidemics on soft red winter wheat in Georgia in 2018 and 2019. Forty-four wheat fields across 23 counties were assessed for FHB incidence (2019 only), Fusarium-damaged kernel, deoxynivalenol (DON) contamination, and thousand kernel weight. Higher levels of FHB were observed in 2019 compared to 2018. A significant correlation was observed between DON and 7-day pre-anthesis weather variables in 2019. FHB parameters were significantly correlated to post-anthesis weather variables at 10-day in both years and at 20 and 30-day in 2018 suggesting that post-anthesis rather than pre-anthesis weather had a greater impact on FHB in our study. The combination of hours of conducive temperature and relative humidity post-anthesis was consistently correlated with all FHB parameters in both years and could be the best predictor of FHB epidemics. FHB has emerged as the leading threat for soft red winter wheat production in Georgia. Planting moderately resistant wheat cultivars along with in-season management including proper fungicide application, by closely monitoring the national FHB forecasting system, would be the best integrated management strategies for Georgian wheat growers.

Transmission of the Invasive Pathogen Phytophthora ramorum from Symptomatic to Healthy Host Plants During a Five-Year Period in California

Reliable data on the transmission of airborne plant pathogens are crucial for the development of epidemiological models and implementation of management strategies. The short-distance vertical transmission of the forest pathogen Phytophthora ramorum from a symptomatic California bay laurel (Umbellularia californica) to healthy containerized rhododendrons (Rhododendron caucasicum × R. ponticum var. album) was monitored for five winters (2016/17 to 2020/21) in a field experiment in Northern California. Transmission events were observed during four winters at a frequency of 1 to 17 per season, but not during the extremely dry winter of 2020/21, and were positively correlated to total rainfall rates. The first leaf symptoms were detected around mid-December and reached the highest numbers in January of most years. Only limited symptom development was observed in the spring, with the last detections in May. The exposure time (the time between the first rainfall after placing a bait plant under the bay laurel and development of symptoms) varied between 3 and over 150 days, with an average between 14 and 21 days. P. ramorum was detected from water samples collected from the canopy of the symptomatic California bay laurel. No horizontal pathogen spread was detected from symptomatic to healthy rhododendrons placed at a distance of 2 to 6 m.

Distribution and incidence of tomato bacterial wilt caused by Ralstonia solanacearum in the central region of Togo

Tomato (Solanum lycopersicum L.) is one of the most important vegetables in Togo. Unfortunately, tomatoes are susceptible to many diseases, among which bacterial wilt caused by Ralstonia solanacearum causes major yield losses. In this study, incidence of bacterial wilt and its distribution was evaluated in the central region of Togo, the major tomato producing area in the country. Overall, 16 localities were surveyed in four prefectures. In each locality, three fields were visited, and the incidence of the disease was recorded, and diseased samples were collected for laboratory investigation. The results showed that bacterial wilt occurred in all the fields visited, indicating a field incidence of 100%, whereas the plant incidence ranged from 10.00±00% to 43.33±3.33%, with an average of 20.94±1.77%. The antibody based Immunostrip test was positive for R. solanacearum in 100% of the visited fields. From 144 samples collected from fields, 45 R. solanacearum isolates were isolated on Modified SMSA media. This survey results show that tomato bacterial wilt is a real threat to tomato production in the central region of Togo.

A Selective Medium for the Recovery and Enumeration of Fomitopsis meliae, Causing Lemon Canker and Wood Rot

A selective medium (FMS medium) was developed for the isolation and quantification of Fomitopsis meliae, the causal agent of lemon canker and brown wood rot, from plants, soil, and air. The optimal concentration and combination of fungicides and antibiotics was evaluated to determine the most selective condition for growing F. meliae. The resultant composition of the medium (FMS) per litre (pH 3.5) was: 16 mg thiophanate-methyl, 8 mg dichloran, 5 mg 2-phenylphenol, 100 mg fluopyram, 0.5 mg fludioxonil, 100 mg chloramphenicol, 100 mg streptomycin, 15 g malt extract, 2.5 g mycological peptone, and 15 g agar. The fungus was successfully isolated and enumerated from air, soil and plant tissues using FMS medium. Furthermore, FMS medium almost completely inhibited the growth of other plant pathogenic fungi, soil and air saprophytes. This selectivity was high enough to estimate spore inoculum of F. meliae in an air sample or as a spore trapping device in commercial lemon orchards. FMS medium will be useful for studying epidemiology and management of F. meliae.