Damping-off, caused by the fungal pathogen Rhizoctonia solani, is a soilborne disease that impacts rice fields. This pathogen infects young seedlings, causing injuries, lack of vigor, seedling death, and reduced plant stands. Delays in seedling emergence due to adverse conditions tend to increase the severity of damping-off. This report evaluates the efficacy of seed treatment programs for managing a rice seedling disease in Arkansas. The trial was carried out in 2023 in Stuttgart, AR, on the Clearfield rice ( Oryza sativa L.) variety ‘CL163’. Results from this trial will assist rice growers in selecting effective fungicide combinations for managing rice seedling diseases.

Boxwood blight, caused by the fungal pathogen Calonectria pseudovaniculata, has been reported in over 30 U.S. states and is a threat to boxwood production worldwide. While considerable research has been conducted to evaluate the efficacy of conventional fungicides and cultural controls for this disease, the potential of host defense inducers remains largely unexplored. This study evaluated the effects of application method and frequency for managing boxwood blight in both container and field production systems in 2018 and 2019 at two locations in North Carolina. Actigard 50WG (acibenzolar-S-methyl) and LifeGard WG (Bacillus mycoides isolate J) were applied as drench and foliar treatments to container-grown boxwoods artificially inoculated with C. pseudonaviculata and to field-grown boxwoods exposed to natural inoculum. Drench applications of Actigard resulted in lower disease incidence than the untreated control plants under container production. High efficacy of Actigard was also observed under field production despite favorable environmental conditions for the development of boxwood blight. Application frequency did not affect disease for either of the tested host defense inducers in either production system. These findings support the integration of host defense inducers into cultural practice- and conventional fungicide-based management programs for boxwood blight.

Grapevine decline is an emerging concern for cold-hardy interspecific hybrid grape (CIHG) cultivars grown in the Midwest, with the fungal taxa associated with this decline remaining poorly characterized. In this study, we conducted surveys across Iowa vineyards in 2023 and 2024, collecting symptomatic samples from multiple cultivars and tissue ages. As a result, over 1,300 fungal isolates were isolated and characterized. Among these, Fusarium, Pestalotiopsis, and Cytospora, generally recognized as pathogens of grapes or other woody plants, were prominently detected. Further analysis showed that the incidence of Fusarium and Pestalotiopsis increased with tissue age, while Cytospora remained consistent. Phylogenetic analyses placed Fusarium isolates within two major species complexes, including well-studied plant pathogens of cereal crops, and identified Pestalotiopsis and Cytospora species related to those reported on grapevines and other woody hosts. Co-occurrence of these fungi was common, with significant variation in incidence and co-occurrence patterns across cultivars, suggesting that host genotype influences fungal colonization dynamics. For example, fewer samples from the cultivar ‘La Crescent’ showed simultaneous detection of Fusarium and Pestalotiopsis compared to other cultivars. While the pathogenic roles of these fungi in CIHG vine decline remain to be confirmed, these results provide a first step for future pathogenicity testing and the development of targeted management strategies to mitigate grapevine decline and its economic impact on CIHG production in the Midwest.

Botrytis leaf blight and Stemphylium leaf blight, caused by Botrytis squamosa and Stemphylium vesicarium, respectively, are common leaf diseases of dry bulb onion ( Allium cepa) in the ‘muck’ production regions of New York. These diseases cause leaf spotting and leaf dieback that may reduce bulb size, quality (indirectly), and yield. The emphasis of this trial was to identify fungicide tank mixes for best disease control using products that individually were previously identified as having moderate or poor activity on these diseases. Also, two products with novel modes of action were tested for their potential use. The results of this trial will inform fungicide management strategies for Botrytis and Stemphylium leaf blight diseases.

Diaporthe humulicola, causing halo blight of hop, is one of the most impactful pathogens of hop in eastern North America. The pathogen, when left untreated, can cause approximately 50% yield loss due to shatter upon harvesting. The disease has a wide variety of symptoms on the cones, leaves, and bines that are not consistent between infections. The pathogen is slow growing on artificial media and can take up to 3 weeks for the development of pycnidia. This diagnostic guide outlines the current list of symptoms and signs for halo blight, offers information on the identification of the pathogen using both morphology and molecular tools, and provides information on pathogenicity testing for D. humulicola.

The genus Pantoea includes bacteria that have been designated as emerging pathogen because of their increasing numbers of previously unreported hosts, as well as their multidrug-resistant traits. In corn and sorghum, members of the genus are associated with four important diseases: Stewart’s wilt caused by P. stewartii, necrotic or white leaf spots or streaks and stalk rot of corn caused by P. ananatis, leaf blight and vascular wilt disease in maize and sorghum caused by P. agglomerans, and more recently, late season decline disease of corn and sorghum caused by P. ananatis. In 2023, bright lemon-green foliar discoloration with interveinal chlorosis were observed on wild grasses in the northwest region of the Texas Panhandle. Later in the year, identical symptoms were observed on corn and sorghum plants. Symptomatic plants were also observed to be stunted, delayed in development, including yield limiting impairment in reproductive growth. In extreme cases, affected plants failed to reach the reproductive growth stage. Diagnosis of symptomatic tissues consistently recovered bacterial isolates that were initially only culturable using phytoplasma media. BLAST searches of 16S rRNA sequences, multilocus sequence and genome sequence analysis identified the bacterial isolates as most closely related to P. agglomerans. Investigation of a causal role of the bacteria using a representative isolate, B1714, from sorghum, relying on Koch’s postulate resulted in the successful reproduction of the symptoms observed on symptomatic field plants. Bacteria matching isolate B1714 was also successfully recovered from symptomatic tissues, thus satisfying Koch’s postulate and attributing causative role to isolate B1714.

Bacterial diseases cause annual onion yield losses of 5 to 40% in Pennsylvania (PA) and New York (NY). More comprehensive knowledge of the bacteria present and further characterization of pathogenic bacteria is important for developing effective diagnostic tools and management strategies. This survey aimed to identify the bacteria associated with symptomatic onion leaves and bulbs and evaluate their pathogenicity. From 2020 to 2022, 30 onion fields across PA and NY were sampled, and 589 symptomatic plants and bulbs were collected. A total of 1957 bacterial isolates were recovered from the samples, and 1165 isolates were characterized to genus level. Of the 53 bacterial genera identified, Burkholderia (22.1%) and Pantoea (16.8%) were the most prevalent. Additionally, 957 isolates from 43 genera were tested for pathogenicity using the red scale necrosis (RSN) assay. Of these, 264 isolates from eight bacterial genera produced necrosis. A subset of 187 RSN-negative isolates was further tested in foliar and whole onion bulb pathogenicity assays. Of these, 25 were pathogenic in both assays, 15 only in the foliar assay, and 28 only in the bulb assay. This survey revealed that numerous bacterial genera are associated with symptomatic onion leaves and bulbs. However, only about one-third of the bacterial genera tested were pathogenic on onion. Of those genera, about one-third of the isolates were pathogenic in at least one of the three assays. These results indicate that most bacteria associated with symptomatic onion tissues are non-pathogenic, highlighting the importance of accurate diagnosis to design effective disease management strategies.

Corn stunt is one of the most significant corn diseases in the Neotropics, leading to severe plant stunting and substantial yield losses. Although four pathogens have been found either singly or in combination in infected plants in the Americas, the corn stunt spiroplasma (Spiroplasma kunkelii) have been the most predominant pathogen associated with the disease in the U.S., due to its widespread distribution in the Rio Grande Valley region and persistent occurrence in California and Florida. During the 2024 growing season, reports of chlorosis, leaf reddening, and stunting in corn fields in Southern, Great Plains, Central Corn Belt, and Northeastern states raised concern regarding the possibility of a more widespread distribution of corn stunt spiroplasma in the U.S. Symptomatic corn leaf samples were collected in commercial and experimental field sites across the U.S. Detection and identification of S. kunkelii were performed using a polymerase chain reaction assay targeting a section of the spiralin gene, followed by amplicon sequencing. This study provides the first report of the pathogen S. kunkelii associated with corn stunt symptoms distributed across six counties in Oklahoma, 14 counties in Kansas, two counties in Missouri and Arkansas, four counties in New York, and one county in each of Nebraska, South Dakota, Wisconsin, Minnesota, Indiana, and Alabama. All states with submitted samples had at least one confirmed case of S. kunkelii.

From November 2023 to February 2024, severe leaf blight symptoms were found on blueberry ( Vaccinium corymbosum L.) plants in a commercial field in Navolato, Sinaloa, Mexico. Three single-spore isolates were obtained and identified as Alternaria alternata by phylogenetic analyses of concatenated sequences of the gapdh, rpb2, and tef1-α genes. The pathogenicity of the isolates was confirmed by inoculating conidial suspensions on healthy blueberry leaves. This represents the first report of A. alternata causing leaf blight of blueberry in Mexico.

Watermelon is a major cucurbit crop grown across the world and in 44 states in the United States. Powdery mildew (PM), caused by Podosphaera xanthii, is an important disease of watermelon that can severely limit fruit production and reduce yield. Extensive work has been done on races of P. xanthii based on melon ( Cucumis melo) differential hosts, and seven major races of have been identified. However, physiological races of P. xanthii have not been classified for many other cucurbits, including watermelon. The objective of this study was to develop a set of watermelon PM race differentials and identify potential races. Ten P. xanthii isolates collected from various states were evaluated using a newly developed set of watermelon ( Citrullus lanatus) differentials that included a highly susceptible germplasm line, ‘USVL677-PMS’; a commercial cultivar, ‘Mickey Lee’; two resistant germplasm lines, ‘USVL608-PMR’ and ‘PI 189225’; and resistant pollenizer ‘SP5’. The well-studied melon ( C. melo) powdery mildew differentials ‘Iran H’ and ‘PMR-45’ were also included. All isolates colonized and produced abundant conidia on the melon Iran H and watermelon USVL677-PMS. SP5 and PI 189225 were resistant to all isolates. USVL608-PMR was resistant to 7 of the 10 isolates and displayed intermediate resistance to three isolates. Of the 10 isolates that grew well on USVL677-PMS, only five colonized and produced abundant conidia on Mickey Lee, which was highly resistant to the remaining five. Based on reactions of the 10 powdery mildew isolates on Mickey Lee and USVL677-PMS, at least two distinct physiological races (0 and 1) can be identified. These two races based on watermelon differentials did not correlate with race structure based on the two melon differentials. As new watermelon cultivars with resistance to powdery mildew are being released, it will be important to determine their reaction to P. xanthii isolates, as a race structure based on watermelon differentials clearly exists. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2025.