Tar spot on corn, caused by the fungus (Phyllachora maydis Maubl. [Phyllachorales: Phyllachoraceae]), is an emerging disease in the United States. In 2018 and 2019, significant but localized epidemics of tar spot occurred across the major corn producing region of the Midwest. After being first detected in 2015, tar spot was detected in 135 and 139 counties where the disease was not previously detected in 2018 and 2019, respectively, and is now established across 310 counties across the United Sates. Foliage with signs (stromata) of P. maydis and symptoms of tar spot were collected from 128 fields in 2018 and 191 fields in 2019, across seven states. Samples were assessed for severity of fungal stromata (percent leaf area covered with stromata) on foliage and the incidence of fisheye lesions (proportion of lesions with fisheye symptoms) associated with fungal stromata. Stromatal severity on samples in 2018 ranged from 0.5 to 67% and incidence of fisheye lesions ranged from 0 to 12%, whereas in 2019, stromatal severity ranged from 0.1 to 35% and incidence of fisheye lesions ranged from 0 to 80%, with 95% of samples presenting less than 6% incidence of fisheye lesions. Tar spot has spread substantially from where it was first reported in the United States. Collaborative efforts to monitor the spread and educate clientele on management are essential as this disease spreads into new areas.

In Illinois, Soybean cyst nematode (SCN: Heterodera glycines), was estimated to cause over 15 million $U.S. in losses as recently as 2021. In addition, populations of SCN insensitive to PI88788 derived resistance, the most commonly used SCN resistance source in commercially available soybeans, continues to increase. Despite this, awareness of this pathogen and its current status in the state are relatively lacking. A survey was conducted in 2018 and 2020 to assess the presence, abundance, and virulence phenotypes of SCN in Illinois soybean fields. Soil samples were collected and processed for SCN eggs after harvest each year and samples exceeding threshold values of SCN eggs were virulence tested using the Hg type test. A total of 95 samples were collected, representing 46 counties. Eighty seven percent of fields sampled contained SCN eggs, with 38% containing population densities over 2,000 eggs /100 cm3. All samples included in the Hg type test had a female index >10 on indicator line PI88788, indicating insensitivity to this resistance source. Extrapolated across soybean production acres, these data indicate that approximately 4.4 million acres of soybeans contain levels of SCN requiring SCN management and over 54% of acres using cultivars derived from PI88788 are not fully protected from this pathogen.

One hundred and forty-seven soil samples were collected from corn fields located within 63 Illinois counties during the 2018 and 2020 corn growing seasons. The soil samples were analyzed for frequency and population density of plant-parasitic nematodes. A total of 10 plant-parasitic nematode taxa were identified. Spiral nematode (Helicotylenchus spp.) was the most frequently observed nematode (frequency: 98.6%), followed by lesion nematode (Pratylenchus spp., 85.7%). Other taxa identified included cyst (Heteroderidae, 66.7%), stunt (Tylenchorhynchus spp., 33.3%), lance (Hoplolaimus spp., 29.9%), dagger (Xiphinema spp., 12.9%), pin (Paratylenchus spp., 12.2%), needle (Longidorus spp., 1.4%), stubby-root (Trichodoridae, 1.4%), and ring nematodes (Criconematidae, 0.7%). Nematodes with the greatest population densities included spiral (89 nematodes per 100 cm3 of soil), pin (36), and cyst nematodes (26). Among the 10 nematode taxa, 4.1%, 7.1%, and 2.3% of spiral, lesion, and lance nematodes positive samples exceeded estimated damage thresholds for corn for Illinois, respectively. Results from this survey will help the agricultural community with understanding pathogenic corn nematode populations in the state and prioritize research in this understudied area.