Data from: Effects of microclimate on disease prevalence across an urbanization gradient

Surveys (park/field and road verge): In each survey, we first identified a patch of Plantago lanceolata or P. rugelii. Within this patch, we arbitrarily chose the first focal plant of either species and marked the survey starting location using a smartphone. For each focal plant, we recorded binary (presence/absence) data on powdery mildew infection, herbivore chewing damage, leaf mines, and lawnmower damage (leaves cut cleanly across by mower blade). In addition, we recorded whether the plant was in the sun or shade at the time of the survey. We also estimated the total number of conspecifics and number of infected conspecifics within a 1.5 m radius of the focal plant (ordered categorical variable in bins of 0, 1-10, 11-50, or 51-100 plants). We then walked a few paces in a predetermined direction (e.g., continuing unidirectionally along a roadside or within a park lawn for the entire survey) and arbitrarily selected the next focal plant. Focal plants were always at least 1 m from the previously selected conspecific in the survey. We continued until 50 plants of each species had been surveyed, and then recorded the end location and time. In some locations where Plantago was relatively rare, fewer than 50 plants were surveyed. Occasionally, surveys were cut short due to inclement weather or physical barriers (e.g., construction). Overall, we performed 68 surveys of Plantago rugelii and 60 surveys of P. lanceolata. Shade experiment: We performed a manipulative experiment to measure the effects of shade on powdery mildew growth and transmission in July 2021. Seven maternal lines of P. lanceolata and six maternal lines of P. major seeds were used. Plants in the inoculated treatment were placed in shallow trays at four sites directly under (shade) and four sites midway between (sun) solar panels in an otherwise open, mowed field at Tyson Research Center. The four large solar panels were each separated by five meters. At each of the four shade and four sun locations, we placed four trays in a “T-intersection” formation with three trays. The central tray at each location contained four or five P. major individuals and four P. lanceolata individuals. For both species, replicates of the maternal lines were distributed among trays as evenly as possible. Due to the low germination rates of P. major and the resulting small sample size for this species, all P. major individuals in the experiment were placed in the central trays. We used sterilized paint brushes to inoculate plants in these first trays by gently brushing one leaf per plant with powdery mildew spores from lab-inoculated source plants. Plants were inoculated with species-specific strains of the powdery mildew pathogen Golovinomyces sordidus that had been previously collected from wild plants in the St. Louis region, isolated to single strains, and propagated on leaf tissue in the lab following standard methods. The remaining P. lanceolata plants remained covered with pollination bags in the hoop house. The next day, we evenly divided these remaining uninoculated P. lanceolata among three additional trays in each shade and sun location (8-9 plants per tray). We assessed whether these uninoculated plants became infected over the following weeks of the experiment. The trays of inoculated plants were watered regularly by filling the trays with an inch of water every other day. Two of the trays of uninoculated plants were similarly watered. The third tray of uninoculated plants had holes in the bottom to allow water to drain; this treatment allowed us to test for plant responses to both the thermal environment and the amount of precipitation experienced in the shade and sun locations. We collected data on the infection status of each plant (number of infected leaves per plant) on 15 July, 23 July, and 6 August 2021. Shade experiment temperature data: We monitored microclimates by placing temperature loggers (HOBO MX2201) just below the soil surface in at least one pot per sun and shade location. To ground-truth these readings, in three locations we measured soil temperature in additional pots using temperature probes attached to Raspberry Pi computers.