For the second year in a row, the UVM Extension, Northwest Crops and Soils Program has been conducting a regional assessment of the disease and insect pests found in industrial hemp throughout New England. Over the last couple of weeks, 10 hemp fields have been scouted from across Vermont and we would love to share a little of what we have been seeing. Depending on the specific location, the 2021 season has presented challenges with the heat, not enough rain, too much rain, or all the above! As a result, we have been seeing various issues related to abiotic (water in particular) stresses popping up.
The most common diseases we are finding this year are fungal leaf spots. They can include several species of pathogens, the one specific to hemp is Septoria cannabis. Like most foliar diseases, Septoria requires moist conditions to germinate, and begins at the ground in the bottom leaves, working its way up the plant. Common signs are yellow spots, and brown or yellow discoloration on the leaves (Figure 1).
A small amount of powdery mildew has also been seen, but we can expect to see increasing amounts throughout the region. Powdery mildew appears as patches of white spores on the surface of leaves (Figure 2). If the infection progresses, and entire leaves, petioles, and flowers become covered, that can lead to reduced flower quality.
It should be no surprise that, by far, the most common insect pest we are seeing in hemp fields are cannabis aphids. Winged and wingless aphids (Figure 3) can usually be found the underside of leaves and stems, sucking the life out of your hemp plants. They are not doing any harm at this point; however, the concern is that as the season progresses and aphid populations slowly grow, high populations might reduce plant vigor or slow growth.
You are probably also seeing chewing damage from flea beetles (Figure 4) and Japanese beetles, but those guys are just nibbling here and there, and your plants can withstand a considerable amount of defoliation without any impact on hemp yields. Kadie Britt (2021), a good friend of ours recently found that “removal of leaf tissue in grain and CBD cultivars did not significantly impact observable effects on physical yield (seed or bud weight) or cannabinoid content (CBD or THC) at the time of harvest”.
For a full report on last year’s results, checkout our 2020 On-Farm New England Hemp Pest & Disease Scouting Report at: (https://www.uvm.edu/sites/default/files/Northwest-Crops-and-Soils-Program/2020%20Research%20Reports/2020_Hemp_On-Farm_Scouting_Report_Final.pdf).
For more information on our Industrial Hemp Research Program, check out the Industrial Hemp page on our website: https://www.uvm.edu/extension/nwcrops/industrial-hemp and/or a full list of our research reports at: https://www.uvm.edu/extension/nwcrops/research