Be on the Look Out!

Hemp Diseases Creeping into Fields Across Vermont

Following are pictures of Septoria.

As the weather cools, rains, dews and fogs are becoming more common and diseases are on the rise. In the past couple of weeks, the UVM Hemp team has been scouting fields in the state and noted Alternaria and Septoria foliar leafspot diseases and Powdery mildew on plants. The foliar leafspots start low in the plant as small discreet circular spots (often with advancing yellow margins) that can coalesce over time and result in defoliation. The spores from these pathogens are rain splashed or blown throughout the foliage with each rain or wetting period. As air circulation becomes poorer in bushy mature plants, leaves are slow to dry off, increasing infection. Plastic mulches can help retain soil moisture and prevent spore splash up to the lower leaves early in the season. In one field, a Vermont grower used mulch both in the rows AND the alley ways, and no foliar leafspots were noted during scouting last week. This extra protection may have reduced humidity and helped minimize the incidence of leafspots. Although leafspots rarely kill a plant, they increase plant stress, reduce vigor and can negatively impact yield depending on their severity.

Powdery mildew is another foliar fungal disease that is becoming common in some fields now. This pathogen’s spores results in the characteristic white powdery coating on the foliage. This disease can be managed with applications of potassium bicarbonates and the horticultural oils. Again, repeat applications are necessary to keep foliage and buds protected. Below are pictures of Powdery mildew.

Fungicides may be necessary at this point in the season to protect the foliage and flower buds from further infection. Fungicides would also help protect buds from botrytis blights as the season progresses. Fungicide options in Vermont are limited to Bacillus spp. (Double Nickel, Serenade); Streptomyces spp. (Mycostop, Actinovate); several mineral or plant oils; hydrogen dioxides and peroxides, Regalia™, potassium bicarbonates, etc.

See link for the full list of what is allowable in the state:

These materials are applied as ‘protectants’ and would need to be reapplied on a regular basis until harvest. As with any pesticide, read the product label carefully and follow the instructions listed on the label.

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