My thanks to Dr. Fulya Baysal-Gurel for preparing the following report. And best wishes to Fulya as she begins her new position as Assistant Professor of Plant Pathology at Tennessee State University, beginning June 1, 2015.
Downy mildew was confirmed on hops from research plots in Wooster, OH and hop yard in Norton, OH on May 13, 2015. Symptoms and signs of the disease were observed on spikes and leaves. Leaf internodes were shortened (upper left photo), yellow (chlorotic) angular spots were observed on the tops of the leaves (upper right photo), and black sporulation typical of downy mildew was seen on the lower surface of the leaves (lower photo).
Early spring pruning is essential to reduce primary inoculum of the downy mildew pathogen, and pruned leaves and shoots must be destroyed to prevent survival and movement of spores. Later on, after stripping, lower leaves should be removed to promote airflow. Several fungicides are effective against downy mildew. Be sure to note label restrictions on application intervals, maximum number of applications per season and pre-harvest intervals, which may range from 0-45 days after application.
If you would like to confirm that downy mildew has infected your hop plants, you may submit a sample to Dr. Sally Miller, Vegetable Pathology Lab at The Ohio State University, 1680 Madison Ave., Wooster, OH 44691.
Instructions and sample submission form can be found here: http://go.osu.edu/4kN. There is not charge for samples from Ohio growers.
| Product group | FRAC Code | PHI | Notes |
| Copper | M1 | 0-day | Over-application of copper products copper accumulation in the soil, contamination of runoff water, and toxicity to non-target organisms. |
| Folpet | M4 | 14-day | Maximum four applications per season at 28-day intervals. |
| Metalaxyl | 4 | 45-day | Apply as drench to the crowns after pruning but before training (early when shoots are 6 inches or less). Foliar application of metalaxyl products is suggested in combination with a copper fungicide registered for hops. |
| Phosphorus acid mono-and di-potassium salts | 33 | 0-day | Apply on 2-3 week intervals. |
| Cymoxanil | 27 | 7-day | Maximum four applications per season. |
| Dimethomorph | 40 | 7-day | Maximum three applications per season; 10 day-interval. |
| Mandipropamid | 40 | 7-day | Addition of a spreading/ penetrating adjuvant such as a non-ionic based surfactant or blend is recommended. Do not apply more than 24 fl oz of product/A/season. |
| Ametoctradin plus Dimethomorph | 45 + 40 | 7-day | Addition of a spreading/penetrating adjuvant is recommended. Maximum three applications per season; not more than two sequential applications before alternating with a labeled fungicide with a different mode of action. |
| Pyraclostrobin plus Boscalid | 11 + 7 | 14-day | Suppression of downy mildew. Apply on 10-21 day intervals. Maximum three applications per season; not more than two sequential applications before alternating with a labeled fungicide with a different mode of action. |
| Product * | PHI | Notes |
| Actinovate(Streptomyces lydicus) | 0-day | Use when conditions favor disease and apply at 7-14 day intervals as needed. |
| Sonata(QST strain 2808 Bacillus pumilus) | 0-day | Use when conditions favor disease and apply at 7-14 day intervals as needed. |
| Regalia(extract of Reynoutria sachalinensis) | 0-day | Use when conditions favor disease and apply at 7 day intervals as needed. Foliar application of Regalia is suggested in combination with another fungicide registered for hops. |
| EcoMate® Armicarb® “O” (Potassium bicarbonate) | 0-day | Use when conditions favor disease and apply at 5-7 day intervals as needed. |
*A list of biorational products and current information regarding OMRI approval is available at http://attra.ncat.org/attra-pub/biorationals/.