Problem-free Panicum Details, Part 2: Cultural Conditions

Our head grower, Bill Hall, gave a well-received talk this summer on Panicum at Cultivate’19. Because so many of our customers grow Panicum virgatum in container production, we are sharing details from his talk in a series of posts. The first post focused on understanding the range and warm-season nature of Switchgrass. You can review it here.

The current post connects the fundamentals to container production. The most common production concerns we hear with Panicum are yellowing, rust, and slow emergence in spring. Yellowing and rust are often related to cultural conditions and management practices, which we’ll address here. Production timing will get the spotlight in a later post.

Get a Good Start

Keeping Panicum problem free starts at the beginning. When transplanting liners or plugs, match the original soil line of the propagule with the media in the container. Grasses are sensitive to having the crown buried, which limits air circulation and can invite disease. Planting too high can leave the root ball vulnerable to drying out.

You’ll also want to make sure there is good root contact with the media and there are no air pockets. Once potted, the root zone should be kept moist, but not wet, until the plants are established.

Manage Water & Nutrients to Prevent Yellowing

Switchgrass grows best in full sun conditions and has average water needs for an ornamental grass. It needs less than Pennisetum but more than Schizachyrium. If you’re growing outside, use a light porous media to facilitate good drainage. Panicum virgatum can take up a lot of water, but that can have a significant downside in production. Frequent, heavy rain events or overwatering can lead to yellowing—one of the major issues we hear about from customers. Keep an eye on your irrigation regimen in the greenhouse and back off if you start to see yellowing.

Use a well-drained soil mix to help with water management. Our current media is 60% pine bark, 30% peat, and 10% perlite. To this basic mix, we add 5 lbs. of dolomitic lime and 1 lb. of Micromax per cubic yard. We also include a 5- to 6-month slow-release fertilizer (SLR). The rate depends on whether we’re potting up for fall/winter production (4 lbs./cu. yd.) or summer production (6 lbs./cu. yd.).

Switchgrasses aren’t heavy feeders, so incorporating SLR in the potting media usually covers a single round of production. However, if we wind up overwintering plants, they get a 1 lb.-rate of SLR just before they break dormancy. Overwatering isn’t the only cause of yellowing in Switchgrass. Nutritional imbalances can send Panicum in the chlorotic direction. Check your EC and pH levels to make sure they’re not way off. If we see yellowing on a crop, a single application of liquid feed 10-10-20 with iron usually turns it around.

Pest Pressures and Management

Compared to other perennials, insect pests are minimal on Panicum. We see spider mites in summer, along with occasional Japanese beetles, thrips, and spittle bugs. The heaviest disease pressure comes from rust (Puccinia and Uromyces). Rust problems tend to be very site-specific, depending on the region and weather conditions. It’s seasonal for us in central North Carolina, usually appearing in September and November.

Our strategy is to spray prophylactically every two weeks starting in mid-August. We use a broad-spectrum fungicide and continue through October or until the plants start going dormant. We rotate chemicals to prevent resistance.

We also see Leaf Spot (Bipolaris oryzae) on Switchgrass. It affects the foliage appearance but does not compromise plant health unless left untreated. In addition, we’ve found the following diseases on occasion, but they are not common: Alternaria, Collectotrichum (anthracnose), brown and root rots, Phyllosticta, and Septoria.

An integrated pest management (IPM) program will keep your Panicum in good shape. Monitor irrigation and limit the time the foliage is wet. Scout regularly and be ready to treat. IPM includes a tolerance for some damage, although we try to keep that to a minimum. Occasionally plants will have residual damage even though there are no active pests present. Work with your vendors and customers to manage expectations and ensure pests aren’t coming in or going out with your Panicum.

Next Steps

We hope these tips lead to successful growing with fewer yellowing and rust problems on your Panicum. Now that you’ve gotten an overview and best management strategies, the next post will address production timing. We’ll give you tips for scheduling so you can take advantage of the Panicum growth cycle. Check back soon!

Ready to see more Switchgrass? Find the ones we offer here.

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Click here to see a list of references consulted for these posts and Bill’s presentation.