Cercospora Leaf Spot on Table Beets

When I started growing vegetables for my local farmers’ market in the 1990s, I began growing a variety of beets (golden beets, baby red beets, white beets, and ‘Chioggia’ or candy-striped beets) to meet the diverse culinary expectations of my loyal customers. In the 1990s, specialty beets were a hot commodity, and today, beets are roasted and served as a component of specialty salads at some of the finest white tablecloth restaurants in the region.

Beets are a relatively easy crop to grow in the Mid-Atlantic region, but a few diseases can impact yield and beet quality. Cercospora leaf spot (Cercospora beticola) is the most serious disease that growers may observe in our region. Growers raising table beets for processing may find that Cercospora leaf spot infections may cause serious defoliation, adversely impacting mechanized harvest and yield loss. Fresh market growers frequently leave the beet tops intact when direct marketing, but when Cercospora leaf spot infections are severe, a grower may be forced to remove the tops to lessen the likelihood that the crop will be rejected by the retail customer.

Cercospora leaf spot symptoms appear as necrotic leaf lesions that are bound by a red or purple margin on red beet cultivars. On yellow beet cultivars, growers will notice necrotic lesions or spots surrounded by a tan margin or border. The centers of Cercospora leaf spot are always gray in color irrespective of the beet cultivar that is being grown.

Cercospora beticola can overwinter on host debris and in the soil for up to 3 years or survive on alternative weed hosts like lambsquarters and pigweed. Cercospora leaf spot will infect spinach, Swiss chard, and sugar beets. Under warm, humid conditions, Cercospora beticola becomes active, and spores are easily dispersed by rain to infect beet foliage or other susceptible hosts. Once infected, Cercospora leaf spot will continue to spread until the entire beet leaf surface becomes covered with lesions.

Beet growers wishing to prevent Cercospora leaf spot on their farm should implement a 3-year crop rotation featuring non-host crops. After harvesting beets, growers should also use deep tillage to bury and incorporate beet crop debris. Weed management is also critical to preventing Cercospora leaf spot in beet plantings. Growers should be proactive in controlling redroot pigweed and lambsquarters on the farm. Eliminating alternative weed hosts is the first step in Cercospora leaf spot prevention. Growers looking to utilize other cultural techniques to minimize Cercospora leaf spot infection should also consider wider row spacings, lower plant densities, and row orientation to facilitate the rapid drying of foliage after rain events.

Figure 2: Lambsquarters is one of the alternative weed hosts that can harbor Cercospora leaf spot. Photo by Thomas Ford, Penn State.

Cercospora leaf spot can be effectively managed with conventional fungicides. Fungicide resistance to strobilurin fungicides (Class 11) has been observed in some areas. Consider tank-mixing strobilurin fungicides with a fixed copper fungicide.  Growers should always rotate fungicides with different modes of action or FRAC codes to prevent fungicide resistance.

Fungicides labeled for the management of Cercospora leaf spot in beets include:

• Fixed copper fungicides (FRAC Code M01)
• Tilt 3.6EC (FRAC Code 3)
• azoxystrobin 2.08F (FRAC Code 11)
• Fontelis 1.67SC (FRAC Code 7)
• Cabrio 20EG (FRAC Code 11)
• Luna Tranquility 4.16SC (FRAC Code 7 + 9)
• Flint Extra 500SC (FRAC Code 11)
• Merivon 2.09SC (FRAC Code 7 + 11)
• Reason 500SC (FRAC Code 11)
• Miravis Prime FRAC Code 7 + 12)
• tebuconazole 3.6F (FRAC Code 3)