Multiple cut flower farms in eastern South Dakota have reported the presence of Northern corn rootworms (Diabrotica barberi) and the less common Western corn rootworm (Diabrotica virgifera virgifera) on a variety of crops, including sunflowers, zinnias, and dahlias. Adult populations of these beetles typically emerge in mid-July predominantly in row crops and remain active until the first hard frost.
As the name suggests, corn serves as the primary host plant for corn rootworm species, with larvae feeding on roots below ground and adults (though less frequently) feeding on leaves, silks, and tassels. Many of the state’s cut flower farms are in rural areas, often near agronomic production. Therefore, movement of adult rootworm populations between corn and other attractive hosts, such as cut flowers, can be expected. For a detailed overview of corn rootworm biology, life cycle, and management in the context of commercial corn production, see Northern and Western Corn Rootworm in South Dakota.
© Tara Lothspeich, 605 Petals & Pines Farm
Due to the relative newness of cut flower production in South Dakota and the limited research on arthropod pests and plant diseases affecting these various crop species, it is important for growers and scientists to monitor pest pressures from season to season. Careful attention to the species present, their timing, and the damage they cause helps inform integrated pest management strategies. This information supports optimizing both marketability (such as bloom quality, stem length, and harvest timing) and profitability by managing labor and production costs effectively.
In 2022, the USDA Census of Agriculture reported that cut flowers in South Dakota were valued at $75,840 across 8.5 acres of open fields and protected cultivation. This equates to approximately $8,920.00 per acre, or $0.20 per square foot. This is well above the value of most other specialty and agronomic crops in the state. These figures highlight the importance of effective pest management to protect these high value crops.
Damage
Thus far, grower observations indicate that larvae are not present in the soil and are not feeding on cut flower root crops, only the adult beetles are present on above ground parts of the plants. Multiple adults congregate on the blooms feeding on the pollen (Figure 1).
© Tara Lothspeich, 605 Petals & Pines FarmFigure 1. Multiple Northern Corn Rootworms causing feeding damage on sunflower petals
Although pollen feeding doesn’t cause direct damage, the presence of the beetles themselves can be unsightly and undesirable for growers who may be conducting daily harvests or allowing consumers on the farm for self-pick business models.
© Tara Lothspeich, 605 Petals & Pines FarmFigure 2. An individual Northern Corn Rootworm feeding on the pollen of a zinnia in full bloom
Aside from pollen, adults may feed on a variety of other above ground plant parts with their chewing mouth parts. Growers have observed damage to both foliage and the petals of the flowers causing small holes or notches on various parts of the bloom. Even minor aesthetic damage can be deemed unmarketable, therefore requiring extra vigilance for monitoring and management.
© Tara Lothspeich, 605 Petals & Pines FarmFigure 3. Multiple Northern Corn Rootworms causing feeding damage and discoloration on an exposed dahlia, shown next to a dahlia bloom protected by an organza bag
Several techniques can be used to manage corn rootworms and other beetles. Yellow sticky cards, placed throughout the production site, can attract and capture adult beetles; while they may reduce some numbers, their main purpose is to indicate population levels over time. Physical exclusion methods, such as using row covers made of spunbond material or insect netting over low tunnel structures, or applying organza on individual blooms, can also help protect plants. In smaller operations, hand removal is effective—beetles can be shaken or dislodged into a bucket of soapy water. Although chemical control may seem appealing when pest pressure increases, it is rarely the best option for cut flower systems, where pollinators and other beneficial insects are highly active. Additionally, few pesticides are specifically registered for cut flower crops in South Dakota, and the phrase “cut flowers” seldom appears on pesticide labels.
Source: South Dakota State University Extension
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