Diseases of red clover and birdsfoot trefoil

Red clover and birdsfoot trefoil are important legume components of many Michigan hay fields and pastures, especially where local soils aren’t suitable for alfalfa. For many years, red clover has been considered a short-lived, 2-to-3 year perennial forage. Plant breeders working with red clover have focused on selecting individual resistant plants to enhance resistance to disease, leading to improved varieties including Arlington, Marathon and others. Birdsfoot trefoil, on the other hand, is known for good persistence, mainly due to its ability to reseed itself when managed properly. Birdsfoot trefoil, however, is slower to establish and more susceptible to competition from other forage species during the planting year. Both species are more suitable for wetter and more acidic field conditions than alfalfa. With good planning and planting conditions, both can also be drilled into live sods, or frost-seeded, to enhance the legume component of older, grassy forage fields.

Why does red clover die out in a few years? According to Wisconsin USDA-ARS researcher R.R. Smith, root rots and the foliar disease northern anthracnose, caused by Fusarium spp., and Aureobasidum caulivora, are the most serious diseases of red clover. Root rots are the worst of the two, resulting in plant death and stand thinning. Maintaining plant vigor by maintaining adequate soil fertility and proper cutting management are the most practical means of minimizing losses to root rots. Northern anthracnose causes severe foliage loss during the first growth of the season. With reduced percentage of leaf material, forage quality and yield decline seriously. Varieties resistant to northern anthracnose are available and provide the only practical control action. Other diseases of red clover include powdery mildew, viruses, sclerotinia crown and stem rot (aka ‘white mold’) and other fungal diseases. Selection of disease-resistant varieties is the primary control option in red clover. Soil fertility and proper harvest management (for example: cutting early if disease problems become severe) are also important in limiting red clover diseases.

Arlington and Marathon are two public red clover varieties developed in Wisconsin that have good disease resistance to help improve longevity. Private seed companies can provide many other excellent red clover varieties. Red clover seed sold as “common,” “common red clover,” or “medium red clover,” may consist of varieties not well adapted for Michigan. It may also have very little disease resistance and persistence.

Although birdsfoot trefoil is more persistent, this is due to the emergence of new plants from self-seeding, not longevity of original plants in a seeding. Diseases that cause problems in birdsfoot trefoil include crown and root rots caused by Fusariumspp. and other fungal pathogens, Stemphylium leaf spot, stem cankers and Fusarium wilt. There are a limited number of birdsfoot trefoil varieties available, and disease resistance remains a challenge. Pardee, a variety developed in Pennsylvania, has greatly improved disease resistance, but lacks adequate winter hardiness for Michigan conditions. To manage disease in birdsfoot trefoil, avoid rapid and complete defoliation (leave some leafy stems at harvest), allow reseeding, avoid stockpiling past early bloom, avoid excessive shading by grasses, and allow plants to rest in fall (September – mid October).

Control measures should be based on proper identification of disease, economic factors, and the effect of the growing environment. Walking your hay fields and pastures is essential to closely monitor disease and other plant development issues.

Spraying to control fungal diseases in forage crops is not a common practice in Michigan. If fungicides are considered, growers must pay close attention to the efficacy of the fungicide, pre-harvest intervals (within a cutting, and season-long), and application rates. For example, Ridomil Gold (mefenoxam) applied as a broadcast soil surface spray at planting is labeled for clover and birdsfoot trefoil to control damping off caused by Pythium spp. and root rot caused by Phytophthora spp. Fungicide seed treatments such as Apron XL (mefenoxam) are more common and should be used if seedling rots have resulted in poor stands in past years.

Source: Jim Isleib, Michigan State University Extension

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