Scouting Dry Bean Diseases
June 19, 2006
Some points to consider in scouting and managing dry bean diseases:
" Seed treatments will help protect the plant from root rots during germination and early growth, but generally do not offer protection against foliar diseases.
" Using bin-run/saved seed may increase your risk of seed-borne diseases, and may leave a crop more vulnerable to key diseases such as anthracnose. Be extra vigilant about scouting for diseases during the growing season when planting bin-run seed.
" Avoid cultivating plants when wet. This helps prevent spread of pathogens, especially bacterial pathogens and anthracnose.
" Foliar fungicides labeled for use in dry beans are preventative, used as protectants to prevent sporulation, before the disease shows up. Labeled preventative products include Strobilurin fungicides (ie Quadris, Headline) and chlorothalonil fungicides (Bravo, Echo). Preventative fungicides work differently than curative fungicides which can be applied immediately after the disease is detected in the area. Preventative fungicides help protect against infection but do not cure established infections. They should be used to prevent infection or at the first sign of disease to prevent additional infections.
North Dakota State University Extension 2006 Field Crop Fungicide Guide online: www.ext.nodak.edu/extpubs/plantsci/pests/pp622w.htm - scroll down to dry bean product information.
White Mold Apothecia White Mold
Rust Asian Soybean Rust
Anthracnose on pods Anthracnose on Leaf
Weather is the primary factor that determines how bad white mold will be in a given year. Soil moisture is needed for the small mushroom structures known as apothecia (at left) to emerge from the soil and release ascospores. Wet foliage provides a conducive environment for disease progression to occur more rapidly. If conditions around the time dry bean plants are flowering are cool and wet, then the potential for white mold problems is intensified.
Keeping an eye on the weather and scouting just prior to and during bloom will help with spray decisions. The apothecia that release ascospores grow from sclerotia in the soil after the top 3 to 4 inches of soil have remained moist for 10 to 14 consecutive days.
Fungicides are effective in managing white mold if they are applied timely and in the best manner. Fungicides registered for control of white mold on dry bean include boscalid (Endura), iprodione (Rovral), and thiophanate-methyl (Topsin M, T-methyl, and others). These fungicides should be applied at the onset of bloom to 7 days after. Rovral is pH sensitive; therefore, the water should be buffered to a pH of 5 to 7.
Fungicides can be applied by air, ground, or fungigation. For ground application, a pressure of 100 psi along with the use of drop nozzles may allow for better coverage and control. For application by air, spray volumes of 7 to 10 gallons per acre may provide for the best coverage and control.
Timing is critical protect the flowers where infection occurs. Research conducted at the University of Minnesota to determine the potential for a fungicide to be profitable on dry bean when total water (rainfall and irrigation) from June 1 until 10 days into bloom was recorded showed that:
3 to 5 inches = fungicide profitable 20% of the time
5 to 7 inches = fungicide profitable 67% of the time
7+ inches = fungicide profitable 85% of the time
Anthracnose, caused by the fungus Colletotrichum lindemuthanium, is a relatively new disease to the Northarvest region. It can cause symptoms on the foliage, pods, and seeds. Symptoms on leaves appear as reddish-brown lesions that occur on the leaf veins on the underside of the leaf. Pod symptoms appear as sunken tan lesions with dark borders.
Bean anthracnose was first detected in North Dakota in 2001, and has made sporadic appearances since then. The anthracnose pathogen is most likely not established in our region; rather, each occurrence in 2001 and since is believed to have been due to seedborne infections. This stresses the importance of planting certified, disease-free seed.
Different races of anthracnose exist throughout the U.S. and Canada; however, only race 73 has been observed in the Northarvest region thus far. Varieties resistant to race 73 are available in some market classes. Fungicides are also available to control anthracnose. Those labeled include Amistar, Quadris, Quadris Opti, Headline, chlorothalonil products (Bravo, Echo, etc.), and thiophanate-methyl products (Topsin M, T-methyl).
Common blight was prevalent last season, spurred in part by hail and damaging winds. Because common blight is caused by a bacteria, only the copper-hydroxide bacteriacides (Basicop, Champ, Kocide, etc.) will provide some control of this disease. In regular production fields, protection against common blight may not be needed; however, in seed production fields, an application of a copper-hydroxide compound may help reduce the number of pods with common blight lesions. Results from an NDSU trial conducted in 2003 at Prosper, N.D. are below. The product used in this trial was Champ DP.
Asian soybean rust
Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, is primarily a soybean disease; however, dry bean is also a known host. Asian soybean rust causes much smaller lesions and pustules compared to common bean rust. Preliminary USDA research indicates dry beans as a whole appear to be less susceptible than soybeans. Differences in susceptibility levels do exist among dry bean varieties, however. Although fungicides may not be needed to control Asian soybean rust on dry bean, the same fungicides used to control common bean rust are also effective against Asian soybean rust.
Asian soybean rust information online:
NDSU -- www.ag.ndsu.nodak.edu/extplantpath (click on Soybean Rust Information)
UM -- www.soybeans.umn.edu/crop/diseases/soybeanrust.htm
and www.oardc.ohio-state.edu/soyrust (excellent info on using foliar fungicides to manage soybean rust)
USDA Rust Tracking & Alerts -- www.sbrusa.net and www.usda.gov/soybeanrust
DTN -- www.dtnsoybeanrustcenter.com
North American Plant Disease Forecast Center -- www.ces.ncsu.edu/depts/pp/soybeanrust