- Author: Rachael Freeman Long
Our cool, wet conditions are favoring white mold (sclerotinia) in garbanzo beans this year. This disease is characterized by a white fungal growth that attacks the above ground plant parts, often near the soil line for garbanzos. The affected tissue dries quickly and bleaches to a pale tan or almost white color. Black sclerotia formed on the stem of dying plants are often visible. These are masses of fungi compacted to form small, dark pellets that range in size from 1-8 mm (about the tip of a pencil to a pencil-size eraser) that allow the fungus to survive in adverse conditions (e.g. hot, dry weather). When the main stem is affected near the soil line, the entire plant wilts and dies; lesser infections will show dead branches, causing yellow flagging in the field.
The black sclerotia pellets formed in the mold can survive many years in the soil and re-infect crops. The development of white mold is greatly influenced by prevailing weather conditions and certain agronomic practices such as late extensive irrigation, plant density, and plant growth characteristics, which are all closely linked with the life cycle of the pathogen. A thick dense plant growth provides a micro climate of cooler temperatures and high moisture beneath the plant canopy where conditions are favorable for disease.
The best control focuses on cultural practices to prevent the disease from developing in the field. This includes higher beds that keep lower plant parts and tops of the bed drier, wider row spacing to increase air movement in the canopy to keep the foliage drier, and planting garbanzo beans later (December through early February) rather than early (November) since the extra growing time can result in heavy canopies that increase humidity and cause infestations late winter/early spring (favorable disease conditions, 68oF-77oF). Crop rotation generally does not prevent white mold infection due to the broad host range of the pathogen.
Fungicides are available for white mold control, but getting good coverage and control is difficult because the inoculum is in the soil and the disease is often deep in the plant canopy. Fungicides would have to be applied when plants are smaller to provide good coverage and protection from this disease. For a list of fungicides available for white mold control in in garbanzos, see http://ipm.ucanr.edu/PMG/r52100111.html.
- Author: Michelle Leinfelder-Miles
I later visited the field with the PCA in order to assess the situation for myself. The disease appeared to be most apparent in one corner of the field where the water tends to sit a little longer. (This is a furrow irrigated field that has had beans for several consecutive years.) Moist or humid conditions favor white mold, as do heavy canopies. The leaves were showing some unusual brown lesions, and some plants had white mycelium growing on the pods (Figure 2). The most detrimental symptom that we observed, however, was complete infection of the stem at the soil line, causing the tissue to dry up (Figure 3). In this case, the upper canopy looked ok, but I am uncertain, perhaps doubtful that the pods will fill on these plants.
What we can hope is that the disease won't appear on more plants in the next two weeks because there are really no management strategies at this stage in the game. The grower needs to think about how to manage this disease in the future, and rotating out of beans to a non-host crop (like small grains or corn) is probably a good strategy.
If wider row spacing is an option, this can also improve air movement in the canopy, which makes conditions less favorable for white mold. Monitoring for the disease should begin at flowering, which is also the best time to apply fungicides (like thiophanate methyl or boscalid) because the plants are small enough for the treatment to penetrate into the canopy.
- Author: Michelle M Leinfelder
In addition to the production manuals previously mentioned, I also consulted UC production manuals produced in the 1950's, including Dry Edible Bean Production in California (1954), Blackeyes: Costs of Production, Suggestions on Growing (1956), and Production of Dry Edible Lima Beans in California (~1951).
- Author: Michelle M Leinfelder
A pest control advisor recently contacted us to ask what pests he should be scouting for in garbanzo beans. His clients had not grown garbanzos in the past but have some acreage this year. Given recent wet weather and relatively mild temperatures, there are three diseases for which we suggest keeping an eye out.
Ascochyta blight (Ascochyta rabiei, Didymella rabiei) is a particular problem in garbanzo beans in wet years, like what we've been having this year. Ascochyta blight can occur at any stage of growth and on any aerial part of the plant. Brown lesions on the stems can cause damping-off symptoms in seedlings or can cause stems to break. At the advanced stage of the disease, concentric circles of spores will form within brown leaf lesions, and these are a good diagnostic characteristic (Figure 1). These concentric circles can also be seen on seed pods (Figure 2), which can result in poor seed set, seed discoloration, and shrinkage. If these beans are used for seed, subsequent crops can get infected. Management of Ascochyta is through the use of tolerant varieties, crop rotations, certified disease-free seed, always using a seed treatment (Mertect), and foliar fungicides. Foliar fungicides, such as Headline or Quadris, should be applied at the first sign of the disease and reapplied if rainy weather is forecasted.
Alfalfa mosaic virus is another disease that could infect garbanzo beans. Alfalfa mosaic virus has a wide host range and is transmitted by aphids. Different strains of the virus may cause symptoms as varied as necrotic spots on leaves to yellow dots or mottling on the entire plant, which can stunt plants or result in pod distortion. Treatment is not recommended for either alfalfa mosaic virus or for the aphids that vector it. Aphids may taste the garbanzo plants but are either killed or deterred by the acidic exudate of the plant, so it is not economical to treat for them. Instead, planting date is important to avoid aphid flights. There are no patterns of infection in fields. Infected aphids land on plants, transmit the disease and then die, so healthy and dying plants may be next to each other (Figure 3).
Lastly, white mold (Sclerotinia sclerotiorum and S. trifoliorum) may be a problem in garbanzos this year, like Ascochyta blight, because of the wet conditions. White mold may appear as a watery rot on stems, leaves, and pods. White mycelium may grow on the stem near the soil line where conditions are moist (Figure 4). Yellow flagging of leaf tissue may appear where stems have been killed. The fungus spreads under moderate temperatures and especially where canopies are dense. Management is through rotations with non-host crops (small grains, corn), and by applying fungicides, such as Endura, during the flowering stage.
Information on products and practices is for educational purposes only and does not constitute an endorsement or recommendation by the University of California.
- Author: Rachael Long
It is not cost effective to spray the aphids for virus control; instead, planting date is important to avoid aphid flights. The best time to plant garbanzos in California is November 15 to January 15 to take advantage of winter rainfall for irrigation. Garbanzos can also be planted in the spring from April 20 through May.
These later plantings (for both winter and spring seeding times) are needed to help avoid the seed corn maggot, a serious pest of beans, and aphid flights that can vector a number of devastating viral diseases. In addition, avoid planting garbanzo beans adjacent to alfalfa fields, a significant host and source of alfalfa mosaic virus.