A little over a month ago, I visited some contiguous garbanzo bean fields in southern San Joaquin County, at the request of the grower. The grower observed that plants were yellowing and dying (Fig. 1) and wondered what might be causing the problem. The grower did not figure that he would be able to do anything about the problem in this year's crop, but he was thinking ahead for future cropping. He doesn't have reliable water at this site, so his cropping options (i.e. rotation options) are limited. He would consider growing garbanzos in these fields again next year unless diagnostics revealed a disease problem.

My observations of the field were that there were patches of several nearby plants with symptoms, but across the three contiguous fields, the patches were widespread. I suspected a vascular disease because of what appeared to be a progression of the disease from yellowing to necrosis to eventually plant death. I submitted samples to the plant pathology lab at UC Davis, and they diagnosed Fusarium oxysporum f. sp. ciceris, which is the Fusarium wilt pathogen for garbanzos. Fusarium wilt (also called Fusarium yellows) has the external symptoms previously described, but in addition to these symptoms, splitting the stems may reveal reddish-brown streaking in the vascular system at the center of the stem (i.e. xylem). The roots won't show discoloration with Fusarium wilt like they will with Fusarium root rot. Fusarium wilt should not be confused with yellowing caused from virus, which will exhibit discoloration in the phloem. Fusarium wilt can reduce yield by reducing seed quantity and size.

In general, cultural practices are the only ways to manage this disease. Luckily, the Fusarium wilt pathogens are crop-specific, so this pathogen will only infect garbanzos. The pathogen, however, can survive for a long time in the soil (upwards of 6 years or more) because it can survive under wide temperature and pH ranges. Therefore, crop rotation is an important management practice. Crop rotation will help to slow the proliferation of the disease, but it generally won't eliminate it. Growers should plant certified disease-free seed. They should not save seed for planting because Fusarium wilt (and Ascochyta blight) can live externally on the seed. Growers should also consider planting UC-27, which has disease resistance and is adapted to the Central Valley. Disease management may also include cleaning soil from equipment when moving from an infected field to a non-infected field. In some studies, soil solarizaton has been shown to reduce Fusarium wilt in subsequent garbanzo crops, but to my knowledge, there hasn't been any work on soil solarization in California garbanzos.

Garbanzo beans are an important crop worldwide for human and animal nutrition. In California, they are grown during the winter months, like small grains, and provide growers with another crop choice that can be winter rain-fed. Because they are a legume, they can fix atmospheric nitrogen to fulfil some of their nitrogen needs. Garbanzos also are more tolerant of soil salinity than common beans and limas. In California, we annually grow approximately 10,000 acres of garbanzos. California garbanzos are generally a high-quality product grown for the canning industry. More information on garbanzo production in California can be found in the UC production manual.

The Insect and Mite sections of the UC IPM Pest Management Guidelines for Dry Beans have been recently revised and updated and are now available online at: UC IPM Dry Beans Pest Management Guidelines.

Authors include UCCE Farm Advisor Rachael Long and UC IPM Advisor Pete Goodell (emeritus). The guidelines include an updated photo page to help identify pests and the damage they cause to dry beans at: Photo Identification. 

These guidelines can help with managing pests in your fields. Interested in Lygus bugs and how to control them? Take a look at the guidelines on lygus and see that the thresholds vary by bean class and type. For example, blackeye beans (cowpeas) have different tolerance levels to lygus than lima beans. Some lima bean varieties are more tolerant to lygus than others. Interested in biocontrol of aphids? See photos of natural enemies that prey on aphids at: Photos to identify natural enemies of aphids.

There is also a newly revised table on the relative toxicities of insecticides and miticides to natural enemies and honey bees in dry bean production, found at: Insecticide Toxicities.

This information and much more is available through the newly revised 2018 UC IPM Dry Bean guidelines!  This follows the recent revision of diseases and abiotic disorders in dry beans. The weed management section is currently in review and will be available later this year.

UC Davis Agronomy Farm 

Directions: In the field across from the UC Davis Bee Biology Lab (same place as previous years). From Hwy 113 in Davis, exit on Hutchison Dr. Go west, turn north at the first roundabout, then west at the second roundabout. Continue west on Hutchison Dr for about 1 mile. Turn south on Hopkins Lane (look for a row of olive trees), make your first left, and park under the trees.  For questions, contact Rachael Long at 530-666-8143. No RSVP needed.

Agenda

10:00  Sign in, introductions, updates, Antonia Palkovic, UCD Assistant Specialist

10:05  UC Dry Bean Blog and IPM update, Sarah Light, Farm Advisor, Sutter-Yuba Co.

10:15  Dry bean breeding program, pest and disease resistance, Dr. Paul Gepts, UCD

10:30  Cooperative dry bean nursery, MAGIC Beans, and interspecific crosses for drought tolerance, Dr. Jorge Berny, UCD Post-doc (with Santos Barrera Lemus)

10:55  Cowpea herbicide trial, Dr. Mariano Galla, Farm Advisor Glenn Co.

11:10  Bean seed moisture and quality at harvest, Rachael Long, Farm Advisor Yolo Co.  

11:20  Diallel Crossing project, Kimberly Gibson, UCD PhD student

11:35  Lima RIL trial, Stephanie Smolenski Zullo, UCD PhD student

11:50  Caravan to field location 1, near sheep barn

12:05  Heirloom breeding and Mesoamerican Diversity Panel; Drones for high throughput phenotyping, Travis Parker, UCD PhD student

12:30  Adjourn

 

A baby lima bean field in the Sacramento Valley was recently found to be infected with southern blight (Sclerotium rolfsii), a fungal pathogen that's found in many crops. The field was double-cropped with barley and planted late June.

Symptoms and signs: Initial symptoms of southern blight include a yellowing of the foliage with a slight darkening of the stem, just above the soil line. Lesions rapidly develop, girdling the stem, causing sudden and permanent wilt of the plant. The fungus grows downward in the stem, causing rot. White mats of mycelium develop on the stem and nearby soil. In a few days, tan to brown spherical sclerotia (tiny compact masses of hardened fungal mycelium) may appear on the fungal mat. If present, these are a good diagnostic feature of this disease.

Comments on the disease: Southern blight is usually a minor disease of beans and other crops in California. However, high temperatures above 85°F together with high moisture favor the disease. High summertime temperatures combined with a later planting date likely stressed the young lima plants in this field, making them more susceptible to this disease. The best time to plant baby limas in the Sacramento Valley is around the third week in May; for large limas it's early May. Last year was a big year for southern blight in many crops, likely due to late plantings and high heat stressing the plants. This year the disease seems to be a little less common, but is still widely detected on many crops, from Kern to Sutter counties. Detections in the northern counties of the central valley have become more frequent in the last three weeks.

Disease Management: The fungus attacks a wide range of plants and survives for a long time in the soil as sclerotia.  Rotations are not considered effective since this pathogen has over 500 hosts. However, it is thought that rotations to corn or small grains for at least 2 years may reduce inoculum; studies are underway to determine whether these rotations are effective. For most crops, southern blight resistant cultivars are not available. However, for vegetable crops such as tomatoes, there are some rootstocks reported to be resistant to southern blight, which are currently under study in field trials in California. Discing and burying plant refuse helps destroy sclerotia.