A new strain of fusarium wilt has been detected in lettuce, putting crops in danger. Researchers at UC Riverside are exploring new ways to combat this potentially devastating fungal disease. Alexander Putman spoke at the World Ag Expo in Tulare and with Matthew Malcolm from Malcolm Media Ag Publishing to discuss the issue. Watch this quick video and learn more in California Fruit & Vegetable Magazine.
Please thank this video’s sponsor Simplot for their industry support.
Last year we had a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.
Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum, is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult.
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields.
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting. Wilting is followed by a yellowing of the leaves and finally necrosis. The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time. Affected plants that do not die are often stunted and have considerably reduced yields. Under high inoculum pressure, seedlings may damp off as they emerge from the soil.
Initial infection of seedlings usually occurs from chlamydospores (resting structure) that have overwintered in the soil. Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge. Infection may be enhanced by wounds or damage to the roots. The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia. Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen.
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management. — By Bindu Poudel, University of Arizona Extension
As processing tomato growers in California begin their 2020 season, watch this brief interview with Bruce Rominger, Chairman of the California Tomato Growers Association as he shares some insights from the past season and what growers can expect this year. Read more about it in Vegetables West Magazine.
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.