- Author: Chris M. Webb
Strawberry production growers face many challenges. One such challenge is strawberry anthracnose, which is caused by Colletotrichum acutatum. This plant pathogen is often undetectable on transplants purchased from nurseries for the planting season, but can become very destructive after transplanted into the field.
UCCE’s Oleg Daugovish and collaborators researched this disease and how to best reduce risk and loss. The researchers studied irrigation systems effects on fruit yields, canopy size, and crown tissue infection to determine best management practices.
Their research has recently been published in the American Society for Horticultural Science Journal. You may view the abstract at this site. The full text may also be viewed by following a link on the abstract page. The full article may also be viewed in the UC Cooperative Extension, Ventura County office.
- Author: Chris M. Webb
California farms produce 93% of the celery grown in the United States. The crop thrives in coastal California’s moderate climate. Celery is an important crop in Ventura County with 40% of the state’s acreage farmed here. Valued at over $182 million, it was the second most profitable crop for Ventura County agricultural producers in 2010, which are the most recent statistics available.
Most celery in the field is planted as transplants. Transplants are typically grown under high humidity and high plant density conditions and are subject to seedborne pathogens. The most significant being Septoria apiicola (the causal agent of Septoria late blight) and Pseudomonas syringae pv. apii (the causal agent of bacterial blight). These diseases can be carried from the transplants into the field. As the plants mature, these diseases can cause plants to become unmarketable at a great loss to the growers.
UCCE’s Oleg Daugovish and collaborators researched these pathogens and how to best reduce disease and loss in the field. Over four years, the researchers documented that: seed, seedlings, weeds located in or near fields that harbor the virus can cause the disease in celery. This disease is likely transmitted by aphids, vectoring the virus.
The studies provided practices growers can use to manage this disease. Findings indicated that growers can control the pathogens by managing poison hemlock weed populations, controlling aphids, and planting celery cultivars that are not susceptible to the pathogens.
The interpretive and technical summaries of the research report can be viewed on this page of the USDA’s Agricultural Research Service. The full text can be accessed through the American Phytopathological Society, or at the UCCE office in Ventura County.
- Author: Chris M. Webb
The Asian citrus psyllid (ACP) has now been found in eight California counties. Quarantines are in place. The psyllid by itself is not much of a problem; it is its ability to spread the fatal disease that has the potential to devastate both the California citrus industry and backyard citrus throughout the state.
Huanglongbing (HLB) is the name of the disease ACP can carry. Citrus and closely related plants are at risk. The disease is transmitted between plants by the psyllid. The psyllids transmit the disease to healthy plants and trees. After feeding on an infected plant, the ACP will transmit HLB to every other plant it feeds on.
While much outreach has focused on citrus trees, it is important to remember there are other plants that can host both ACP and HLB. This list from the University of Florida provides both the common and Latin plant name for many known hosts. Hosts include: curry leaf, ornamental orange-jasmine, and all the varieties of citrus, including kumquat, mandarin, grapefruit, orange and all of their hybrids.
Please remember to check your citrus and closely related plants regularly for signs of ACP or HLB. General information about this pest disease complex can be found on this section of the CDFA website. For local updates, the Ventura County ACP Task Force is a great source of information.
- Author: Oleg Daugovish
We have many highly salt sensitive crops in Ventura County: strawberry, avocados, blueberries. Rainwater, the purest kind, is excellent for leaching salts, but, in years with low rainfall, salt accumulation and resulting toxicity is a big concern.
Plant reaction to salts varies among varieties, stages of growths and environmental conditions and, perhaps most importantly, with the type of salts that they are exposed to. We typically determine salinity of water and soil by measuring Electrical Conductivity (EC): the more salts are present the greater is the capacity to conduct electric current. In fact, there are guidelines for most crops that show at which EC level you would expect negative effects on plant growth and productivity. Yet there seems to be a discrepancy between the guidelines and what actually happens in the field. For example, University of California (UC) guidelines suggest that strawberry injury and yield reductions can occur at EC=1 dS/m. However, in several Ventura County fields we have healthy productive strawberry in soils with EC >4 dS/m. These large differences in tolerable EC levels result from the fact that the guidelines were developed using sodium chloride, while Ventura county soils/waters most frequently have calcium and sulfates as primary components of EC. Recent studies at UC Riverside showed the specific negative chloride effect on strawberry fruit production, while studies elsewhere have documented that sodium can also be more harmful than other ions such as calcium and potassium. Because we have calcium-rich soil, and even irrigation water often contains calcium sulfate, our crops can manage well even with EC levels well above 1 dS/m. In fact calcium and magnesium help to counteract the negative effects of sodium in the soil salt solution.
In a demonstration, we wanted to show that a very salty water (EC=20 dS/m) will have different effects on mature strawberry plants depending on the ion composition of the salts in that water. Indeed, after four days of watering with sodium chloride solution, the plants had severe injury symptoms and were dying. However, the same salt concentration of potassium sulfate only resulted in slight marginal leaf burn and mild stunting. Plants irrigated with distilled water (that imitated rain water) looked perfect, of course.
The important points of these demonstrations and field evaluations were:
- EC values in water or soil analyses only show total salinity and one needs to look at specific ions in the report to evaluate the potential effects on sensitive plants.
- Sodium and chloride are a lot more damaging that potassium and sulfate and we’re planning to evaluate several other salts and develop realistic thresholds for safe strawberry production in their presence.
- At high concentrations in the root zone fertilizers (such as potassium sulfate, a ‘safer’ salt) can injure plants and reduce their productivity
- Typical irrigation with drip lines placed between planting rows does not affect salts in the root system, unless excessive amount of water are applied to induce leaching.
- Author: Chris M. Webb
Caused by the bacterium Erwinia amylovora, fire blight is a common and frequently destructive disease of pome fruit trees and related plants.
Symptoms commonly appear in spring. The first sign is usually a watery, light tan ooze that leaks from cankers. After being exposed to the air, the ooze darkens and leaves streaking on branches or trunks. Other signs of infection are petal fall, flower stem wilt, and the blackening and shriveling of flowers, shoots, and/or young fruit.
As the disease progresses, the pathogen spreads into the wood. The infected wood tissue can become sunken and cracks often develop in the bark around the infected areas.
Ideal conditions for infection, disease development and spread of the pathogen are rainy or humid weather with daytime temperatures from 75 (degree sign) F to 85 (degree sign) F.
Home Gardeners can learn more about fire blight in UC IPM’s Pests in the Gardens and Landscapes: Fire Blight publication. Subjects include: identification and damage; life cycle; and management.
Commercial growers can find fire blight information by crop on UC IPM’s Agricultural pest page.