Tim Hartz published a comprehensive guide to nutrient management for vegetable crops. The information provided in this book is of great relevance to growers, PCAs, fertilizer industry professionals and all who are interested in the principles of nutrient management and who need specific and relevant information on managing nutrients in vegetable crops.
Nutrient management is critical to successful vegetable production, given the high value and exacting market standards for size, appearance, and postharvest quality for vegetable crops. Growers are now facing increasingly stringent regulations designed to minimize nutrient losses to the environment and this guide provides the detailed information needed to address these issues by providing detailed background information on nutrients and current information on best practices management practices for the industry.
Drawing on over 25 years of industry experience, Tim Hartz outlines the principles of nutrient management that are specifically of interest to vegetable producers on the Central Coast and other areas of the state.
Ordering Information:
112 pages
ANR Publication #3555
ISBN 978-1-62711-070-9
$35.00
Direct product link: https://anrcatalog.ucanr.edu/Details.aspx?itemNo=3555
- Author: Alejandro Del Pozo-Valdivia
Upcoming online meeting on July 30th 2020 from 8:30am to 12pm.
Register for this ZOOM event at:
https://ucanr.edu/survey/survey.cfm?surveynumber=30593
You will receive the ZOOM link for the meeting by email after the registration.
Agenda for this meeting is below.
Richard Smith, Vegetable Crops and Weed Science Farm Advisor
Steve Koike, TriCal Diagnostics
Clubroot disease can be a serious production issue for broccoli, cauliflower, and other brassicas in the Salinas Valley. The disease is caused by a unique organism (Plasmodiophora brassicae) that is closely related to ciliate protozoans but is classified in its own taxonomic group. It survives over 20 years as resting spores in the soil that are released as the clubbed root tissue decays. At temperatures above 65 °F, the resting spores release zoospores that swim to host plant roots and infect through root hairs. Once inside the plant, the organism grows into a large multinucleate plasmodium (a multinucleate mass of protoplasm) which stimulates changes in the plant hormones, resulting in enlarged root cells and the characteristic clubbing of the roots (Photo 1). Root infections by the clubroot pathogen can occur in both acid and alkaline soils; however, acidic soil conditions favor the development of the root symptoms. In addition to the main brassica crops, Plasmodiophora can infect arugula, radish, mustard cover crops, and weeds such as shepherd's purse and even some grasses. Plants that develop severe root swellings will exhibit above ground symptoms (Photo 2) indicative of non-functioning root systems, which includes yellowing, wilting, poor growth and stunting, drying and death of lower leaves, and eventual plant death.
Clubroot in the Salinas Valley is mostly controlled by maintaining soil pH above 7.2 to 7.3 by liming. The high pH does not kill the pathogen but inhibits the formation of the root clubs. Soils where control of clubroot by liming is achieved are called “responsive” soils. However, soils where liming is less effective are called “unresponsive” soils.
In 2020 we had calls regarding the incidence of clubroot on brassicas. In each situation the grower/PCA had soil lab results that indicated that the soil pH was greater than 7.2. To investigate this situation, a small study was conducted. At three fields soil was collected from symptomatic and asymptomatic areas of the crop and soil pH was determined using a pH meter at the UCCE or UC Davis Analytical Lab. The results shown in Table 1 indicate that clubroot was more severe in soils with lower soil pH levels. These findings are consistent with what we know about clubroot, that higher pH soils should have less concern with this disease.
So why did clubroot occur in soils that had test pH values greater than 7.2? It is important to keep in mind that soils have a great deal of inherent variability. The goal is to determine if the soil pH for a 5 or 10 acre field is ≥7.2. This is typically done by collecting 15 – 20 soil cores from various parts of the field and mixing them together as a composite sample. However, if sample collection by chance missed areas of lower soil pH, the lab results may be skewed to represent areas of the field that had relatively higher pH values. If this is the case, such a sample could have an artificially high pH (greater than 7.2) while some parts of the field may have a lower pH value. One way to have greater confidence in the soil pH is to collect more soil cores in fields where clubroot disease has been noted in the past.
At present, we have not seen evidence in Monterey County that soils are unresponsive to liming or that the liming treatment is failing to control clubroot, given variability in soil pH and pH testing. In our intensive vegetable production system, soil pH tends to decrease over time through the use of ammonium fertilizers. The loss of calcium, magnesium and potassium from crop removal and leaching can also contribute to lower soil pH on lighter soils. Given the longevity of clubroot resting spores in the soil, it is important to maintain a liming program to assure that soil pHs are above 7.2 to 7.3 to thoroughly suppress clubroot throughout the field.
Table 1. Three evaluations of soil pH in clubroot affected fields
|
Site |
Soil pH |
Crop |
Location |
Soil Type |
|
|
Symptomatic |
Asymptomatic |
||||
|
1 |
6.01 |
6.25* |
Broccoli |
Blanco |
Pacheco clay loam |
|
2 |
6.60 |
7.58 |
B. sprouts |
Eastside |
Chualar loam |
|
3 |
7.13 |
7.67 |
Cauliflower |
Near river |
Metz complex |
* These plants were also affected but to a lesser degree.
Photo 1. Typical clubbing of broccoli roots
Photo 2. A weak localized area in a cauliflower field infected with clubroot (note stunting, wilting and yellowing of affected plants)
- Author: Richard Smith
Pythium Wilt Project Underway
JP Dundore-Arias and Richard Smith, Professor of Plant Pathology, CSU, Monterey Bay and Farm Advisor UCCE, Monterey County
Pythium wilt is becoming an increasing concern in the Salinas Valley and has been responsible for significant lettuce yield losses. The disease appears to be spreading, and currently we have limited knowledge about its biology and epidemiology. The California Leafy Greens Research Board funded a project this year to explore the following aspects of the disease: 1) monitor the geographic distribution of Pythium wilt to better understand areas that may have greater incidence and the conditions that may lead to greater infection; 2) evaluate the sensitivity of isolates of Pythium to commercial fungicides; and 3) characterize Pythium isolates to confirm if previously identified Pythium uncinulatum is the lone species affecting lettuce or if other species are also involved. All of these objectives will feed into our ultimate goal of developing a rapid and accurate diagnostic technique for identification.
In order to carry out this project we need your help. We need Growers and PCA's to bring samples of suspected Pythium wilt to the UC Cooperative Extension office. Richard Smith will collect and prepare the samples for delivery to JP's lab at CSU, Monterey Bay. Given the current situation with COVID-19, we have a box in front of our office where the samples can be dropped off. Please fill out the green form and place the sample in a plastic bag. Be sure to provide a location where the sample was collected.
To help with distinguishing samples that are suspect for Pythium wilt, look for stunted plants that may have yellowing lower leaves (Photo 1). The older leaves of the plant may be yellowed or necrotic and may be wilted, particularly in the afternoon. Dig up the plants and look for dark discoloration on the feeder or tap root (often lower down on the tap root, Photo 2). If a plant has these symptoms, it is highly suspect for Pythium wilt and we would appreciate a sample.
We appreciate your help on this important project. If you have any questions, do not hesitate to call or text Richard at 831-596-7086.
Photo 1. Note small plants in foreground with wilted older leaves
Photo 2. Note dark colored and rotted main roots
20Pythium Wilt Project Underway 2
- Author: Jessica C Rodriguez
Here are useful links to practical information for addressing the Covid-19 Pandemic:
