In the months of July and August of 2010, a number of vegetable crops in California’s central coast were affected by calcium deficiency disorders. Usually referred to as “tipburn” (except in the case of celery, for which the disorder is called “blackheart”), these problems are often triggered by environmental factors and hence can affect a large number of acres and plantings during windows of time when tipburn is occurring in Salinas and other coastal valleys.
Tipburn symptoms on lettuce, endive, radicchio, and spinach are distictive. Symptoms occur on the margins of developing leaf tips and initially consist of light to dark brown lesions and necrosis. In romaine, tipburn is often first seen on the small veins along the margin of young leaves. In severe cases tipburn can progress and result in extensive damage to these leaf margins. Symptomatic leaves are usually found within the inner whorls of open head vegetables and underneath the enclosing wrapper leaves of closed head vegetable types. For spinach, tipburn always affects the inner, newly developing leaves which may develop a hooded appearance as the leaf continue to expand around the dead tissue. For blackheart of celery, symptoms form on the margins of developing leaf tips deep within the central growing point. Such symptoms consist of light to dark brown speckling, lesions, and necrosis. As the celery grows, the damaged tissues turn black and the affected foliage grows up and out of the inner plant whorl.
For tipburn of artichoke, the margins of immature leaves turn black as in celery. In addition, the immature artichoke flower buds develop black lesions along the upper tips and edges of flower bracts. Cauliflower also develops tipburn, with the inner wrapper leaves enclosing the cauliflower head turning tan to light brown.
Tipburn is a localized calcium deficiency. It often develops along the margins of leaves in the final weeks before harvest when the plant growth rate is at its highest. It is often unrelated to soil calcium levels. Because calcium is not very mobile within the plant, expanding tissues on young leaves and growing points may run short of this essential element and begin to develop deficiency symptoms. Conditions that favor rapid plant growth (warm temperatures and high fertilization rates) or low transpiration rates (foggy conditions) may create conditions that trigger this disorder.
Managing this disorder is difficult. Varieties vary in susceptibility, but tipburn resistance is only available in head lettuce. Maintaining even soil moisture levels and preventing the root zone from drying out helps increase calcium uptake and may reduce the risk or severity of tipburn. For field grown vegetables, soil and foliar calcium supplements have not provided consistent control.
For further information on tipburn see Monterey County Crop Notes - July/August 2007
Initial symptoms of tipburn on romaine occur on veins at the edge of the leaf.
Tipburn of butter lettuce.
Tipburn of cauliflower.
Blackheart of celery.
Tipburn of artichoke.
Agendas have been set for upcoming UC Cooperative Extension meetings in Salinas. On November 9, weed biology and management information will be presented at the Salinas Valley Weed School 2010 (contact: Richard Smith). On November 16, updates on plant diseases of vegetable and strawberry/cane crops will be shared at the 2010 Plant Disease Seminar (contact: Steven Koike). There are no fees for these meetings and continuing education units have been requested.
For more information check the calendar section at the UC Cooperative Extension—Monterey County website.
- Author: Steven T. Koike
As the coastal California lettuce crop heads into the ending fall season and as the inland county region initiates its fall lettuce cycle, both crops are being affected by Tomato spotted wilt virus (TSWV). Diseased plants have leaves with irregularly shaped, brown to dark brown lesions and dead (necrotic) areas (Photo 1); this necrotic tissue can resemble burn damage caused by pesticide or fertilizer applications. Chlorosis (yellowing) can also be observed. Depending on the age of the plant when first infected, these necrotic and chlorotic symptoms can occur on both the older, outer foliage as well as the younger, inner leaves. If plants are affected with TSWV early in their development, growth may be severely stunted. The virus is vectored by thrips and in California is primarily spread by the western flower thrips (Frankliniella occidentalis) (Photo 2).
All lettuce types are susceptible, and TSWV has been identified in iceberg, butterhead, romaine, and leaf lettuces. TSWV has an extremely wide host range that includes over 500 crop and weed species. Vegetable crop hosts include basil, bean, celery, cucumber, eggplant, endive, escarole, fava bean, lettuce, pea, pepper, potato, radicchio, spinach, and tomato. This host range may explain, in part, why TSWV has been observed in a number of lettuce fields in the San Joaquin Valley. The relatively cool summer temperatures have resulted in delayed tomato harvests, causing an overlap of the summer tomato and fall lettuce crops. Thrips vectoring TSWV are therefore able to readily move from the late tomato plantings and into the lettuce fields. (For related information see research conducted by the Gilbertson team (UC Davis) and sponsored by the California Processing Tomato group.)
Growers and pest control advisors should exercise caution if attempting to identify TSWV in the field and without testing. In the coastal region, symptoms caused by the very closely related, thrips-vectored Impatiens necrotic spot virus (INSV) are identical to those caused by TSWV. Romaine and leaf lettuces are susceptible to the lettuce dieback virus complex (Lettuce necrotic stunt virus [LNSV] and Tomato bushy stunt virus [TBSV]) which is also common on the coast.
Photo 1: Tomato spotted wilt virus (TSWV) on lettuce.
Photo 2: Western flower thrips, vector of TSWV.
- Author: Richard Smith
The draft Agricultural Order issued by the Central Coast Regional Water Quality Control Board (CCRWQCB) on November 19 increased the regulation of discharges of nitrate-nitrogen to surface and ground water from agriculture. As written, all vegetable operations that produce over 1000 acres of lettuce, cole and several other ‘high risk’ crops and that use chlorpyrifos or diazinon are placed into Tier 3 compliance category which has specified regulations concerning the movement of nitrates to surface and ground waters. The new regulations may require growers to implement a certified Irrigation and Nutrient Management Plan (INMP) to document information on nitrogen applied to crops vs nitrogen removed by crops. This information would be used to calculate a nitrogen balance ratio and growers are given three years to demonstrate nitrogen balance ratios of 1.0 for annual rotations that are double cropped. In other words, if double cropped lettuce annually removes 240 lbs of N/A (120 lbs N/A/crop), the annual amount allowed to grow two crops of lettuce in order to comply with the nitrogen balance ratio would be 240 lbs N/A/year. Given current production practices and traditional fertilization programs, complying with these new restrictions will require many growers and their fertility consultants to make a shift in their approach to fertilization of leafy green vegetables.
The ultimate goal of the regulations issued by the CCRWQCB is to reduce the load of nitrate that is added to agricultural operations in the hope to improve the quality of ground and surface waters in the valley. It is therefore important for us to explore ways that we can be more efficient with applied nitrogen fertilizer and reduce unnecessary loading of nitrate when possible. The good news is that there are tools that can help growers manage nitrogen and safeguard yields in this new regulatory era. If anyone is interested in more information on this subject, there are a number of Monterey County Crop Notes articles that deal with this issue. One point that I will make today regarding the lowest hanging fruit in terms of nitrogen savings in lettuce production is the use of fall applied preplant nitrogen. We observed rapid and nearly complete loss of this nitrogen in a series of rain storms in January of this year (Figure 1). I realize that fall nitrogen applications are often mixed with decision regarding phosphorus and potassium applications; for more information on phosphorus applications to cool season vegetables check out the following publication.
The draft rules issues by the CCRWQCB are yet to be finalized by the full board in March 2011. Whatever shape the final rules take, it appears that we have to begin the process of rethinking our approach to fertilizing lettuce and other leafy greens. The good news is that there are solid tools that can help the industry cope with this new regulatory era. Click here to view the draft Agricultural Order.
Figure 1. Fate of fall applied nitrogen in one storm even in January, 2010
- Author: Steven T. Koike
Experienced growers, pest control advisors, and other field professionals involved with broccoli already know that the winter period can signal increased problems due to head rot (also known as pin rot). Favored by cool temperatures and prolonged periods of moisture from rain, dew, and fog, broccoli head rot continues to be a damaging and yield-reducing factor because preventative measures have yet to be consistently effective. Spray applications have not proven to be consistently reliable tools to prevent head rot. While some cultivars (especially those having rounded, dome-shaped heads) may be less susceptible to head rot, true resistance has not been demonstrated for cultivars grown in California. Trying to avoid the use of overhead sprinkler irrigation is apparently the only cultural practice that helps reduce disease; however, the winter and early spring weather will enhance head rot even if growers use drip or furrow irrigation.
Field personnel should remember that two types of head rot affect the crop in California. For bacterial head rot, initial symptoms on the immature broccoli heads consist of a water-soaked or greasy discoloration of the surfaces of small groups of the unopened flowers. Later, the affected portions of the head turn brown to black and the infection spreads and affects larger parts of the head. The tissue becomes soft and gives off a very bad odor. For bacterial head rot there will not be any fungal growth unless secondary molds colonize and cause further decay.
The second type of head rot is Alternaria head rot. For this fungal problem, early symptoms consist of a water-soaked discoloration that later turns dark brown to black. Tissues infected with Alternaria are usually not as soft and smelly as heads infected with the bacterial pathogens. Alternaria readily produces dark green spores on the diseased head tissue. Secondary molds and bacteria cause further decay.
Photo 1: Bacterial head rot of broccoli
Photo 2: Bacterial head rot of broccoli
Photo 3: Alternaria head rot of broccoli
Photo 4: Alternaria head rot of broccoli