NEWSLETTER ARTICLES

Vegetables and Plant Pathology

MINERAL NUTRITION OF CELERY
by Milt McGiffen, Vegetable Specialist, Univ. of Calif., Riverside

A good fertility program starts with the beginning of the crop. Transplants are used for most California celery. Studies show that the optimal concentration of nitrogen in the nutrient solution for celery transplants is 400 parts per million (ppm). Feeding transplants more or less nitrogen in the greenhouse results in a lowered yield at harvest.

A soil test before planting is always recommended. Soil tests are the basis for determining how much of each nutrient to apply. Guide for Fertilizing Vegetables (ANRP 012) from the Small Farm Center’s Family Farm Series provides a good discussion of how to conduct and interpret soil tests. The best way to fertilize celery or any crop is with regular monitoring of nutrient concentrations in the crop tissue and the soil solution. Tissue samples can be sent off to a laboratory for precise determination of nutrient content. Research has determined the optimum nutrient concentrations that should be present in a dried sample from the outer petiole of celery:

Many growers now own nitrate-selective electrodes (e.g. Cardy meters) that they can use to guide nitrogen fertilizer applications. Adequately fertilized celery petioles should have a dried tissue concentration of 7,000-10,000 ppm NO₃-N in the middle of the season, and 6,000-8,000 ppm NO₃-N by the end of the season. Fresh sap samples for the middle and end of the season should be 300-500 and 300-400 ppm NO₃-N, respectively.

Excessive fertilization of celery is the rule rather than the exception. Field experiments on the central coast found that 60 percent of the nitrogen applied is leached or denitrified. Growers frequently use over 500 pounds of nitrogen per acre of celery, although most authorities recommend no more than 200-300 pounds per acre. Excessive nitrogen can lead to blackheart, brown checking, and other disorders. The current recommendation is to sidedress 40 percent of the nitrogen at planting, and sidedress the remaining 60 percent three weeks later. Nitrogen applications would probably be more effective if made later in the season, as celery takes up most of the nitrogen in the last month of growth. But three weeks after planting is recommended as a safeguard against not being able to get into the fields in time. Bob Brendler, Emeritus Farm Advisor from Ventura County, recommends applying ten percent of the total nitrogen fertilizer for the season when the beds are formed. Thirty percent of the remaining nitrogen fertilizer can be sidedressed thirty days after planting, and the remaining sixty percent sidedressed sixty days after planting. Applying the bulk of the fertilizer 60 days after planting will maximize soil fertility when celery most needs nitrogen and other elements — during the last thirty days of growth.

A starter application of 100 lbs. of phosphorus per acre is often banded two inches to either side of the plant row, and two inches below the roots. This will not be necessary if the soil test for phosphorus is high. Years of high fertilizer application rates mean that many growers can grow an excellent celery crop without any added nutrients other than perhaps nitrogen. For growers applying manures, 300 cubic feet of poultry manure or 12-14 tons of steer manure (dry weight) per acre will supply adequate phosphorus. BUT, celery is somewhat salt-sensitive, and care should be taken as manures contain plenty of salts. There are a number of good, portable ion sensors that can be invaluable aids in monitoring salt levels.

Most California soils have plenty of potassium, but celery is sometimes planted in very sandy soils that can be K-deficient. Further, high rates of ammonium fertilizers can change pH and induce a potassium deficiency. If the soil test is below 150 ppm for potassium, broadcast and disc 150-300 lbs. of K₂O per acre prior to planting.

Celery is very sensitive to boron deficiency. Symptoms include a brown-russet color on the inner side of the rib, or ribs with brown stripes or crosswise cracks. Young plants can be sprayed with 0.5 pounds of boron per acre, which is equivalent to 2.5 pounds of sodium borate. Boron deficiency often occurs when nitrogen or potassium are in excess, an all too common situation in celery. A lot of our irrigation water contains high amounts of boron, and boron can be mismanaged from deficiency to levels so high as to damage plants.

Magnesium deficiency symptoms are striking, with older leaves turning yellow between the veins (interveinal chlorosis). Weekly sprays of ten pounds of magnesium sulfate in 100 gallons of water should correct the deficiency. However, include calcium nitrate in the application to prevent blackheart.

The proximal cause of blackheart is a deficiency of calcium. This is generally induced by high temperatures, rapid growth, lack of water, or excessive salinity or nitrogen. When conditions favor blackheart, spray 15 pounds of calcium nitrate in 100 gallons of water on young plants, or 150-200 gallons of the same mixture per acre of older plants.

Bell Pepper

Maturity Indices:

Green peppers: fruit size, firmness, color

Colored peppers: minimum 50% coloration

Uniform shape, size and color typical of variety

Firmness

Freedom from defects such as cracks, decay, sunburn

Peppers should be cooled as soon as possible to reduce water loss. Peppers stored above 7.5^oC (45^oF) suffer more water loss and shrivel. Storage at 7.5^oC (45^oF) is best for maximum shelf life (3-5 weeks); peppers can be stored at 5^oC (41^oF) for 2 weeks, and although this reduces water loss, chilling injury will begin to appear after that period. Symptoms of chilling injury include pitting, decay, discoloration of the seed cavity, softening without water loss. Ripe or colored peppers are less chilling sensitive than green peppers.

>95%; firmness of peppers is directly related to water loss.

18-20 ml CO₂/kg · hr. at 20^oC (68^oF); 5-8 ml CO₂/kg · hr. at 10^oC (50^oF); 3-4 ml CO₂/kg · hr. at 5^oC (41^oF); respiration rates of red and green fruit are similar · To calculate heat production, multiply ml CO₂/kg · hr. by 440 to get BTU/ton/day or by 122 to get kcal/metric ton/day.

Bell peppers are nonclimacteric in behavior and produce very low levels of ethylene: 0.1-0.2 µl/kg-hr. at 10^o-20^oC (50^o-68^oF).

Bell Peppers respond very little to ethylene; to accelerate ripening or color change, holding partially colored peppers at warm temperatures of 20-25^oC (68-77^oF) with high humidity (>95%) is most effective.

Peppers generally do not respond well to CA. Low O₂ atmospheres (2-5% O₂) alone have little effect on quality and high CO₂ atmospheres (>5%) can damage peppers (pitting, discoloration, softening), especially if they are stored below 10^oC (50^oF). Atmospheres of 3% O₂+5% CO₂ were more beneficial for red than green peppers stored at 5^oC (41^oF) to 10^oC (50^oF) for 3-4 weeks.

Blossom end rot - This disorder occurs as a slight discoloration or a severe dark sunken lesion at the blossom end; it is caused by temporary insufficiencies of water and calcium, and may occur under high temperature conditions when the peppers are rapidly growing.

Pepper speck - This disorder appears as spot-like lesions that penetrate the fruit wall; cause is unknown; some varieties are more susceptible than others.

Chilling injury - Symptoms of chilling injury include surface pitting, water-soaked areas, decay (especially Alternaria), and discoloration of the seed cavity.

On California-grown bell peppers, the most common decay organisms are Botrytis, Alternaria, and soft rots of fungal and bacterial origin.

Botrytis or Grey Mold Decay - This is a common decay-causing organism on peppers; field sanitation and prevention of wounds on the fruit help reduce its incidence. Botrytis will grow well at the recommended storage temperatures. High CO₂ levels (>10%) can control Botrytis damage to peppers.
Hot water dips of peppers can effectively control botrytis rot (55^oC [ 130^oF] water for 4 minutes) without causing fruit injury.

Alternaria Rot - The presence of black Alternaria rot, especially on the stem end of the pepper, is a symptom of chilling injury; best control measure is to store at 7.2^oC (45^oF).

Bacterial Soft Rot - Soft rotting areas can be caused by several bacteria which attack damaged tissue; soft rots are also common on washed or hydrocooled peppers where water sanitation was deficient.

Mechanical damage (crushing, stem punctures, cracks, etc.) is common on peppers; physical injury not only detracts from the visual quality of the peppers, but also causes increased weight loss and decay.