Quality / Factors Influencing Quality
Variety Selection | Mineral Nutrition | Plant Population | Water: Soil Moisture and Rainfall
Pest Management | Growing Temperature | Wind | Harvest Time | Harvest Method
Washing | Cooling | Packing | Storage
Variety Selection top
The selection of a variety may be dictated by the market in general or by the needs of a specific buyer. In markets where a variety has no unique identity, the grower may choose the variety that can be grown the most profitably, recognizing any risks of using that variety. For instance, a pepper grower may choose to grow the variety 'Camelot' because yield, size and overall quality are excellent. However, 'Camelot' is not resistant to bacterial spot or phytophthora. The decision to grow 'Camelot' embraces the risk that a portion or all of a field or crop could be lost to these diseases. Planting 'Camelot' only in fields with no history of these diseases while planting varieties with resistance in fields more likely to develop problems would be a way to reduce risk to the entire crop. As another example, consider zucchini: many growers will plant varieties without resistance to virus diseases only in first and second plantings. Later plantings come under more virus pressure and virus resistant or tolerant varieties are chosen.
Growers involved in direct to consumer sales may have developed a demand for a specific variety. The decision to change varieties may have to be implemented over several growing seasons to win customers over to an improved variety.
It is important to know the strengths and weaknesses of a variety. Cultural and pest management practices can be modified to overcome poor characteristics and enhance or maintain the best characteristics. For example, most pepper varieties are not resistant to phytophthora; using raised beds with plastic mulch and trickle irrigation will help avoid the problem. Some tomato varieties are susceptible to yellow shoulder disorder. If temperatures exceed 90 F, chances are the problem will occur. Some cabbage varieties like 'Market Prize' are vulnerable to bolting if exposed to cold temperatures. A variety that is not as likely to bolt is better for early spring plantings.
Mineral Nutrition top
Fertilization practices can influence flavor, texture, color, size, shelf life, and content of nutrients and phytochemicals. Applying fertilizer materials according to a soil test and crop nutrient requirements will provide the basic nutrients needed for a variety to yield well and have marketable quality. Insuring that the soil pH is in the proper range will make nutrients available to the crop. Quality can be reduced by nutrient excess as well as by a nutrient deficiency.
Some crops have high responses to secondary or minor elements. Cauliflower, celery and beets have a high response to boron. A boron deficiency in these crops causes a breakdown in internal tissue. Side dressing or banding is an excellent way to supply needed boron; foliar applications are also effective. Broccoli, cauliflower, beets, lettuce, onion and spinach have a high response to molybdenum. Snap beans may show manganese deficiency above pH 6.8. Supplemental applications of these and other nutrients may be necessary to avoid deficiency symptoms and poor growth.
Plant Population top
A uniform plant stand at an optimum plant population is important to both quality and yield. If plant population is too low the yield will be reduced and concentration of set may be affected, as in pickling cucumber and snap beans.
Plant population influences size of the harvested part in many crops. The lower the plant population in cabbage the larger the heads will be. Plant populations higher than optimum will reduce size and result in misshapen roots in carrot, beet and onion. Sweet corn planted at too high a density will develop blind stalks. High plant populations create a denser canopy which may complicate disease control efforts.
Water: Soil Moisture and Rainfall top
Water stress from either too little or too much water is a leading cause of poor quality. A shortage of water coupled with a high transpiration rate is associated with blossom end rot in tomato, pepper, melons and squash and with tipburn in lettuce and cabbage. The same condition may cause an increase in nubs and curved fruit in cucumber. Sweet corn will experience poor tip fill if water stress occurs during ear development. Moisture stress during flowering can cause flower abortion in bean and pea. Cauliflower is very sensitive to excess water in the root zone. Standing water or soil at field capacity for more than 24 hours can seriously damage the crop.
Rain during later stages of fruit development will cause increased cracking of tomato, pepper, cabbage and melons. It also allows pathogens to infect all portions of the plant including the marketable portion. Splashing of soil spreads the pathogens throughout the field. Excessive rain leaches nutrients needed to develop the crop.
Pest Management top
Insects and mites, diseases, and weeds reduce fruit and vegetable quality if not managed properly. Insects and mites may eat and diseases may damage crops so that they can not produce enough energy to develop high yield or quality of the harvested part. The harvested part itself may be eaten or infected, reducing quality directly. Weeds compete with the crop for limited light, nutrients, and water, and if competition is stiff enough may prevent the crop from developing high yield or quality due to lack of resources. In some instances weeds or their fruit contaminate the harvested portion, as is the case when eastern black nightshade grows in a pea crop and the berries of the weed can not be separated from the harvested peas.
Pest management requires decisions from before planting through postharvest handling and packing. Crop rotation, variety selection, perennial weed control, tillage systems, seed treatments, pre-plant pesticides, spacing, pesticide choices, crop monitoring, application methods, dump tank and rinse treatments, curing, bruise reduction, cooling and storage management are all part of producing and maintaining quality.
Growing Temperature top
Both hot and cold temperatures affect vegetable quality. Cold can induce flowering in cole crops, carrots, lettuce, radish and others resulting in loss of yield. In the fall cold will stop growth and cause poor pollination in crops like bell pepper, causing short, poor quality fruit. Cold may prevent normal tomato coloring, but can lead to better color of beets and carrots. High temperatures inhibit formation of the red color lycopene in tomato, and promote the formation of undesirable flavor compounds in lettuce and broccoli.
Wind can be damaging by its force and by carrying soil particles. Sand-blasted crops are more susceptible to bacterial infection. Young plants can be damaged so severely that replanting is necessary. For instance, sand blasting of the stem of young cucumber plants will cause them to become glazed and brittle. Sand-blasting on the harvested portion of the crop can reduce quality directly.
Harvest Time top
Quality is dependent on timing the harvest correctly for most vegetables. Size, flavor, tenderness, texture and color can all be influenced by harvest timing. Snap beans must reach a certain sieve size, summer squash and cucumbers must be harvested within a narrow size range, melons must reach an acceptable sugar content, tomatoes to be shipped must be harvested at mature green or as "breakers" but usually not past the "pink" stage. Tomatoes for direct sales can be harvested when ripe. Sweet corn is harvested when the kernels are milky or when they are at about 75% moisture. Cabbage, winter squash, pumpkins and peppers have a wider harvest window.
Harvest Method top
Harvest method affects quality in part because of its effect on the amount of injury sustained by the product during harvest. Some fresh market vegetables can be machine harvested; snap beans, sweet corn, potatoes, sweet potatoes, onions, carrots and celery are included in this category. Quality problems involved are bruising and breakage of beans, carrots and celery petioles by the harvester. Additional damage results from the drop involved in transfer to wagons or bins. Padding at impact points or belt and chain speed adjustments may reduce damage. Sorting prior to packing is necessary to remove damaged produce.
With hand harvest, injury to the product can occur when it is thrown or otherwise inappropriately handled. Good field management is required to prevent this. The harvest crew also needs to be trained to select only marketable produce, leaving the rest in the field. Harvest aids to improve efficiency are common with melons, cabbage, sweet corn, lettuce, cauliflower and winter squash. Field packing may be associated with harvest aids. "Mule train" harvesters are common with sweet corn, cabbage, cauliflower and lettuce: in these systems produce is harvested and packaged for shipping in the field. Quality control rests with well-trained packers as the rig moves through the field.
Tomatoes, peppers, summer squash and cucumbers are usually harvested and placed in buckets. The harvest crew receives instructions on what to leave in the field and what to send into the packing house. The quality of individuals' work can be monitored if workers are required to put their own ãticketsä into each bucket they harvest.
Washing or brushing improves quality by removing soil, spray residues, aphid honeydew or any other foreign material. Washing may also facilitate transfer of decay-causing organisms from one item to another, and so decrease quality. Tomatoes, peppers and cucumbers typically enter the packing line by being dumped into a dump tank. This avoids bruising and removes most of the soil that may be adhering to the fruit. The water typically contains chlorine to reduce surface contamination and kill microbes that may be in the water. Managing the chlorine content is important for maintaining quality.
Cooling and storing at proper temperatures can influence flavor, texture, tenderness and decay, depending on the product. Cooling reduces respiration, reduces internal water loss and wilting, decreases the production of ethylene and slows growth of decay organisms. The reduction in respiration is important because respiration causes loss of sugars and other flavor compounds and produces heat, known as 'vital heat'. Rapid pre-cooling to the product's lowest safe temperature is critical for crops with inherent high respiration rates such as asparagus, broccoli, peas or sweet corn. When managing temperature of produce both vital heat and field heat must be considered. Harvest during morning hours is one way to reduce the amount of field heat. Cooling can be accomplished by forced air cooling, hydrocooling, vacuum cooling, room cooling, and by ice or slush ice applications. The method selected is dependent on the commodity and the temperature drop needed. Room cooling is useful for most commodities, however it may not be fast enough for best quality management.
Packing affects produce quality because of the potential for injury to the product during packing, the potential of disease or decay spreading from one item in a package to others, and the reduction in quality of an entire package because of a few below-grade items included in the pack.
Packing lines should be maintained with quality in mind. Padding at drop points and where shunts change the flow of product will help avoid bruising. Containers should not be over filled so that crushing and bruising will result when lids are secured. Forcing fruit into too small an area in place packs will result in bruising or splits. Packing tables should be cleaned, especially of sand. Summer squash are easily scratched by soil particles. Usually the market determines the type of container, however, cardboard should be strong enough so as not to crush when palletized. If hydrocooling or ice is to be used the container must have adequate wet strength. If wood containers are used to pack soft skinned fruit, they should have a minimum of splinters and raised staples that will injure the pack.
The lighting in the packing area should be bright enough to see defects and color. The packing line crew must receive instruction in grading. They must be aware of the meaning of "fairly well shaped" compared to "well shaped". Often the grower will pack a combination grade that includes a certain percentage of two grades. For example, slicing cucumber grades are U.S. Fancy, U.S. No.1 and U.S. No.2. Buyers specify "Super Selects" or "Selects" which correspond closely to U.S. Fancy/U.S. No.1 and U.S. No.2 respectively. However, depending on demand, the pack may shift to an overall better grade when prices are low and to a lower grade when prices are high. This shift involves shape, not diseased or damaged fruit.
Storage conditions influence the flavor, firmness, disease incidence, shelf life, and sometimes color of produce. The best temperature and humidity ranges for storage of fruits and vegetables are available in the USDA Handbook 66 and through various state Extension Service publications. Quality is maintained when respiration is lowered and the humidity is high enough to prevent wilting (usually 90% to 100%). Winter squash and pumpkin store better at 50% to 70% relative humidity.
Chilling injury occurs when storage temperatures are above freezing but low enough to cause tissue damage. Tomatoes, peppers, eggplant, cucumbers, snap beans, summer squash, pumpkins and watermelons are among the species that are susceptible to chilling injury. Chilling injury symptoms may include surface pitting, discoloration, water-soaked spots, development of necrotic spots, shorter storage life and loss of flavor and aroma.
Many vegetables are sensitive to ethylene and should not be stored or shipped with ethylene producing commodities. Apples, pears, tomatoes and muskmelon are examples of products that produce ethylene.
Variety Selection |
Plant Population | Water: Soil Moisture and Rainfall
Content authors: J. Neibauer and E. Maynard, 2002. Content last modified: March 2011.