Posts Tagged ‘kale’

Summer Vegetable Plantings for Fall Harvest

Thursday, July 28th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Plantings for fall harvested vegetables are underway. Timing these plantings can be a challenge, especially where multiple harvests are needed. Plantings from mid-July through the end of August may be made, with cutoff dates depending on the crop, variety, and season extension methods such as row covers, low tunnels, and high tunnels.

These plantings can be divided into 2 groups: 1) warm season vegetables for harvest up to a killing frost and 2) cool season vegetables for extended harvest in the fall.

The three main factors influencing crop growth and performance in the fall are daylength, heat units, and frost or freeze events. A few days difference in planting date this time of year can make a big difference in days to maturity in the fall.

Warm season vegetables for fall harvest include snap beans, squash, and cucumbers. July plantings of sweet corn can also be successful to extend seasons for farm stands. Mid-July plantings of tomatoes and peppers also are made for late harvests, particularly in high tunnels.

Cool season vegetables for fall harvest include cabbage, broccoli, and cauliflower; the cole crop greens, kale and collards; mustard and turnip greens; turnips for roots; spinach; beets; lettuce; leeks; green onions; and radishes.

To extend harvest in the fall, successive plantings are an option. However, days between plantings will need to be compressed. One day difference in early August planting for a crop like beans can mean a difference of several days in harvest date.

Another option to extend harvest in the fall is with planting different maturing varieties at the same time. This is particularly successful with crops such as broccoli and cabbage where maturity differences of more than 30 days can be found between varieties.

Another way to get later harvests is by use of row covers or protecting structures. This can allow for more heat accumulation and will aid with protection against frost and freezes. Decisions on what type or combination of covers/protection to use and when to apply the protection will influence fall vegetable maturation and duration of harvest.

A final factor for summer planting for fall production is on planting cutoff dates. For example, a crop such as cucumber may produce well with an August 2 planting but poorly with an August 8 planting; broccoli has a wider planting window than cauliflower; turnip greens have a wider planting window than kale.

Diseases of Cole Crops

Friday, September 10th, 2010

 Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Downy mildew and Alternaria can be a problem in fall crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days. Quadris, chlorothalonil, Cabrio, Endura (Alternaria only), Ridomil Gold Bravo, or Switch (Alternaria only) and Actigard (Downy mildew only) and Aliette (Downy mildew only) are labeled for control. For more information on control please see the 2010 Delaware Commercial Vegetable Production Recommendations.

Cole Crop Disorders

Friday, August 27th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Cole crops, including cabbage, broccoli, cauliflower, Brussels sprouts, collards, kale, and kohlrabi are important fall crops in the region. The following are some common disorders that affect these crops and their causes.

Tipburn of Cauliflower, Cabbage, and Brussels Sprouts
This problem can cause severe economic losses. Tipburn is a breakdown of plant tissue inside the head of cabbage, individual sprouts in Brussels sprouts, and on the inner wrapper leaves of cauliflower. It is a physiological disorder which is associated with an inadequate supply of calcium in the affected leaves, causing a collapse of the tissue and death of the cells. Calcium deficiency may occur where the soil calcium is low or where there is an imbalance of nutrients in the soil along with certain weather conditions. (High humidity, low soil moisture, high potash and high nitrogen aggravate calcium availability). Secondary rot caused by bacteria can follow tipburn and heads of cauliflower can be severely affected. Some cabbage and cauliflower cultivars are relatively free of tipburn problems.

Boron Deficiencies
Cole crops have a high boron requirement. Symptoms of boron deficiency vary with the cole crop. Cabbage heads may simply be small and yellow. Most cole crops develop cracked and corky stems, petioles and midribs. The stems of broccoli, cabbage and cauliflower can be hollow and are sometimes discolored. Cauliflower curds become brown and leaves may roll and curl.

Hollow Stem in Broccoli and Cauliflower Not Caused by Boron Deficiency
This condition starts with gaps that develop in the tissues. These gradually enlarge to create a hollow stem. Ordinarily, there is no discoloration of the surface of these openings at harvest but both discoloration and tissue breakdown may develop soon after harvest. Some cultivars of hybrid cauliflower and broccoli may have openings from the stem into the head. Both plant spacing and the rate of nitrogen affect the incidence of hollow stem. Hollow stem increases with wider spacings and as the rate of nitrogen increases. The incidence of hollow stem can be greatly reduced by increasing the plant population.

Cabbage Splitting
Cabbage splitting is mainly a problem with early cabbage. A problem can develop when moisture stress is followed by heavy rain. The rapid growth rate associated with rain, high temperatures and high fertility cause the splitting. Proper irrigation may help prevent splitting and there are significant differences between cultivars in their susceptibility to this problem. Splitting may also be partially avoided by deep cultivation to break some of the plant roots.

Cauliflower and Broccoli Buttoning
Buttoning is the premature formation of a head and because the head forms early in the plant’s life, the leaves are not large enough to nourish the curd to a marketable size. Buttoning may occur shortly after planting in the field, when normal plants of the same age should be growing vegetatively. Losses are usually most severe when transplants have gone past the juvenile stage before setting in the field. Stress factors such as low soil nitrogen, low soil moisture, disease, insects, or micronutrient deficiencies can also cause this problem. Some cultivars, particularly early ones, are more susceptible to buttoning than others.

Lack of Heads in Broccoli and Cauliflower
During periods of extremely warm weather (days over 86°F and nights 77°F) broccoli and cauliflower can remain vegetative (does not head) since they do not receive enough cold for head formation. This can cause a problem in scheduling the marketing of even volumes of crop.

Cauliflower Blanching and Off Colors
The market demands cauliflower which is pure white or pale cream in color. Heads exposed to sunlight develop a yellow and/or red to purple pigment. Certain varieties such as Snow Crown are more susceptible to purple off-colors, especially in hot weather. Self-blanching varieties have been developed to reduce problems with curd yellowing. For open headed varieties, the usual method to exclude light is to tie the outer leaves when the curd is 8 cm in diameter. Leaves may also be broken over the curd to prevent yellowing. In hot weather blanching may take 3 to 4 days, but in cool weather, 8 to 12 days or more may be required. Cauliflower fields scheduled to mature in cool weather (September and October) that are well supplied with water and planted with “self-blanching” cultivars will not need tieing. Newer orange cauliflower and green broccoflower varieties are being planted. They are less susceptible to off-colors but still can develop purpling under warm conditions.

Cauliflower Ricing
“Riciness” and “fuzziness” in heads is caused by high temperatures, exposure to direct sun, too rapid growth after the head is formed, high humidity, or high nitrogen. “Ricing” is where the flower buds develop, elongate and separate, making the curd unmarketable.

Development of Curd Bracts in Cauliflower
Curd bracts or small green leaves between the segments of the curd in cauliflower is caused by too high of temperature or drought. High temperatures cause a reversion to vegetative growth with production of bracts on the head. In a marketable cauliflower head, the individual flower buds are undeveloped and undifferentiated.

Loose Heads in Cauliflower and Premature Flowering in Broccoli
Loosely formed curds in cauliflower can be due to any stress that slows growth making them small or open. Fluctuating temperatures and moisture will also cause less compact growth. In contrast, excess vegetative growth caused by excessive nitrogen can also cause loose heads in cauliflower and broccoli. Premature flowering and open heads in broccoli can be brought on by high temperatures.

Edema on Cole Crop Leaves
Edema is water blistering on cole crop leaves. The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Under these conditions the roots absorb water at a rate faster than is lost through transpiration. Excess water accumulates in the leaf, some parenchyma cells enlarge and block the stomatal openings through which water vapor is normally released from the plant; thereby contributing to further water retention in the leaf. If this condition persists, the enlarged cells divide, differentiate a cork cambium, and develop elongate cork cells externally to form a periderm. The rupture of the epidermis by the enlarged inner cells and the periderm account for the raised, crusty appearance of older edema spots.

Black Petiole
Black petiole or black midrib is an internal disorder of cabbage that has been occasionally noted in recent years. As heads approach maturity, the back side of the internal leaf petioles or midribs turn dark gray or black at or near the point where the midrib attaches to the core. The affected area may be quite limited or may extend for 2 or 3 inches along the midrib. It is believed that this disorder is associated with a potassium (K)-phosphorus (P) imbalance and results when the K level in the soil is low and the P concentration high. High rates of nitrogen may contribute to the problem. Probably, as in the case with tipburn, black petiole is a complex physiological disorder in which environmental conditions play an important role in symptom expression. Variety evaluation trials have shown that there are differences in degree of susceptibility between varieties.

Floret (Bead) Yellowing in Broccoli
The florets are the most perishable part of the broccoli head; yellowing may be due to overmaturity at harvest, high storage temperatures after harvest, and/or exposure to ethylene. Any development of yellow beads ends commercial marketability. Bead yellowing due to senescence should not be confused with the yellow to light-green color of areas of florets not exposed to light during growth, sometimes called “marginal yellowing”.

Brown Floret (Bead) in Broccoli
This is a disorder in which areas of florets do not develop correctly, die and lead to brown discolored areas. This is thought to be caused by plant nutritional imbalances but also may be due to feeding damage on florets from insects such as harlequin bugs.

Vegetable Crop Diseases – September 11, 2009

Friday, September 11th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Lima Beans
Continue to scout for downy mildew. The recent weather is very favorable for downy mildew. If downy is found apply RidomilGold/Copper, Phostrol or other labeled phosphorus acid (phosphonate) fungicide. If disease has not appeared in the field Headline, Forum or fixed copper fungicide can be applied preventatively in addition to Ridomil Gold/Copper and phosphorus acid fungicides.

Sweet Corn
Field corn is not the only host for the fungus that caused Northern corn leaf blight. I have seen several fields of sweet corn recently with very high levels of infection clear to the top of the plant. Ears from badly infected plants were not filled out and will not be worth harvesting. Northern has been favored by the cooler and wetter season.

Northern corn leafblightTypical large lesion (3-4 inches long) caused by Northern corn leaf blight

Tomatoes
Late blight
is resurging on backyard tomato plantings at the present time. There is nothing besides chlorothalonil and mancozeb for homeowners but late season commercial planting should be protected from late blight with any of the late blight specific fungicides.

Cole Crops
Downy mildew and Alternaria
can be a problem in fall cole crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears apply a fungicide every 7 to 10 days. Quadris, chlorothalonil, Cabrio, Endura (Alternaria only) Maneb, Ridomil Gold Bravo, Switch (Alternaria only), Actigard (downy mildew only) and Aliette (downy mildew only) are labeled for control. For more information on control please see the 2009 Delaware Commercial Vegetable Production Recommendations.

Food Safety for Leafy Greens

Friday, September 5th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

With fall vegetable season approaching, cabbage, collards, kale, mustard, turnips, lettuce, Chinese cabbage, and other leafy greens will be harvested. The following are some considerations in the production, harvest and handling of leafy greens from the Southern Regional Fresh Produce Food Safety Training Program.

Many leafy greens (including cabbage, collards, kale, mustard, turnips, lettuce, and Asian greens) are cut by hand and packed directly in the field for the fresh market. Cabbage also may be cut by hand, loaded into a bulk container, such as a field wagon, and hauled to a packing shed for trimming, grading and packaging. Field sanitation practices are very important to reduce the spread of disease among plants and to prevent the possibility of contamination by microorganisms that are pathogenic (cause illness) to humans.

The principal food safety hazard from leafy greens is microbial contamination. Ensuring the safety of raw leafy greens begins with preventing hazards in the field.

Grazing animals on or near crop land can introduce bacteria harmful to humans into the soil. Growers should ensure that land has not been used for animal husbandry and that it is not close to animal feedlots or water runoff from grazing lands.

Incompletely composted organic fertilizers (manures in particular) may contain bacteria harmful to humans from animal or human feces. If organic fertilizers are used, they must be properly and completely composted so pathogens are not present. To avoid potential for contamination, raw manures should not be used for the production of leafy greens within that growing season, even if incorporated before planting.

Natural surface water (e.g., ditch, stream, pond) provides enough organic matter to support the growth of bacterial pathogens. It may be used with caution for irrigation but should be tested for the presence of the bacterium Escherichia coli (E. coli), which is an indicator of fecal contamination. Well water is less likely to harbor human pathogens but still should be analyzed for contamination.

Overhead irrigation is more likely to spread contamination to above-ground plant parts than is root-zone irrigation. Growers should document how water is stored, if animals are confined nearby, and if water is potable (safe to drink).

Hand-harvesting also may lead to pathogen contamination if field workers practice poor hygiene. Field crews must be trained and monitored regarding personal hygiene practices, and portable bathrooms and hand washing facilities must be provided at convenient locations in the field. The same personal hygiene precautions apply to family operations. Frequent hand washing is a key and provisions need to be made to be able to wash hands in the field.

Hand-harvesting using knives can wound produce, encouraging contamination from the soil. Knives should be routinely sanitized to keep disease inoculum from building on their surfaces and infecting sound cabbage heads or leafy greens. For best protection, place buckets of sanitizing agents at the ends of selected rows in the field. This will allow workers to sanitize their knives at regular intervals and reduce disease buildup over the course of the production day. Fresh sanitizer should be introduced throughout the work day. Routine knife sanitation is also critical for smaller farms using family labor.

Containers for harvesting fresh produce should be washed with detergent prior to use. After detergent cleaning, field bins, buckets, baskets, wheel barrows, etc., should be sanitized by using a very strong sodium hypochlorite solution dispensed from a high pressure sprayer. This should be repeated each harvest day. If wagons or trucks are used, the same procedure should be followed.

Leafy greens may be cleaned in sanitized water (75 to 100 ppm free chlorine) before marketing. Direct field-packing of boxed leaves or heads also may be done, without washing. It is critical to make sure that no dirt has contaminated the greens if doing field packing and to pack into clean boxes or containers.

Ice used to cool and preserve quality during transit can be a source of contamination. Steps should be taken to minimize ice exposure to workers, soil, and airborne dust.

If water is used in cleaning and cooling it should be chlorinated at a concentration of 75 to 100 ppm of free chlorine. Chlorination can be accomplished using a gas injection system, adding bleach, or using calcium hypochlorite tablets. Chlorination levels in the water should be monitored frequently during operation, through the use of a chlorine test kit. Water pH should be maintained between 6.5 and 7.5 to avoid having to use excess chlorine and in order to maintain recommended free chlorine levels. Excessive use of chlorine causes gassing off (which can lead to objectionable chlorine odor, irritation of workers’ skin, corrosion of equipment, and increased sanitation cost).

Information reprinted in part from “Good Agricultural Practices for the Production and Handling of Cabbage and Leafy Greens” by William C. Hurst and Darbie Granberry, Food Science and Horticultural Science Departments, University of Georgia, Athens, Georgia. This is a factsheet from the Southern Regional Fresh Produce Food Safety Training Program. Information in italics is from Gordon Johnson, Extension Agriculture Agent, UD, Kent County.