Posts Tagged ‘pickling cucumber’

Pollination Disorders in Cucurbits

Thursday, July 12th, 2012

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

Watermelon harvest is underway on Delmarva; cantaloupe harvest started early this year, squash and cucumbers have been producing for over a month; and pumpkins and winter squash are setting fruit in earlier plantings. Each year, we see pollination problems with vine crop fruits, especially when weather conditions are unfavorable.

Signs of incomplete pollination in cucurbits include bottlenecked fruit or fruit with a pinched end, crooked or lopsided fruit, fruit small in size or nub-like; and fruits with prominent lobes or that are triangular in shape. Causes of incomplete pollination may be inadequate pollen transfer by pollinating insects; inadequate pollen sources (pollenizers); or hot, dry weather that reduces pollen viability or that desiccates flower parts during pollination. Research has shown that a minimum of 1,000 grains of pollen are required to be distributed over the three lobes of the stigma of the female flower of a watermelon to produce a uniformly shaped fruit.

Hollow cavities in fruit and vacant seed cavities are related to lack of seed formation, again traced back to poor pollination. Fruit tissue separation, such as hollow heart in watermelon, may also be due to inadequate pollination and may be worsened by rapid fluctuation in environmental conditions affecting fruit development.

Sunburn in Fruits and Fruiting Vegetables

Friday, July 6th, 2012

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

High temperatures, clear skies and high light radiation, and long daylengths are a recipe for developing sunburn in fruits and fruiting vegetables. We commonly see sunburn in watermelons, tomatoes, peppers, eggplants, cucumbers, apples, strawberries, and brambles (raspberries and blackberries).

There are three types of sunburn which may have effects on the fruit. The first, sunburn necrosis, is where skin, peel, or fruit tissue dies on the sun exposed side of the fruit. Cell membrane integrity is lost in this type of sunburn and cells start leaking their contents. The critical fruit tissue temperature for sunburn necrosis varies with type of fruit. For cucumbers research has shown that the fruit skin temperature threshold for sunburn necrosis is 100 to 104°F; for peppers, the threshold is 105 to 108°F, and for apples the critical fruit skin temperature is 125-127 °F. Fruits with sunburn necrosis are not marketable.

The second type of sunburn injury is sunburn browning. This sunburn does not cause tissue death but does cause loss of pigmentation resulting in a yellow, bronze, or brown spot on the sun exposed side of the fruit. Cells remain alive, cell membranes retain their integrity, cells do not leak, but pigments such as chlorophyll, carotenes, and xanthophylls are denatured or destroyed. This type of sunburn browning occurs at a temperature about 5°F lower than sunburn necrosis (115 to 120° F in apples). Light is required for sunburn browning. Fruits may be marketable but will be a lower grade.

The third type of sunburn is photooxidative sunburn. This is where shaded fruit are suddenly exposed to sunlight as might occur with late pruning, after storms where leaf cover is suddenly lost, or when vines are turned in drive rows. In this type of sunburn, the fruits will become photobleached by the excess light because the fruit is not acclimatized to high light levels, and fruit tissue will die. This bleaching will occur at much lower fruit temperatures than the other types of sunburn.

Genetics also play a role in sunburn and some varieties are more susceptible to sunburn. Varieties with darker colored fruit, those with more open canopies, and those with more open fruit clusters have higher risk of sunburn. Some varieties have other genetic properties that predispose them to sunburn, for example, some blackberries are more susceptible to fruit damage from UV light.

Control of sunburn in fruits starts with developing good leaf cover in the canopy to shade the fruit. Fruits most susceptible to sunburn will be those that are most exposed, especially those that are not shaded in the afternoon. Anything that reduces canopy cover will increase sunburn, such as foliar diseases, wilting due to inadequate irrigation, and excessive or late pruning. Physiological leaf roll, common in some solanaceous crops such as tomato, can also increase sunburn.

In crops with large percentages of exposed fruits at risk of sunburn, fruits can be protected by artificial shading using shade cloth (10-30% shade). However, this is not practical for large acreages. For sunburn protection at a field scale, use of film spray-on materials can reduce or eliminate sunburn. Many of these materials are Kaolin clay based and leave a white particle film on the fruit (such as Surround, Screen Duo, and many others). There are also film products that protect fruits from sunburn but do not leave a white residue, such as Raynox. Apply these materials at the manufacturer’s rates for sunburn protection. They may have to be reapplied after heavy rains or multiple overhead irrigation events.

Fruit Loads in Vine Crops

Friday, June 29th, 2012

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

Early watermelons are sizing now, later plantings are setting fruit, pickle harvest is underway, and pumpkin planting is finishing up. A common question from growers and crop consultants is how many fruit should a plant carry and what will affect fruit set and fruit “carry” in vine crops.

For watermelons, a healthy, vigorous plant may set 3-7 fruits initially. However, for mid-size and larger watermelons, the plant will only carry 2-4 fruit at any time. Smaller fruited varieties will more fruits per plant but essentially the same amount of pounds as larger types. This is the carrying capacity of the plant and is directly related to the quantity of photosynthates being produced by the plant, mostly in the leaves. Any additional fruits, even if initially set, will be aborted. Once the first fruit ripens and is harvested, additional sets can be carried. To carry the maximum amount of fruit, it is necessary to maintain high plant vigor and good foliage health. This requires paying close attention to irrigation and fertility programs; having excellent disease, insect, and mite control; and having good pollinator activity during pollination and fruit set. If average fruit carry is less than 2 per plant in watermelons, that is a sign that the plants have reduced vigor and are under stress. Repeated fruit set depends on maintaining vine health through the season.

Another factor to consider is where fruit set is occurring. Crown sets are desired in watemelons, especially in early plantings. Crown sets are those that occur on nodes closest to the base of the plant, within the first 8 nodes. Having good crown sets requires that plants have good early growth so that adequate leaf area is produced that can support early set fruit as well as proper pollination (sufficient bees). Lack of crown set is a sign of poor early growth, early plant stress, or of problems with pollination.

With pumpkins the carrying capacity is similar; however, because pumpkins are not repeat harvested as are watermelons, harvest is limited to those fruits set initially. Medium sized Jack-o-lantern types will carry 1-2 fruits, larger types closer to 1. All others will be aborted. Smaller types will carry more depending upon their size in pounds (for example a variety with 5 lb. average will carry 4-7 fruits). Maximum carrying capacity in pumpkins is largely affected by variety (varieties with some heat tolerance will carry more fruits in our climate) and foliage health. Excess nitrogen fertilization will often delay fruit set in pumpkins.

In gynoecious cucumbers grown for once over pickle harvesting, there will be two fruits set on adjacent nodes that are ready for harvest at any one time. These will be set on nodes 2-6 commonly. The pollinizers that make up a small percentage of the population will set pickles every fifth node generally and therefore only one fruit will be ready for harvest. Yield reductions in gynoecious pickling cucumbers occur when there is a loss of set so that fruits are not on adjacent nodes. Parthenocarpic pickle varieties that set fruit without pollination will commonly have 4-6 pickles on 3-5 adjacent nodes ready for harvest at any one time. This allows them to be planted at much lower densities.

Leaf Aging in Cucurbits

Friday, June 22nd, 2012

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

We are starting to see the oldest leaves (crown leaves) in watermelons, cantaloupes, squash, cucumbers, and pumpkins with large areas that are discolored (white, tan, or bronze). These leaves will be brittle to the touch and may start to tear or shred with high winds and storms. This condition is common in cucurbit crops and can be due to a number of leaf aging factors including mineral nutrient scavenging (export of mobile nutrients from oldest leaves to newer leaves), ozone air pollution damage, chemical phytotoxicity, repeated stress cycles, and wind injury. Leaf cells that die will leak their contents, releasing enzymes and oxidizing chemicals affecting nearby cells thus accelerating the “aging” process. This results in large patches of dead leaf cells that then dry, making the leaf feel brittle. If leaf veins are damaged, water and food transport will be compromised, accelerating leaf decline. This leaf aging is not to be confused with damage from mite feeding which is also concentrated on oldest leaves.

Cucumber Downy Mildew Update – June 22, 2012

Friday, June 22nd, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew was confirmed on cucumber in Sussex County, Delaware this week. It was also confirmed on cucumber in the New Castle County CDM sentinel plot in Newark on Friday, June 22.  Continue with a good preventative program. The hotter weather is not as conducive to disease development.

Cucurbit Downy Mildew Alert!

Friday, June 15th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Cucurbit downy mildew was confirmed in Dorchester and Caroline counties in Maryland on June 12. Symptoms first appeared on June 8. This downy mildew occurrence is one month earlier than any occurrence in recent years. Growers should scout aggressively for this disease on cucumber and other cucurbits. This disease is favored by cool, humid weather including cool dewy nights. Weather during June 12-14 is forecast to be conducive to further spread. Tank-mix Ranman or Previcur Flex with a protectant fungicide and alternate sprays with a material with a different mode of action. Be careful not to rely on one fungicide class. Use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program. Presidio, which was commonly used in previous years, was not as effective as expected in 2011 University trials.

Downy mildew on the lower surface of a cucumber leaf. Notice the angular, water soaked lesions on this newly infected leaf. (Image courtesy of Bugwood and Gerald Holmes)

Consult the Commercial Vegetable Production Recommendations for further information on resistance management and available fungicides (in Maryland, Extension Bulletin 236 and in Delaware, Extension Bulletin 137). Because downy mildew has only been found on cucumber, targeted sprays on other cucurbits crops such as pumpkin, squash, watermelon, etc. are not necessary, at this time. Instead scout these crops aggressively and continue to apply a broad-spectrum spray program.

Cucurbit Downy Mildew Found in New Jersey

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Cucumber downy mildew was confirmed in Gloucester County, NJ on May 30 and reports of CDM from North Carolina are increasing. Cucumber growers are encouraged to apply preventative fungicides immediately and scout their crop for symptoms of disease. The progress of the disease can be monitored online at North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at http://cdm.ipmpipe.org/index.php.

Cucurbit Downy Mildew Present Early in North Carolina

Thursday, May 24th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Cucumber growers should monitor their crops for downy mildew. Symptoms of downy mildew on cucumber are angular yellow to tan lesions on the upper surface of the leaf and brown to black sporulation on the lower surface.

Downy mildew was found a second time last week in North Carolina on greenhouse grown cucumbers. This outbreak may have started two months ago. Although there are no reports north of the Carolinas, it is extremely troubling that downy mildew is present there so early in the season. Growers should scout their fields and monitor the Cucurbit Downy Mildew ipmPIPE site http://cdm.ipmpipe.org/ for the progress of the disease. Preventative fungicide applications should begin when disease occurrence is predicted in our region.

Downy mildew on cucumber leaf. Angular necrosis on upper leaf surface and dark sporulation on lower leaf surface.

Cucurbit Downy Mildew Fungicide Decisions

Friday, May 11th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew on cucurbits has been a problem on Delmarva beginning in early July for the last few years. Good fungicides for management are available. However, last year in my trials, one of these fungicides, Presidio, was not as effective as expected. Looking ahead to your spray program, be careful not to rely on one fungicide class. It is difficult to know which fungicides will be effective here, because our population does not overwinter and is reintroduced from the South each year. Therefore use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program.

Fungicide Resistance management guidelines by crop are available online http://mdvegdisease.umd.edu/Disease%20Management/Fungicide.cfm and hard copies are available in Delaware at the county Extension offices.

Processing Acres Up This Year

Friday, March 2nd, 2012

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

Processing vegetable acres will be up this year in Delaware and on Delmarva including peas, lima beans, and sweet corn. Pickle acreage will remain steady. This increase in acres is largely due to reduction in stocks. For example, for lima beans, cold storage stocks in January 2011 were 58 million pounds and in January 2012 these stocks were down to 44 million pounds. Peas were down from 234 to 210 million pounds and sweet corn was down from 521 to 436 million pounds. This drop in sweet corn stocks is a major driver in picking up acres. It is interesting to note that in 2011, Delmarva lima bean acres were close to 19,000. This represented over 60% of the US acres and 40% of the production. California acres are down due to competition for land with more profitable crops.