Wisconsin Fresh Fruit and Vegetable Newsletter
September 1, 2007

Contents:

Fruit Report
Vegetable Report
Storing Produce
Using produce from flooded gardens
Peninsular Station Report
Degree Day report
UW Specialist contact information

Fruit Report

Harvest of early season apples is in full swing.  We are seeing a wide variety of cultivars at farmers markets and roadside markets.  Even though the season is ahead of normal by a week to 10 days, harvest of mid-season apples likely won't begin until after Labor Day.  We have had reports of apples cracking as orchards quickly transitioned from very dry to saturated soils.  Cracking is caused by water penetrating the cuticle and being imported through the xylem and the water enters faster than cells can expand and still maintain contact with neighboring cells.  Apple cracking is similar to what happens to sweet cherries following a rainstorm.

Apple Storage.  Click on the link to the left to be taken to a thoughtful article about apple storage by Mosbah Kushad at the University of Illinois.  Growers sometimes give too little thought to apple storage resulting in poor results.

Late-season Fruit Diseases

The wet August and cooler weather across the southern part of the state will likely lead to some disease problems on fruit crops in the coming weeks. In some cases, fungicides could still provide some benefit. In other cases, spraying this late in the season is impractical because of label restrictions and the presence of pickers. Here are some thoughts about the effect all this recent water might have:

All fruit crops are prone to root and/or crown rot following infection by species of the water mold Phytophthora if water was standing for prolonged periods. Phytophthora depends on water for spore germination, swimming, and infection. The development of root or crown rot after soil has been saturated depends on many factors such as soil type, host plant and cultivar, age of the host plant, and amount and species of Phytophthora present. Fungicides are only marginally effective for Phytophthora control in woody plants, but fare a bit better for strawberries. Ridomil, Aliette, and phosphorous acid products are labeled on many fruit crops. Check the label for use restrictions and pre-harvest intervals.

 Apple scab may rear up by early September, following the wet, cool mid and late August. Apple fruit are relatively resistant at this point in the season, but leaves actually become more susceptible as they age. Fungicides are not recommended, but growers should survey the orchard for scab, paying especially close attention to the undersides of leaves, to know what to expect for next year (the scab fungus over winters on leaves). The scab fungus can build up quickly during fall, even in orchards that have clean fruit in the present year.

Flyspeck and sooty blotch of apple and pear develop under conditions of high humidity and mild to moderate temperatures. Many fungi are involved in this disease complex that causes black spots and smudges on fruit. The disease is usually worse in dense canopies and near woodlots, which serve as a source of inoculum and also impede air movement in the orchard. Apple varieties that are harvested by early to mid September are not usually affected severely. Late varieties, and those with pale skin, are more prone. Golden Delicious is both late and pale and therefore would benefit from another fungicide spray. Care must be taken regarding pre-harvest and re-entry intervals, especially if treating Golden Delicious trees that are adjacent to earlier-ripening varieties. The strobilurin fungicides Sovran and Flint are effective, but have pre-harvest intervals (PHI) of 30 and 14 days, respectively. Pristine has a 0-day PHI, and the combination of Captan plus thiophanate-methyl has a 0-day PHI.

Cherry leaf spot can develop with a vengeance in late summer and cause severe early defoliation that in turn leads to delayed hardening and winter injury. Just one or two years of early defoliation can kill a cherry tree, even with moderate winter temperatures. A post-harvest fungicide application is necessary in most years, and in southern Wisconsin in 2007, it is a must. See UW-Extension bulletin A3314, Midwest Commercial Tree Fruit Spray Guide, for post-harvest fungicide recommendations.

Raspberries could see significant development of cane and leaf spot diseases, including rust.  By this late in the season, canopies are dense and in some cases, plantings are pretty thick with weeds. All this leads to slower drying, which enhances fungal growth. Anything that improves air movement (e.g., weeding, thinning) will help slow down disease. See UW-Extension bulletin A1934, Strawberry and Raspberry Pest Management in Wisconsin, for information on fungicides. Where cane diseases are severe, it would be prudent to make a delayed-dormant application of lime sulfur next spring.

Grapes are facing heavy disease pressure for black rot, downy mildew, and Botrytis bunch rot. It will be difficult to impossible to control these diseases without further fungicide use this summer. UW-Extension does not publish recommendations for grape, but Michigan State University recommendations are available at: http://web1.msue.msu.edu/epubs/pestpubs/E154/  

Patty McManus, Extension Fruit Crop Pathologist

Vegetable Report

Tomato fruit disorders - Now that tomato fruit have begun to ripen, growers are beginning to notice various anomalies in the uniformity of the fruit color. Specific observations include the appearance of blotchy ripening, tomato yellow shoulder, and grey wall. Each of these disorders is characterized by uneven color through the tomato fruit. In each case, the disorder is believed to be a physiological disorder that persists even after the fruit has ripened. More importantly, each disorder causes the fruit to develop a woody and sometimes bitter flavor reducing the salability of the crop. Although the specific cause of blotchy ripening, tomato yellow

shoulder, or grey wall is unknown, several factors are believed to contribute to their development. Stressful growing conditions such as drought, warm temperatures, or sudden changes in the environment contribute to the development of all three disorders. However, adequate potassium fertility has been shown to contribute to the development of blotchy ripening, tomato yellow shoulder, and grey wall.

If any one of these disorders is developing and persisting within your tomato crop, evaluate you potassium fertility program closely. Potassium is important for fruit color development in tomato. Tomato requires 180 lb/a K2O which is much more than is required for other vegetable crops such as sweet corn, pepper, or pumpkin. Potassium deficiencies have occurred in multiple problem fields I have inspected with tomato yellow shoulder or grey wall. Within several of these fields manure was applied to meet the nitrogen demand of tomato, but the application resulted in 1/3 to ½ the required K rate. In one other case, no potassium was applied, even though nitrogen and phosphorous had been applied. Potassium fertility needs in tomato can be met with broadcast applications of potash in the fall or spring prior to planting. If disorders are already occurring, foliar fertilizers containing potassium at appropriate rates can be applied to help alleviate the disorder.

Early maturing pumpkins - Powdery mildew, drought stress, and/or inadequate fertility have led to early vine death and resulting maturation of pumpkin and winter squash in several areas of Wisconsin. The question is what to do with the ripened fruit 5 to 6 weeks prior to the targeted harvest date. I would recommend harvesting the crop and storing fruit in well ventilated building. Cut the fruit off of the vines with a sharp shears. Do not set the fruit directly on the ground or on cement, rather place on racks several feet off of the ground. Keep the fruit out of direct sunlight to minimize potential for sun damage on ripened crop. Fruit setting in direct sunlight can quickly warm to greater than 95 F causing damage to the tissue.

Pumpkins and winter squash can typically be stored for 2 to 4 months. Store whole mature pumpkins in a dry, airy location. Cure pumpkins at 80 to 85 F with 80 to 85% relative humidity for 10 to 14 days after harvest. This allows the fruit to heal any damaged tissues that occurred during handling. Preventing any damage to pumpkins during harvest minimizes potential infection points for pathogens into the fruit. After curing, store the pumpkins and squash at 50 to 55°F with a relative humidity of 60 to 75%. Remove pumpkins showing any signs of spoilage from storage shelves.

AJ Bussan, UW-Madison Extension Horticulturist

Continued captures of adult European corn borer, resulting from the second flight, remains under way in several locations of southern and now central Wisconsin. Sweet corn in tassel and beyond, peppers and snap beans with flowers and developing fruit should be protected. European corn borer larvae can be effectively controlled by several insecticides identified in the Wisconsin Guide to Commercial Vegetable Production (A3422). The current degree day accumulations further indicate that peak periods of flight reach as far north as north central Wisconsin along a line extending from Spooner southeast to Manitowoc. Steady increases in the numbers of adult Corn earworm continue to occur through the early part of this week with elevated temperatures over last weekend. Trap counts should continually be monitored at this time of year to determine if treatment is necessary. Moth collections greater than 10 moths per night in pheromone traps or 5 moths per night in black light traps suggest that the risk of ovisposition (egg laying) is sufficiently high enough to warrant treatment. In turn, as corn reaches the silking stage and adult counts increase to 100 moths per night in pheromone traps, or 25 moths per night in black light traps, insecticides should be applied 3 - 4 days, or until silks turn brown. Corn earworm is a migratory pest and recent weather conditions over the last two weeks have been conducive for insect migration into Wisconsin from southern areas.

Russ Groves, UW-Madison Extension Entomologist

Snap Beans – Symptoms of cucumber mosaic virus are beginning to appear in commercial fields in southern and central WI. So far, we haven't seen reports of blossom drop or "chocolate" pods. Plants that were in the two week period before flowering during the past 2-3 weeks seem to be the most prone to losses. Recent weather has been ideal for white mold development so be on the lookout for it. If you do see it in your fields at harvest, consider applying the biocontrol Contans® after harvest, before crop debris is disked in. We have had good results from application of this product in trials in past years.

Sweet Corn – Rust is being reported on sweet corn as far north as central Wisconsin. Many varieties have useful levels of resistance and there are several fungicides labeled for rust management if the level of infection continues to increase.

Vegetable disease reports during the last week from Brian Hudelson, Plant Disease Diagnostics Clinic, include a variety of problems on cucurbits (angular leaf spot, Verticillium wilt, Fusarium wilt, Pythium root rot) and Bacterial leaf spot spots on peppers.

Walt Stevenson, UW-Madison Extension Plant Pathologist

Storing Produce

Last August a new publication describing how to store produce in smaller quantities was published by UW-Extension.  The target audience for the publication is backyard gardeners, but the storage conditions would hold for market gardeners as well.  As the season begins to draw to a close some producers may wish to store some produce to lengthen out the market season.  The publication is available for viewing and printing on-line at:
http://learningstore.uwex.edu/pdf/A3823.pdf

The publication covers storing both fruits and vegetables.

As a result of recent flooding, questions have been raised about the safety of consuming produce from gardens that were under water for a day or two. How concerned you have to be about using garden produce after a flood depends, to a large degree, on whether that flood water was "clean", i.e. standing rain water, or water that may have been contaminated with sewage, river or creek water, farm run-off, or industrial pollutants.

The most conservative answer — one that eliminates any and all risks — is that you discard all produce that was covered by contaminated flood water. However, with weeks left in the growing season, you may wish to salvage some crops. Here are tips for considering what can be salvaged and what must be discarded from your flooded garden.

Begin by discarding all leafy vegetables such as lettuce, cabbage, or spinach. It's not possible to scrub these crops, and they have many ridges and crevices that could contain contaminated silt or bacteria. All soft fruits such as berries should also be discarded because they too are impossible to clean.

Examine produce carefully before picking it. If it is soft or cracked, or has open fissures where contamination might have entered, throw it out. Produce from plants that survive flooding with water that was not contaminated should also be discarded if it is bruised, cracked, or otherwise blemished. Root crops from "clean" flooding should be OK if the upper parts of the plants survive essentially undamaged.

Produce that can be safely consumed in the short term is produce that will be cooked.  Begin by washing green beans, tomatoes, peppers, summer squash and other mid-season crops in water.  Do not use soap. Rinse with clear tap water and soak for 2 minutes in a weak chlorine solution of 2 Tablespoons bleach to a gallon of water. Rinse in cool, clean tap water. Peel and cook thoroughly before eating. Change the bleach solution if you notice the water is no longer clean. 

For underground vegetables such as beets, carrots and potatoes, wash in water, rinse and sanitize as directed above. Peel and cook thoroughly before eating. Note: beets may be peeled after cooking, if desired.

Melons and other fruits which will be eaten raw should not be consumed. Recent foodborne illness outbreaks linked to melons suggest that these low-acid fruits may not be safe even if surface-sanitized.

Late-season vegetables that result from flowers produced on growth that develops after flood waters subside should be OK. To increase safety, cook them thoroughly, or at least wash them well and peel them, if possible, before eating. This could include tomatoes, peppers, eggplants, squash, cucumbers, and similar vegetables.

 Flood-damaged garden produce that is otherwise unfit for eating – such as tomatoes that are cracked or decaying – should not be canned or otherwise preserved. Garden produce that would be safe to consume after washing, sanitizing and cooking may alternately be safely canned.  Do not attempt to freeze or dehydrate these items, however.

Never sell produce from a flood-damaged garden at a farm market or farm stand until you are sure that all contamination has been removed from the garden, usually a period of at least one month after the last incidence of flooding. Check with the Division of Food Safety of the Department of Agriculture, Trade, and Consumer Protection (608) 224-4000 if you have questions about market sales of garden-flooded produce.

Barbara Ingham, Department of Food Science, University of Wisconsin Extension

UW Fresh Fruit and Vegetable Contacts