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 MOFGA's 2010 Pest Reports - Compiled by Eric Sideman, PhD Minimize

September 22 | August 23 | August 9 | July 26 | July 20 - Late Blight Update | July 19 - Late Blight Is Here | July 7 | June 24 | June 19 - Late Blight Update | June 18 | June 8 | May 25 | May 20 | May 3 | April 22
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Pest Report - August 23, 2010

In this issue:
  • Corn Smut
  • Some common summer disorders of vegetables
  • When is my winter squash ready to harvest?
Late Blight Update

There is quite a bit in Knox and Lincoln county but very little elsewhere in the state. If you think you may have late blight in your crops, please contact Eric Sideman, MOFGA's Organic Crops Specialist, at esideman@mofga.org.

Corn smut often occurs in fields but usually losses are very small. Rarely does one find more than an infected ear here or there. Once you see it you will never forget it. Roundish galls that are from a half inch to an inch and a half in diameter and range from glistening white to green form in the ears. As they grow they burst the ear open and the ear is filled with these galls. The disease is favored by dry conditions and poor fertility. I have seen more than usual this year. The organism that causes smut is in the group of fungi that include mushrooms. It is not surprising that some people consider the smut gall delicious gently fried in butter. Similar to the other fungi in this group, there are a few different kinds of spores produced. The spores released from the galls (teliospores) overwinter on the soil and germinate in the spring to release another kind of spore (basidiospores). These spring-produced spores blow in the wind and if they land on corn they germinate and can infect the ear through the silk. Proper fertility and irrigation help. If you find an ear full of galls, pick the ear and burn it before the galls rupture and release spores.

(Reprinted and modified a bit from an article by Becky Sideman in the August University of New Hampshire Vegetable, Berry and Tree Fruit Newsletter)
While pests and diseases are troublesome, it is often disorders caused by abiotic stresses that cause the most aggravation for growers. With the high heat we have experienced this summer, growers have reported seeing some of the following disorders. Understanding the causes of some of these issues may help you prevent them in the future, or at the very least, might help reduce your frustrations!

Tomato Physiological Leaf Roll
Pruned tomato plants in a high tunnel showing physiological leaf curl.
Physiological leaf roll starts with upward cupping of leaf margins and eventual inward rolling of the leaves. This phenomenon has been associated with heat and prolonged periods of wet soil; conditions that are common in well irrigated high tunnels. High-yielding indeterminate varieties seem to be more prone to leaf roll, and the problem is more pronounced on heavily pruned plants. While plant growth, fruit yield, and fruit quality are not believed to be affected by physiological leaf roll, in extreme cases, sunscald could be more likely when leaves are strongly curled.

Management tactics: plant determinate cultivars, maintain adequate but not excessive soil moisture, do not overfertilize, provide adequate levels of phosphorus, avoid severe pruning, and maintain cool temperatures through the use of ventilation, shading.

Tomato Internal White Tissue
In fruits with this disorder, portions of fruits remain hard and white while the rest of the fruit ripens normally. The hard white tissue may be spread throughout the pericarp or, more commonly, may be concentrated in the outer wall of ripe fruit. The white tissue can range from a few white fibers to a solid white mass. Fruits within a cluster may not be evenly affected. This disorder has been shown to be caused by poor potassium nutrition and heat stress; though other factors may also be involved.

Management tactics: Provide adequate levels of potassium, maintain cool temperatures through the use of ventilation or shading.

Waxy Breakdown of Garlic
This disorder is a physiological degradation of the garlic cloves after harvest. It begins as small, sunken, light yellow areas appear on the clove tissue. These areas enlarge and the affected cloves eventually turn deep yellow amber. The tissue becomes translucent and sticky or waxy. The problem may be obscured by the coverings of the cloves, until the cloves shrink and the dark amber color is visible through the outer coverings. This disorder is poorly understood. High temperatures during growth and/or after harvest, and poor ventilation and/or low oxygen during storage, have been proposed as causes of this disorder, but these have not been confirmed.

Sunscald or White Drupelet Disorder of Raspberry
The raspberry fruit is an aggregate fruit that contains many individual fruits called ‘drupelets’. As the raspberry ripens fruits with white drupelet disorder have some drupelets that turn white and never ripen completely. Stinkbug damage is similar in that it causes a random pattern of white spots on mature fruit, however, in the case of white drupelet disorder and/or sunscald, the cooler side of the fruit will appear normal. Varieties vary in their susceptibility to sunscald.

Management tactics: Avoid planting in sites with strong summer winds, which can promote sunscald. Orient planting rows north-south. Shading after pollination, using a shift-trellis system, and installing overhead irrigation for mid-day (not late afternoon) evaporative cooling) can all help to minimize sunscald.

Acknowledgements: Damicone and Brandenberger, Oklahoma State Univ. Bull. EPP7627: Common diseases of tomato part III: Noninfectious diseases; Pacific Northwest Vegetable Extension Team Bulletin PNW616: Physiological leaf roll of tomato; New York Berry News Vol.4 No.8 August 18, 2005; and Cantwell, Garlic Recommendations for Maintaining Postharvest Quality, UC Davis Postharvest Technology Research & Information Center.

(Reprinted and modified a bit from an article in the U Mass Vegetable Notes by Ruth Hazzard)
Winter squash and pumpkin fruit sitting in the field face a daunting list of diseases and insects – not to mention possible passing hurricanes -- that could threaten fruit quality. Early harvest and careful storage is often preferable to leaving fruit in the field. This is especially true if you know that your pumpkins or squash are in fields that are infected with Phytophthora blight.

Since the pumpkin market lasts from Labor Day to Halloween, pumpkins may need to be held for several weeks before they can be marketed. When is it best to bring then in, and when to leave them in the field? If the vines are in good condition, the foliage can protect the fruit from sunscald. If foliage is going down from powdery mildew or downy mildew, this may help with ripening and make harvesting easier, but also increases the risk of sunscald or injury to pumpkin handles. There can be extra work involved in bringing fruit in early, especially for growers who normally have pick-your-own harvest, but we recommend that growers harvest as soon as crops are mature and store under proper conditions, if it is feasible. Attention to curing and handling will go a long way toward improving the life of winter squash and pumpkin fruit.

What about pumpkin stems, i.e., handles? In some cases, it’s the handle that sells the pumpkin. Pumpkins may not be marketable if the handle is broken off or dried up. Ideally, if the timing is right, pumpkins would be cut one to two weeks prior to marketing. However, if they are harvested now they may sit much longer before being sold. The discussion of how early to cut handles is an old one with many different opinions. One view is that it is advisable to cut the handles from the vine to save them from advancing powdery mildew and reduce shrinkage. Whether or not handles shrink and shrivel after cutting is affected by plant stress, genetics (variety), moisture and temperature conditions, and disease. There are many diseases that can affect handles, including Plectosporium, Fusarium, Black Rot, and Alternaria. Again, proper curing and storage conditions are key.

Ideally, pumpkins should be harvested when fully mature, with a deep orange color and hardened rind. However, as long as pumpkins have started to turn color, they will ripen off the vine if held under the proper conditions. While not ideal, this may be preferable to leaving them in the field if conditions are not favorable. If necessary, pumpkins can be ripened in a well-ventilated barn or greenhouse. The best temperatures for ripening are 80-85 degrees Fahrenheit with a relative humidity of 80-85%. Night temperatures should not drop below the sixties. Even if pumpkins are ripe, a period of curing can improve storage life. The curing period should be about 10 days. During this process, the fruit skin hardens, wounds heal and immature fruit ripens – all of which prolongs the storage life.
Pumpkins should be stored in a cool, dry place. Ideal temperatures are between 50¡ and 60¡ F and relative humidity of 50 - 70%. Higher humidity allows condensation on the fruit with risk of disease, and lower humidity can cause dehydration. Higher temperatures increase respiration and can cause weight loss. Temperatures lower than 50 F cause chilling injury (see squash, below). In a greenhouse, temperature can be managed with ventilation on sunny days. Unless it is quite cool, heat is not likely to be needed if the house is closed up at night.

Often it is not feasible to harvest pumpkins early and store them until they can be marketed, and so they must be ‘stored’ in the field. If vines and fruit are healthy, storage in the field can be successful for a few weeks. If the vines die back, damage to the fruit from sun, disease and insects is more likely. In any case, it is important to scout for insects feeding on the fruit and handles, which may include squash bug nymphs or adults, or striped cucumber beetle. Control them if damage is evident. In fields that have a history of Phytophthora blight, Fusarium fruit rot, or black rot, field storage may increase the incidence of these problems, particularly if we have a period of wet weather or a major storm while fruit is sitting in the field. This has been one of the causes of significant losses in recent years, and one reason that we recommend bringing fruit in as soon as it is mature.

Growers often plan to store winter squash for much longer than eight weeks. Fruit that are free from disease and haven’t been subject to much chilling (below 50¡F ) should be selected for long-term storage. Many years the challenge is to harvest the winter squash before it is subject to much chilling, but waiting long enough for it to be ripe. This year much of the winter squash began to look ripe in early August, but it was not. Even though it had the right color and a tough rind, it did not have the sugars yet for good taste. It is quite a challenge to tell when winter squash is ripe. To learn more about this see Blanchard, Chris. 2000. Harvest timing critical for winter squash. Growing for Market. September. p. 1, 4–5.

Storage life depends on the condition of the crop when it comes in and your ability to provide careful handling and a proper storage environment. All fruit placed in storage should be free of disease, decay, insects, and unhealed wounds. When harvesting squash and pumpkins, it is important to handle the fruit with care to avoid bruising or cutting the skin. Despite its tough appearance, squash and pumpkin fruit are easily damaged. The rind is the fruit’s only source of protection. Once that rind is bruised or punctured, decay organisms will invade and quickly break it down. Place fruit gently in containers and move bins on pallets. Use gloves to protect both the fruit and the workers. Removal of the stem from squash (butternut, Hubbard, etc.) will also decrease the amount of fruit spoilage because the stems frequently puncture adjacent fruit, facilitating infection.

A period of curing after harvest can help extend storage life of squash. This may be done in windrows in the field -- especially with a series of warm, dry days -- or by placing squash in a warm dry atmosphere (70-80¡F) with good air circulation, such as a greenhouse, for up to two weeks. This pre-storage treatment permits rapid drying of the outer cell layers, and when combined with a dry atmosphere for storage inhibits infections that can take place at this time. Any clean cuts during harvest a likely to heal over and are no longer a source for injury or infection.

Take care to avoid subjecting squash to chilling injury. Chilling hours accumulate when squash or pumpkin is exposed to temperatures below 50¡F in the field or in storage. Injury increases as temperature decreases and/or length of chilling time increases. Chilling injury is of particular concern with squash intended for storage because it increases the likelihood of breakdown. If squash has been exposed to chilling injury it should be marketed first and not selected for long-term storage. Remove squash from the field if temperatures likely to drop below fifty degrees for any length of time.

After curing, move squash or pumpkins to a dry, well-ventilated storage area. Pressure bruises can also reduce storage life, so avoid rough handling, tight packing, or piling fruit too high. Fruit temperature should be kept as close to the temperature of the air as possible to avoid condensation, which can lead to rot. Ideally, the storage environment should be kept at 55-60¡F with a relative humidity of 50-70%. Lower relative humidity increases water loss, resulting in reduced weight, and if excessive, shriveling of fruit. High relative humidity provides a favorable environment for fungal and bacterial decay organisms. Under ideal conditions, disease-free pumpkins should have a storage life of 8-12 weeks and butternut squash up to three or four months. Even if it is difficult to provide the ideal conditions, storage in a shady, dry location, with fruit off the ground or the floor, is preferable to leaving fruit out in the field.

As you plan for storage and marketing, keep in mind that the market for pumpkins seems to get earlier every year. Fall decorative displays include pumpkins, and those displays begin showing up as Labor Day approaches. One of the best solutions to early-maturing pumpkins may be finding an early market.

--R. Hazzard; many thanks to the following sources: J. Howell, A. Carter, and Robert Wick. University of Massachusetts; Dale Riggs & Robert Rouse, Pumpkin Production Guide, NRAES; Maurice Ogutu, University of Illinois Extension, in Vegetable Growers News, August 2004; and Liz Maynard, Purdue University; Andy Wyendandt, Rutgers Univ.

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