WISCONSIN FRESH FRUIT AND VEGETABLE NEWSLETTER
June 15, 2007

Wisconsin Apple Summer Field Day

The Wisconsin Apple Summer Field Day will be held on Tuesday July 24 at the Peninsular Agricultural Research Station north of Sturgeon Bay.  Registration materials will be sent to all known apple growers by the Wisconsin Apple Growers Association.  If you would like information about the field day please contact the WAGA.  acminc@verizon.net  (920-478-3852). You can see the program here.

• Schedule the most strenuous physical work early in the day when temperatures should be coolest.

• Pay special attention to new workers since they typically won’t be acclimated to working in hot conditions. 80% of heat illnesses occur within the first four days of employment.

• Have cold water readily accessible at all times. Provide one quart of water per person per hour. Drinking only when thirsty won’t replenish water lost through sweating when you are working hard.

• Have a buddy system so that workers look out for one another.

• Teach workers the symptoms of heat related illnesses and how to respond to them.

• Wear loose fitting light colored clothing to assist the body in dissipating heat.

Cedar Apple Rust

 Many parts of southern Wisconsin were wet and cool the weekend of June 2-3. Juniper trees were laden with oozing, gelatinous masses of spores that cause cedar apple rust. Usually the emergence of these “spore horns” coincides with apple bloom. However, I suspect the dry weather in mid May held the spores back. In any case, symptoms on apple leaves are now showing. Most commercial growers keep cedar apple rust in check with their scab fungicides. Nova and Rubigan are both highly effective in controlling rust. Mancozeb and the strobilurins (Flint, Sovran, and Pristine) are also good if applied before infection. Sulfur is moderately effective; captan and copper are not effective. Growers who have reduced their use of Nova or Rugiban because of fungicide resistance should be on the lookout for more rust than they have been accustomed to. Organic growers in the southern part of the state should focus on rust-resistant varieties, since the chemical available to them are not highly effective for rust control. Removing junipers near the orchard will reduce disease pressure. However, the spores that form on junipers ride adrift in winds and infect apple trees at a distance of 2 miles or more, making it impractical to remove all sources.

 For more on cedar apple rust, including a list of relative susceptibility of cultivars, see the tree fruit web site from West Virginia University Kearneysville Station:

 http://www.caf.wvu.edu/Kearneysville/disease_descriptions/omcar.html

Black Knot of Plum (and Sometimes Cherry)

 Black knot can be found almost every year on plum, wild plum, wild cherry, and some ornamental plums and cherries. Less commonly it develops on sweet and tart cherries. Black knot is very aptly named for the black, swollen galls that form on branches. See UW Extension bulletin XHT1056 for more details on identifying black knot and how this disease develops at

 http://www.plantpath.wisc.edu/pddc/factsheets/BlkKnotLC.pdf

 Black knot galls can enlarge and eventually encircle branches, cutting off movement of water and carbohydrates. Often it’s just small twigs that are killed, but when black knot forms on scaffold branches or trunks, the affect parts can die within a few years. If trees are under drought stress, death can happen even faster. The best control measures for black knot are sanitation:

1. Avoid the pathogen by removing wild plum and cherry within 500 feet (or more if possible) of the desired trees.
2. Prune out black knot. This can be done at any time of the year, but it’s easiest to find knots when trees are dormant. Become familiar with the appearance of first year knots (bulbous, spongy, green) so that you can get the galls out before galls become hard and black and release spores. Cuts should be made at least 6-8 inches below the gall to get all of the pathogen out. If you are doing this during the growing season, disinfect pruning tools between cuts.
3. Surgical removal of knots from trunks and large scaffolds can slow the disease down and buy a few years, but it is nearly impossible to eliminate the pathogen this way. Use a chisel to cut off the knot plus at least an inch of surrounding healthy appearing tissue. The benefit of applying wound dressings is debatable, but if trees are being treated with fungicides for other diseases, the fungicides might protect the wound from various canker pathogens and slow down black knot as well.

Patty McManus, UW-Madison Extension Plant Pathologist 

Weed control in Strawberries at Renovation 

When strawberry harvest is complete the process to renovate the planting for the coming crop year should begin.  An important step in the renovation process is to control weeds that may have escaped whatever pre-harvest control measures were taken.  Renovation is a good time to control weeds because many weeds are actively growing at this time, harvest is complete so residue problems are miniscule, and flower buds for the following year’s crop have not yet begun to form.

The first step in renovation weed control is to determine what weeds are present.  Have grasses encroached, or are broadleaf weeds like thistles, dandelions, and groundsel most prevalent?  If grasses are the biggest problem then a product like Select Max would be best.  However, if the grasses are too large control may be poor this time of year.  If broadleaf weeds are your biggest problem then you have several options. 

2,4-D amine.  Make the application 5-7 days before mowing.  This gives time for the herbicide to be absorbed before the canopy is removed by mowing.  If you mow before applying 2,4-D you have removed the absorptive surface and control will be minimal.  Make sure that the product you purchase has strawberries on the label.  Not all 2,4-D amine products are labeled for strawberries.

Sinbar.  Sinbar should be applied after mowing.  If you did not apply Sinbar in the spring you can apply at the 6 oz/a rate.  If a spring application was made reduce the application rate to 3-4 oz/a.  Do not apply more than 8 oz/a of Sinbar in any growing season.  Be extremely cautious with Sinbar on coarse sandy soils.  Sinbar application can be made following a 2,4-D application to control existing weeds.

Spartan.  This herbicide is available once again as a Section 18 Emergency Exemption for control of Common Groundsel, Lambsquarters, Corn Spurry, Ladysthumb, Mayweed, Redroot Pigweed, Pineapple Weed, Prostrate Knotweed, and Wild Buckwheat in strawberries.  At least one of these weeds must be present in a field or it should not be treated with Spartan. Two windows of opportunity are provided for application.  The first is between June 20 and July 20 with the second from October 15 to December 15.  Use 4-8 oz/a of Spartan per application, but don’t exceed 12 oz/a during any crop year.  This is a soil active herbicide that requires incorporation either via rainfall or irrigation, or light mechanical incorporation.  Spartan can be applied after mowing following a 2,4-D application to control existing weeds.

            For small and occasional weeds a sharp hoe is still a good way to manage growing weeds.  Rotavating used to narrow rows will also control most weeds between the rows, leaving just the row centers for chemical control.  Remember to carefully calibrate your sprayer before making an application to ensure you are applying the proper amount of active ingredient.  Read all product and supplemental labels prior to making an application and follow the label directions.

            If weeds are carefully controlled at renovation weed problems through the remainder of this year and even into the spring will be reduced.

Teryl Roper, UW-Madison Extension Horticulturist
http://learningstore.uwex.edu/pdf\A1934.pdf

Reducing the Risk of Microbial Contamination of Fresh Produce

Because of the recent, nationwide outbreaks of food-borne illnesses, growers have been under the gun to practice “Good Agricultural Practices” (GAPs). There has been a steady increase in the consumption of fresh fruits and vegetables as a result of the USDA’s push for the 5-a-day program. At the same time, there has also been an increase in food-borne illnesses.  The primary culprits are Salmonella and E. coli 0157:H7 however Shigella, Giardia, Norwalk and Hepatitis A viruses, Cyclospora, and Cryptosporidium have also been associated with food borne illness outbreaks. These diseases can affect people of all ages but are most serious in young children, the elderly, and patients undergoing chemotherapy or have had transplants, and those with HIV or AIDS. A wide variety of fruits and vegetables are affected.

Potential sources of on-farm contamination include soil, irrigation water, animal manure, inadequately composted manure, wild and domestic animals, inadequate field worker hygiene, harvest equipment, transportation carriers, wash and rinse water, unsanitary handling during sorting and packaging, equipment used to soak, pack or cut produce, transport vehicles, improper storage temperatures, cross contamination in storage, display and preparation.

Some actions that can be taken to reduce the likelihood of contamination include proper composting of manure and when applied to the field, immediate and complete incorporation. Regular testing of irrigation, cooling, washing and processing water should be a part of your operation. This should be done annually if using municipal water, twice a year for well water and 3 times a year for surface water. Complete records of all water tests should be available to anyone who wishes to see them. When manure is used, be sure to observe a 120 day waiting period before planting all crops except sweet corn.  To meet these requirements, apply and incorporate manure the fall before planting. The most critical practice you can employ is location your production field up stream from any feedlots or other areas where livestock will be kept. Along those same lines, keep wild and domestic animals out of the fields and packing areas.

The other key preventable areas of contamination are harvest, post harvest and handling operations. Proper worker hand washing techniques, cleaning and sanitizing packing and storage facilities, maintaining clean wash water, cooling produce quickly and maintaining proper storage temperatures throughout the duration of storage all contribute to the prevention of food-borne illness. Use chlorinated water or other labeled disinfectants to wash produce and equipment.

By keeping track of all actions from field to sale will provide documentation on where infestation may have occurred.

This brief article only highlights the general agricultural practices necessary to assure proper food safety. For more detailed information visit:

www.GAPs.cornell.edu
Producers Guide to Reducing Microbial Contamination of Fresh Produce

Karen Delahaut, UW-Madison Fresh Vegetable Crop Specialist

Peas and Snap Beans: The biggest concern for both of these crops early in the season is root rot.  Thus far the fields I've viewed appear uniform
without symptoms of root rot.  Adequate moisture, not in surplus, during the germination and emergence period along with long rotations between these
crops are key to avoiding severe root rot problems.  We continue to look for the "silver bullet" seed treatment that will protect plantings from root
rot, but so far, no luck.

Other Vegetable Crops: Most other vegetable crops are in the early stages of development.  We are not seeing samples of other vegetable crops to indicate any problems at this point.  Conditions are ideal for crop establishment and with an occasional rain, long periods of soil and foliage drying, crops are healthy at this point.

Walt Stevenson, Extension Vegetable Specialist

Phytophthora blight is a destructive disease that has been around for a long time and sporadically has caused epidemic outbreaks in several locations in the United States. The first major outbreak in Wisconsin occurred on cucumbers in 1995. Phytophthora capsici is capable of causing complete destruction of zucchini, pumpkin, and summer squash fields. The fungus is also capable of infecting cucumber, muskmelon, tomato, pepper, eggplant, snap and lima beans. It has not been observed on watermelon. Long-season crops appear to be more severely affected by this disease.

            The most devastating form of Phytophthora blight is root and crown rot. It starts as small, brown lesions on the lateral and taproots. Infected plants will begin to show signs of stress and the crown will become chlorotic. As the disease spreads outward from the crown toward the runner tips, the crown begins to die out. Plants may also wilt mid-day and recover in the evening – similar to the symptoms expressed by vine crops infected with bacterial wilt or infested with squash vine borer larvae. The plant will die 2-4 days after the wilting begins.

            Fruit rots are another common expression of the disease. This starts with water-soaked lesions on the part of the fruit in contact with the ground. These lesions rapidly enlarge and become covered with a white, yeast-like growth until finally the entire fruit collapses.

Relative susceptibility of various vegetables

            Phytophthora blight overwinters on infected debris in the field. It is suspected that spores can survive in the soil without a host for up to 10 years. The disease is spread by splashing rain, flies, and human activity in wet fields. New fields become infested when equipment moves soil with the disease from an infested field. Phytophthora capsici may also be seed-borne.

            Warm, wet weather favors disease outbreaks that typically occur in July and August after a heavy rainfall. Low-lying areas in the field will show symptoms first.

            To reduce the likelihood of infection, rotate crops out of cucurbits, and other susceptible crops for a minimum of 3 years. Only plant certified disease-free seed from a reputable dealer. To reduce overwintering spores, clean up and destroy all plant debris from the previous year.

 Colorado Potato Beetle (CPB) adults have emerged statewide and are rapidly colonizing field edges and have begun to move toward field centers.  First instar larvae are migrating to the growing points of infested plants where they feed in the newly emerged, terminal growth.  With warmer temperatures, early instar CPB larvae can be expected to molt to successive, and more damaging larval stages quite rapidly.  Reduced risk insecticides effectively target these developing, early instar CPB larvae once thresholds have been exceeded.  CPB economic thresholds for the use of Rimon^® 0.83EC occur when 10-40% of egg hatch has occurred whereas either SpinTor^® 2SC or Agrimek^® 0.15EC should be considered when small larvae (L1-L2) exceed 4 individuals / plant.

Russ Groves, Vegetable Extension Entomologist.

 Dry weather may result in the development of Onion Thrips. Onion crops are progressing well and a few thrips have been collected in yellow sticky traps and within the crop itself during the past week.  Yellow sticky traps monitoring the dispersal of inbound thrips should be located along the outer edges of the field and examined twice weekly. Once an influx of thrips has been detected, scouting should become more intense in the crop.
Russ Groves, Vegetable Extension Entomologist.

 Cabbage - Similarly, scouting for thrips in cabbage can be integrated with scouting for Lepidopteran larvae (worms). A total of 20-30 plants should be examined twice weekly with a focus on the field perimeters where thrips infestations often first appear. Both adult and immature thrips are frequently observed on the undersides of leaves or within the developing head. They are often difficult to find, making it important to also look for signs of feeding. Russ Groves, Vegetable Extension Entomologist.

 “Leps” in cabbage and other cole crops: Just a reminder: For control of diamondback moth, imported cabbageworm, and early stages of cabbage looper before heading in cabbage and broccoli, avoid using pyrethroids if possible. The pyrethroids can be excellent clean-up sprays before harvest to get rid of potential contaminants and prevent damage to heads, but if they’re over-used throughout crop development and over the whole season, resistance can develop in diamondback moth populations. When this happens, keeping the crop clean in mid and late summer can become very difficult. Alternatives to pyrethroids that are useful in resistance management and early season and early stage control of lepidopteran insects (caterpillars) in cabbage and broccoli include Bacillus thuringiensis products (Agree, Biobit, Dipel, Javelin, Lepinox, and Xentari), Proclaim, and SpinTor/Entrust.
Russ Groves, Vegetable Extension Entomologist.

 High winds over the past few weeks has favored the migration of Corn Earworm, Aster Leahopper, and Potato Leafhoppers into the state. This means the earworm traps should be up and baited and scouting of potatoes and snap beans should be conducted on a regular basis.  The economic threshold for potato leafhoppers in snap beans is 1 adult per sweep or 1 nymph per 10 leaves. In potatoes, sample for nymphs and adults. Do not treat if fewer than 0.5 adults per sweep unless there are more than 2/5 nymphs per 25 leaves. If there are 0.5-1.0 adults per sweep, treat if they remain at the same level for 10-14 days or if nymphs are present. If there are 1.0-1/5 adults per sweep, treat within 5-7 days or immediately if nymphs are present. If there are more than 1.5 adults per sweep, treat immediately.

Sweet corn growers should be on the lookout for both the European Corn Borer and Corn Earworm.  In the southwest and west central parts of the state, ECB larvae are in the treatment window. This window is present between 800 – 1000 DD₅₀. In the remainder of the state, if weather conditions remain the same, expect to treat early crops within a week. Recommended insecticides include Warrior and Capture. For treatment intervals, visit http://www.horticulture.wisc.edu/freshveg/Managing%20Sweet%20Corn%20Worms.doc.

Growing Degree Days

Degree Day maps are available for several crops at the following URL:
http://www.soils.wisc.edu/wimnext/

UW Fresh Fruit and Vegetable Contacts