Wisconsin Fresh Fruit and Vegetable Newsletter
July 1, 2007

Contents:

Diagnosing fruit mineral nutrition
Strawberry Renovation
Off-site herbicide deposition
Vegetable Report
Peninsular Station Report
Growing Degree Days
Drought Monitor
UW Contacts

Table 2.   Fertility status of apples in relation to nutrient content in leaves.

Table 3.  Fertility status of strawberry in relation to nutrient content in leaves.

Table 4.   Fertility status of raspberries in relation to nutrient content in leaves.

Strawberry Renovation

    Strawberry harvest is tapering off in the southern part of the state and is in full swing in central and northern areas.  Immediately following the final harvest of a field the process of renovation should begin for fields that will be carried over for 2008 or beyond.  Renovation consists of these steps:

Weed control.  Renovation is the best time to control many problem weeds.  2,4-D amine can be used to control dandelions and other broadleaf weeds.  For best control treat with 2,4-D, then wait 7-10 days before mowing off foliage.  That allows for weed canopy to absorb the herbicide and allows time for translocation to the roots for a complete kill.  For 2007 Spartan Herbicide can be used to control a number of broadleaf species and renovation is one of two application windows.  You must have the Spartan Section 18 label in your possession at the time of applications.  Supplementing herbicides with a sharp hoe will provide more complete control.

Mowing the canopy.  If leaf diseases have been a problem, they can be reduced by mowing off the leaves with a rotary type mower set high enough to not damage the crowns.  If leaf diseases have not been a problem then mowing is not essential.

Narrow the rows.  Yield in strawberry is more closely related to the linear feet of row edge than to the surface area of soil covered with plants.  Keeping the rows narrow provides better light penetration to the canopy and greater productivity and quality. 

Incorporate mulch.  As you narrow the rows, the straw mulch remaining from winter protection will be incorporated.  Rotovating in the straw helps to maintain soil organic matter.

Apply fertilizer.  This is the best time to fertilize strawberries.  Nitrogen is critical not only to support plant growth, but to break down the mulch that was incorporated.  Typical rates are 20 pounds of actual N per acre during renovation and another 20 pounds about a month later.  This will need to be adjusted according to the results of tissue testing that is done now as well.  If the field was well prepared prior to planting no P or K fertilizer will be needed.

Even though harvest is over strawberry fields will still need to be irrigated through the summer if rainfall is lacking. 

Teryl Roper, UW-Madison Extension Horticulturist
For more information see this article from the University of Massachusetts.

Off-target herbicide movement:
Risk-reduction strategies and reminders.

Jed Colquhoun, University of Wisconsin-Madison, Department of Horticulture, Colquhoun@wisc.edu.

       Each year at about this time we get a few complaints of suspected herbicide movement to non-target vegetation.  While instances of herbicide injury on non-target vegetation are still rare, the risk for such injury has increased in recent years for several reasons.  First, expansion and interspersing of residential areas into traditionally agricultural lands increases the chance of non-target exposure.  Two acres of farmland are lost every minute of every day in the U.S. (American Farmland Trust 2006).  In Wisconsin, about 18,000 agricultural acres per year were developed from 1992 to 1997, representing an increase in rate of 70% over the previous 5 years.  Second, recent expansion of specialty and value-added crops in traditional field crop land increases the probability that sensitive vegetation is nearby.  Vineyards, orchards, ornamental nurseries and organic farms tend to be particularly at risk from nearby herbicide applications.  In organic farming, for example, the organic certification that adds value to the crop can be compromised by non-target sources of herbicide residue.  Third, some newer herbicides cause very obvious symptomology on non-target plants, even at very low doses.

      The Association of American Pesticide Control Officials (AAPCO) conducted a national survey of suspected pesticide drift cases in 2005 (AAPCO 2005).  Nationally, agricultural crops were the intended target of 70% of confirmed drift cases, and lawns and landscapes were the most frequent recipient (43%) of drift.  Fifty-three percent of cases involved commercial applicators for hire, and 22% involved certified private applicators.  In Wisconsin, it is worth noting that more confirmed drift cases occurred from applications to non-agricultural land (51%) than agricultural crops (42%). 

      Issues surrounding potential non-target herbicide damage to nearby sensitive vegetation can be somewhat mitigated by taking measures to reduce the risk for herbicide movement at or after application.  In general, the risk of herbicide movement can be reduced with the following strategies.  Keep in mind, though, that all herbicides can drift in the wrong climatic conditions or in a poor application. 

1. Don’t spray when:
   1. The wind speed is excessive or the direction is toward sensitive sites.  As a matter of fact, a light breeze away from the sensitive site may be the most appropriate timing for an application (check the herbicide label for wind speed limitations).
   2. Temperature and humidity favor herbicide volatilization (conversion of an herbicide to the gaseous form that can travel long distances).  In general, high air temperature and low humidity favor volatilization.
   3. Air inversions exist.  In an air inversion, cool air is trapped near ground level, with a layer of warmer air above it.  The inverted air can carry pesticides near ground level to non-target sites, instead of allowing vertical dissipation.  Air inversions often occur during calm, clear nights, when ground cooling occurs rapidly.
   4. Nearby sensitive vegetation is at a sensitive growth stage.  Grapes, for example, are most sensitive to phenoxy herbicides from bud break to bloom. 
2. Consider pesticide application techniques and equipment
   1. Drift reduction nozzles and spray additives can reduce the risk for spray particle drift, but will not overcome applications during poor climatic conditions, such as on a windy day.
   2. Spraying at lower pressures will increase spray droplet size, thus creating heavier droplets that fall to the target site faster than small droplets that are prone to drift prior to deposition.

    

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Vegetable Crop Report

Crop Progress. Degree days are currently ahead by 175 – 300 DD₅₀ from the 30 year average. This can be recognized in crop development. Pea harvest has begun. Early pea plantings are now being harvested in southern and central parts of the state. The crop looks good with very little disease. Cabbage is beginning to cup in southern Wisconsin. Late April and early May sweet corn is now at least waist high in most fields except northern counties. Strawberry harvest is underway and the berries are extra sweet this year as a result of the hot, dry, sunny conditions. However these same conditions are expected to shorten the harvest season to just over 2 weeks.

 Rainfall has been scarce in many parts of the state and this is beginning to show in crop progress. Irrigation pipe is being moved and drip tape is being utilized at full potential.

 Time to renovate asparagus plantings. This is the time of the season to renovate asparagus beds. After the eight week harvest period – late June in southern Wisconsin, fertilize with a complete fertilizer (10-10-10) to help rejuvenate the crowns that have been depleted during the harvest season. Allow the ferns to grow until fall, at which time they should be cut back to prevent the overwintering of diseases and pest insects.

 Managing Diseases of Tomatoes in High Tunnels by Sally Miller, State Extension Specialist – Vegetable Disease Management, Department of Plant Pathology, The Ohio State University
 
High tunnels offer farmers an opportunity to stretch the tomato season at both ends – by allowing earlier planting, earlier first harvest, and extension of the growing season into the fall.  High tunnel production includes elements of both field and greenhouse management.  The “protected culture” of high tunnel production may result in lower incidence of diseases exacerbated by rainfall such as Septoria leaf spot and bacterial spot and speck.  However, diseases that often occur in greenhouses, but are uncommon in open fields, may appear in high tunnels. Botrytis blight/gray mold, white mold and leaf mold are among the most important of these diseases.  Late blight may also occur under cool, moist conditions. These diseases can be managed by employing appropriate cultural tactics and by the judicious use of fungicides.

 As tomatoes begin to fruit, Blossom End Rot will begin to become a problem. The disorder begins as water-soaked spots at or near the blossom end of mature fruits. The spots enlarge rapidly and may merge to form large damaged areas. As the damaged tissues dries, the surface becomes shrunken, leathery, and dark brown to black.

The lesions provide an entry area for secondary organisms that cause soft rot and fruit decay.

In some cases, there may be no external symptoms, but the inside of the tomato may be discolored and shrunken.

Blossom end rot is caused by a shortage of calcium in the developing fruit. Calcium, which is carried in the water-conducting vessels, becomes deficient when water is limiting. To reduce the incidence of blossom end rot, provide timely irrigation, mulching to conserve soil moisture and avoiding excessive nitrogen fertilizer applications. In crops that traditionally have a problem with blossom end rot, timely and repeated spraying of tomato fruit and foliage with a dilute solution of calcium chloride has been reported to prevent blossom end rot, but the benefits are often variable. For more information on blossom end rot and other tomato disorders, visit http://learningstore.uwex.edu/Tomato-Disorder-Physiological-Fruit-Problems-P533C103.aspx.

 Now that tomatoes are beginning to flower and produce fruit, the plant becomes susceptible to the “blights” – Early Blight and Septoria. Both are potentially serious diseases that affect the leaves, stems, and fruit of tomatoes and eggplant. This fungi overwinter in plant debris, weedy hosts, or in the soil. It can survive for 1 year on infected plant debris so it’s important to rotate crops so susceptible hosts aren’t planted in the same location 2 seasons in a row.

Infection begins on the lower leaves and spreads upward. Spores splashed on to uninfected tissue spreads the disease to healthy tissue. Early-maturing cultivars are most susceptible to the blights.

Early blight leafspots appear first on the older leaves. The lesions spread out in concentric rings enlarging to ¼ - ½ inch in diameter. A yellow halo may surround the spots. In serious infections, entire leaves may yellow and drop off. As the plant defoliates, the fruit becomes exposed to the sun and is susceptible to sunscald. Infected fruit has dark, leathery, sunken spots near the stem end. Only green fruit is infected.

Septoria leafspots begin as small, circular spots with water-soaked areas on the lower leaf surface. Infection does not occur until after fruit set has begun. As the spots enlarge, they develop dark brown margins with sunken gray centers. Tiny black fruiting bodies may be found in the center of these lesions. Infected leaves often drop from the plant exposing the fruit to sunscald.

Both diseases can be managed by practicing a 3-4 year crop rotation of any solinaceous crop. Several tomato cultivars have some resistance to these diseases but you must determine whether your market will support these cultivars. Mulching around the plants will also delay the initial infection as will increasing air circulation around individual plants. For more information on blight diseases, visit http://learningstore.uwex.edu/pdf/A2606.pdf.

 The European Corn Borer treatment window is present in the southern and central parts of the state. This treatment window occurs between 800-1000DD₅₀. Warrior and Capture insecticides are recommended for control, however this year ECB numbers are much lower than in previous years, most likely because of the Bt field corn planted across the state.

 There has been an abrupt increase in the number of potato leafhoppers in potatoes and early planted snap beans. This increase is likely due to the storm front that came through the southern part of the state earlier in June.  At this time, populations are moderate to high.

 Just yet another reminder that growers should have their Corn Earworm traps up as this insect migrates into the state on the same storm fronts as the Potato Leafhopper.

 The third generation of the Seed Corn Maggot has recently peaked (1000DD₃₉). This insect is a perennial pest of the seeds and seedlings of a wide variety of vegetable crops. In addition to corn, maggots will attack beans, beets, cabbage, cucumbers, peas, radishes, squash, and turnips. Seed corn maggots can decimate a crop stand if left untreated. They are more of a problem when susceptible crops are planted in succession.

            The larvae feed in the cotyledons and the below-ground hypocotyl tissue of the seedlings, resulting in a variety of damage symptoms. Feeding damage in germinating seeds can kill the seedlings before they emerge. Poor germination or poor plant stands may indicate a seed corn maggot problem. To diagnose, dig up the seeds to loof for damage. Plants that survive maggot damage to the seed often have holes in the first pair of true leaves or no leaves at all (snake-head seedlings). Damage to the hypocotyls will leave the plant yellow and wilted.

Since the adult seed corn maggot is attracted to decaying organic matter, do not plant susceptible crops in fields where animal or green manure has recently been applied. Also, the faster the seeds germinate and grow, the less opportunity the less opportunity the maggots have to damage the crop. Hence, wait until soil temperatures are at least 50ºF before planting most susceptible crops. Peas and radishes may be planted when soil temperatures are above 40 ºF. Plant seeds as shallowly as feasible to speed germination. Soak untreated pea and bean seeds in water for 2 hours before planting to soften the seedcoat. If you have seed corn maggots one year, you are likely to have them in succeeding years. To prevent damage, you have two options: plant treated seed or make a soil application at planting. For details on insecticide recommendations, refer to http://learningstore.uwex.edu/Commercial-Vegetable-Production-in-Wisconsin2007-P540C104.aspx.

 The peak flight of the Cabbage Looper is beginning to show up in cole crop plantings. The cabbage looper got its name from the way it arches its body while moving. When fully grown, its greenish body is 1 ½ inches long and tapers near the head. There is a thin white line along each side and two white lines along the back. The cabbage looper adult is a grayish-brown, night-flying moth. The mottled brown forewings are marked near the middle with a characteristic small, silver-white figure 8 or letter Y.

            Feeding damage caused by the cabbage looper is similar to that of the imported cabbageworm. Most of the damage appears in late summer and is caused by the second generation larvae. Head boring is also common in early cabbage and can result in unmarketable heads.  For more information on the cabbage looper and other cabbage “worms” visit  http://learningstore.uwex.edu/Caterpillar-Pests-of-Cole-Crops-P565C104.aspx.

 Cucumber Beetles can be a serious annual pest of vine crops in Wisconsin with the striped cucumber beetle being more of a problem than the spotted variety. Both insects are yellow-green in color and 1/5 inches long. The striped cucumber beetle has three black stripes running the length of its back while the spotted has 12 black spots on its back. The adult striped cucumber beetle resembles the western corn rootworm beetle, which can often be found feeding on the pollen of cucurbit blossoms later in the summer. To distinguish between the two, turn them over. The cucumber beetle has a black abdomen while the western corn rootworm ahs a yellow-green abdomen.

            Feeding damage by the striped cucumber beetle larvae can stunt or kill seedlings or transplants. Adult betles feed on the aboveground plant parts and fruit. More importantly, these beetles spread the bacteria that causes bacterial wilt. This disease plugs the water-conducting vessels of the plant, eventually resulting in plant death. The adult cucumber beetles are such efficient carriers (vectors) of the bacteria that serious crop damage can occur if only 10% of the beetles are infective. For more information on cucumber beetles, visit http://learningstore.uwex.edu/Cucumber-Beetles-P557C104.aspx.

Now that the chicory is in bloom it’s time to think about controlling the Squash Vine Borer. This is an annual pest of pumpkins and squash. The borer is 1 ½ - 2 inches long. The adult is a clear-wing moth that has a cloudy, greenish-brown forewings and transparent hindwings with a fringe of reddish-brown hairs. The wingspan is 1 ¼ - 1 ½ inches.

            The first symptoms of feeding damage is when plants wilt midday. As the larvae tunnel through the vines, they destroy the vessels that transport water. These wilt symptoms may be confused with those caused by bacterial wilt or Fusarium wilt. Look for entrance holes near the base of wilting pumpkin or squash stems for sawdust-like frass near these holes. If frass is present, split the stem lengthwise to confirm the presence of larvae. Fields that have been severely damaged in the past are more likely to be damaged again.

            Management is targeted at the newly hatched larvae before they bore into the plant. Once in the plant they are protected by the plant itself. For information on control of the squash vine borer visit http://learningstore.uwex.edu/Commercial-Vegetable-Production-in-Wisconsin2007-P540C104.aspx.  

 Onion Thrips– Warm and dry conditions have helped to drive increases in the populations of onion thrips in both direct-seeded and transplant onion crops.  In early transplants, onion thrips populations are nearing thresholds (1 immature thrips / leaf), and perhaps may have very recently exceeded this threshold at some locations.  Yellow sticky traps setup surrounding onions have detected dispersing populations of thrips throughout the week and more are expected as climatic conditions remain favorable for these populations (warm and dry).

The treatment interval for onion thrips varies depending upon the method of onion planting (transplanted vs. direct seeded) and maturity of the variety.  Dr. Brian Nault, Cornell University entomologist who has worked extensively with these insect pests, suggests that action thresholds for thrips control are often reached in mid-June for transplanted onions in New York and are often reached or exceeded in early July in the later-maturing, or direct seeded fields.  Furthermore, he recommends the following sequence of materials for use based upon the planting methodology and also revised action thresholds. 

Sequence of insecticides to apply for onion thrips control in onion fields.  Two applications of each product should be used and timing should be based on an action threshold.  For Carzol, sprays may be timed 10 days apart or longer.  For most other products, sprays will likely be timed 7 days apart.  However, if there is a field that is experiencing a significant influx of thrips from an adjacent field or if the population is high, the spray interval may be shortened to every 5 days, label permitting.

Transplanted onions and early maturing direct seeded onion varieties

1. SpinTor 2SC @ 1 thrips per leaf (2 applications, probably 7 days apart)

2. Carzol SP @ 3 thrips per leaf (2 applications, probably more than 7 days apart)¹

3. Lannate LV, or Vydate L @ 1 thrips per leaf (2 applications, if needed)

Direct-seeded onions (late-maturing varieties)

1. SpinTor 2SC @ 1 thrips per leaf (2 applications, probably 7 days apart)

2. Carzol SP @ 3 thrips per leaf (2 applications, probably more than 7 days apart)

3. Lannate LV, or Vydate L @ 1 thrips per leaf (2 applications, if needed)

4. Pyrethroid insecticide @ 1 thrips per leaf (2 applications, if needed)

Russell L. Groves, Vegetable Entomologist, Applied Insect Ecologist, UW-Madison, Department of Entomology

For more information on Onion Trips visit http://learningstore.uwex.edu/Onion-Thrips-P562C104.aspx.

Potato Leafhopper – As reported in a recent newsletter, weather conditions during the late spring have contributed to significant, long-distance immigrations of several problematic insect pests including the potato leafhopper (PLH).  In both potato and the early-planted snap bean crop, populations of adult PLH are increasing and populations have exceeded thresholds in potato over the last 2 weeks in several areas.  In early planted snap beans, populations of leafhoppers have continued to increase again this week and some early nymphs have been reported.  Furthermore, action thresholds of 0.5 – 1.0 adult PLH / 25 sweeps have been exceeded in some younger fields and initial insecticide applications have begun.  Damage caused by the insects include stunting of early plants, leaf bronzing, and overall chlorosis with plant decline.  Damage to the vascular tissue results from a toxemia injected into the plant found in the saliva of the feeding PLH.  Affected areas initially become necrotic and eventually progress from the leading edge of affected leaves towards the leaf base over time.  Sufficient control of these problematic populations can be achieved using lower to mid range rates of synthetic pyrethroids including, but not limited to, Capture^® 2EC, Asana^® XL, or Mustang Max^®.  Russell L. Groves, Vegetable Entomologist, Applied Insect Ecologist, UW-Madison, Department of Entomology For more information on the Potato Leafhopper visit http://learningstore.uwex.edu/Potato-Leafhopper-P558C104.aspx.

The last Cherry Leafspot infections were recorded June 20-21, at all weather station on the peninsula. On the same date, Apple Scab infections were recorded at Casco, Southern Door and Sister Bay, but not at Sturgeon Bay or Egg Harbor. Overnight on June 18-19th Cherry Leafspot and Apple Scab infections were recorded at all weather stations on the peninsula.

Codling moth 1st generation flight should be winding down and control applications should be out. Spray dates for this pest are calculated in the table below. European Red Mites are heavy in some apple blocks and have resulted in some very early application of miticides.

Degree Day Map

Current Drought Conditions

For more information about current drought conditions see:
http://drought.unl.edu/dm/monitor.html

UW Fresh Fruit and Vegetable Contacts