Fungicides will be needed for the duration of the growing season to protect cucurbit crops from downy mildew. This disease is extremely destructive and can kill an unprotected crop within 7 to 10 days. Since downy mildew is spreading across Michigan, no one should assume that their crop will not become infected.

There are three elements mandatory for a successful downy mildew program:

1.Use only those fungicides proven to be effective. Data from Michigan State University shows the following program works.

Spray 1: Previcur Flex (1.2 pt.) + Bravo (or Mancozeb)

Spray 2: Tanos 50 DF (8 oz.) + Mancozeb (or Bravo)

All products listed above must be used at full label rates. Cutting rates will leave the crop vulnerable to downy mildew. As a mixing partner, Mancozeb is good against downy mildew but carries a 5-day pre-harvest interval. This makes Mancozeb use especially difficult for growers of hand-harvested cucumber, zucchini and summer squash. Remember, Mancozeb is not registered for use on pumpkins, but Maneb can be used. Some growers are using copper as a mixing partner with Previcur Flex or Tanos 50 DF when the pre-harvest interval prevents the use of Mancozeb. Copper should not be applied under extremely hot conditions or when the weather prevents rapid drying on the leaf surface.

I’ve received a number of questions regarding additional fungicides and their use against downy mildew. I have a large 25-treatment downy mildew trial currently underway. My preliminary observations indicate that Ranman (2.75 fl oz), a relatively new fungicide, can be included in the program of Previcur Flex + Bravo (or Mancozeb) alternated with Tanos 50 DF + Mancozeb (or Bravo) if the downy mildew is not yet present in the field. Last year, when Ranman was included in a field trial where the disease was well established, it did not look good. However, growers of hand-picked cucumbers are in a real bind because of pre-harvest intervals. Previcur Flex has a 2-day pre-harvest interval, Tanos 50 DF has a 3-day pre-harvest interval, and Mancozeb has a 5-day pre-harvest interval. Ranman has a 0-day pre-harvest interval and should be a big help to those needing to get into the field to harvest. However, Ranman must be used prior to downy mildew infection for best results.

2. Keep the spray interval short. Cucurbits grow rapidly and the new growth must be protected. That means a 5-day spray interval for many growers is the only option. Especially growers near the hardest hit areas of the state (see map) must assume that the downy mildew spore load is high (see spore chart) and so is the threat of disease. Those growers with the most severe downy mildew problems have stretched their spray interval and left their crop unprotected at critical times. Remember, that if you use a fungicide in your rotation that is not effective against downy, you also leave your crop vulnerable because the interval between the fungicides that are working becomes too long. The extremely high temperatures of the last several days will limit the spore production of the downy mildew, but the pathogen will rev back up again as soon as the temperatures go back to a seasonal level.

3.Use ground sprayers. Some growers are reporting downy mildew problems in fields that have been sprayed with airplanes. Fungicides for downy mildew control should be applied with ground rigs in a volume of water of at least 30 gals. Using a higher amount of water such as 50 gallons is preferred to ensure uniform and thorough plant coverage.

Strobilurin-insensitive isolates of Alternaria solani were reported by Dr. Neil Gudmestad (North Dakota State University) for samples of the disease taken from potato fields in southwest Michigan and Dr. Walt Stevenson (University of Wisconsin) for samples taken in Tuscola County, Michigan in 2005. In 2006, it is intended to widen this survey to all potato growing regions of Michigan. Samples should be collected and mailed to Dr. Willie Kirk, MSU (address below). These samples will be divided and sent to NDSU and UW for analyses as part of a wider North Central region survey.

1. Individual leaf samples should be cut from the main stem and folded into a dry paper towel.
2. Ten leaf samples per field will be adequate.
3. The paper towels containing the leaves should be placed into a zip-lock sandwich bag and labeled with the following information:

• Variety
• Location, township, county
• Field ID
• Number of applications of Group 11 fungicides (Quadris, Headline, Gem, Tanos and Reason)
• Date and contact ID – name will be fine.

We hope to collect as many samples as possible for Michigan. The samples should be sent to:
Dr. Willie Kirk
35 Plant Biology Building
Plant Pathology
Michigan State University
East Lansing, MI 48824, USA
Phone 517-353-4481, Mobile 517-775-6048
http://lateblight.org

The second flight of European corn borer has begun throughout most of Lower Michigan. Numbers caught in pheromone traps during the period of July 25 to August 1 were higher than the previous week, but still fairly low (an average of 13 per trap in Ingham County, 10.5 per trap in Macomb County, 5 per trap in Mason County and 0.3 per trap in Oceana County.) GDD50 accumulations are just beyond the point where we expect the second flight to start (1450 to 1500 GDD). Snap bean, pepper and sweet corn growers should protect vulnerable crops.

Onion thrips populations remain high in many onion fields due to the high temperatures. (view image) Numbers are decreased somewhat, but heavy rainfall, but can quickly rebound. Carzol appears to be working well to control thrips (See the July 19 issue of the Vegetable CAT Alert.).

We have received reports of high populations of corn leaf aphids in sweet corn. Corn leaf aphids are about a sixteenth of an inch long, blue-green and have short black cornicles (“stovepipes”). Like other aphids, females give live birth to offspring (all of which are also females) without fertilization. Also, like other aphids, populations can build very rapidly, especially in hot weather.

The Michigan Department of Agriculture (MDA) has approved a SLN (Section 24c) label for use of Dual Magnum on several additional vegetable crops. The new label will include uses on the following crops: asparagus, bell peppers, broccoli, Brussels sprouts, carrot, cauliflower, celery, Chinese cabbage, eggplant, red beets, horseradish, leek, onion (dry bulb and green), Oriental radish, radish, rhubarb, spinach, Swiss chard, turnip, and rutabaga.

The new label will not require membership in the Michigan Vegetable Council, but will require growers to register on the Syngenta website and agree to hold the company harmless if there is any crop injury. It takes a little effort to go through the process, but it can be done with some patience. The website is www.farmassist.com. Chemical sales people and dealers should be able to help growers with the indemnification.

The label is effective as of August 7, 2006, and expires August 7, 2011. The EPA has 90 days to revoke the label but no problem is anticipated.

EPA has approved the registration of REFLEX for postemergence broadleaf weed control in snap beans. This is a Section 3 full federal label. The provisions of the label are similar to those in the Section 18 emergency labels that we have had the past few years in Michigan.

The label indicates that a Reflex rate of 0.75 pt/acre controls pigweeds and some other broadleaves, but that a rate of 1 pt/acre is needed for most other broadleaves. In our experience, a rate of 0.5 pt/acre gives good control of most broadleaves when they have 2 or fewer true leaves. Successful broadleaf control with Reflex depends on applying it when the beans have at least one fully expanded true leaf, and weeds are small. Always include nonionic surfactant (NIS) at 0.25% of volume (0.5 pt in 25 gallons) or crop oil concentrate (COC) at 0.5% (1 pt in 25 gallons).

Two applications may be made if necessary, and the yearly dose may not exceed 1.5 pints/acre. Reflex may be applied only once to any field in 2 years. This is to avoid build up of the herbicide in the soil.

Reflex may be tank mixed with Assure II, Basagran, Dual Magnum, Eptam, Poast, Prowl, or Treflan. Tank mixing with other herbicides with strong solvent systems may result in increased foliar burn on snap beans.

The label has rotational crop restrictions that should be followed to avoid injury to following crops. See the label for details.

Regional reports
1 -- Southwest
Ron Goldy

Volume of tomatoes and peppers has increased. All types of tomatoes (fresh market, roma, cherry and grape) are now being harvested. Blossom end rot and sun scald can be observed in these fields, especially in peppers.

Hot weather has caused many crops to mature quickly. This is especially evident in sweet corn, yellow squash and zucchini.

2 -- Grand Rapids Area
Amy Irish-Brown

Tomato foliage is very nice with no to very little noticeable foliar diseases. Very little local harvest is going on. There are many green tomatoes on plants, but they don’t seem to be ripening as quickly as expected.

Cabbage continues to look pretty good despite all the very hot weather. Growth is slowed.

Celery is developing nicely, and harvest is ongoing. Continue to monitor leafhoppers and control them where needed to prevent the spread of aster yellows. The weather lately has been favorable for foliar diseases.

Onions should be harvested soon. Thrips numbers have been normal to high with some controls going on for thrips.

Sweet corn harvest is in full gear due to the hot weather, but quality is good. There continues to be very little corn borer and no earworm damage in well managed fields.

Vine crops continue to grow. Pumpkin plants are growing quickly, but fruits seem to be setting a bit lightly – perhaps due to the hot weather and lack of female flowers.

Pickle harvest has begun around the Grand Rapids area. Still no symptoms of downy mildew in this area are being seen, but expect it to be reported soon. Be on the look out for it, especially as fields are nearing harvestable size.

3 -- Oceana County
Norm Myers

Weather continues to be hotter and wetter than normal with standing water slowing field activities, including harvest, in many fields. Weather has been perfect for diseases and insects, and we are beginning to see a lot of both.

Commodity reports
Disease problems are really ramping up in asparagus. I am getting a lot of rust reports, especially on Canadian varieties, which are more rust prone. Purple spot symptoms aren’t widespread yet, but wet, windy weather has put most growers behind, and we are basically generating the 15 Tom-Cast Disease Severity Values in less than a week under these conditions.

Disease Severity Values have also jumped greatly in carrots, but it has been difficult for growers to get back on to fields and spray under these conditions. Cercospora and Alternaria are both present in most fields, but generally aren’t out of control.

In pickles and cucumbers, most growers have been following Dr. Hausbeck’s downy mildew recommendations as picking schedules allow. We have not seen any sign of downy mildew yet, and yields have been heavy on the first plantings.

We are seeing a few more virus-like symptoms in zucchini. The soybean aphid suction trap in Mason County caught its first soybean aphid last week, so viruses may be spreading more quickly now. Fresh market growers are covering young fields for Downy Mildew control, but are struggling with the Pre-Harvest Interval of materials on harvested fields.

In winter squash, fresh market growers are also covering up this crop in case downy mildew moves north. Processing growers are still debating the economics of treatment.

Most growers have put a spray on their pumpkins, as much for powdery mildew as for downy mildew. The pumpkin crop looks very good this year and growers are hoping for a good market.

In sweet corn, corn earworm activity continues, and I caught two more moths in my trap this week. I have not seen the beginning of second generation European corn borer in my traps yet.

4 -- Mason-Newaygo counties
Jim Breinling

Weather
Above normal temperatures have persisted in the area during the past week. Official high temperatures have been at 92 degrees but nighttime temperatures have also remained high, mostly in the 65 to 70 degree range. Although hot, moisture has been adequate with amounts of approximately 1 inch during the last 8 days.

Commodity reports
Carrot harvest is underway in Newaygo County. Aster leafhopper numbers were low in fields where sprays are being applied.

Snap bean crop is being effected by above normal temperatures. Pod set can be reduced in fields now in bloom. Maturity is rapid in fields nearing harvest and high field heat negatively effects bean quality. European corn borer counts in the Mason County traps this past week were 3, 0, and 11.

The first corn earworm moth was caught in the trap at a sweet corn site in Mason County this week.

Vine crops generally continue to do well. Warm temperatures have accelerated harvest of summer squash, slicing and pickling cucumbers. Butternut squash for processing is sizing with some fruit 12 inches plus in length. No downy mildew has been observed or reported yet in vine crops in the area.

5 -- Macomb, St. Clair and Lapeer counties
Hannah Stevens

Weather
The 101 degree temperatures in central Macomb topped off a brutally hot and humid week. The low temperature yesterday was 75°, the warmest night we have seen this season. Moisture is generally adequate and, in some areas, showers have been too frequent. Some vegetable crops are maturing too rapidly while others, such as tomatoes, seem to be experiencing retarded ripening in some varieties. Foliar diseases are a challenge on many crops. Early morning harvest and fieldwork has been unpleasantly hot on still days. Still, many farm markets are enjoying good business in melons, sweet corn and other vegetables.

Commodity reports
Sweet corn is maturing more quickly than it can be harvested. Aphids and resulting honeydew are a problem. European corn borer trap catches are remaining fairly constant, as they have throughout the season.

It has been difficult to keep up with vine crop harvest. In particular, muskmelons are maturing quickly in the heat, presenting some quality problems for growers. Downy mildew is under control in one cucumber field where it was identified. New growth looks healthy under a stringent program of protectant fungicides. Angular leaf spot (view image) is widespread in one cucumber field. Gummy stem blight appeared in the last two weeks in one watermelon field but seems to be under control. Sanitation controls are in order as growers move from field to field. Disinfestation of equipment (view image) , shoes and cheap plastic shoe coverings for visitors may not always prevent disease spread, but it takes little time and may help. Phytophthora blight of hard squash was verified in one localized area. Some pumpkins are beginning to color.

The tomato crop is experiencing slow ripening on some varieties due to the high temperatures and one can see many acres of green fruit. Pepper harvest is underway with one incidence of cucumber mosaic virus confirmed.

Carrot harvest began last week. The crop looks excellent with a high percentage of jumbos. Early onions are being rolled (view image). Foliar disease and thrips are proving difficult to control but, the bulbs continue to size.

6 -- Monroe County
Paul Marks

Weather
Hot, hot, hot! The weather has been taking its toll on commodities and people. We are very fortunate to have received between one quarter and one half inch of rain on Sunday (July 30) over most of our area to reduce the stress of this heat on most crops. We are now at 1775 GDD50, for the season, still putting us about three calendar days behind a long term normal. Every day for the last week has been ideal for any fungal pathogen to infest crops.

Commodity reports
Sweet corn is maturing very rapidly during this heat with many growers having difficulty keeping up with harvest. If that is not enough, they are also finding it difficult to cool the corn for packing with night temperatures barely reaching the low 80s. Corn borer counts in my traps averaged less than two per trap.

Tomatoes for market are being packed in much larger volume these last two weeks. Sunscald and blossom end rot both are in this crop. Early blight is easy to find. Processing tomatoes are nearing full growth in early fields and nearing Ethrel application time. Late fields are full of flowers.

Cole crops are suffering the most in this heat with late planted fields being irrigated to establish the crop. Field heat in this crop is also very difficult to remove for packing and marketing.

Pumpkins are developing fruits and look to be free of downy mildew and powdery mildew at this point. Most growers are using fungicides to protect from both of these diseases.

Cucumbers over our entire area are being destroyed by downy mildew. Fields that have been protected on the five day schedule are holding their own much better than fields with less protection, but the mildew still appears to be progressing in these fields, just at a slower rate. Late planted fields now show symptoms even at the cotyledon stage when unprotected.

Pepper harvest has begun with large sizes and thick walls in the fruits. This crop looks much better than last season’s CMV infested crop. Biggest problem appears to be sunscald. Growers are concerned about the heat in this pack as well.

Potatoes are being packed for market on an as-need basis in order to minimize the potential loss from heat once they are in the bags. Yields and quality both look good. Early blight is difficult for growers to keep in check with these weather conditions.

Weather news
Jeff Andresen
Agricultural Meteorology
Geography

The oppressive heat and humidity of the past several days will come to an end soon as a frontal boundary over northern sections of Michigan Wednesday morning (August 2) slowly passes through the state during the next 24 hours. Given extreme heat and humidity ahead of the front, showers and thunderstorms will be likely for northern sections of the state during the day Wednesday and across central and southern sections Wednesday evening into Thursday. Some severe thunderstorms will be possible Wednesday and Wednesday evening with primary threats of high winds and heavy rainfall. Rainfall totals during the next 24 to 36 hours will range from less than 0.25 inches in some southern sections of the Lower Peninsula to more than 1.0 inch across northern Lower Michigan. Some localized 2.0-inch or more totals and flooding will be possible Wednesday over the northern Lower Peninsula. High pressure will move into the region by late Thursday and persist through at least the first half of the upcoming weekend with fair and dry weather expected. Temperatures behind the front will fall back to more normal levels by Thursday and Friday with highs in most areas in the upper 70s to low 80s and lows from the mid-50s to low 60s. Temperatures will warm back to above normal levels by Saturday and Sunday with highs generally in the 80s and lows in the 60s. Average temperatures during the next five days will remain at above normal levels with means running 3 to 6 degrees F above the climatological normals. A frontal system will approach the region from the west late Sunday or Monday with the next chance for significant precipitation.

The medium range forecast guidance strongly suggests the re-establishment of an upper air ridge over the central United States by late next week, which would likely translate into above normal temperatures for the Great Lakes region and much of the Midwest. Not surprisingly, the official 6-10 day and 8-14 day outlooks from the NOAA (covering August 7-11 and 9-15) both call for above normal temperatures state- and region-wide. Precipitation totals during both time frames are forecast to range from near normal levels in northern sections of the state to below over southern sections. Forecaster confidence in these outlooks is considered greater than normal due to good agreement between individual forecast tools and temporal continuity in recent forecast model runs.