In this issue
Five-day sprays needed for downy mildew on cucumbers
Corn earworm numbers high
Second flight of European corn borer
Aster leafhopper and aster yellows test results
Regional reports
The heat wave of 2006: An epilogue
Weather news

As downy mildew moves across the state (see map), cucumber growers can be certain that their crop will become infected if it isn’t protected. With a few more weeks until the end of the growing season, it is unlikely that unprotected cucumbers will escape this disease.

Downy mildew has also been reported on muskmelon and winter squash in Michigan . Downy mildew on pumpkin has been reported in Ohio and New Jersey . Fungicides will also be needed for the duration of the growing season to protect these crops from downy mildew. This disease is extremely destructive and can kill an unprotected crop within 7 to 10 days.

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. As a mixing partner, Mancozeb is good against downy mildew but carries a five-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.

Ranman (2.75 fl oz) + Mancozeb can also 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 two-day pre-harvest interval, Tanos 50 DF has a three-day pre-harvest interval, and Mancozeb has a five-day pre-harvest interval. Ranman has a zero-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.

The weather front that moved through a week ago brought insect migrants into the state, including many corn earworm moths. Pheromone trap catch numbers jumped in almost all areas, sometimes dramatically (see accompanying table). Growers should protect vulnerable crops (corn with fresh silk; snap beans and tomatoes with flowers and fruit) now.

On sweet corn, corn earworms lay eggs on fresh silk. Upon hatching, the larvae move up the silk into the ear, where they are protected from insecticide sprays. Insecticides should be applied within two days of silking. Thorough coverage of the silk is important. Insecticides must be present on the silks when the larvae hatch. When temperatures are moderate and pheromone trap catch is low (less than 30 per week), spray intervals of five to six days are adequate. When pheromone trap catches are moderate (30 to 180 per week), spray intervals should be four to five days. When temperatures are high (highs in the 90s and lows in the 60s) or trap catch exceeds 180 per week, insecticides should be applied every two to three days. Bt sweet corn does provide good protection against corn earworm, but does not provide 100% control. Additional insecticide applications are needed if pheromone trap catch is high. See the article by Dr. Bill Hutchison, University of Minnesota , at: http://www.vegedge.umn.edu/MNFruit&VegNews/vol3/803zeamap.htm

Corn earworm can also infest tomatoes (It is also called the tomato fruitworm.). Eggs are laid on leaves near fruit or flowers. Once again, upon hatching larvae quickly move to and infest the fruit. Insecticides must be present on the foliage to control larvae before they enter the fruit. Corn earworm may also lay eggs on snap beans from flower to harvest. Although corn is the preferred host, these other crops may be attractive if corn is not available or if it is not attractive (after silks have dried or before silking).

Michigan State University is cooperating in a Midwest corn earworm migration and insecticide resistance monitoring network lead by Dr. Bill Hutchison, University of Minnesota , Dr. Rick Foster, Purdue University and Dr. Rick Weinzierl, University of Illinois . Cooperators throughout the Midwest are publishing corn earworm trap counts regularly on http://www.vegedge.umn.edu/ZeaMap/zeamap.htm

The project also includes testing earworm moths for resistance to pyrethroids. As of yet, none of the tests of moths collected in the Midwest have been completed. We continue to recommend pyrethroids as the most effective material to control corn earworm. See Bulletin E-312, 2006 Insect, Disease and Nematode Control for Commercial Vegetables. This bulletin can be viewed at http://veginfo.msu.edu

The second flight of European corn borer is well under way in most Michigan locations (see graphs). Sweet corn in tassel and beyond, peppers and snap beans with fruit should be protected. European corn borer larvae can be controlled by insecticides used for corn earworm, and this is where growers should be targeting their effort.

We have received results of tests on aster leafhoppers collected from celery fields in southwestern Michigan ( Ottawa , Allegan and southern Newaygo counties) during July 15-19. None of these leafhoppers tested positive for aster yellows. We recommend a treatment threshold of 35 aster leafhoppers per 100 sweeps for these areas. The latest test results we received on leafhoppers collected from carrot fields in Oceana, Mason and Newaygo counties indicate higher infectivity. See the August 2 issue of the Vegetable CAT Alert for these treatment thresholds.

Regional reports
1 -- Southwest
Ron Goldy

Weather
Temperatures are significantly lower than last week with highs of 76^oF to 93^oF and lows from 58^oF to 64^oF. The area received 2 inches of rain as the cool front passed Wednesday evening (August 2). Some wind damage also occurred. Soil moisture remains sufficient at this time.

Commodity reports
Virus symptoms are increasing especially in vine crops, but symptoms remain well below last year. Conditions have been good for powdery mildew and symptoms can be found in some fields. Downy mildew alert remains high with most growers protecting as recommended. However, Previcur Flex supplies remain low or non-existent. Striped cucumber beetles are still active, and squash bugs can be found in limited numbers.

Watermelon and cantaloupe harvest has begun. Harvest of cucumbers, zucchini and yellow squash has slowed due to hot weather, and quality is also down. Volume and quality should increase by the weekend. Pumpkins and fall squash are sizing well.

Volume of tomatoes, peppers and eggplant continues to increase as more fields come into production. Blossom end rot and sun scald continues to be a problem, especially in peppers.

The hot weather caused many crops to mature quickly. This was especially true in sweet corn where some fields had to be bypassed.

3 -- Oceana County
Norm Myers

Weather
It has been dry this last week with normal temperatures. A little irrigation has started in drier parts of the county.

Commodity reports
A big flush of new fern is coming on in most asparagus fields. Second flushes are generally a bad thing, but if we have a normal to warm September, the crowns should have time to recover from this second flush. Diseases are still a concern, but the dry weather has allowed growers to catch up on their spraying.

Both foliar diseases are active in carrot fields, but growers have pretty much caught up on their applications.

In pickles and cucumbers, there have been no reports of downy mildew as of yet. Yields so far have been good.

Watermelon mosaic virus has been identified in some zucchini fields. This is the least serious of the viruses that affect zucchini. If you keep stresses to a minimum, you can still pick with this virus. Because of color changes, this virus is more serious for yellows than greens. No sign of powdery mildew, but phytophthora is active in some fields.

Set seems light in some winter squash and pumpkin varieties. Bacterial diseases are about the only foliar diseases active, but phytophthora is active in these crops, too. Most fresh market growers have been protecting against downy mildew.

In sweet corn and snap beans, corn earworm catch has taken a huge jump with nearly 200 moths caught on Monday (August 7). Corn borer moth catches jumped, but are still below average for a second generation.

4 -- Mason-Newaygo counties
Jim Breinling

Weather
The change from above normal to normal temperatures occurred for most of the past seven days with highs in the low 80s and lows generally around 60. The last significant rainfall amounts were 1.02 inches on August 2 at Ludington and 0.56 inches on August 3 at Fremont .

Commodity reports
Carrot harvest for fresh/cut and peel markets continue. Aster leafhopper numbers were reported to be higher this week in the Newaygo County area. Irrigation of carrots on mineral soil has resumed in Newaygo County .

Onions are showing the effects of the recent heat with tops showing browning and tip burn. Tops remain standing at this time, and most bulbs are 1.5 to 2 or more inches in diameter.

Snap bean fields at the European corn borer trap location in Mason County were harvested this past week. European corn borer counts on Monday (August 7) were 11, 3, and 40.

As reported in most areas of Michigan , corn earworm flight occurred at the sweet corn site in Mason County . Trap count on Monday (August 7) was 46.

Vine crops in general continue to do well in the area. Fruit in butternut squash for processing is now 12 to 15 inches in length.

Foliage in hand harvest pickles and slicing cucumbers remains good and new growth is healthy. There have been no reports or observations of downy mildew in these crops.

Pumpkins are growing well with fruit now over a foot in diameter.

Fruit size in hubbard type hard winter squash is now about six inches in diameter. Deer damage has been observed and reported in pumpkin and winter squash fields.

Pepper harvest is started in the area.

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

Weather
The heat wave passed on Wednesday (August 2) bringing more temperate conditions as rainfall varying from a trace to 5 to 6 inches in the northern part of the region where some crops were flooded. High temperatures have ranged from 89° to 80°F with a low of 51° this morning (August 9).

Commodity reports
In sweet corn, European corn borers trap catches are similar to last week, but corn earworms have appeared in the Macomb County . A number of growers have mentioned to me that they are less concerned now that BT varieties are coming in, but please check the article by Beth Bishop in this issue so are not caught unaware.

At this time it seems as if no cucumbers or pickles have escaped downy mildew if they have not been on a protectant program. An article in the Detroit free press on Saturday raised awareness of the disease and phone calls and samples began coming to our office on Monday. I have seen melon foliage with foliar disease but not the same blight symptoms as on cucumbers.

The pumpkin, gourd and winter squash crop is coloring and ripening. Several growers have told me that the rinds are as hard as they get. Powdery mildew, however, is prevalent on susceptible varieties. Growers should be aware of squash bugs at this time. The broad brown lesions on leaf surfaces may look like leaf blight but nymphs may be found on the leaf undersurface. Virus symptoms are now appearing on some vine crops but at this time virus does not seem widespread or severe.

The tomato crop has now resumed ripening with the less stressful temperatures. Foliar fungal disease seems to be under control while bacterial disease, not serious or widespread at this time, is more difficult.

6 -- Monroe County
Paul Marks

Weather
The last seven days have been dry in our area. We “coasted” through the heat of last week on soil moisture reserves. We are now at a point where irrigation systems are beginning to go into service for the first time in more than a month.

Commodity reports
Sweet corn is being packed at the peak of the season with some very good corn now in the market. Corn borer moths are active at low numbers and we now have pressure from corn earworms as well. I have seen rust for the first time this season this week (see photo).

Market tomatoes are finally maturing in volume on most farms with good quality and size now being packed. Early blight is in many fields. Bacterial speck is in many fields. I have seen several fields where apparent thrips feeding has left yellow streaks on the fruits (see photo).

Processing tomatoes are now being treated with Ethrel in earliest fields with what looks like a good crop in the field. No harvest has been done yet.

Pepper harvest is now underway for both fresh market and processing. Wall thickness is very good, as are yields.

Pumpkins have filled the fields with fruits now evident in most fields. I have not seen any downy mildew or powdery mildew yet. Cooler nights and heavy dews will no doubt bring on the powdery mildew soon.

Cucumbers in our area are a mixed bag. Growers who have followed the five-day application schedule are continuing to harvest a reasonable crop, while those who were skeptical of the downy mildew situation and “stretched” the application schedule have now lost their crop. With all of the thrips in our crops, I still have not seen a cucumber field with a thrips problem this season.

Melons are being harvested in volume this last week with very little impact from downy mildew in this crop.

Potatoes are being harvested for fresh market on an as need basis. Vines are maturing in some early fields maturing tubers and making for better quality packs. Early blight has actively infested many fields during the last two weeks.

Unusually hot and humid weather impacted nearly all continental United States during the last two weeks of July and the first week of August. Nationally, more than 2,300 individual daily records for high temperatures were broken as well as 50 new records for the hottest July temperature ever. More than 200 fatalities were associated with the stressful conditions, the majority occurring in California during the initial week of the event. The unusually hot temperatures also led to record or near record warm mean temperatures for the month of July across the country. July 2006 will go down in the record books as the second warmest on record nationally (since 1895) at 77.2^oF, following only July of 1936 at 77.5^oF. The heat wave was associated with meteorologically with a broad upper air ridge over a massive subtropical air mass that moved slowly from west to east across the country.

While maximum air temperatures near or above 100^oF were common during the event, one of the most important aspects of the heat wave was extremely high dew point temperatures. The dew point temperature is the temperature at which water vapor in the air would begin to condense out at liquid if the air were cooled at constant pressure. It is a direct measurement of how much water vapor is in the air at a given time. The greater the dew point temperature, the greater the water vapor content of the air. The more water vapor in the air, the lower the rate of evaporation of perspiration and the lower the rate of cooling. This is why humans and other animals that perspire become increasingly uncomfortable as the dew point temperature rises (for most individuals, discomfort begins at dew points around 60^oF or higher). During the heat wave, dew point temperatures at or above 70^oF were common over widespread areas with some approaching 80^oF, which is near the absolute climatological limits for most regions of the United States, including Michigan.

To put this in another perspective, I remember when working as a young meteorological intern with the National Weather Service, the operational dew point sensor used at that time (late 1970s) had a maximum of 80^oF on the readout dial (Technology has advanced since then!). Readings at a few locations during the recent event actually exceeded 80^oF, which would have necessitated old, manual observations (most likely a sling psychrometer) given the limitations of the earlier technology. Finally, it is also important to remember that the dew point temperature serves as a general base for minimum air temperatures during the nighttime hours. Thus, overnight readings with this event were also at near record warm levels, with little or no relief for humans without climate control.

In Figure 1, representative hourly temperatures and relative humidity levels are plotted vs. time (dates are labeled just below the times) during the peak of the heat wave event in the Great Lakes region. The data were taken from the MAWN automated weather station near Bath , Michigan . The diurnal cycles are clearly evident with air temperatures reaching 90^oF or higher on three consecutive days. Heat index values are also plotted, which depict the temperature which humans “feel” due to the combined effects of high air temperature and high humidity. The peak heat index value of 105^oF at this location was reached early afternoon on August 1. Note from the graphs the symmetrically opposite diurnal patterns of air temperature (thick solid line) and relative humidity (thin dotted line). As air temperature rises, the relative humidity value falls (since warmer air can hold more water vapor) and vice versa.

The dew point temperature is a more straightforward indicator of how much water vapor is actually in the air. It reaches the mid-70s during the peak of the event and basically remains there until another air mass moves into the region on August 3. Note also that there is some diurnal change in the dew point: it tends to drop off a few degrees during the overnight hours and rise by about the same amount during the mid and late morning. This is due (no pun intended!) to the daily dew cycle and is a result of moisture leaving the atmosphere from vapor to liquid as dewfall/dew accretion during the overnight hours and going back into the atmosphere again the next morning as solar radiation and daily heating evaporate the dew back into vapor.

If you are wondering about the decreases in dew point during the early afternoon hours of July 31 and August 1, this is actually the addition of some relatively drier air from aloft being brought down to the surface during the peak turbulence and vertical mixing of the day in the planetary boundary layer. It did not occur on August 2, most likely because the lower-middle layers of the atmosphere were moistening as a cool front approached from the west (Note air temperatures on August 3 behind the front). Finally, from a climatological perspective in Michigan , the recent heat wave was noteworthy. Considering the number of hours the heat index temperature was at or above 90^oF, this event (with approximately 50 hours above 90^oF) would generally rank as the most significant since the heat wave of August 10-16, 1995 (The same event that claimed more than 500 lives in the Chicago area alone.).

Weather news
Jeff Andresen
Agricultural Meteorology
Geography

Northwesterly flow aloft and high pressure in place across the Great Lakes region has resulted in the recent spell of fair and mostly sunny weather across Michigan since last weekend. A cool front will move across the state beginning late Wednesday into Thursday (August 9-10), bringing a chance for isolated showers. Precipitation totals should remain less than 0.1 inches where rain falls (best chances will be across western and northern sections of the state). The vast majority of the state will remain dry. Fair weather will return statewide on Friday and continue through at least the first half of the upcoming weekend. High temperatures during the next couple of days will generally range from the low to mid-70s far north to the low to mid-80s far south with lows falling to the upper 40s north to the 50s elsewhere. High temperatures will slowly increase once again this weekend to the upper 70s to mid-80s statewide by Sunday. Another cool front is expected to move across the region by late Sunday into next Monday, bringing the next chance for significant precipitation.

Recent medium range forecast guidance is currently suggesting a number of possible scenarios for the next one to two weeks, which translates into a low confidence forecast. The official forecast pattern calls for weak upper air troughing features along the west and east coasts of the United States during the first week of the period gradually becoming more west to east or zonal during the second week.

The 6-10 day outlook from the NOAA Climate Prediction Center (covering August 14-18) calls for above normal temperatures and below normal precipitation statewide. During the 8-14 day time frame (covering August 16-22), some moderation is forecast with mean temperatures and precipitation totals expected to return to near normal levels. Further ahead, the latest 30-day outlook for the month of August calls for increased odds of above normal temperatures across the state, with near equal odds of above-, near-, and below-normal levels of precipitation.