August 8, 2007

In this issue

§ European corn borer and corn earworm update

§ Aster leafhoppers and aster yellows

§ Phytophthora and irrigation water

§ Development of drought conditions in Michigan

§ Regional reports

§ Weather

European corn borer and corn earworm update

Beth Bishop
Entomology

The second flight of European corn borer moths has begun throughout most of Michigan, and the number of moths caught in pheromone traps last week increased (see chart). Female corn borer moths will be laying eggs on attractive crops for several weeks. Sweet corn at tassel and beyond, and peppers and snap beans with fruit, should be treated to avoid European corn borer damage.

We also captured small numbers of corn earworm moths in pheromone traps last week (from zero to seven corn earworm moths per trap; see http://www.pestwatch.psu.edu/sweetcorn/tool/tool.html. Corn earworm is a migratory pest and recent weather conditions have been favorable for insect migration into Michigan from southern areas. Right now, corn earworm moth numbers are low, and insecticides applied to prevent European corn borer damage will also be effective against corn earworm if care is taken to ensure thorough coverage of the silks. Corn earworm females lay their eggs on corn silk and green silk is highly attractive. See Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables for insecticide options for control of European corn borer and corn earworm. You can find this bulletin online at http://web4.msue.msu.edu/veginfo/E312.

Aster leafhoppers and aster yellows

Beth Bishop
Entomology

Aster yellows symptoms are showing up in carrot fields in northwest Michigan. Leafhoppers recently collected from carrot fields in Oceana and Mason counties have been tested and have an infectivity rate of 1.2 percent to 3.7 percent. This infectivity rate (proportion of leafhoppers carrying the aster yellows disease) translates into a treatment threshold of 15 to 25 leafhoppers per 100 sweeps.

Phytophthora and irrigation water

Mary Hausbeck
Plant Pathology

Many Michigan vegetable crops such as squash, cucumber, eggplant, pepper, beans, watermelon, melon and tomato are susceptible to Phytophthora capsici. This pathogen causes disease on plant crowns, roots and fruit. Phytophthora can move in surface water, which is often relied upon for irrigation in Michigan. Research conducted by Michigan State University from 2002 to 2005 identified Phytophthora in a river, ponds and ditches in several Michigan counties.

In standing water, Phytophthora produces swimming spores which can be spread with moving water. Swimming spores can survive and cause infection for 8 to 10 hours. Therefore, when surface water is contaminated with Phytophthora, the pathogen can be spread to a field through irrigation.

Pear and cucumber baits, along with temperature sensors, were placed in plastic milk crates kept afloat by attaching polyethylene foam pool noodles to the lid. Floating the baits was important because swimming spores always move to the surface of the water.

The crates were then suspended in the water for three to seven days before baits were removed for examination.

Pieces of infected pear and cucumber baits were placed onto media plates which promote Phytophthora growth. After three days, the plates were examined for Phytophthora. Some of the Phytophthora collected from surface water was found to be resistant to the fungicide mefenoxam (Ridomil).

Phytophthora was detected in several surface water sources in multiple years, even when

non-host crops were planted nearby. Most of the infestations occurred when the water temperature was between 59°F and 77°F.

It is important to take precautions when irrigating crops. If irrigation is necessary, do not use surface water sources. Drip irrigation from well water or ponds fed by well water is recommended to reduce the risk of Phytophthora spread on susceptible vegetable crops. Irrigate conservatively, and try to limit irrigation close to harvest.

Development of drought conditions in Michigan

Jeff Andresen
Agricultural Meteorology
Geography

Scattered showers and thunderstorms brought some much needed rainfall to a few locations across Michigan during late July, but the rainfall was localized and drought conditions persist in many areas of the state. For the growing season thus far (beginning April 1), precipitation deficits have grown in many areas to the 3-5 plus inch range, although these figures are somewhat misleading since the majority of the drier than normal conditions have taken place since early June when crop water needs are relatively greater. Normal precipitation for this time frame is on the order of 11.5-13.0 inches. Precipitation totals across the state as estimated by National Weather Service radar are given in Figure 1 and illustrate the areas of greatest deficits including areas of southwestern and eastern Lower Michigan as well as the western Upper Peninsula where totals remained less than 25 percent of normal. In some areas of the state, July 2007 will go into the books as one of the five driest on record. Meteorologically, the dryness has been associated with a persistent upper air ridging feature anchored across western North America that has reduced the amount of low-level moisture flow (the “raw material” of precipitation) into the Great Lakes Region. As of the beginning of August, drought conditions were reported across sections of the Upper Midwest in Minnesota, Wisconsin and Michigan southward through the Ohio Valley into the southeastern United States. These patterns are illustrated in the most recent version of the Palmer Drought Severity Index (Figure 2), which depicts areas of long term precipitation surpluses and deficits. Note that some of the drought conditions in Michigan have now slipped into “Severe” and “Extreme”categories.

Figure 1. Percent of normal precipitation between June 2 and July 31, 2007. Precipitation values are based on National Weather Service Stage III precipitation estimates (courtesy of the National Oceanic and Atmospheric Administration).

As an example of the gradual depletion of soil moisture, volumetric soil moisture at a 10-inch depth under grass taken from the MAWN automated weather station at East Lansing is plotted versus time and with daily precipitation totals in Figure 3. The soil at the site is capac loam. Soil moisture can be seen to decrease from a value of approximately 0.25 inches³/inches³ following the rainfall of early June to about 0.10 inches³/inches³, then peak once again in late June following a 1.3 inches rainfall event before falling to its end of July level of approximately 0.08 inches³/inches³, which is near the soil=s wilting point.

Figure 2. Palmer Drought Severity Index values across the United States as of July 28. (figure courtesy of NOAA Climate Prediction Center).

Figure 3. Volumetric soil moisture (inches³/inches³) at a 10-inch depth under grass and daily precipitation totals (inches) versus date at East Lansing, Michigan, June 1 through July 31 (data courtesy of Michigan Automated Weather Network and the Enviro-weather program).

Regional Reports

1 - SW Michigan Research and Extension Center

Ron Goldy

Weather

Temperatures during the week were generally above average (82^oF) with highs of 83^o to 90^oF and lows from 54^o to 72^oF. The area received from 2.0 to 7.0 plus inches of rain. Rain on August 6 and August 7 was heavy with close to 1.0 inch an hour for two hours. Erosion is evident in many fields. Some areas are still under water. Significant yield losses are expected from some fields. Field conditions and temperatures will make pesticide application difficult.

Crop reports

Harvest of most crops has been accelerated due to high temperatures and has been made more difficult due to wet soil conditions. High temperatures have also contributed to blossom end rot in peppers and tomatoes. Vine crop growth has responded well to increased temperatures and moisture.

Insect and diseases remain low in most crops; however, this may change given the current weather conditions.

Miscellaneous

There will be a high-tunnel meeting at SWMREC on August 15 at 6:00 PM. Researchers involved with high tunnels will be present to discuss the current research projects on cherries, raspberries and tomatoes. Call Ron Goldy at 269-208-1651 for details and directions.

3 – Oceana County

Norm Myers

Weather

The weather has been extremely dry this past month. Irrigation is of course going flat out, but can’t keep up with demand. Where irrigation is not present, it is so dry that trees are dropping leaves and conifer Christmas trees that are four to five years old are dying from drought.

Crop reports

In asparagus, I am seeing more and more symptoms of drought dormancy on the very sandy soils. As with any stress situation, Phytophthora symptoms are very common in many fields. We have enough dew each night to keep up foliar disease pressure. Insect pressure is about normal for this time of year.

In carrots, keeping up with irrigation is difficult for this crop. Pivot corners are suffering greatly from the drought. All of the irrigation has kept disease pressure high in this crop.

Most of our pickles are not irrigated, and I keep stopping to look for downy mildew and finding drought damage instead.

Zucchini yields have been good, with no viruses reported yet. Powdery mildew is now common in many fields.

In winter squash and pumpkins, I am seeing some abortion of second sets of fruit as the drought worsens. The first set is very advanced for this time of year. Powdery mildew is also common in this crop.

Sweet corn/snap beans: I am now catching a few more corn earworm moths and a couple of corn borer moths, but that is more than I have been catching.

4 – Mason-Newaygo counties

Jim Breinling

Weather

The lack of rainfall continues in the area. In Mason County, 0.09 inch was reported during the last week. At this point, crops on irrigated acres and heavier soil types are still doing well. The situation is very different in Newaygo County where only 0.03 inch has been reported at the Fremont MAWN station in the last 24 days. The last significant amount of precipitation was 0.54 inch on July 14. Temperatures remain fairly consistent at or slightly above normal.

Crop reports

Carrot harvest will begin this week. Aster leafhopper numbers continue to be variable from field to field. Samples will be taken for diagnosis from some fields of processing carrots where lack of vigor and top growth persists.

Overall, vine crops at this time continue to do fairly well. Pumpkins and hubbard squash on heavier soils in Mason County are sizing well with some pumpkins nearing 15 inches diameter and hubbard squash at 10 to 12 inches in diameter. In Newaygo County, on lighter soils the effects of irrigation are very evident in butternut squash fields where water does not reach corners or edges of fields. Some squash bugs and cucumber beetles were seen in a planting of acorn squash.

Snap bean fields look good at this time. However, the need for rain will soon become critical on non-irrigated plantings. Yield to date on harvested acres has been reported at average to above average. European corn borer counts in traps at the Mason County site were of 1-1-33 this past week.

The corn earworm trap counts on August 7 at the sweet corn site in Mason County were zero for both the small and large traps.

5 – Macomb, Lapeer, St. Clair counties

Hannah Stevens

Weather and crop conditions

The region finally received sustained rainfall yesterday, amounting to from 0.75 to over 2.0 inches according to on-farm reports. It followed a week with high temperatures ranging from 69ºF to 99ºF accompanied by windy days and actual or looming water shortages. It was a relief.

Crop reports

Sweet corn is developing rapidly, and I expect the rainfall will bring on some fields more quickly than they can be harvested. Some varieties are showing sunburn on the husks. (view photo) European corn borer trap catches are on the rise once again, probably signaling the flight of the second generation. No corn earworms have appeared in the traps. Bird, raccoon and deer damage continues to be reported.

Vine crops: We have confirmed a report of downy mildew on cucumbers in a garden in New Baltimore. This is unfortunate for vine crop producers as spray intervals may need to be tightened up.

Carrot harvest began this week. I understand that roots are exceptionally long but may be slender due to lack of water. Onions are sizing slowly, and growers expect harvest to begin later than usual.

6 - Monroe County

Paul Marks

Weather

Rain on Sunday, August 5 and again on Tuesday provided most of our area with between 1.0 and 3.0 inches of additional moisture. Continued high humidity and high temperatures, both day and night, are creating an ideal environment for fungal pathogens on all vegetable crops. Irrigation systems are all shut down.

Crop reports

Tomatoes for fresh market are now ripening at a much faster pace. Processing tomatoes, which have had Ethrel applications, are maturing at an increased rate since the rains. Both crops are infested with bacterial diseases, and now early blight and anthracnose has begun to appear.

Sweet corn harvest is in full swing with a very nice crop being harvested and packed. There has been very little damage from insects or disease in this crop this year. Bird damage has been a problem for several growers during the dry conditions. Several growers have made some very late plantings this season, which may mature in very late September. Corn borer and corn earworm traps had very few moths again this week even though we are now above 1950 degree days base 50 level.

Melons are being harvested as fast as possible. Maturation appears to be ahead of scheduled harvest, and this crop may end early this year. Downy mildew can be found in this crop.

Pumpkins and hard squash are developing fruits now. Powdery mildew has appeared everywhere this last week. Corn rootworm adults are increasing in this crop. So far, I have not seen any fruit damage from beetle feeding. I have seen as many as ten per flower in several fields.

Cucumbers are producing very well, but are infested with downy mildew at various levels, even in fields where growers report the five day spray schedules. Even with low incidence of the disease, many fields are producing a nice crop.

Pepper harvest is in full swing with very nice size and quality being harvested. Color seems to be developing very early this year in all peppers. Insect problems in this crop are absent so far this season.

Weather news

Jeff Andresen
Agricultural Meteorology
Geography

Showers and thunderstorms brought more rainfall to many areas across southern Michigan during the last few days, while northern sections of the state were largely missed. Overall, drought conditions continue to be a major problem in many areas of the state. Forecast guidance for the next few days suggests another chance for rain Thursday, August 9 and again late Sunday into Monday with more dry weather in between. On Wednesday, a weak frontal boundary stretched from an area of low pressure over eastern Ontario westward through the Great Lakes and Great Plains regions. A second area of low pressure is expected to ride eastward along this front late Wednesday and Thursday, bringing another round of showers and thunderstorms to Michigan before it moves south of the state late Thursday evening.

At this point, best chances for precipitation will be across central and southern sections of the Lower Peninsula, with decreasing chances north of this area. Rainfall totals will generally be in the 0.25-0.50 inch category, with some isolated 1.0 inch amounts possible, especially along the Indiana/Ohio border. High pressure will move in behind the low pressure, leading to fair and dry weather statewide on Friday and Saturday. Temperatures during the next several days will remain at above normal levels, with highs ranging from the upper 70's far north to near 90ºF south and lows from the upper 50's north to mid and upper 60's south through Saturday. The next chance for rainfall after Thursday will likely come late Sunday or Monday of next week in association with a frontal system approaching from the northwest. At this point, any precipitation with the front is expected to be scattered in nature, with many areas remaining dry.

In the medium range time frame, both 6-10 day and 8-14 day outlooks, covering August 13-17 and August 15-21, call for a continuation of above normal temperatures state- and region-wide. Precipitation totals during the 6-10 day time frame are forecast to range from below normal levels in southern Lower Michigan to above normal over the Upper Peninsula. Precipitation totals are expected to remain at normal to below normal levels statewide during the 8-14 day period.