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| Vol. 23, No. 8, May 30, 2008 |
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In this issue |
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| Widespread frost/freeze event across Michigan on May 28 A large Canadian-origin air mass centered over the central Great Lakes region brought widespread frost and freezing temperatures to Michigan the morning of May 28. Sub-freezing minimum temperatures were recorded across the majority of the state with minimum temperatures in the morning ranging from 23ºF at Chatham and Elk Rapids to the mid- and upper 30s across southwestern and southeastern sections of Lower Michigan. The event was climatologically unusual with several new record lows for the date. In terms of a last freeze event (being hopeful here), the event was generally one to three weeks later than the normal last freezing temperatures of the season. The freeze was a radiation-type freeze event in which surface temperatures fell rapidly in response to clear skies and relatively calm winds. Landscape topography is critical in such events, as relatively colder air that pools along the ground surface tends to flows downhill like a fluid over time, leading to colder conditions in low-lying areas such as valleys and depressions and to relatively warmer temperatures on ridges and hilltops. This was apparent in minimum temperatures reported across the state; with readings differing several degrees over only short distances. (e.g. The minimum temperature at the Elk Rapids Enviro-weather station was 23.1ºF while less than five miles away at the Kewadin station the low was 30.1ºF.) |
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| As a result of the strong spatial variability of minimum temperatures, a wide variety of damage and plant cold injury have been reported across the state thus far. One interesting observation was the absence of frost in some areas, even with sub-freezing temperatures. This was due to the very dry air mass associated with the event with dew point temperatures only in the mid- and upper 20s in most cases. (The air temperature must drop to the dew point temperature for the formation of dew or frost to begin.) In retrospect, somewhat higher dewpoint temperatures that persisted across some southern sections of the state probably prevented air temperatures from falling to sub-freezing levels. (The air temperature in radiation cooling events typically falls to a minimum value at or near the dew point temperature.) In addition, seasonal growing degree accumulations and resulting phenological development rates had been lagging at least several days behind normal thus far, which may have prevented even greater damage. A plot depicting representative conditions during the event is given in Figure 1. The data were taken from the Enviro-weather automated weather station near Ludington from 8:00 AM local time on May 27 through 8:00 AM on May 28. The air temperature fell to a minimum value of 25.8EF at 5:55 AM, and temperatures were at or below freezing between 12:45 AM to 7:15 AM, for a total of 6.5 hours duration. The role of the wind in a frost event can be seen clearly in this example, as the air temperature dropped rapidly to sub-freezing levels after 11:00 PM as the wind decreased to calm. In general, wind acts to mix up the lower boundary layer of the atmosphere, slowing or preventing the formation of relatively colder air that forms just above the surface (This is why wind machines are used for frost protection.) Dew point temperature can be seen to decrease during the day and evening preceding the event, which was mainly due to large scale synoptic conditions (drier air moving into the state from the north). In contrast, the decreases late in the evening and the following morning are due more to the formation of dew and subsequently frost, as water vapor leaves the air and is deposited on the surface as water or ice. The reverse of this can be seen following sunrise on May 28, as sun shining on the surface leads to re-evaporation of the frost.
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| My maple tree is dropping leaves, what’s wrong? Nothing is wrong. Early June is when maple petiole borer larvae finish feeding in the petioles of maple leaves, causing the blackened, restricted petiole (leaf stems) to break and the leaf to fall. The stems usually break at a darkened area near the leaf blade. Usually infestations are limited to sugar maples and only about 25 to 30 percent or less of the leaves fall to the ground. While spectacular, the leaf drop has little effect on tree health. Sometimes spring storms also cause some maple leaves to drop. The best way to tell why the leaf dropped is to look at where the leaves came from. If you can still see a small petiole stub attached to the tree, it was most likely due to maple petiole borer. However, if the petiole broke cleanly at the base where it is attached to the tree, it was probably due to wind damage. |
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| Worms are eating my tree! By “worms” you probably mean caterpillars. Don’t get too excited by all the holes in your tree leaves, because caterpillar feeding damage does not affect tree health until more than 30 percent of the tree canopy is removed, and 30 percent canopy loss means that one-third of every leaf has been eaten, or one-third of all the leaves are gone. That level of feeding injury is rare and usually only happens with occasional outbreaks of gypsy moth, eastern tent caterpillar, forest tent caterpillar, fall webworms, orange-striped oakworm, mimosa webworm and a few others. Most of the feeding damage that I have seen on shade trees this week has been caused by spring and fall cankerworms. Cankerworms are caterpillars with only two or three pairs of fleshy prolegs instead of the standard five pairs of prolegs that most caterpillars have. This causes them to “inch” or “loop” when the walk, and is why many people call them inchworms or loopers. Cankerworms rarely cause enough feeding damage to hurt shade trees, and the same is true for a large group of caterpillar species that are often referred to as “spring defoliators.” Enjoy the inchworms and don’t worry about your tree. |
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| Maple trees show high seed numbers Many maple trees across the area have a heavy population of maple samaras (i.e. helicopters, whirlers, twisters, etc.). Over the past week, these seeds have rained down on lawns, decks, roofs and gutters in many locations. Once they drop from the tree the canopy looks quite sparse. When trees put a great amount of effort into seed production leaf production took a back seat thus the tree looks sparser than normal. However, with adequate moisture and normal summer temperatures, most people will not notice this by late June as the trees will continue normal leaf development. The main reason for the heavy seed crop in 2008 goes back to stressed growing conditions in 2007, which helped produce above average flower bud numbers. Also, no early freezes were observed to reduce flower numbers and good weather when flowers were out this spring contributed to a higher than normal percentages of flowers pollinated and forming seeds. This type of issue is often present in commercial fruit tree orchards and is termed “alternate bearing” with some years a light crop of fruit and others being a heavy crop year. Get ready to rake, sweep and pull maple seedlings over the next few weeks. |
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Frost-covered plants caught on video |
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| Volcano mulch kills tree The volcano mulch challenge ends this week with a submission from reader Brien Worrell. He could not resist sending us this photo of a poor tree buried by a 10 foot pile of mulch spotted in Novi, Michigan. Actually, the tree was placed in a pile of mulch by the local staff of Novi Middle school as a joke. This wraps up our volcano mulch challenge: look for a new topic in next week’s issue
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| Crabgrass explosion in the future? Every now and then I like to take out the turf crystal ball to see what may be lurking in the future. This spring the weather may have created the perfect storm for a crabgrass outbreak this summer. Temperatures have been cool with soil temperatures throughout much of May hovering between 50ºF and 60ºF at zero to two inches depth. Any significant rainfall has been lacking, which likely further delayed crabgrass germination. Eighty to 90 percent of crabgrass germination occurs when adequate moisture is present and soil temperatures are between 60ºF and 70ºF at zero to two inches depth. Neither of these requirements for crabgrass germination has been consistently met during May. Instead of the spring being the time when the turfgrass recovered from any previous injuries and filled in the thin spots with aggressive growth, this year the turf has basically stood still and in some cases has probably even thinned due to the lack of rain. When there are thin spots in the turf, there is an opportunity for weeds to encroach. There’s a nice rain system developing across Michigan today, and if the rain actually hits the ground this time and warm temperatures follow, don’t be surprised to see crabgrass emerge. Preemergence application timing for crabgrass is usually between April 15 and May 15. Most lawn care companies will err on the early side because of the reliable medium and long-residual products available. Long residual preemergence products (Dimension and Barricade) provide eight to 10 weeks of control and should be fine if crabgrass germination tails off by mid-June. Timing is somewhat more critical for medium residual products (Team Pro and Pendulum) that typically last six to eight weeks. Even professional applications and homeowners that properly timed their preemergence applications based on soil temperatures may have breaks in control this year. Although trying to accurately predict weed germination is probably as difficult as predicting long range weather forecasts, don’t be surprised if 2008 is one of those banner crabgrass years. See MSU Extension bulletin E0002 “Crabgrass Control in Home Lawns” for specific management and herbicide recommendations. The web link for the bulletin is www.turf.msu.edu/docs/E0002TURF.pdf. |
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Freezing temperatures
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| Gypsy moth spray window update Growers should note that the Dimilin spray window open date for the Upper Peninsula counties of Zone 5 has been set as Thursday, June 5. Statewide, the continued cool weather is expected to result in delayed end dates for all zones. Spruce, fir and Douglas-fir nursery stock being shipped to destinations outside the gypsy moth regulated area requires a new treatment once the spray window is open. The reason is that gypsy moth hatch is imminent and nursery stock is at risk for infestation by larvae “ballooning” on their silk. Those who ship nursery stock outside the regulated area should consult with MDA staff for obtaining certification to meet the USDA Gypsy Moth Quarantine. The following chart shows actual and projected open/close dates for application of the two groups of pesticides used for regulatory treatment of gypsy moth in nursery stock and Christmas trees. We are listing the projected dates as guidelines to help you plan your pest management program. Since gypsy moth development will vary by location, you will need to monitor development around your farm. Weather conditions will affect caterpillar development and may effect end date of the spray windows. Growers should watch the Landscape Alert for additional announcements.
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Skeeters are out and they’re hungry
If you or your children get a rash or other bad reaction from an insect repellent, stop using the repellent, wash the repellent off with mild soap and water, and call a local poison control center for further guidance. If you go to a doctor because of the repellent, take the repellent with you to show the doctor. For more on the active ingredients in insect repellents see the EPA web site at: http://www.epa.gov/pesticides/health/mosquitoes/ai_insectrp.htm |
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| European paper wasps Our cool weather has likely slowed the work of the European paper wasp too. Polistes dominulus was first discovered in the United States in Cambridge, Massachusetts in 1981. It was first found in Michigan in 1994. P. dominulus is the most common paper wasp in Western Europe. The European paper wasp prefers to nest in cavities, but will build on a vertical surface as long it is protected by some type of overhang. This wasp seems to attack people with much less provocation than our native species of paper wasps. Paper wasps can be controlled by spraying the nests with one of the many long-range wasp and hornet sprays, and now is the time to do it because the nests are small and the wasps are not as aggressive as they will be later in the summer. I recently completed a survey of our top ten insects that invade Michigan homes for Dr. Whitney Cranshaw with Colorado State University. I mentioned the European paper wasp. Here is what Whitney had to say about them in Colorado. “I noticed your comment on the European paper wasp. That insect has been huge out here in recent years. It took over in a phenomenally short period of time. In addition to the stinging/nuisance issues (complicated by its very close superficial similarity to the western yellowjacket), the insect has decimated backyard Lepidoptera. It has had such an impact that I no longer discuss cabbageworms or hornworms in Master Gardener programs – they are too rare. Also, I usually drop butterfly gardening as a topic, as they eat the butterfly larvae.” Whitney put together a very nice fact sheet on them. See it at: http://www.ext.colostate.edu/pubs/insect/05611.html
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| Don’t eat frost-damaged rhubarb Editor’s note: With the recent frost event, this article from the University of Illinois Extension is timely. This article was originally published on April 14, 2007. "Rhubarb should not be harvested when the leaves are wilted and limp after a hard freeze," warns Elizabeth Wahle, University of Illinois Extension horticulture specialist. "Not only do the leafstalks acquire a poor flavor and texture, but the leaves and eventually the stem may become toxic." Wahle says rhubarb leaves should never be eaten, and petioles (the part you eat) should be harvested only from plants that have suffered no frost damage. Rhubarb leaves contain oxalic acid, a toxic substance that may move into the petioles after frost damage. When consumed, the oxalic acid can crystallize in the kidneys and cause permanent damage to the organs. All petioles that have been exposed to freezing temperatures should be removed and discarded. The re-growth is safe to eat. As normal harvest begins, always leave at least one-third of the petioles un-harvested to sustain the plant. Asparagus harvest has been interrupted by the recent cold weather as well. Unlike rhubarb, asparagus does not become toxic after exposure to freezing temperatures. In fact, rhubarb is one of the few crops that have this characteristic. "As asparagus starts to re-grow, expect to see some frost damage on the tips of the first spears," says Wahle. "The spears are still edible but most likely will have a softer texture which results in an even shorter shelf life. "Harvest can continue until spears become thinner, appearing somewhat spindly. This thinning is a signal from the root system to stop harvesting and allow the ferns to grow. |
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| Agricultural labor statistics for spring 2008 This April, the hourly wage for agricultural workers in the United States stood at $10.60, up 40 cents from a year ago. Field workers received $9.65, up 30 cents from a year ago. Livestock workers made $10.32, up 63 cents from a year ago. This wage rate includes supervisors and other workers, such as bookkeepers and pilots. Wage rates do not include the value of benefits. Total hired workers are estimated at 919,000 individuals, down by 7 percent compared to last year. The number of hours worked is up only slightly at 41 percent Michigan, Minnesota and Wisconsin make up the Lake region. For the three states, the number of hours worked stood at 39.0 hours during this April. The total number of workers, excluding agricultural service workers, is estimated at 52,000 individuals, compared to 56,000 during last April. The average wage rate for all hired workers was $11.25 per hour, up 17 cents from a year ago. Only, Hawaii with $13.28, the Cornbelt I region (Illinois, Indiana, and Ohio) with $11.43, and the Cornbelt II region (Iowa, Missouri) region with $11.88 paid higher wages. Field workers in the Lake region earned $10.57 per hour, up 46 cents. Livestock workers earned $10.78 per hour, up 79 cents. In addition to analyzing wage rates by type of worker, NASS provides wage data by type of farm with slightly different results. These data combine field workers and livestock workers, but exclude other typically higher paid groups. The average hourly wage rates in 48 states, excluding Alaska and Hawaii, during this April were $9.87 overall, $9.84 for field crop farms, $9.66 for other crop farms, and $10.20 for livestock and poultry farms. Last year those rates were $9.41, $9.36, $9.39, and $9.47, respectively, indicating notable wage increases. The hourly wage rates in the Lake region were $10.70 for all farms, $10.08 for other crops, and $10.78 for livestock and poultry farms. There was insufficient data to calculate the wages for field crop farms. Last year the wages in the Lake region were $10.05 for all farms, $10.82 for field crop farms, $9.72 for other crop farms, and $10.13 for livestock and poultry farms. Overall, the Lake region has seen considerable wage increases. To read Dr. Bitsch’s complete newsletter go to her website at http://www.msu.edu/user/bitsch. Under “News” click on “U.S. Agricultural Labor Statistics for Spring 2008” or click on “Agricultural Labor Issues in Michigan” for a list of available newsletters. For more details, the NASS release is available at http://www.usda.gov/nass/. Select “Publications” and then “Reports Calendar” or “Publications” and then “Search,” by “Title” or “Subject” (Farm Labor). |
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| Weather news A strengthening area of low pressure over the central Great Plains on the morning of Friday, May 30, will make its way through the Great Lakes region during the next 24-36 hours, leading to several rounds of showers and thunderstorms across Michigan. Some storms may become severe across southern sections of the state Friday afternoon and evening, especially if clouds thin enough Friday afternoon to allow surface heating. Scattered showers may linger in spots early Saturday, followed by clearing late in the day. Significant rainfall is expected over much of Michigan through Saturday morning with 0.50-1.0 inch totals expected across much of the state. Following the passage of the low pressure area Saturday, fair weather with seasonable temperatures are expected in most areas of the state Sunday and Monday. Temperatures during the next several days will remain at more seasonable levels with highs ranging from the low or mid-60s north to the upper 70s south and lows from the upper 40s north to the upper 50s south. A second area of low pressure is expected to bring another chance for rainfall by late Tuesday or Wednesday of next week. In the medium‑range forecast period, a broad upper air ridge across central sections of the United States with troughs on both west and east coasts is expected to gradually give way to a trough across the western United States with southwesterly flow across the Midwest. The National Weather Service 6‑10 day outlook covering June 4 through June 8 calls for an active weather pattern with temperatures ranging from above normal levels in extreme southeastern sections of the state to near normal elsewhere and for above normal precipitation totals statewide. The 8‑14 day outlook for June 6 through June 12 reflects the upper air transition noted above and calls for temperatures to increase to above normal levels statewide with precipitation ranging from near normal in the Lower Peninsula to above normal levels in the Upper Peninsula. New NOAA long lead outlooks In our discussion of the new long lead outlooks, it is worth taking note of the recent series of tornadoes and severe weather across the Midwest and other sections of the country. As of the May 26, NOAA=s Storm Prediction Center had tallied 1,191 tornadoes across the United States so far this year, which is more than 500 more than normal for the date and approaching the normal annual total of 1,270. One of the tornadoes last weekend in Iowa was an extremely violent enhanced Fujita scale level 5 tornado (the most severe type) with winds in excess of 200 mph and a path more than one mile wide. If this unusual frequency and pace of accumulation were to continue throughout the entire 2008 severe weather season into the fall (very unlikely), this year=s total would break the all time record of 1,819 tornadoes set in 2004. Causes of the unusually active season are not completely clear at this point. One important issue was the abnormally early start of the severe weather season in January (including a very rare tornado outbreak in Illinois and Wisconsin on January 7) across sections of the south and Midwest. Climatologically, a very likely link was/is the presence of a La Niña event in the equatorial Pacific, which in turn was linked with an abnormally active jet stream storm track from the southwestern United States into the Midwest (and to record heavy seasonal snowfall totals in portions of the Upper Midwest). Tornado outbreaks in the central United States are typically associated with an upper air trough in the western United States and a ridge across the east, a strong southwesterly jet stream, and to a warm and humid air mass (Gulf of Mexico origin) on the surface. These key ingredients have unfortunately been present together much more frequently than usual so far this year. There is some suggestion in the long lead outlooks that the pattern so conducive to severe weather may gradually come to an end at some point during the next several weeks. La Niña conditions in the Pacific are expected to gradually diminish by mid- or late summer, which is reflected in the new NOAA outlooks. For June, the outlook is linked to recent weather patterns and to medium-range forecast guidance in suggesting cooler and wetter than normal weather for nearly all of Michigan and other adjacent sections of the Great Lakes region. For the 3-month June through August period, the outlook for mean temperatures and precipitation totals remains in the climatology scenario of near equal odds of below-, near- and above normal levels. The outlook generally calls for Michigan to remain between areas of cooler and wetter than normal weather across southern sections of the country and warmer and drier than normal to our west (see http://ipm.msu.edu/cat08fruit/pdf/5-27weather.pdf). |
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