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| Vegetable Crop Advisory Team Alert newsletter | |||||||
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| Vol. 23, No. 7, June 4, 2008 |
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In this issue |
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| Vegetable insect update Aster leafhoppers and potato leafhoppers have been reported in the state. These are largely migratory insects, although a few aster leafhoppers may overwinter as eggs in certain areas, and move into the state each year. Aster leafhoppers have been found over the past few weeks in western Michigan vegetable fields. Diagnostic Services tested a sample collected from Decatur, Michigan and none of the leafhoppers were infected with aster yellows. At this point, growers should use treatment thresholds of 25 leafhoppers per 100 sweeps for lettuce, 35 leafhoppers per 100 sweeps for celery, and 50 leafhoppers per 100 sweeps for carrots. Potato leafhoppers have been found in potato fields in Monroe County. Numbers are still low, but these insects are often found in alfalfa fields early in the season. Potato leafhoppers damage plants by injecting a toxic saliva when feeding, resulting in collapse of conductive tissue and symptoms known as “hopperburn.” Damage occurs before symptoms occur, so growers must scout fields regularly. Crops are particularly vulnerable when nearby alfalfa fields are cut since the potato leafhoppers look for new “homes”, and can quickly infest crops such as potato and snap beans. Treatment thresholds are five adult leafhoppers per ten sweeps in potatoes. For snap beans, examine the underside of leaves. Treatment thresholds are two potato leafhoppers per foot of row for seedlings and five per foot of row for snap beans in the third trifoliate to bud stage. |
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| A few European corn borer moths have been captured in pheromone traps over the past week. An average of two to three moths per trap were caught in Macomb and Ingham counties. As yet, no moths were caught in traps in Mason or Monroe counties. Most areas of the state are at or near the beginning of the first flight of European corn borer moths. This generally occurs when heat accumulations in the area reach 450 to 500 degree days (base 50). At this time in the growing season, corn is generally the most attractive plant for European corn borer, with the largest corn preferred. In some areas, corn growth has been slowed by the cool, dry weather, and if plants are small, other crops such as potatoes, may be more attractive for egg laying. In general, sweet corn plants with less than seven leaves are not susceptible to corn borer infestation. With much higher temperatures predicted next week, insect activity is expected to increase dramatically.
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| Managing cereal rye cover crop to reduce crop injury and improve benefits Because of its ability to survive the winter, cereal rye fits easily into most vegetable rotation systems. It can be sown relatively late in the fall when most vegetable crops are harvested. After the winter season, it grows quickly in late spring when temperatures become warmer. During the rapid growth stage, large amounts of biomass are accumulated. While biomass accumulation is desired to build soil organic matter and soil quality, it is important to remember that this may cause nutrient tie up in the cover crop residue if the cover crop is not managed adequately. Also, rye produces chemicals known as allelochemicals that have been shown to injure vegetable crops, including species established from transplants if residues are not managed properly. The process known as allelopathy is well documented. In commercial field, it is usually difficult to document the allelopathic effects of rye because there are no control plots (with no cover crop) to use for comparison. However, in years with excellent rye stand, there are always complaints of poor crop germination and stand establishment. Crop injury is generally more important if rainfall is not adequate after rye residue incorporation. Crop injury from rye allelochemicals can easily be misdiagnosed as herbicide carryover, frost damage, and even diseases. Here are a few management tips that can help reduce the potential for crop injury and improve benefits from a rye cover crop. Kill rye cover crop when it is still tender Experienced growers would tell you that it is better to kill rye before it reaches your knees. Indeed the cover crop should be killed at the vegetative stage when the tissue is still tender. The ideal stage would be at jointing during the initial phase of stem elongation but before the flag leaf stage. When rye reaches boot stage, it becomes difficult to kill, the residue breaks down much slower due to high C/N ratio, and there is greater potential for nutrient, especially nitrogen, tie up. If for some reason a rye cover crop gets out of control, consider mowing it to speed up tissue break down. |
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| In most vegetable production systems, benefits of rye cover crop are optimized when it is killed at a tender (vegetative) stage, incorporated into the soil as green manure, allowed enough time for residue breakdown before planting and when rainfall/irrigation is adequate. | ||||||
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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 23EF 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 23.1EF while less than five miles away at the Kewadin station the low was 30.1EF.) 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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Regional reports Lows for the area ranged from 36°F to 61°F and highs from 63°F to 84°F. Soil temperatures are in the mid- to upper 60s. We’ve received 0.18 inches of rain for the period. We have only had 0.54 inches of rain over the past three weeks, so irrigation is being applied. Crop reports Asparagus harvest is winding down. Last weekend was the final picking for some fields and this weekend will be the final harvest for most fields. Growers are noting yields off by 30 percent or more and not all can be attributed to the April 30 freeze. Peas are in bloom. Sweet corn has responded nicely to warmer temperatures and is now 10 to 12 inches tall. Peppers and eggplants are now being planted. Tomato planting continues. Stakes are being put in tomato fields and early planted, tunneled fields are being suckered and tied. Vine crops have put on good growth, and early planted, tunneled fields are approaching first bloom. |
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2 -- Grand Rapids Area Frost damage occurred in scattered pockets on the morning of Wednesday, May 28. Overall damage to vegetable crops was light. With temperatures picking up, so is crop development. During the past week, 0.4-0.7 of an inch of rain fell in much of the region during the past week, although areas farther south in Allegan and Barry counties received very little. Crop report On the muck, onion stands are doing well overall with a few unsatisfactory stands. Celery, radish, leek, and beet plantings are growing and ready to benefit from the greater warmth in the upcoming forecast. The same is true for most upland crops. Warm-season vegetable growers are busy establishing more acres of peppers, tomatoes and cucurbits. Only light insect pest pressures have been reported. Cover crop management can have a great impact on planting success. Where rye was killed with Roundup well in advance, the zucchini are doing well. However, in a portion of the field where the rye was killed and plowed down only a few days prior to planting, most of the crop never established due to the toxic (allelopathic) effect of the decomposing rye biomass. Rye has been used as a natural weed control agent for a long time. Like most herbicides, however, it also has the capacity to injure crops under certain circumstances. |
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3 -- Oceana County Oceana County has received some rain since last week’s report. Amounts have been highly variable with the lowest amount recorded at the Asparagus Research Farm which has received .69 of an inch to a high in the southwestern part of the county in the 1.75 inch range. While temperatures have been near normal since the frost and freeze during the middle of last week, we are still behind normal in terms of heat accumulation. Crop report While the asparagus industry largely escaped the worst effects of the cold weather last week, the slow growth rate of asparagus during the cold May weather has many people worrying about whether they will have enough tonnage in June to meet marketing demand, especially in the processed market. We are fortunate that we have received some rain before the heat arrives this weekend, or the fields could just have burnt up. Asparagus beetle pops up as a problem whenever the temperature jumps into the 70s, and the first asparagus rust showed up late last week. Fortunately, the Folicur Section 18 label showed up on Monday, so growers have the tool they need to deal with the disease. The dry weather has resulted in a lot of thin carrot stands. Cover crops are dying very slowly because of the stress they have been under which has contributed to the dry soil conditions. A lot of new irrigation has gone in over the winter and spring, but many growers have delays in starting the new systems, either on the well side or on the system installation side. Globular springtails were reported in large numbers in a few fields last week, but warmer weather and insecticide applications have dropped those populations. I should have my first aster leaf hopper sample coming in today and will bring it to campus tomorrow. Growers are still holding off planting vine crops in hopes of better soil moisture and warmer soils Now that we have received some rain, I would expect planting to commence as soon as the soils are ready, but the planting of processing zucchinis and jack o’lantern pumpkins has yet to really get underway. Some sweet corn has emerged, but growth continues to be slow and anemic. There was some frost damage in a few low-lying areas. |
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4 -- Mason-Newaygo counties Temperatures have returned to more seasonal normals after the extreme cold experienced the morning of May 28. Low temperatures persisted one more day, with lows of 28°F recorded at the Ludington Enviro-weather station and 32.7°F was the low recorded at the Fremont Enviro-weather station on May 29. Two rainfall events occurred in the area during the past week with 1.01 inch at Fremont and .86 of an inch at Ludington. Unofficial rainfall amounts in the 1.25 to 1.5 inch range were reported in some areas of the counties.The precipitation was very much needed after a three-week-plus dry period. Crop reports Fields of peas for processing in Newaygo County are now in full bloom. Carrot planting in Newaygo County will continue for approximately two weeks. First plantings are now at the two and three true leaf stage. Onion stands can be evaluated now that protective cover crops have been killed. Onions are at the third leaf stage (6 inches) and stands are good. Spinach continues to do well and is at the six plus leaf stage of growth. Potato plantings on the muck soils were damaged by the freezing temperatures. Hilling in plantings helped to minimize damage by protecting growing points. An early planting of slicing cucumbers was injured by the freezing temperatures; plant stands are good in some areas of the field and lost in slightly lower areas of the field. Acreages of summer and winter squash were planted in Mason County last week after the cold weather ended. The first sweet corn plantings in Mason County are at the fourth and fifth leaf stage and all plantings were not damaged by the low temperatures. ECB trap counts this past week at the Mason County snap bean site were 0 - 0 - 0. The field is scheduled for planting on June 17. |
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5 -- Macomb, St. Clair and Lapeer counties The cool temperatures continued to prevail this week with scattered frosts on May 28 and maximum temperatures barely hitting 80°F. The frost caused significant injury to a range of crops. On the muck soils, temperatures of 20°F were reported, which may have set-back crops but is also significantly slowing cover crop growth and making barley difficult to kill in some fields. On mineral soils, growers in some areas lost potatoes, tomatoes and other warm season crops that were not protected. Lettuce, cole crops and other cool season crops did not suffer the same kinds of injury. Much needed rainfall on Friday, May 30 and Tuesday, June 3 amounted to a third to a half inch and many acres of vegetable crops now need only some heat to flourish. First alfalfa cutting is underway which might bring some potato leafhoppers and their associated injury into snap beans and potatoes. Crop report The onion crop continues to progress nicely with no evidence of pest pressure. Cover crops are under control In carrots, two or three leaves have emerged. The main challenge here is cover crop competition. Apart from earlier reported flea beetle activity, the early cabbage crop to date seems to be free of cabbage maggot injury or worm damage and one monitoring site. Holes in snap bean foliage at one site have been reported, and would likely be due to bean leaf beetle feeding. In sweet corn, European corn borer flight has started with an average trap catch of two male moths. Crop growth is slow on bare ground with phosphorus deficiency (Photo 1) visible on some plants, but not dramatic. Development of the early crop ranges from three leaves to eight leaves on plasticulture corn. Corn is seeing the benefit of plastic this season; much taller and of better color, even with frost set-back. (Photo 2). Cool-temperature induced herbicide injury was observed in several fields last week (Photo 3) in April seeded corn. The twisted shoot in roughly 5-10 percent of the seeds did not emerge and the plant died within a week. Even under plastic row covers the muskmelon and watermelon crop needs some higher temperatures to begin rapid growth. Seeding is underway for squash, pumpkin, and cucumber crops with some beginning to emerge, in some cases slowly. The tomato crop has made good growth since last week, even under these cool conditions. The cool temperature sensitive pepper crop is now being transplanted. Early leaf lettuce is now arriving at farmers markets. No aster leafhoppers have been found as of yesterday in monitoring sites.
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6 -- Monroe County Weather
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| Weather news Jeff Andresen Agricultural Meteorology Geography Summer is on the way... Last week, I mentioned the gradual change of the upper air configuration across North America to a western trough, eastern ridge pattern. As of the morning of Tuesday, June 3, that transition is under way with the development of southwesterly flow aloft and very summer-like weather conditions expected across the Great Lakes region during the next couple of days. A stationary frontal boundary stretching from the central Great Plains eastward through the Ohio Valley to the Mid-Atlantic region Tuesday will begin to move northward as a warm front Wednesday, bringing a very warm and humid air mass into Michigan for Thursday and Friday. The front will also bring a good chance for showers and thunderstorms across central and southern sections of the state Tuesday evening into Wednesday, and across northern sections of the state Wednesday night and Thursday. The front will temporarily move back south and eastward across the state late Friday and Saturday as a cool front, bringing more showers and thunderstorms. Fair and drier weather is expected Sunday, but more rainfall is possible next Tuesday as the front returns northward as a warm front once again. Rainfall totals during the next five days are expected to be highly variable, ranging from 0.25 inch in some locations to more than one inch in others. Some one to two inch totals are possible, especially across far northern sections of the state. Temperatures during the next few days will warm to above normal levels with highs Wednesday in the mid-60s to mid-70s increasing to the upper 70s to upper 80s on Thursday and Friday and lows from the mid-40s to mid-50s Wednesday morning increasing to the mid-50s to mid- or upper 60s Thursday and Friday mornings. Some 90EF high temperatures are possible in southern sections both Thursday and Friday. Humidity levels behind the warm front will also increase with dew point temperatures Thursday and Friday reaching the 60s to near 70EF in some spots, leading to uncomfortable conditions especially during afternoon and early evening hours. The medium‑range forecast guidance calls generally for the upper air pattern mentioned above with a broad upper air ridge expected across central and eastern sections of the United States. The National Weather Service 6‑10 day outlook covering June 8 through 12 calls for mean temperatures to range from near normal levels across northern sections of the state and for above normal levels across the south. Precipitation totals are forecast to range from near normal levels across extreme southeastern sections of the state to above normal levels elsewhere. The 8‑14 day outlook for June 10 through June 16 is similar, calling for near normal temperatures across northern and central sections of the state and above normal levels across the south. Precipitation totals are forecast to range from near normal levels in eastern sections of the state to above normal levels in the west. |
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