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| Vegetable Crop Advisory Team Alert newsletter | ||||
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| Vol. 22, No. 6, May 30, 2007 |
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In this issue Insect update Corn flea beetle and Stewart’s wilt Petiole sap nitrate guidelines Regional reports Weather |
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| Insect update European corn borer moths in traps The first European corn borer moths were captured in pheromone traps in southern Michigan last week. An average of five moths per trap were captured in pheromone traps in Monroe County and 51 moths per trap were captured in Ingham County. In these locations, degree-day accumulations (base 50) have exceeded the required 450 to 500 for the first moth flight. Locations farther north have not yet reached this threshold, but with the warm weather predicted over the next week we can expect moth flight to start in many locations. (Consult degree day table in this issue of the Vegetable CAT Alert or visit the the station closest to you at: www.enviroweather.msu.edu) At this point in the growing season, most sweet corn fields are too small to be attractive to (or to support development of) corn borers. Most females will be laying eggs in field corn. Aster leafhopper Aster leafhoppers have been found in celery and carrot fields in western Michigan. The first samples were submitted last week to Diagnostic Services for testing. Both samples tested negative for aster yellows. We therefore estimate the infectivity rate to be low –1 to 1.5 percent. The corresponding treatment thresholds are as follows: |
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Potato leafhoppers arrive in Southeast Michigan Potato leafhoppers have been reported from potato fields in southeast Michigan. These insects migrate into Michigan early in the season and many colonize alfalfa fields. (view photo) As the time for first cutting approaches, potato and snap bean growers should prepare to scout their fields and take action if appropriate. Large numbers of potato leafhoppers may migrate into potatoes and snap beans when alfalfa is cut. To prevent hopperburn and associated yield reduction in potatoes, treatment threshold is 25 adults per 100 sweeps for adults or 2.5 nymphs per 25 leaves. For snap beans, treatment threshold is one leafhopper per two sweeps (or 4 ft of row) during the seedling stage and one leafhopper per sweep or (or per 5 ft of row) during the trifoliate to bud stage. Many insecticides are effective against potato leafhopper. Consult Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables insecticides registered for control of potato leafhopper on potatoes and snap beans or order a print copy by calling the MSU Bulletin office at 517-353-6740. |
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| Corn flea beetle and Stewart’s wilt Stewart’s wilt symptoms have been found in a sweet corn field in southwest Michigan. Stewart’s wilt is a bacterial disease that is harbored inside of and spread by the corn flea beetle.(view photos) Michigan winters are hard on corn flea beetles, and the overwintering survival of the beetle (and the disease) depends on how severe the winter. We predicted higher than normal Stewart’s wilt infestation this year based on both winter temperatures and a high prevalence of Stewart’s wilt symptoms in field corn last fall (see Vegetable CAT Alert article from April 18, 2007). The best prevention against Stewart’s wilt in sweet corn is planting resistant varieties. If susceptible varieties are planted when the risk of Stewart’s wilt is high, they should be protected with a seed treatment of a neonicitinoid insecticide (Cruiser, Poncho, etc.). If a susceptible variety was planted without a seed treatment, foliar insecticides can be used for some protection against corn flea beetles. Growers should scout for flea beetles on a sunny day with little or no wind (flea beetles hide on cloudy days or in wind.) Treatment threshold is six beetles per 100 plants for susceptible varieties and two per plant for resistant varieties. A number of foliar insecticides are registered for control of corn flea beetle on sweet corn (Consult Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables insecticides registered for control of potato leafhopper on potatoes and snap beans. However, because the corn is rapidly growing, thus creating new unprotected foliage, and because beetles move quickly in and out of corn fields, foliar insecticides are not as effective as at plant treatments. Also, corn plants become less susceptible to Stewart’s wilt as they grow. Protection is not required after plants reach the 7-leaf stage. |
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| Petiole sap nitrate guidelines The total nitrogen or nitrate nitrogen concentration in plant leaf or petiole tissue provides an indication of the nitrogen status of the plant. Many testing labs do tissue analyses for total nitrogen and nitrate nitrogen content of dry plant tissue. Time is required for sending, drying, grinding and analysis of the plant tissue. A quicker diagnostic test is the petiole sap nitrate test. Sap is squeezed from petiole tissue, and the nitrate content is determined with a handheld nitrate meter or with nitrate test strips. Tests can be done frequently to monitor changes in the nitrate status of a crop. Guidelines are available getting an indication of the relative nitrogen status and the potential needing to apply nitrogen. The nitrate concentration in petiole tissue does gradually decline as the plant goes through various maturation stages. Some decrease in nitrate content is normal. To do the test, collect 15 to 20 petioles from the area of interest. Chop the petioles into quarter-inch pieces, mix well and squeeze the juice from a subsample. A garlic press works well for expressing the juice. Table 1 provides some general guidelines for various crops at various stages of growth. The actual adequate levels will vary with variety and growing conditions. These guidelines are a compilation of information from California, Florida and Michigan. Use the first time a petiole sap nitrate test is done on a crop as a benchmark to compare future test results. Table 1. General Petiole Sap Nitrate Guidelines. (ppm Nitrate x 0.23 = ppm Nitrate N)
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| Regional reports 1 -- Southwest Ron Goldy Weather Temperatures during the week ranged from highs of 70 to 88oF and lows from 47 to 66oF. The area received an inch or more of much needed rain. Hot, windy conditions have added to transplant stress. Crop reports Many asparagus fields are finished and growers are applying post-harvest weed control and fertilizer. Tomato, pepper and eggplant transplanting continues. Early, tunnel-grown tomatoes are at bloom and early fruit set. Watermelon and cantaloupe transplanting is underway. Cucumbers have responded well to warm temperatures and those grown under tunnels are in bloom. Yellow squash and zucchini in tunnels are also in bloom. No reports of cucumber beetles at this time. Sweet corn has responded well to increased temperatures and rainfall. Colorado potato beetle adults are active. |
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| 2 -- Grand Rapids Area Bill Steenwyk Weather During the past week, rainfall varied from 0.1 inch in West Olive to 0.9 inch at Clarksville, averaging 0.55 inch throughout the Allegan-Kent-Ottawa-Ionia district. Van Buren County stations report 1.0-1.5 inches. With evapotranspiration totaling 2.0-2.5 inches for the week, the water deficit continues. One positive outcome is that the current dry conditions keep disease pressures slight. Crop reports A major productivity challenge across many vegetable crops is broadleaf weed control. Annual grass herbicides appear to be working very well, but substantial growth of broadleaf weeds are appearing in upland and muck vegetable fields. Many are still small enough to deal with, but in some fields they have grown to the point where control options are more limited and crop yield losses will begin. Yellow nutsedge is another occasional problem. Competition from weeds can be a serious dollars and cents issue, so farmers and scouts should watch carefully, being ready with herbicides or cultivation. On organic soils, onions range in maturity from the 2-7 true leaf stage, and look good overall. The March plantings have become quite large. Some have initiated bulbing. Irrigation may be critical to maintain vigor if more rain does not arrive. Leeks are developing well, but have few options available for broadleaf weed control. Celery looks good as well. Scouts are finding aster leaf hopper, but at numbers still well below threshhold. Celery transplanting and greenhouse seeding continues at a steady pace. Red beets, radishes and leafy greens are doing well with irrigation. On upland soils, sweet corn, cabbages, squash and most others are developing well. Some cabbage shows shothole feeding from diamondback moth. I have seen Stewart’s wilt on approximately 10 percent of the plants in one sweet corn field. |
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| 3 -- Oceana County Norm Myers Weather We only had a couple of tenths of rain over the weekend and soils are getting pretty dry. High winds have also made spraying difficult over most of the last week. Crop report Asparagus is past the 60 percent mark in production. Growers are having a tough time keeping up during hot spells, with the tight labor supply. Common asparagus beetle has been a steady problem this year, and because so much of the crop now goes to processed spears and the fresh market, tolerance for beetle eggs is dropping. Eunice Boulet, the Crop Management Association manager, showed me the first aecial lesion of rust yesterday. Demand is still strong from both processors, and the fresh market and current plans are to keep picking into late June. Damping off problems are showing up in a few carrot fields. Many growers are putting on post-emergent herbicides. Planting of winter squash is underway, but we could use some rain to germinate the seed and activate the herbicides. Fresh market zucchini began to go in last week. The processing crops should go in next week. |
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| 4 -- Mason-Newaygo counties Jim Breinling Weather It appears that rainfall amounts were less in the northern growing areas of the state over the weekend. In Newaygo County, 0.49 inch was reported at Fremont compared to only 0.08 inch at Ludington in Mason County. Temperatures were generally above normal for the week with highs of 80ºF plus on three days. Growing degree days base 50 are 466 at Fremont, 376 at Ludington. Crop reports First carrot plantings are at 3-4 true leaf stage. Some fields are variable in plant vigor and exhibit some root damage. Samples were sent to MSU for diagnosis. Again this week, very few aster leafhoppers are reported. Onions are at 3 and 4 leaf stage. Yellow nutsedge is severe in some fields. Spinach plantings for processing are now at 4 to 6 true leaf stage. Most winter squash for processing was planted this past week. Transplanting of peppers got underway during the latter part of last week. Snap bean fields are planted at the Mason County European corn borer trap location. No moths in traps on May 29. |
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| 5 -- Macomb, St. Clair and Lapeer counties Hannah Stevens Weather and crop conditions We experienced two days in the 90ºF range this week, May 23 and 24, otherwise the high temperatures have ranged from 63-82o F in central Macomb with lows from 44-53oF. Rainfall totaling 0.6 inches in Central Macomb, slowed field work on May 26 and more plastic is going down. While some fields are still wet, much field work is underway on well drained or tiled fields. Soil temperatures are favoring quick emergence and establishment of seeded and transplanted crops. Crop reports Sweet corn looks good, emerging in five to six days. Lettuce, over-wintered spinach and parsley were at the farmers market last week, a record early season. (see photos) Snapbeans have emerged and in the second-third true leaf stage. Cole crops are now under pressure from the complex of insect pests: diamondback moth, flea beetles and a low level of imported cabbage worm. Tomatoes, peppers and melons continue to be set on plastic as weather allows. Support stakes are going up in tomato fields Rye cover crops are beginning to head. Miscellaneous Twenty-three sh2 and SE sweet corn varieties are being trialed in Romeo this season. The field day has been set for August 23. There will be more information to follow. |
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| 6 -- Monroe County Paul Marks Weather This last week has provided some moisture for most of our area ranging from one quarter of an inch to just over one inch, depending on which side of the road you were located. Degree days base 50 now total 529 putting us about four calendar days ahead of the long term normal for the end of May. Most growers have been able to continue with field work throughout this last week. Crop reports Sweet corn continues to make good progress with warmer air and soil temperatures. Early fields in open culture are now about a foot tall. Corn borer traps this week caught the first moths of the season and averaged six per trap. I have not seen any corn advanced enough to merit control from this early flight. Flea beetles have been very few. Early planted potatoes are in the bud stage with small tubers beginning to develop on the stolons. Latest planted fields are yet to emerge. Leafhoppers have increased this week to above the threshold of 10 hoppers per 20 sweeps, in about half of the earliest fields that I have checked. I have not seen any potato beetles. Cabbage, which was planted early, is now beginning to form heads with harvest still three weeks away. Diamondback moth pressure is still heavy with adults; larvae and pupae all in the fields. Root maggots are now beginning to show as plants have increased in size and the warm temperature shows the stress of reduced roots. Some rhizoctonia is present in many fields at a low incidence. Imported cabbage worm adult activity has been low. Pepper planting is nearly completed. Earliest fields have made very good growth. Tomatoes for early market are flowering and setting fruit where tunneled and very close to flowering in early planted open fields. All tomatoes in our area have made tremendous growth this last two weeks. Processing tomatoes are close to 75 percent planted. Cucumbers, which were tunneled, are flowering, both male and female, and beginning to tip in early planted open fields. I have not seen any disease in this crop and only a few cucumber beetles so far. |
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| Weather news Jeff Andresen Agricultural Meteorology Geography An upper air trough across the northern Great Plains on the morning of Wednesday, May 30, will very slowly move eastward towards the Great Lakes region by the end of the work week. These conditions will set the stage for a couple more days of very summer-like weather with an almost daily chance for showers and thunderstorms. However, given the lack of an organized focusing mechanism for convection, any rainfall that develops through Friday will be isolated, with most areas remaining dry. Best chances for rainfall will be during late afternoon and early evening hours. Temperatures through Friday will range from highs in the upper 70's in lakeshore areas to the upper 80's inland, with lows generally in the upper 50's to mid 60=s. As the upper air trough approaches this weekend, there will be a better chance for widespread rainfall, especially Saturday and early Sunday. Temperatures will fall back to highs in the 70's by Sunday, with lows in the 50's. Cooler, unsettled weather is expected early next week, with the possibility of showers. In the medium range time frame, forecast guidance suggests that upper air troughing will dominate regional weather conditions through the middle to latter part of next week before being replaced by a ridging pattern by next weekend. With the troughing pattern in place, the NOAA 6‑10 day outlook for June 4-8 calls for cooler than normal temperatures and for above normal precipitation totals statewide. During the 8-14 day period covering the June6 -12, the outlook calls for mean temperatures to moderate to near normal levels and for precipitation to fall back to below normal levels. New long lead outlooks NOAA long lead outlooks for the next few months call for the gradual development of cooler than normal sea surface temperatures (La Nina conditions) in the equatorial Pacific. However, any related impacts in the United States, at least for the remainder of the summer and fall seasons, are expected to be only minor. For Michigan and the Great Lakes region, the official outlooks for June and the June-August periods both call for the climatology scenario of near equal odds of below-, near-, and above-normal temperatures and precipitation. By late summer and fall, the outlooks are a bit less vague, calling for increased chances for above normal temperatures across most of the region, with no direction on precipitation. The outlooks also call for milder than normal temperatures during the upcoming winter season. |
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