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| Vegetable Crop Advisory Team Alert newsletter | |||||||
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| Vol. 23, No. 9, June 18, 2008 |
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| In this issue Soil conditions contribute to poor plant growth Vegetable insect update Section 18 label issued for Carzol SP® use to control thrips in dry bulb onions. Regional reports Weather |
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| Soil conditions contribute to poor plant growth Growing conditions have been variable and challenging across Michigan; cool and wet, hot and dry, hot and wet, now cool with scattered showers. Plants have to be tough and resilient to grow through all these conditions. The recent heavy rains have provided the most challenging soil conditions. Soils are compacted by intense rainfall and standing water. Excess water tends to seal the soil surface, even on some sandy soils. These conditions impede drying of the soil and movement of air into the soil. The root environment is oxygen deficient and roots cannot function properly to take up water and essential nutrients. Many beneficial microorganisms also have a difficult time functioning when oxygen starved. When these conditions persist for more than two to three days, roots will become non-functional and may begin to degrade. Cultivation is essential to open the soil and allow air to move in. Renewed aeration of the soil will stimulate root growth and microbial activity that will mineralize nitrogen and other nutrients. With aeration, new root growth will occur. During flooded or saturated soil conditions 50 lbs N/a or more may be lost by leaching or denitrification. Once soils dry sufficiently, sidedress 40 lbs N/a to enhance root and plant growth. Spraying nitrogen and other nutrients on the foliage of stressed plants may help them get through the stress period. However, under stress conditions plants are less able to absorb nutrients through the leaves, so the benefit may not be as great as anticipated. Urea ammonium nitrate (28 percent nitrogen) is a good source of nitrogen for foliar application as long as the rate does not exceed three gallons per acre. Small amounts of nutrients may be able to be added in with other spray materials, but be sure to check compatibility. When excess rainfall occurs, the primary nutrient of concern is usually nitrogen. In sandy soils, significant amounts of potassium may also be leached out of the root zone so that topdress application may be beneficial for high potassium requiring crops, celery and tomatoes. Boron is also subject to leaching out of the root zone in sandy soils and muck soils. For celery, celeriac, broccoli and root crops consider spraying 0.25 lb actual boron per acre on the foliage. |
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| Vegetable insect update The severe weather during the first week of June brought more insect pests into Michigan. We continue to catch corn earworm moths in pheromone traps on campus. Last week (June 10-17), we caught 48 earworm moths in one trap and 54 in the second trap. This is very early for such high numbers of corn earworm to be present. Most sweet corn is not at risk for infestation, but any corn in silk is at risk. Furthermore, corn earworm moths lay eggs on tomatoes in fruit and the larvae (also known as tomato fruitworm) will eat into the fruit. Growers with sweet corn or tomatoes at vulnerable growth stages should apply an insecticide to prevent infestation. See bulletin E312: 2008 Insect, Disease, and Nematode Control for Commercial Vegetables for insecticides registered to control corn earworm/tomato fruitworm on these crops. For sweet corn, it is critical to make sure the silks are thoroughly covered with insecticide. Eggs are laid on the silks and newly-hatched larvae travel down the silk to enter the ear. Aster leafhoppers The storm fronts also brought in new populations of aster leafhoppers. All leafhoppers collected prior to June 4 and tested by Diagnostic Services were not infected with aster yellows. However, we received and tested three samples of leafhoppers that were collected June 9 -11 that had a fairly high infectivity rate. About eight percent of leafhoppers collected from celery fields in Hudsonville and Decatur were carrying aster yellows. Over 15 percent of leafhoppers collected from carrot fields in Oceana County were infected with aster yellows. Consequently, treatment thresholds are much lower than they were a few weeks ago. Celery fields should be treated if the number of aster leafhoppers caught in sweep net samples exceeds three to five leafhoppers per 100 sweeps. Carrot fields should be treated if the number of aster leafhoppers exceeds three to seven per 100 sweeps. Lettuce fields should be treated if the number of leafhoppers exceeds two to four leafhoppers per 100 sweeps. We have not yet received samples from other parts of the state, but to be cautious growers throughout Michigan should use these thresholds for now. European corn borer The first flight of European corn borer is well underway and growers are reporting a high percentage of sweet corn plants infested with small larvae. In general, once the tassel starts to emerge, sweet corn should be treated through harvest to prevent the larvae from infesting ears. In whorl-stage corn, larvae are often found feeding deep in the whorl. Growers or scouts can pull up the whorl leaves and see evidence of feeding. As the tassel emerges from the whorl, corn borer larvae leave the whorl and travel to the ears. To prevent this, growers should check whorl-stage corn and treat at tassel emergence if corn borers are found. Also, if 15 percent or more of whorl-stage corn is infested with corn borers, a treatment of granular insecticide may be warranted. A number of insecticides, such as Avaunt, Capture, Dipel, Lorsban and Pounce are registered for whorl-stage corn. Granules should be directed into corn whorls. First alfalfa cutting A significant event for pest control in many vegetable crops is the first alfalfa cutting. Alfalfa is a preferred host for many insect pests, including tarnished plant bug and potato leafhopper. When alfalfa is cut, these insects are forced to find new homes and may invade vegetable fields. Potato leafhopper can damage potatoes and snap beans. Tarnished plant bug is a pest of many vegetable crops, including snap beans, peppers, lettuce, celery and asparagus. Alfalfa cutting is occurring throughout Michigan. Growers with vulnerable crops near alfalfa fields should be scouting regularly for these pests. |
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| Cucumber beetles With the advent of warmer weather, striped and spotted cucumber beetles are finally making an appearance. Striped cucumber beetles overwinter as adults in leaf litter and resume activity when the weather warms. During cool periods, they are relatively inactive. So far this year, we’ve seen alternating periods of cool and warm weather, which causes a sudden influx of these insects into fields when temperatures rise. Cucumber beetles are pests of curcurbit crops. High populations of adults can severely stunt or kill young plants in the seedling or cotyledon stages. In addition, cucumber beetles transmit bacterial wilt disease. Cucumbers, melons, hubbard squash, butternut squash and processing pumpkins are susceptible to bacterial wilt. Jack-o-lantern pumpkins, watermelons, and most other squash varieties are rarely susceptible. The most effective treatment for early-season cucumber beetles is an at-planting treatment of carbofuran or a neonicitinoid, such as imidacloprid or thiamethoxam. If such a treatment has not been made, or if the protection is no longer effective, a number of foliar insecticides are registered for control of cucumber beetles. For crops vulnerable to bacterial wilt, the treatment threshold is 0.1 to 1.0 beetle per plant. For crops that are not susceptible, the treatment threshold is five beetles per plant. Seedlings require treatment when large numbers of beetles are feeding. Growers should scout fields regularly, especially field edges. Early in the season cucumber beetles may be concentrated along field edges so spot treatments can be effective. Care should be taken to protect pollinators during flowering by careful selection of insecticides, applying insecticides at night when flowers are closed and covering or moving hives.
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| Section 18 label issued for Carzol SP® use to control thrips in dry bulb onions The Environmental Protection Agency (EPA) and the Michigan Department of Agriculture (MDA) have issued a Section 18 label for the use of Carzol SP® (Gowan®) for the control of onion thrips in dry bulb onions for Michigan onion growers. The Section 18 label expires September 15. Growers should pay special attention to the plant back restrictions, the application rate, as well as the maximum number of applications when using this product. View the Michigan Section 18 label for specific guidelines and directions, or contact the MDA (www.michigan.gov/mda). To download the Section 18 label go to: http://www.michigan.gov/mda/0,1607,7-125-1569_16988_35290-127656--,00.html and complete the form. |
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Regional reports Temperatures were generally near normal for the period with lows from 49°F to 68°F and highs from 66°F to 88°F. There was 0.1 to 0.3 inches of rain across the immediate area. Moisture levels are getting low in many soils, and irrigation is becoming necessary. Crop reports Asparagus harvest is complete and growers are applying post-harvest herbicides and fertilizer. Peas are being harvested. Sweet corn is now 20 inches tall, but growth will slow with the cooler temperatures. Pepper and eggplant transplanting is complete. Staking, tying and of these crops continues. Cucumber, yellow squash and zucchini are being harvested from tunneled fields. Watermelon and cantaloupe are at early flower and runnering off the plastic. The only insect of consequence is Colorado potato beetle. |
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| 2 -- Grand Rapids Area Bill Steenwyk Weather Most areas were not plagued with much additional rain. Conditions for recovery from the stress of field flooding were favorable. However, substantial damage occurred in some fields. Some muck crops were completely destroyed. Crop report As reported last week, celery, onions, radish, lettuce and sweet corn, along with a few acres of various upland vegetables, were stressed, injured or killed on muck soils. Flooded fields are often coated with a skin of green algal growth (see photos). Some celery fields are recovering surprisingly well. The more mature onions are in the fifth leaf. Some flooded fields are experiencing heavy weed pressure. Celery transplanting is 40-50 percent complete. Some of the more newly transplanted leeks were laid sideways with part of the root system exposed by the flooding. They must be manually placed back into the soil to avoid growing in a curved, "goosenecked" manner (see photos). Upland vegetable crops are doing well enough, except where stands were reduced on low, flooded areas and eroded slopes. I have received a few reports of flooding damage on fine-textured soils as well. For the most part, however, cabbage, peppers, tomatoes and vine crops look okay. We just need some warmer weather to push faster growth and development. I am concerned about the probability of nitrogen deficiency in areas that received heavy rain. A drive around the countryside in Ottawa, Allegan and Kent counties reveals acre after acre of yellow field corn and soybeans. This is most likely an indicator of nitrogen loss from leeching and denitrification, exacerbated by cool temperatures that slow plant root growth. I believe that many growers would do well to apply another thirty to fifty pounds of nitrogen per acre. On muck, black sands and other high-organic matter soils, bacteria will mineralize additional nitrogen. However, if the crop is at a stage where nitrogen is needed now or very soon, the nitrogen may not be mineralized soon enough. The bottom line is that growers need to watch carefully for signs of nitrogen deficiency.
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3 -- Oceana County Oceana County has had a relatively dry week, so soils are draining rapidly. Fortunately we missed the downpours that Mason County received. Our county received from half an inch to two inches, but the two-inch rains were mostly in a few sections along the Mason County line. The high winds we’ve had the last couple of days have helped dry soils also. Most growers plan to be back in the fields by the end of this week. Many growers are worried by the continued cool weather and whether crops will mature in the proper marketing window. Crop report Asparagus growers have begun to shut down a few of the young, three- to four-year-old, fields. A few people will aim to shut down on Friday, June 20, but the majority of the growers are aiming for June 25. That is partly because Michigan production at the end of last week was five million pounds behind last year on that date. Common asparagus beetle continues to be only a sporadic problem, and we are having fewer than normal reports of rust. Perhaps the weather has just been too cold for it. The Phytophthora asparagi damage is abating somewhat now that soils are drying out. In carrots, it appears that we will lose less than 20 acres total to flooding. Scouts report that aster leafhopper numbers are up, which is a concern under Beth Bishop’s adjusted threshold. Fortunately, most growers have thrown an insecticide in when they resumed their weed control sprays. Scouts also report that globular springtails have returned with cooler temperatures. Except on heavy soils, zucchini and pumpkin fields planted before the heavy rain are emerging normally. How much the loss of pesticide and fertilizer will affect the crop is still uncertain. Interruptions of the planting schedules may interrupt processing schedules, especially if the weather continues to be below normal temperatures. As of yet, I haven’t found anything in my European corn borer traps. I am moving them to a grassier area to improve catch. Corn earworm and Western bean cutworm traps are also set. The sweet corn is so far behind that growers have written off what we would normally call the early market. |
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4 -- Mason-Newaygo counties Weather |
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5 -- Macomb, St. Clair and Lapeer counties |
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| 6 -- Monroe County Sudeep Mathew Weather |
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| Weather news Jeff Andresen Agricultural Meteorology Geography A new record? A large area of training thunderstorms (storms which form and move repeatedly across the same areas) brought torrential rains and widespread flooding to sections of northwest Lower Michigan last Thursday and Friday (June 12-13). More than six inches of rain fell from Mason and Manistee counties northeastward into Wexford, Lake, Osceola, and Missaukee counties. There was an observation of 11 inches in the Ludington area from roughly 9:00 PM on the Thursday through 7:00 AM on Friday. If this observation stands, it would be a new state record for precipitation in both 12 hour and 24 hour periods (the old one day record of 9.78 inches was set in Bloomingdale in 1914). Considering that the statistical 100-year, 24 hour extreme precipitation event (an event expected to occur on average only once every 100 years) for Michigan ranges from about four inches in far northern and eastern sections of the state to about seven inches in the extreme southwest, this event will serve as a new upper end benchmark for extreme precipitation. In contrast to the turbulent and quickly changing weather experienced during the past couple of weeks in Michigan and across much of the Midwest, the forecast for the next several days is relatively simple and straightforward. An upper air trough across the Great Lakes region is expected to result in a cloudy and cool weather pattern through much of the remainder of the work week. A series of weak disturbances moving counterclockwise around the trough will bring a chance for showers and a few thunderstorms Wednesday and Thursday, especially during the afternoon and early evening hours. Best chances for rainfall will be in northern and eastern sections of the state closest to the center of the trough. Daily rainfall totals will generally remain in the 0.10-0.25-inch range where rain occurs with most areas expected to remain dry. Temperatures during the next few days will remain below average but gradually moderate towards the weekend. Highs Thursday and Friday will generally ranging from the upper 50s north to the low 70s south with lows from the upper 40s north to the mid-50s south. By Saturday and Sunday, look for highs back into the 70s with lows in the 50s across most areas of the state. A cool front is expected to pass from northwest to southeast through the region Saturday, and will bring the next chance for precipitation beginning late Friday in northwestern sections of Michigan and spreading south and east by late Saturday. Some lingering showers will still be possible Sunday into early next week as well. With only limited low level moisture expected to be in place this weekend with the frontal passage, rainfall totals through next Monday are expected to remain on the light to moderate side, with 0.25-0.50-inch totals where rain falls. In the medium range forecast, the National Weather Service 6‑10 day and 8-14 day outlooks covering June 23 through June 29 and June 25-July 1, both call for precipitation totals to remain at below normal levels. Mean temperatures are forecast to remain at below normal levels during the 6-10 day period, moderating to near normal levels during the 8-14 day time frame. |
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