| Insect update: Soybean aphids and alfalfa weevils | As of this writing (June 16), I had a report this morning of heavy soybean aphid numbers in Monroe County. According to crop scouts in the area, aphid numbers range from 75 to 100 aphids per plant on V3-V5 plants. Approximately 500 acres have been sprayed so far. Note that I personally have not seen these fields, but I have two independent reports of these numbers. Monroe County is full of buckthorn, so I assume these are local homegrown aphids. Early infestation presents a problem for the 250 threshold – on smaller plants, V1-V4, where flowering has not yet occurred, the threshold may have to be reduced to 100 aphids per plant. I don’t have data to base this on, only a gut feeling. However, please note that in the past, aphid infestations early in the season in past years were “cleaned up” by beneficial insects such as ladybugs recruiting to the field as the aphid population increases. Spraying now will kill these beneficial insects and may actually exacerbate the aphid problem later. In any case, now is the time to scout fields. If you are unsure about counting aphids, then use the speed scouting technique and data sheet presented in the May 26 Field Crop CAT Alert. If a treatment decision is made, optimize your application by using higher pressure, GPA and appropriate nozzles. After treatment, especially this early, be sure to keep scouting in case aphids rebound. Recent heavy rains may have reduced soybean aphid numbers at certain locations. We have observed that pounding rain drives small V1 plants into the ground and may dislodge aphids from the plant. However, light rain, or a heavier rain on larger plants, seems to do little to reduce aphid numbers directly because the aphids hang out on the undersides of leaves or on the tip of the plant. While rainfall itself may not normally reduce aphid numbers, adequate moisture does help plants compensate for aphid sucking. Also, if a rainy pattern persists and humidity increases for 48 to 72 hours, there are natural fungal pathogens that infect and kill aphids. The chances of a fungal outbreak are greater under hot conditions in a dense canopy, thus most of the aphid reduction due to fungus occurs later in the year in soybean – say mid-July into August. However, if you want to observe killed aphids now, check out mature alfalfa stands for fungus-infected pea aphids. The fuzzy dead pea aphids die stuck to upper leaves of the plant. In central Michigan, alfalfa weevil development appears to be delayed, and larvae are persisting in second-growth fields. Many fields are within a week or two of second cutting, especially with the recent rains. Therefore, treating these fields may not be the best option, given the size of the plants and the 7- to 21-day pre-harvest intervals of many insecticides. If possible, cut to reduce weevil population and scout regrowth (as you would after first cutting) for larvae. |
| Soybean rust fact sheets provide information for growers |
Five new fact sheets containing Asian soybean rust recommendations are now available for Michigan growers. The fact sheets can be found online by clicking on the agriculture link at: www.msue.msu.edu. They are also available at any county Michigan State University (MSU) Extension office. The fact sheets focus on scouting for soybean rust, modeling and forecasting web sites for soybean rust, an introduction to fungicides, soybean rust fungicide application strategies and fungicide application technology for soybean rust. “The most critical steps for reducing the adverse impact of soybean rust are monitoring the disease’s progress, applying the proper fungicides at the right time and providing adequate canopy penetration and leaf coverage when applying fungicides,” says Mike Staton, MSU Extension educator for Van Buren and Berrien counties. “These fact sheets contain all the information soybean growers need to meet these objectives in a concise and usable format.” The fact sheets were produced by the MSU Department of Plant Pathology, the MSU Extension Field Crops Area of Expertise Team and the MSU Integrated Pest Management (IPM) Program. |
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| Four fundamental stages of corn grain yield determination | At what point in the growing season is corn grain yield determined? Well, of course it involves the continuous interaction of genetic, climatic, soil, plant pest and nutrient factors present for a specific growing season. However, from a crop management standpoint, it is helpful to characterize the most critical stages of development in the life of a corn plant with respect to determining final grain yield. Following are four critical stages in the development of a corn plant that are fundamental to determining corn grain yield. The first of these critical stages is emergence. Corn does not have the ability to compensate for poor stands as well as other crops such as soybean. Establishing a uniform, optimum population stand is the first step in developing corn grain yield potential. Studies on the genetic evolution of corn indicate that modern hybrids tolerate field stress associated with higher plant populations better than their earlier genetic predecessors. Growers should continually evaluate the carrying capacity of their fields by putting in a few strip trials to determine the optimum plant population for each field. Keep in mind that as corn genetics continue to evolve, you will likely need to continually adjust your planting population upward to find that optimum plant population for each field. The second critical growth stage is when the plant determines the number of kernel rows and the number of potential kernels (ovules) per row. This is primarily determined during the rapid phase of corn vegetative growth, which generally occurs in early to mid-July in Michigan. The number of kernel rows per ear is heavily influenced by genetics and is generally determined by growth stage V12, which corresponds to the 12 leaf collar stage. The number of potential kernels per row is being determined at V12 and is usually completed a week to 10 days prior to silking (V17). The number of potential kernels per row is strongly influenced by field conditions. Managing corn to reduce environmental, pest, moisture and nutrient stress during this time will maximize the potential number of harvestable kernels. Follow a plan to ensure adequate nutrient levels and minimize stress from pests such as weeds and insects during this critical period to establish the potential for high yield. The third critical stage is pollination. Successful pollination is required to convert potential kernel numbers to actual developing kernels. Pollination occurs when a pollen grain is shed from the tassel, lands on an emerged silk, grows down the length of the silk and successfully fertilizes the ovule. It generally takes two to three days for all the silks on an ear to be exposed and pollinated. Pollen shed generally occurs in the late mornings and early evenings and the pollen shed period typically lasts from one to two weeks. From a management perspective, there is not a lot that can be done to ensure good pollination since it is highly dependent upon the weather. Droughty conditions can de-synchronize pollen shed and silk emergence and also can desiccate silks and pollen grains. This results in barren ears or in short ears with barren tips. Insect pests such as adult corn rootworm beetles can feed on emerging silks and reduce pollination and therefore should be scouted during silk emergence. Finally, because the tassel and all leaves are completely exposed, the plant is especially vulnerable to hail damage at this stage. The final critical growth stage for determining corn yield is the grain fill or kernel development period. The grain fill period that begins at pollination and ends at kernel black-layer formation generally takes from 60 to 70 days (855 to 1200 GDD) for Michigan conditions depending upon climate, planting date and hybrid relative maturity. The size and weight of harvested kernels are determined at this time and under adverse conditions kernel number can also be reduced. Stress on the corn plant during the grain fill period can affect final yield by reducing either of these factors. Although field and machinery conditions can still influence final harvestable yield, the corn plant photosynthetic factory has completed its work at the kernel black-layer formation stage of development. |
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| PSNT summary – N credits
| Through June 5 the MSU Soil and Plant Nutrient Lab has analyzed 268 PSNT (presidedress soil nitrate test) soil samples. Table 1 presents a summary of soil test values for 266 of these samples. Samples are presumably taken from the 0 to 12 inch depth. Note the projected nitrogen credit in the top two feet of soil is the nitrate N soil test value multiplied by 6. About 27 percent of the samples had soil test values above 25 ppm; adequate nitrogen is present to meet the needs of the corn crop. Of the samples testing above 25 ppm the percent that was indicated to have received manure is quite high compared to those having lower test values. Two samples had test values over 100 ppm, these received manure. Hence, in fields that have received manure there is a good probability that the manure will provide adequate nitrogen for the corn crop. Table 1. Summary of 266 PSNT soil samples received by MSU SPN Lab
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| Agricultural and family emergency and disaster resources |
Michigan State University Extension has been dealing with disasters for decades. Major pest outbreaks, floods, frosts, droughts, hail and other weather events wreak havoc on crops and farming operations. While these events are not necessarily a national disaster, they can be a disaster to farms and families who are affected. Extension has also been assisting families for many years on flooded basements, landscaping and lawns that have been affected by weather or pests, safety during lightning or damage from tornadoes or winter storms. The MSUE Emergency Management web site focuses on preparing for, or responding to, disasters. There are MSU materials as well as links to other credible sites. All of this information, whether for farm or family, is now available at the MSU Extension Emergency Management web site at: www.msue.msu.edu/emergency/ |