County Farm Centre May 2014 Your May issue:

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1 : Your May issue: Click on title to go directly to that article Monitoring The effects Black of cool Cutworm variable moth arrival temperatures with Pheromone on corn traps Early start to post-emergence nitrogen application is best! Don t be fooled by clean-looking fields! Alfalfa Weevil activity 2014 planting dates for corn and soybeans May 2014 Effects of cool or variable temperatures on corn Seed that is placed in a cool, moist environment will soak up (imbibe) moisture, even though it may not be warm enough to trigger germination. Some damage to cell membranes inevitably occurs during this process. Research has also shown that cell mitochondria may be affected with cold water imbibition in corn seed. Rapid water uptake under cool conditions, can reduce the protective nature of the seed coat, damage some embryonic cells, and allow entry of seed-rotting pathogens. However, if warm soils allow the seed to germinate rapidly and the seedling continues rapid growth, the developing corn seedling can often repair the early damage and escape problems from these pathogens. Conversely, if growth is slowed from cool conditions, then the pathogens have the advantage. A similar situation exists for crops that successfully emerge and begin growth, only to be slowed by a later period of cool and/or cloudy weather. Root and stem pathogens find this to be ideal conditions for infection. Actually, any type of stress that slows growth or diverts resources away from growth, can cause increased disease infection. Another common effect associated with chilling injury of corn seed and seedlings is distorted growth. Corn seed that imbibes cold water will often exhibit varieties of distorted growth. The most dramatic effect is to have the coleoptile shoot curl back on itself or just grow the wrong direction. We also often see the radicle or coleoptile fail to emerge, or emerge and then stop growing. In some cases, the coleoptile sheath will rupture prematurely, as if it hit a compaction layer. Be aware that it is not only cold, moist soils that can cause early corn growth problems. Research has also shown that wide swings in dayto-night temperatures can also cause distorted growth. Herbicides can injure corn seed or seedlings that are in cool, moist soils. A seed that germinates and grows rapidly can avoid a selective herbicide s harmful effects by metabolizing and breaking down the product. However, if emergence and growth is slowed by cool soil or air temperatures, the seed/seedling may be unable to effectively metabolize the herbicide, which then becomes injurious. Following corn emergence, a period of rapid growth allows equally rapid uptake of the selective herbicide. Then if a period of slowed growth (from cool or cloudy weather) intervenes, this can result in increased crop injury. We have witnessed isolated instances of this type of injury for several seasons. Herbicides, which normally are quite safe to crops, suddenly can cause crop injury symptoms GROWMARK, Inc. The information provided in this letter is general in nature and specific information should be obtained by review of product labels and consultation with the manufacturer. Such information can be materially affected by inaccurate data or assumptions, varying circumstances, known or unknown risks and uncertainties, and many other factors which are beyond the control of GROWMARK, Inc. and results can vary widely. The user will not rely on any information provided herein and GROWMARK, Inc. will not be liable for any reliance on that information. The FS and FS Agronomy logos are trademarks of GROWMARK, Inc. and all trademarks contained herein are the intellectual property of their respective owners.

2 What can we expect to see with corn affected by chilling injury? Elevated amounts of seed rotting or seedling diseases Increases in herbicide injury to the seed and seedling Distorted growth such as the radicle or shoot may fail to successfully emerge from the seed, the radicle or shoot may emerge but then stop growing, the shoot (coleoptile) may experience distorted growth, curling back on itself or growing the wrong direction, the shoot prematurely ruptures, causing the plant to leaf out underground. In summary, the risk associated with planting into cool or cool/wet soils is not only from reduced germination, although that is significant. There is additional risk that early season variable growing conditions may result in increased disease infection, distorted seedling growth, or increased herbicide injury. Although the calendar would not agree, current weather conditions have been like those several weeks earlier in a normal season. Distorted corn growth caused by variable soil temperature One final concern is that soils, right now, have a significant temperature variation with depth and field location. Slight variations in soil temperature can have large effects on the evenness of crop emergence. The best crop stands are created when soil temperatures are consistently at, or above, the minimum for germination and growth, and with a positive 10-day forecast. Early start to post-emergence nitrogen application is best Post-applied nitrogen (N) use continues to be a sound agronomic, economic and environmentally-friendly practice with effective N Management Systems. Start the post-applied N applications at, or soon following the V3 stage of growth. The plant begins to rely on the nodal root system for nutrient and water uptake once three leaves are extended. Unless planted into a coarse-textured soil (sandy), delaying N applications for a later stage of growth may result in missing an application window due to frequent rain events or having no rain available to help get the applied N into the plant. Post-emergence urea application

3 Don t be fooled by clean-looking fields! Don t be fooled if untouched fields look clean right now! The late spring warm-up has delayed many things, including weed growth. However, in southern areas, fields have already greened up with weeds, and the need for herbicide application is obvious. In contrast, winter annual weed growth in central and northern areas has been slow to start. As a rule of thumb, rapid winter annual weed growth begins once soil temperatures consistently hit 7 C and daytime high air temperatures get into the 15 C range. To adequately evaluate fields for early weed growth, move the crop residue, using your hands or a garden rake. In most cases, you will find that the winter annual weeds are there, but they are small and still in the rosette stage, about the size of a quarter or silver dollar. These weeds have been hiding and are just waiting for optimum temperatures to allow them to bolt. Remember this: All winter annual weeds have small seeds that need only three things to stimulate germination which are sunlight, soil moisture, and adequate soil temperatures. As you may recall, once a winter annual weed begins growth, it bolts and grows extremely fast. This results in a short herbicide application window if you hope to get complete and consistent weed control. This is particularly true for weeds like Fleabane (horseweed). There are no herbicides labeled for control of Fleabane once it hits six inches in height or taller. For this reason, your weed management system must include a complete burndown program plus a residual herbicide. Be sure to stay with the original weed management system that you developed last fall and early winter. We cannot expect to completely control small-seeded broadleaf weeds with only a postemergence program, so a naked acre is a wasted acre! Fleabane rosette Alfalfa Weevil activity Feeding by weevil larvae normally doesn t start in our area until about 300 heat units (base 9 C) are accumulated. First crop harvest in northern areas often takes place in time to reduce or eliminate the weevil threat. As a general threshold, insecticide treatment may be advised when between 30 and 40% of the stems show obvious feeding Early alfalfa tip feeding and 1 st instar Weevil larvae and there is an average of three or more larvae per stem, if at least seven to ten days remain before the crop can be harvested. This is a static threshold that does not account for varying value of the hay crop or differences in treatment costs.

4 Or, here is a different approach to the alfalfa weevil threshold, provided by Dr. John Tooker, assistant professor, Pennsylvania State University Department of Entomology. This table uses alfalfa height, value of the alfalfa hay, and cost of treatment to arrive at the number of weevil larvae, in a 30 stem sample, that will justify insecticide application: Table from PennState College of Agricultural Sciences, Entomology 2014 planting dates for corn & soybeans Corn: The optimum planting date for corn varies slightly from year-to-year. As a rough approximation, optimum dates for corn planting average about April for southern Illinois; April for central Illinois and southern Iowa; April for northern Illinois, northern Iowa, and southern Wisconsin; and May 5-10 for northern Wisconsin. Ontario would be similar to southern Wisconsin and northern Illinois and Iowa (April 25- May5). The target planting window is usually one week either side of these dates. Because of annual variability in the season and growing conditions, we usually advise that soil temperature be the guiding factor for corn planting, up until one week before the average optimum planting date, then planting should proceed as long as soil conditions are favourable. The soil temperature should be at least 10 C (some advise C) at the four-inch depth at midday, with a favourable 10-day weather forecast.

5 When should the switch to an earlier maturing corn hybrid be considered? Years of experience suggest that growers can stay with regionally adapted hybrids into and through most of the month of May without a significant yield penalty. Growers who are planting hybrids, considered very full season, may wish to switch to adapted maturity hybrids by May 20. Soybeans are less affected by planting date than is corn. For most latitudes, soybeans can be planted through the end of May without significant yield penalty. In some cases, full season soybean varieties may benefit from early May planting, whereas shorter season varieties may hold yield potential with planting up until late May. Soil temperature is important for soybeans, and soybean planting is generally not advised until the midday fourinch soil temperature is at least 13 C (some advise C), with a favourable 10-day weather forecast. It is seldom advisable to plant soybeans before the end of April, although early planting occasionally is beneficial. Whenever cool soils or stressful conditions are expected to delay soybean emergence, use of a fungicide seed treatment is advised. In some instances, it may be worthwhile to also use a growth promoter and inoculant, such as Trident. When should the switch to a shorter season soybean variety be considered? Surprisingly, experience has taught us that growers should stay with their adapted soybean varieties well into the month of June. There has simply not been much reward for going to earlier maturing soybeans. In fact, there is frequently a yield penalty associated with switching to shorter season soybean varieties for late planting. For more discussion on any of the topics covered in this edition of Crop Solutions That Work, contact your local County Farm Centre FS crop specialist.