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| Field Crop Advisory Team Alert newsletter | ||||
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| Vol. 22, No. 13, July 12, 2007 |
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In this issue  Aphids slow, but mites may show Corn rootworm adults emerge Western bean cutworm moths captured for a second season Fungicide applications of strobilurins to corn and soybeans when there is little disease Regional reports WeatherNext issue July 26 |
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| Aphids slow, but mites may show After a big debut in June in some locations, soybean aphids are for the most part sitting quietly. Aphids are still present in all fields we sample, and the percentage of infested plants is slowly increasing. However, the number of aphids per plant remains low. Contrast this to 2005 the last outbreak year in Michigan, when aphid numbers were already increasing towards threshold in mid-July in many fields. The slow aphid growth mirrors the condition of the soybean crop. It has been hot and dry in many locations, so small beans flowered early. Aphids do better on actively growing parts of plants. Also, aphids reproduce best at moderate temperatures in the mid 80’s. I’ve noticed in many of my research fields the plants are short and the rows have not filled in, and on hot days it is very hot in the canopy. This could also contribute to slow growth. If temperatures were moderate and rains were more frequent to increase plant growth, the aphid populations might also increase. For now, check fields with no or few aphids every 7-10 days until infestation increases to 50-70 percent of plants, then scout more frequently. Meanwhile, hot dry weather brings up the potential for spider mites in soybeans. I haven’t heard of any symptomatic fields just yet, but mites are present at low numbers in beans by this time of the year waiting for their big break. Spider mites feed on numerous crops and under certain conditions increase to the point where they affect yield. This is especially true under dry conditions (recall the 2001 field season) or on sandy soils where water stress is an issue. Mites pierce individual plant cells and suck out the contents, initially causing tiny yellow spots called stippling on leaves. Stippling increases water loss from the plant. As populations increase, symptoms include yellowing of leaves and in more severe cases browning, bronzing or death of foliage. As leaves yellow and die from mite damage, the photosynthetic ability of the plant is reduced. With additional water loss, leaf drop, and reduced photosynthesis, yield and quality is reduced by severe mite feeding. |
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| Note that yellowing of leaves may not be due to spider mite – yellowing may be caused by herbicide injury, nutrient deficiency, poor root growth or other mysterious causes. Do not let someone convince you to spray yellow beans for spider mite unless you have actually seen the spider mites yourself. Mite populations will be heavy on beans that are yellowing, easy to see by tapping a leaf over white paper, and stippled plant cells will be obvious using a hand lens. Note that even if you do have spider mites, control is difficult. Multiple insecticide applications can lead to resistance and make the problems worse. It is thus very important to avoid unnecessary sprays, including insurance applications for soybean aphid. “I’m going across the field anyway, so I’ll just throw something in the tank” may actually increase mites under the right conditions. Mite predators are not obvious to you, but by killing them you may notice the increase in mites. It is also important to avoid unnecessary insurance applications of fungicides. Mite entomopathogens (beneficial mite-killing fungi) are not obvious to you either, but if you remove or inhibit their growth you may again notice mites. In other words, the pest management choices you make now can create or exacerbate a mite problem later in the season. Certainly some situations (if you are over threshold for soybean aphid or if soybean rust spores are carried into Michigan on a weather front) warrant pesticide applications. But an application made as “insurance” or for a “yield boost” in the absence of pest pressure is a recipe for a mite problem. Recipe for spider mite surprise (Acarides voila!)
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| Corn rootworm adults emerge Corn rootworm adults are emerging in southern and central Michigan. Now is the time, particularly in the southern tier of counties, to assess corn for corn rootworm larval damage. I have already observed lodging in one of my research fields on the MSU campus. However, even corn that isn’t lodged may have significant root damage – the only way to tell is by digging and washing roots. Note that in southwest Michigan, rotated as well as continuous corn should be checked due to the presence of corn rootworm variant. Note also that even fields treated with insecticide or planted to Bt corn can be damaged by corn rootworm larvae. Damage and yield loss may increase later in the season from storm fronts with heavy winds (lodging) and by dry weather that further exacerbates water uptake by root-pruned plants. For a light read to put you in the mood for root digging, check out a good article by rootworm gurus Mike Gray and Kevin Steffey from the University of Illinois: “Comparing Soil Insecticides and Bt Corn Rootworm Hybrids: Do Root Ratings Make Sense Anymore?” This article discusses the problems with rating larval damage in conventional versus Bt hybrids. It is available at: http://www.ipm.uiuc.edu/bulletin/article.php?id=796. |
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| Western bean cutworm moths captured for a second season Last season I reported that western bean cutworm, an emerging pest of corn in the Midwest, was trapped for the first time in Michigan (Southwest Michigan, Cass County). This year, there are 23 trapping sites in Michigan in 15 counties, and hundreds of other trapping locations in surrounding states. As of this week, western bean cutworm moths were captured in two traps in Cass County (four and nine moths respectively), a location in Van Buren County (two moths), and near Eaton Rapids in Ingham County (one moth). This suggests that western bean cutworm has spread further into Michigan. I did not confirm larval damage to corn last season, but there was a suspicious sighting made by a producer in northern Van Buren County. You can view the current list of trap sites and captures through the Western Bean Cutworm Monitoring Network at: http://www.ent.iastate.edu/trap/westernbeancutworm/isite. |
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| Fungicide applications of strobilurins to corn and soybeans when there is little disease Some growers may be contemplating the use of foliar fungicides on hybrid corn this season, due to higher market prices for corn, marketing of fungicide products, or concern over increased disease risk from planting corn-on-corn. Growers may have similar thoughts of applying foliar fungicides to soybeans due to higher market prices. Conditions are not favorable for the development of most foliar diseases in corn. In many parts of the state, rolled leaves can be seen during the middle of the day, clear evidence that corn is experiencing moisture stress. Conditions for foliar diseases of soybean are similarly unfavorable. Substantial areas of Michigan are experiencing droughty conditions, and the extended forecast is for above normal temperatures and below normal rainfall through the end of July. In Michigan, foliar diseases have not commonly been serious enough in field corn or soybeans to warrant the use of a fungicide, although they are used regularly in seed corn. The 2007 Insect, Nematode and Disease Control bulletin in Michigan Field Crops, E-1582 contains a complete listing of fungicides registered to control foliar diseases in both corn and soybeans . However, the issue of applying foliar fungicides to hybrid corn or soybeans [primarily Headline and Quilt (corn) and Headline (soybeans), which contain an active ingredient in the family of fungicides known as strobilurins] when there is little disease continues to come up. In many parts of Michigan, corn is starting to tassel, and so we are entering the critical period of development that determines yield. Similarly, soybeans are flowering and nearing their critical period of development. With high prices for both corn and soybeans, growers may be looking at avenues for increased yield. Certain strobilurins can change the plants physiology in a manner that sometimes enhances yield, even when diseases are not present, but there is no cookbook formula to consistently achieve this result. So far, there has been little university-conducted research in Michigan to evaluate the yield effects of using strobilurins on field corn where there is little disease present, and this is an area in need of greater study. Our field research with soybeans has not demonstrated significant increases in yield using strobilurins in soybean where little disease is present. In some other states, university research has found increased yield in soybeans, even when diseases are not present. However, research results in corn have been much more mixed. Most of the studies done on field corn show no statistically significant improvement in yield from foliar fungicides applied to corn in trials when there are minimal amounts of disease through the grain fill period. A few studies showed yield increase when strobilurin fungicide disease activity was low, and a fraction showed yield increases that would more than pay for the cost of the application at $4.00/bu corn prices. In the article “Can foliar fungicide raise corn yield when there's little disease?”(The Bulletin, University of Illinois, Extension, No. 14 Article 10/June 29, 2007 http://ipm.uiuc.edu/bulletin/) Emerson Nafziger, Professor of Agronomic Extension writes, “Because we are talking here about the decision to apply fungicide for something other than disease control, hybrid traits such as foliar disease resistance might not help us make a better decision. Previous crop might also be of little help, since the effect of previous crop on current crop stress level might be more important than its effect on disease. The fact that we saw some yields above 240 bushels per acre and no effect of fungicide indicates that high yields are not always associated with a positive effect of fungicide on yield, either. We simply do not have a way to predict when there might be a yield benefit from the use of a foliar fungicide when there is not a disease present. We have clear evidence that such an effect can take place, but because it's likely to be a product of complex interactions between crop stress level, weather, and previous growing conditions, we do not know in advance, based on current knowledge, when it will happen.” Resistance is an inherited change in a plant pathogen’s susceptibility to a fungicide. Intensive use, overuse or misuse of certain fungicides can result in the development of resistance. Using fungicides containing strobilurins as a product for yield enhancement when disease activity is below levels that threaten yield, contributes to the risk of development of fungicide resistance. Spores can be transported over long distances and millions of spores are produced. Remember, these products are fungicides. Strobilurins are in the “high risk” category for resistance. Resistance has been already documented in several crops for several different pathogens. If you still plan to “experiment” with the plant health aspect of strobilurins, Ohio State developed the following guidelines for setting up a fair evaluation in your field to determine whether or not these products are truly providing any benefit. (From the C.O.R.N. OSU newsletter July 7, 2007 “So you are trying fungicides on corn and soybeans, how to evaluate if they are worth the cost?” - Anne Dorrance, Pierce Paul, Dennis Mills.)
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| Regional reports 1 -- Southeast Ned Birkey Weather It has been unusually hot and dry with rains seeming to skip parts or the entire area. Everyone can use a good soaking rain. Crop reports Alfalfa growth is “stalled” somewhat with the dry conditions. Potato leafhoppers are out in force. Some second cutting has occurred and more probably should, as harvest weather has been great. Corn is suffering in the 90-degree heat and without precipitation. Many fields are at the VT growth stage and many fields have uneven plant development. European corn borer numbers are very low. Oats are turning quickly in this heat. Yields and test weights may be off. Soybeans do not seem to be growing much at all, as I do not have to move up the yellow, sticky traps in some counties. Most fields are at the R2 flowering growth stage. One western bean cutworm moth was in a trap in Washtenaw County earlier this week. Variant western corn rootworms are not being found, and aphid numbers are very low. I have not seen such short soybeans in several years. Wheat harvest started on July 2 with balers and drills following some combines in western Lenawee County. Harvest is nearly complete now with test weights and yields both in the 60’s. Post harvest weed control will be a problem in several fields. Miscellaneous It has been hot and dry since the Memorial Day holiday. We’ve had only a few days of cooler temperatures and some scattered rain. |
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| 2 -- Southwest Bruce MacKellar Weather The drought continues throughout southwest Michigan. Dan Rajzer reports that significant areas of Cass County received about 0.7 inch since June 1. We have similar levels in eastern St. Joseph County. We have had limited areas in each of the counties in the southwest cluster that have received significant rainfall levels, but these areas are very narrow bands. Storms that moved through the area on Monday and Tuesday (July 9-10) provided precious little relief to the parched region, with rainfall totals less than 0.1 of an inch received in many locations. Crop reports The earliest planted commercial corn is at or just past pollination. Irrigated commercial corn looks fairly good. Even under irrigation, we seem to have more variability of crop height than we have seen in recent years. Dryland corn has really been hurt by the drought. The stress has been severe enough to see actual plant stand loss in many portions of fields. Plants have been under severe moisture stress for more than 10 days in many locations. Some fields have probably suffered more than 50-60 percent loss of yield potential. Other areas are approaching this level of stress very quickly. If we do not see significant rainfall within a week, much of the area’s dryland corn production will be lost. We have seen significant Asiatic garden beetle mating activity in the Centreville area this week. Actually, there were thousands of the beetles swarming around the halogen lights outside the St. Joseph County MSU Extension building on Monday evening. They appear to like to gather in areas at night where there are shrubs or trees adjacent to bright lights. We have seen significant pockets of damage caused by Asiatic garden beetle larval feeding on corn where soybeans were planted in the field the previous year. The larval stage of this new insect pest is a white grub, similar in size and appearance to a Japanese beetle grub. Look for Asiatic garden beetle mating activity around brightly lit trees and shrubs to determine if the new pest is active in your area. We have seen beetles active in areas as far north as Paw Paw. We have seen some western bean cutworm activity in southwest Michigan. Cass County ANR educator Dan Rajzer reported catching nine moths in a trap in Cass County. I have caught 2 moths in southern Van Buren. Western bean cutworm lay eggs near the ear leaves of corn plants. The larvae move to the silks of the plants, and eventually cause damage similar to corn earworms. European corn borer activity had a small spike a week ago, but has gone down again. We are in the process of de-tasseling seed corn. Producers are struggling to keep up with the water demand through irrigation. Fields are being treated with fungicides to help protect against leaf diseases. Cooler temperatures should be favorable for pollination. The activity of silk clipping insects such as western corn rootworm adults and Japanese beetle adults should be monitored to make sure they do not impact pollination. Late splits on nitrogen are also being applied. Irrigated soybeans continue to grow well. The best beans are approaching 26-28 inches in height, and are setting pods. Dryland beans are also suffering from the drought with stand loss in some fields, especially those planted later in the season that did not get a chance to develop significant root systems. Plants are very short. Soybeans have better potential to recover from drought stress conditions than corn at Vt, but impact on yield potential will still be significant. Mike Staton, the Van Buren/Berrien County ANR educator, reported a field of irrigated soybeans in Berrien County that had a spider mite infestation. Spider mites thrive in hot dusty and dry conditions. The pest is just 0.2 of an inch in length, so detection is best accomplished by looking for leaf stippling or bronzing symptoms. You can also tap infested leaves over a sheet of white paper and look for “moving dust particles” on the paper. As the drought conditions continue, we can expect more chances of seeing spider mite damage on soybean fields. Soybean aphid numbers have remained low during this drought period, but we need to watch fields for rapid development from now through pod fill. Alfalfa and pasture growth has really slowed down to a crawl for fields that are not irrigated. Many livestock producers will have to start (or already have been) feeding hay. On alfalfa, potato leafhoppers continue to be found in high numbers. Wheat harvest is nearing completion. Yields have been steady, but are lower than perhaps what we expected. Yields of 55-65 bu per acre are common, even on irrigated fields. |
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| 3 -- West Central Fred Springborn Weather A few scattered showers came through the area over the past two weeks, giving a lucky few some temporary relief from the dry weather we have experienced this season. Most growers are experiencing near drought conditions. Irrigation systems are running across Montcalm County with some pumps and wells running nearly continuously. Crop reports Wheat harvest is well under way with average to poor yields reported. Oats are turning with harvest two weeks away for many fields. Corn growth ranges from V5 and tightly rolled to pollinating with the majority in the range of V10 to tassel emergence. Irrigated corn is progressing well. European corn borer trap catches are very low with most traps catching zero moths. One corn earworm trap caught 32 moths this week at our Trufant location Dry bean stands are very good where there was adequate moisture, where soil was allowed to dry out before planting emergence is spotty. |
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| 4 -- Central Paul Gross Weather It has been a mixed bag of weather the last two weeks across the region. The needed rain that was predicted has been disappointing for the most part. Parts of the region have received over two inches, while other areas measured only 0.2 of an inch. There was an area in Gratiot County that received hail that caused some crop damage. The cooler temperatures this week will reduce the stress on crops in need of moisture. With all that said, crops are really better than they should be based on the amount of rain we have received this growing season. Rain will be needed soon, or we will have significant yield losses in most crops. Crop reports The corn crop ranges from knee high to tasseling. The cooler temperatures will provide some relief as the crop enters the pollination stage. Corn on light soils will have yield loss due to lack of rain fall. Corn on heavier soils is showing signs of drought stress. These fields will need rain soon to prevent yield loss. Soybeans are growing very slow and are shorter than normal for this time of year. Stands are okay, and we are not seeing any disease problems. Scout fields for soybean aphids. Aphid populations are still very low. Wheat harvest is well under way. The southern part of the region will complete harvest in a few days and the northern part of the region is just getting going. Most are reporting just average yields and good quality. The fields on light ground are yielding very poor. There are no reports of head scab, so most farmers are pleased with little to no docking even though yields are less than expected. Harvest of second cutting alfalfa is underway with most reporting poor yield due to lack of rain and leafhopper damage. Scout fields after green up for this pest. There are reports of hay being in high demand and bringing a premium price. Pastures are burning up and farmers are feeding hay. Oats are turning, and an average to below average yield is expected due to lack of rain. Dry beans stands are good. Leafhopper populations are high and need to be controlled. |
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| 5 -- Thumb Mark Seamon Weather On and off breaks from the high temperatures have been welcomed by people, as well as the crops where rainfall has been slim. Rainfall has been good in some areas and very short in others. The source of rainfall in the past six weeks has been small intense thunderstorms, which makes each rain event variable from field to field. The amount of rainfall has been mostly less than 0.5 inch per event, which is welcomed and appreciated, but will not get the large crops through for very long. The next couple of weeks will be critical, especially in pollinating corn. Crop reports Alfalfa re-growth is slow and fighting against potato leafhopper feeding. Sugar beets continue to add growth and are filling the rows in most fields. Weeds are now breaking through the crop canopy. Some fields are showing some dying beets, likely from rhizoctonia, which is shown as tip rot. Watch for DSV accumulations for cercospera leafspot prevention. The wheat harvest has nicely begun across the Thumb. Late planted fields are slower to mature and have delayed harvest. Grain quality is reported to be good with high test weight and low or no vomitoxin. The test weight will likely decrease as some fields get rained on just before harvest. Grain yields have been reported in the 60-90 bushel range. This yield is pretty impressive with the late season moisture stress that this crop suffered. Corn is moving quickly through growth stages with the accumulation of heat units. Crop height has become uneven through the past dry period. Tassel emergence has begun in early planted fields. The recent rainfall and lower temperatures will be good for pollination. Other areas with less or no rainfall may struggle through this period. In soybeans, most fields have good stands with steady but slow growth. Soybean aphids are widespread, but mostly low in populations. Some fields are being sprayed with the second application of glyphosate. Dry beans, similar to soybeans, have had good emergence, but are progressing somewhat slowly. Some fields that received some rainfall are quickly adding size. Potato leafhoppers continue to pressure new growth. |
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| Weather news Peter Kurtz Geography The heat wave that began last weekend and continued through Tuesday in the southern half of the Lower Peninsula came to an abrupt end yesterday with the passage of a strong cold front. Some areas in the central part of the state received over 0.5 inch of rainfall on Tuesday, July 10. Unfortunately, many locations in the southern and western parts of the state, which have been unusually dry since early June, were missed completely. Currently, a large trough will give us unseasonably cool weather for this time of year both today and tomorrow. A stationary upper level low over the Hudson Bay in Canada will supply cool air aloft and a secondary cold front will swing through today touching off a chance of showers. A warming trend will begin on Saturday. Highs will range today from the low 60’s in sections of the Upper Peninsula to the upper 70’s in the southeast. Highs on Friday will range from the mid 60’s in the north to the low 70’s south. Tomorrow appears to be the coolest day for the Lower Peninsula with temperatures struggling to reach 70 degrees in many locations. We might even see lake effect clouds tomorrow, quite unusual for mid July! Lows will range the next couple of days from the upper 40’s and low 50’s north to the mid and upper 50’s south. A significant warming trend will take place next week with highs approaching 90 degrees again in southern counties by Tuesday. The best chance for showers the next few days will occur today in the central and northern parts of the state with a smaller chance elsewhere, and during Friday night and Saturday in the Lower Peninsula. Right now, Sunday appears dry statewide with some isolated showers possible again on Monday. The 6-10 day outlook covering the period July 17-21, which was issued yesterday, is now dramatically different from the outlook issued a couple of days ago. Above normal temperatures are now likely statewide with normal precipitation in the Lower Peninsula and slightly above normal precipitation in the Upper Peninsula. The 8-14 day outlook, which covers the period of July 18-24, continues this warm pattern with a good chance of above normal temperatures statewide. Precipitation ranges from near normal in the western half of the Upper Peninsula to below normal in the rest of the state. |
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