Issue 4, April 29, 2016 • USDA-NIFA Extension IPM Grant
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After every mild or harsh winter, we are asked to speculate on what it means for insect pests. For many pests, winter temperatures are an important predictor of populations the following year. But the western corn rootworm is not one of them. The eggs are exceptionally hardy, and can withstand prolonged (10 days straight) exposure to soil temps well below freezing (14oF) before significant mortality occurs. This very rarely happens in Indiana. As a result, winter kills are not a factor in rootworm populations. By the same logic, warm winters are not of great benefit to the populations. In fact, there may be a benefit to warm winters in rootworm control. A key source of egg mortality is predation by other insects in the soil, including ground beetles, many of which are far less tolerant of cold temperatures.
One weather factor that does have a large potential to affect populations is spring rainfall. See the graph below – rootworm emergence times vary slightly and are driven by spring heat unit accumulations, but generally occur in late May and early June. The larvae must find corn roots within 24 h of emergence, or they will starve to death. A spring rain that results in saturated soils during this time, although not desired for crops, does have the silver lining in that it drowns many young larvae and prevents many more from finding host plants – the larvae can’t “smell” their way to corn roots without air pockets in the soil. And they subsequently starve to death.
Although it’s not the headliner it used to be, the western corn rootworm is still the key insect pest of corn most everywhere, including here in Indiana. Bt corn hybrids targeting this pest have been highly effective in allowing producers to manage rootworms effectively and without need for insecticide boxes or liquid application systems. The changes in planting equipment have reflected these trends. In fact, according to the USDA, 81% of all corn planted in the US last year was Bt corn (http://tinyurl.com/9qm9ssv), with the percentage likely being closer to 100% in Indiana. This approach is still effective, and no additional insecticides are required or recommended. Most producers have used Bt corn effectively for over a decade of rootworm control, and can safely continue to do so. Planting the refuge remains as important as ever, however, given that reports of confirmed resistance in states to the west continue to trickle in. However, Indiana has not joined that group – likely because of our extensive crop rotation with soybeans, which remains an effective tool for population reduction.
Alfalfa fields in southern and central Indiana need to be inspected immediately for weevil tip feeding and skeletonization of leaves. Winter’s mild temperatures have allowed for successful egg and adult over-wintering. Also, based on the numbers and size-variability of larvae, egg laying occurred over an extended period. This means that egg hatch and larval development will be occurring over a longer period than normal.
Our management guidelines for this time period suggest that fields be treated when there are 3 or more larvae per stem and tip feeding is at least about 50%. Most insecticide labels suggest using higher rates for increased residual control, we concur with this recommendation. Refer to “Alfalfa Insect Control Recommendations – 2016” (mobile friendly web page) or <https://extension.entm.purdue.edu/publications/E-220.pdf>
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|County/Cooperator||Wk 1||Wk 2||Wk 3||Wk 4||Wk 5||Wk 6||Wk 7||Wk 8||Wk 9||Wk 10||Wk 11||Wk 12|
|Dubois/SIPAC Ag Center||0||0||348|
|Jennings/SEPAC Ag Center||0||0||15||18|
|Knox/SWPAC Ag Center||0||6||197||63|
|LaPorte/Pinney Ag Center||0||25||317||296|
|Lawrence/Feldun Ag Center||4||97||155||76|
|Randolph/Davis Ag Center||0||0||0||24|
|Whitley/NEPAC Ag Center||7||21||619||1,091|
Wk 1 = 3/31/16 - 4/6/16; Wk 2 = 4/7/16 - 4/13/16; Wk 3 = 4/14/16 - 4/20/16; Wk 4 = 4/21/16 - 4/27/16
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4/14/16 - 4/20/16
4/21/16 - 4/27/16
|Adams||Kaminsky/New Era Ag||6||6||11||52*|
|Clay||Bower/Ceres Solutions - Clay City||0||0||0||0|
|Clay||Bower/Ceres Solutions - Clinton||0||0||0||1|
|Clay||Bower/Ceres Solutions - Bowling Green||0||0||1||0|
|Clay||Bower/Ceres Solutions - Brazil||0||0||1||3|
|Clinton||Emanuel/Boone Co. CES||0||2||11||16*|
|Elkhart||Kauffman/Crop Tech Inc.||1||4||7||37*|
|Fayette||Schelle/Falmouth Farm Supply Inc.||1||1|
|Fulton||Jenkins/N. Central Coop - Airport||0||0||1||1|
|Fulton||Jenkins/N. Central Coop - Landfill||0||0||0||2|
|Gibson||Schmitz/Gibson Co. CES||0||0||0|
|Hamilton||Truster/Reynolds Farm Equipment||0||1||0||2|
|Jasper||Overstreet/Jasper Purdue CES||0||0||2|
|Jay||Shrack/Ran-Del Agri Services||0||0||13*||6|
|Jay||Temple/Jay County CES - Redkey||0||0||4||10|
|Jay||Temple/Jay County CES - Pennville||0||0||0||3|
|Knox||Bower/Ceres Solutions - Fritchton||0||2||1||0|
|Knox||Bower/Ceres Solutions - Vincennes||5||7||10*||4|
|Lake||Moyer/Dekalb Hybrids - Shelby||0||1||17*||2|
|Lake||Moyer/Dekalb Hybrids - Schneider||1||1||10||1|
|Madison||Truster/Reynolds Farm Equipment||0||0||0||0|
|Miami||Myers/Myers Ag Service||0||0|
|Pulaski||Capouch/M&R Ag Services||0||0||2||0|
|Rush||Schelle/Falmouth Farm Supply Inc.||1||1||3|
|Shelby||Fisher/Shelby County Co-op||0||0||0||0|
|Sullivan||Bower/Ceres Solutions - Farmersburg||0||0||1||6|
|Sullivan||Bower/Ceres Solutions - Sullivan E||0||0||5|
|Sullivan||Bower/Ceres Solutions - Sullivan W||0||1||0||6|
|Whitley||Walker/NEPAC1 - Main||1||2||
|Whitley||Walker/NEPAC2 - Kyler||3||4||34*||54*|
* = Intensive Capture...this occurs when 9 or more moths are caught over a 2-night period
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Wheat growth stages vary greatly across the state, but as wheat approaches flowering in southern Indiana it is important to consider the risk for Fusarium head blight (FHB), or scab, development. The fungus that causes FHB, Fusarium graminearium, infects wheat during flowering, beginning at FGS 10.5.1. Symptoms appear later in the season and include bleached spikelets on the head, and small or shriveled grain kernels, commonly called “tombstones”. The fungus also produces mycotoxins, such as deoxynivalenol, or DON, which can accumulate in the infected grain.
Rainy, warm, and humid weather conditions favor disease development. It will be critical to watch the FHB risk assessment tool to assess the risk of Fusarium head blight in Indiana as wheat enters flowering over the next few weeks across the state. This model can be accessed through the following link: http://www.wheatscab.psu.edu/. This model uses weather information including temperature, rainfall, and relative humidity to calculate risk levels for FHB. The model has been updated and improved for 2016, and now also includes an option to predict risk based on variety susceptibility to FHB. Keep in mind that the model does not provide a guaranteed prediction for whether or not FHB will occur in individual fields, and additional factors such as the local weather forecast, crop conditions, and Extension commentary should be considered when assessing the level of risk. Farmers and crop advisors can sign up for alerts courtesy of the U.S. Wheat and Barley Scab Initiative. Alerts can be sent to a cell phone or email, and will be sent out as the risk map updates risk of scab in Indiana. To sign up for alerts, visit: http://scabusa.org/fhb_alert.php.
If varieties susceptible to FHB have been planted, or farmers are worried about the risk of FHB development, they may want to consider a fungicide application at early flowering for suppression of FHB. Indiana research indicates that applications of the fungicides Prosaro and Caramba are most effective at managing FHB if they are applied at early flowering. Other products are available, but may not be as effective. Fungicides that have a strobilurin mode of action are not labeled for Fusarium head blight suppression. To accurately growth stage wheat and determine when wheat is beginning to flower, please see Purdue Extension publication ID-422 “Managing Wheat by Growth Stage”.
The foliar disease stripe rust has been observed in fields throughout the state, but is still at relatively low levels in most of Indiana. Fungicides applied at flowering for FHB suppression will also provide some level of protection from foliar disease on the flag leaf. If farmers are considering a foliar fungicide application for stripe rust through boot stage, they should keep in mind that applications made prior to flowering will NOT suppress FHB or the associated mycotoxin deoxynivalenol, or DON. If the risk for FHB increases after foliar fungicide applications occur, it may be necessary to make another application at flowering for FHB suppression.
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