Frequent rains, mild temperatures, and high humidity across Indiana have increased the risk for foliar disease development in corn. So far, disease observations have been limited, but with more rain and mild temperatures forecasted over the next week, more disease may begin to appear in Indiana corn. The two diseases that I have seen most frequently in Indiana this week are Holcus leaf spot and northern corn leaf blight.
Holcus leaf spot is very common in Indiana fields this year. I have received many emails and calls asking if these are early symptoms of northern corn leaf blight or gray leaf spot, and it is important not to confuse Holcus leaf spot with other foliar diseases. Holcus leaf spot is a disease caused by the bacterium Pseudomonas syringae pv. syringae, and is characterized by round, discrete lesions that are initially pale yellow to white and then enlarge and turn gray or brown. Lesions have a water-soaked halo and on certain hybrids, the margin of the lesion may appear brown or purple (Figure 1). Holcus leaf spot is seen sporadically in Indiana, and is not known to limit yield. Although the disease may cause concern based on symptom appearance, no in-season treatment is available or necessary. Fungicide applications will not have efficacy against this bacterial disease.
Northern corn leaf blight (NCLB) is the more concerning disease present in corn. NCLB is caused by the fungus Exserohilum turcicum, and is characterized by long, tan, cigar-shaped lesions on leaves (Figure 2). This disease caused yield loss in some areas in 2014, and it has already been observed in the lower canopy of a few Indiana fields this year. Currently we do not have thresholds available for determining when fungicide applications are needed for NCLB, but we follow similar guidelines as gray leaf spot, in that fungicides will typically be more beneficial when applied to susceptible hybrids in high-risk fields for disease development, such as those that are in minimum or no-till. Scouting fields around V14, or just prior to tassel emergence, can help determine the level of disease pressure in a field. When scouting, if 50 percent of the plants in a field have disease lesions present AND additional factors or conditions that favor disease development are in play (residue present, favorable weather conditions) a fungicide application may be warranted. Research in Indiana indicates that fungicides are most effective at preventing yield loss due to NCLB when applied at the tasseling to early silking (VT-R1) growth stage. For fungicide recommendations, please see the updated fungicide efficacy table for management of corn diseases, which is developed by the national Corn Disease Working Group: http://www.extension.purdue.edu/extmedia/BP/BP-160-W.pdf. For more information on northern corn leaf blight, please read Purdue Extension bulletin BP-084-W: http://www.extension.purdue.edu/extmedia/BP/BP-84-W.pdf.
Before deciding on any in-season disease management strategy this year, keep this in mind: The condition of corn in Indiana varies widely, and farmers should think carefully before making decisions to add inputs into their crop. Consider expected crop price, crop condition, planting date, predicted weather conditions and what impact these factors may have on your economic return this year.
It is important to remember that a V4-V6 application of fungicide to corn will not protect the ear leaf or above from disease that develops around tasseling. Farmers may be concerned about foliar diseases like anthracnose leaf blight (caused by the fungus Colletotrichum graminicola), which can be present in young corn. Typically, symptoms of this disease are confined to lower leaves throughout the growing season, and do not typically require management.
Farmers considering applying foliar fungicides at early growth stages of corn to improve the health of stressed or damaged corn should consider that past research indicates that the most consistent yield advantage from a fungicide application occurs when fungicides are applied in response to a high risk of disease development at VT-R1.
For more information on the current state of NCLB this year, please read the articles by my plant pathology colleagues in surrounding states:
Paul Vincelli, University of Kentucky: https://kentuckypestnews.wordpress.com/2015/06/23/watch-for-northern-leaf-blight/
Alison Robertson, Iowa State University: http://www.extension.iastate.edu/CropNews/2015/0616Robertson.html
Continual saturated soils this spring have put soybean stands at risk to seedling blights. Symptoms of blights include wilting or dead seedlings, missing plants, and delayed emergence. There are four main types of seedling blights, they are Fusarium, Rhizoctonia, Phytophthora, and Pythium. They each are favored by unique environmental conditions, and this season has had them all. Unfortunately, it is difficult to diagnose specific blights in a field. Positive confirmation of one, or more, of these diseases is necessary for future management considerations with fungicidal seed treatments. The publication, Fungicide Efficacy for Control of Soybean Seedling Diseases (BP-163-W) will assist in selecting affective fungicides for the blight(s) in fields.
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Heavy and numerous rainstorms have kept many Indiana farmers out of the field the last two weeks and likely delayed postemergence herbicide applications. As some fields begin to dry out enough to allow sprayers to re-enter fields, producers may need to consider a couple of factors before spraying.
The delay has likely allowed weeds to grow well beyond their recommended postemergence application height of 4 to 6 inches. Producers may have to consider adjusting their planned application to higher labeled rates to control those larger weeds. In some situations producers may need to consider an alternate herbicide option to overcome the additional weed size caused by the wet conditions.
During this multi-week delay not only have many of the weeds advanced past their optimal growth stage, but crops will also be approaching or exceeding growth stages in which herbicide applications may be restricted. As crops approach their reproductive stages the chances of herbicide injury and yield loss is increased. Two tables from the Ohio, Indiana, and Illinois Weed Control Guide are included in this article that outline the corn and soybean growth stage restrictions for many of the commonly used herbicides.
Producers also need to consider the replant intervals of postemergence herbicides to avoid herbicide residue carryover into next season as the month of July approaches. For example the fomesafen containing products that are often used on tough to control amaranths and ragweeds in have a 10-month replant interval for corn. Applications made in July versus June will have a higher probably of causing carryover problems for next years corn crop.
While it has already been a difficult season for many farmers, they will need to keep these considerations in mind as they return to the fields to make postemergence applications in order to further protect their current crop yield as well reduce the risk of future crop injury.
Table 8. Rainfast Intervals, Spray Additives, and Crop Size for Postemergence Corn Herbicides
This table shows the required time interval between herbicide application and rainfall and summarizes label recommendations for spray additives and maximum crop stage. Check herbicide labels for additive rates. Information in this table applies to field corn only.
|Herbicide||Rainfast Interval (hours)||Spray additives/Maximum Crop Size|
|2,4-D Amine||6-8||No additives. Broadcast up to 8-inch corn; directed spray before tassel stage.|
|2,4-D Ester||2-3||No additives. Broadcast up to 8-inch corn; directed spray before tassel stage.|
|Accent Q, NIC-IT||4||MSO, COC or SURF (Addition of UAN or AMS is recommended). Broadcast up to 6 collars or 20-inch corn; directed spray up to 10 collars or 36-inch field corn.|
|Aim||1||SURF. AMS or UAN may be added if required by tank-mix partner. Do not use COC or tank-mix with EC formulations of other crop protection chemicals except as specifically directed by label. Apply up to 8-collar corn.|
|Atrazine||2||MSO or COC. Apply before corn is 12 inches tall.|
|Basagran||8||COC, MSO, UAN, or AMS or COC or MSO + UAN or AMS, depending on weed species present.|
|Beacon||4||MSO, COC, or SURF (UAN or AMS may be added). Broadcast 4 to 20-inch corn; directed spray before tassel emergence.|
|Bestow||4||NIS + UAN or AMS. Broadcast up to 12 inches or 5-collar stage.|
|Bromoxynil||1||No additives. Apply before tassel emergence.|
|Bromoxynil+atrazine||2||No additives. Apply before corn is 12 inches tall.|
|Cadet||4||NIS, COC, or MSO. UAN or AMS can be added. Preplant up to 48 inches tall, and before tassel emergence.|
|Callisto||1||COC + UAN or AMS. Apply up to 30-inch or 8-leaf corn.|
|Callisto GT||-||NIS + AMS. COC can be used instead of NIS but increases risk of crop injury. Broadcast up to 30-inch or V8 corn.|
|Callisto Xtra||-||COC or NIS + UAN or AMS. Apply up to 12-inch corn.|
|Capreno||1||COC + UAN or AMS. Apply broadcast from V1 to V6 corn; directed spray up to V7 corn.|
|Dicamba||6-8||Add UAN if velvetleaf is present. SURF, COC, or UAN may be added under dry conditions. Do not apply with COC when corn height exceeds 5 inches. Broadcast up to 5th-leaf stage or 8-inch corn; directed spray up to 36-inch corn.|
|Dicamba/atrazine||6-8||Add UAN if velvetleaf is present. SURF, COC, or UAN may be added under dry conditions. Do not apply with COC when corn height exceeds 5 inches. Apply broadcast up to 5-leaf stage or 8-inch corn.|
|Halex GT||2||SURF + AMS. Broadcast up to 30-inch or 8-leaf corn.|
|Harrow||4||SURF, COC, or MSO plus UAN or AMS. Broadcast from spike to 2-collar stage, and not more than 6 inches tall.|
|Hornet||2||SURF, COC, or MSO. UAN or AMS may be added under extremely dry conditions. Broadcast up to 20-inch corn or 6 col- lars; directed spray up to 36-inch corn.|
|Impact/Armezon||1||MSO or COC + UAN or AMS. SURF can be used in combinations with other broadleaf herbicides. Apply broadcast or directed up to 45 days before harvest.|
|Laddok||8||MSO, COC, UAN, AMS, DASH, or combinations of these. Apply before corn is 12 inches tall.|
|Laudis||1||MSO + UAN or AMS. Broadcast up to V8 corn.|
|Laudis + atrazine||2||COC + UAN or AMS. Broadcast up to 12-inch corn|
|Liberty||4||AMS. Broadcast or directed up to 24-inch or V7 corn. Directed spray up to 36-inch corn.|
|Northstar||4||SURF, COC or MSO up to 12-inch corn. Only SURF between 12 and 36-inch corn. UAN or AMS may be added. Broadcast 4 to 20-inch corn; directed spray up to 36-inch corn.|
|Peak||4||COC unless mixed with glyphosate. Broadcast up to V6 or 20-inch corn; directed spray up to 30 inches.|
|Permit/Sandea/ Halomax||4||SURF, MSO, or COC. UAN or AMS may be added. Apply through layby stage of corn.|
|Permit Plus||4||SURF or COC + UAN or AMS. Broadcast or directed from 1- to 5-collar stage.|
|Realm Q||4||SURF or COC + UAN or AMS. Broadcast or directed up to 20 inches and prior to the 7-collar stage.|
|Resolve Q||4||NIS + UAN or AMS, unless mixed with a glyphosate product or Ignite. Broadcast up to 20-inch or 6 collar corn.|
|Resource||1||COC. UAN or AMS may be added to improve control of certain species. Apply up to the 10-leaf stage.|
|Shotgun||6||No additives. Apply before 12-inch corn.|
|Solstice||1||COC or NIS + UAN or AMS. COC is preferred adjuvant. Do not use MSO. Up to V8 or 30-inch corn.|
|Spirit||4||COC, MSO or SURF.UAN or AMS may be added. Broadcast 4 to 20-inch corn; directed spray up to 24-inch corn or after 6 collar corn.|
|Starane||1||An adjuvant can be used if required by tank-mix partner. Broadcast up to the V5 stage; directed spray after the V5 stage.|
|Status||4||SURF, COC, or MSO + UAN or AMS. Broadcast from 4 to 36-inch corn (rates up to 5 oz/A)|
|Steadfast Q||4||COC, MSO, or SURF + UAN or AMS. COC or MSO is preferred over SURF. Broadcast up to and including 6 collars or 20- inch corn|
|Stinger||6-8||No additives. Up to 24-inch corn.|
|WideMatch||6||No additives. Broadcast up to the V5 stage; directed spray after the V5 stage.|
|Yukon||4||SURF or COC. UAN or AMS may be added. Apply broadcast or directed up to 36-inch corn.|
|Zemax||1||SURF or COC. Apply up to 30-inch or 8-leaf corn.|
Table 18. Harvest and Feeding Intervals for Soybean Herbicides
|Soybean Herbicides||Days to Harvest|
|Aim||Apply up to third trifoliate||Do not feed|
|Assure II/Targa||80||Do not feed|
|Basagran + 2,4-DB||60||60|
|Basagran + thifensulfuron||60||Do not feed|
|Basagran + Reflex||Apply prior to bloom||Do not feed|
|Basagran + Cobra||90||Do not feed|
|Cadet||60||Do not feed|
|Cheetah Max||70||Do not feed|
|Classic||Apply 60 days before maturity||Do not feed|
|Clethodim||60||Do not feed|
|Cobra||45||Do not feed|
|Extreme/Tackle/Thunder Master||Apply prior to bloom and 85 days before harvest||Do not feed|
|Flexstar/Rhythm/Flexstar GT||45||Do not feed|
|Fusilade DX||Apply prior to bloom||Do not feed|
|Fusion||Apply prior to bloom||Do not feed|
|Liberty/Cheetah||Apply prior to bloom.||Do not feed|
|Poast/Poast Plus||75||Do not feed1|
|Previx/Vise||90||Do not feed|
|Pursuit||85||Do not feed|
|Raptor||85 and apply prior to bloom||Do not feed|
|Reflex/Dawn||45||Do not feed|
|Reflex + 2,4-DB||Apply prior to bloom||Do not feed|
|Resource||60||Do not feed|
|Storm||50||Do not feed|
|Synchrony XP||Apply 60 days before maturity||Do not feed|
|Thifensulfuron||60||Do not feed|
|Torment||85||Do not feed|
|Ultra Blazer||50||Do not feed||1Soybean hay may be fed.|
Due to extreme weather conditions the Palmer Amaranth Day is CANCELLED and will not be held on Tuesday, June 30th, at our Palmer Amaranth research site near Rensselaer, IN.
Please plan to attend the Purdue Weed Day, scheduled for Thursday, July 2nd at the Throckmorton Purdue Agricultural Center, 8343 US 231 South, Lafayette, IN 47909-9049. Registration will begin at 8:00 AM EDT, and the program will begin at 8:30. We will view the plots on the west side of highway 231 in the morning, and a waterhemp site about 1 mile east of the farm in the afternoon. The farm is located approximately 5 miles south of Lafayette on the corner of county road 800S and U.S. 231 South. For those attending the 2015 Purdue Weed Day at Throckmorton, we have applied for 3 CCH’s for category 1A.
|Adams||Kaminsky/New Era Ag||0|
|Clinton||Emanuel/Boone Co. CES||0|
|Elkhart||Kauffman/Crop Tech Inc.||1|
|Fayette||Schelle/Falmouth Farm Supply Inc.|
|Fulton||Jenkins/N. Central Coop-Rochester||0|
|Fulton||Jenkins/N. Central Coop-Kewana||1|
|Gibson||Schmitz/Gibson Co. CES|
|Hamilton||Truster/Reynolds Farm Equipment|
|Henry||Schelle/Falmouth Farm Supply Inc., Millville|
|Jay||Shrack/Ran Del Agri Services|
|Jay||Temple/Jay County CES|
|Lake||Moyer/Dekalb Hybrids, Shelby||0|
|Lake||Moyer/Dekalb Hybrids, Schneider||1|
|LaPorte||Rocke/Agri-Mgmt Solutions, Wanatah||0|
|LaPorte||Rocke/Agri-Mgmt Solutions, LaCrosse||0|
|Miami||Myers/Myers Ag Service|
|Newton||Moyer/Dekalb Hybrids, Lake Village||0|
|Rush||Schelle/Falmouth Farm Supply Inc.|
* = Intensive Capture...this occurs when 9 or more moths are caught over a 2-night period
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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||1||0||2||1||0||4||0||3||1|
|Jay/Davis Ag Center||0||0||2||0||4||1||0||0||0||0||3|
|Jennings/SEPAC Ag Center||0||0||0||0||1||0||0||2||4||0||3||11|
|Knox/SWPAC Ag Center||0||0||0||1||0||0||2||3||1||1||4|
|LaPorte/Pinney Ag Center||0||0||3||0||17||35||29||5||0||11||87||88|
|Lawrence/Feldun Ag Center||0||2||0||1||0||11||3||5||7||12||19||37|
|Randolph/Davis Ag Center||0||0||0||0||0||0||0||0||0||0||6||13|
|Whitley/NEPAC Ag Center||0||1||5||2||17||25||4||0||5||3||9||5|
|Whitley/NEPAC Ag Center (Hartstack)||792||404||137||103|
Wk 1 = 4/2/15 - 4/8/15; Wk 2 = 4/9/15 - 4/15/15; Wk 3 = 4/16/15 - 4/22/15; Wk 4 = 4/23/15-4/29/15;
Wk 5 = 4/30/15-5/6/15; Wk 6 = 5/7/15-5/13/15; Wk 7 = 5/14/15-5/20/15; Wk 8 = 5/21/15-5/27/15;
Wk 9 = 5/28/15-6/3/15; Wk 10 = 6/4/15-6/10/15; Wk 11 = 6/11/15-6/17/15; Wk 12 = 6/18/15-6/24/15
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