May 9, 2006
Time to Scout for Black Cutworms
Black cutworm pheromone trap catch data is being reported at: www.ent.iastate.edu/trap/blackcutworm.
on these traps, scouting for the pest in southeast and east central
Corn Flea Beetles
The mild temperatures of last winter suggest potential problems with corn flea beetles attacking seedling corn further north than normal. Monitor corn for this pest from emergence through V5. See pages 90 – 91 of the April 17, 2006 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/2006/4-17/stewarts.html and pages 63 - 64 of the May 7, 2001 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/2001/5-7-2001/fleabeetleexpect.html for scouting and management details.
In general corn emergence has been good this
spring. However, some fields planted in mid-April that were just ready to
emerge 2 weeks ago when the cold weather hit had some leafing out underground
resulting in somewhat reduced stands. Fields planted a few days later were not
affected as much. It is not likely that it will pay to replant stands of 26,000
or more, if the remaining stand is fairly uniform. The uniformity of the stand
and replanting costs need to be considered in making decisions on stands of
less than 26,000. The following table can help in making replant decisions:
Influence of planting date and plant population on corn grain yields
Stand April 20 - May 13 - May 26 - June 10 - June 24 -
X 1,000 May 5 May 19 June 1 June 16 June 28
28 - 32 100 99 90 68 52
24 94 93 85 64 49
20 81 80 73 55 42
16 74 73 67 50 38
12 68 67 61 46 35
Numerous gaps of up to 4-6 feet can reduce yields by an additional 5-6%.
For more information, see Pm-1885 "Corn Planting Guide," which is also available at http://www.extension.iastate.edu/Publications/PM1885.pdf and NCR 344 "Uneven Emergence in Corn" at http://www.extension.iastate.edu/Publications/NCR344.pdf.
Delayed Herbicide Applications
The recent wet weather has meant that some producers need to change their
planned weed control programs because the preemergence herbicides haven’t
gotten on. The amide products, such as Dual, Harness, and Outlook, will not
control emerged grasses. The premixes containing atrazine, such as Bicep,
Harness Xtra, and Guardsman Max, can control small (less than 1”) emerged
foxtail, but generally control is lower than the expectations of most
producers. After corn has emerged, do not apply herbicides with a UAN
solution. See the latest ICM Newsletter for more details at http://www.ipm.iastate.edu/ipm/icm/2006/5-1/postemerge.html. Postemergence options for grasses include
Accent (nicosulfuron), Steadfast (nicosulfuron + rimsulfuron), Resolve
(rimsulfuron), and Option (foramsulfuron). In most
Bean Leaf Beetles
Bean leaf beetles are showing up in alfalfa fields and early planted soybean fields. The mild winter has likely resulted in greater than normal overwintering of this pest. So, as soybeans emerge, be sure to scout for this insect. See pages 81 – 82 of the May 27, 2002 ICM Newsletter or http://www.ipm.iastate.edu/ipm/icm/2002/5-27-2002/manageblb.html for scouting, threshold, and management information. In addition to the management strategies offered there, remember that Gaucho 480 and Cruiser 5FS seed treatments offer good protection. Additional information can be found at http://www.extension.iastate.edu/Pages/eccrops/blb3.html.
Asian Soybean Rust
No soybean rust has been found yet on soybeans in 2006 in the
Leaf Diseases in Hail Damaged Fields
Some fields that received some hail in mid-April are showing an increased incidence of leaf diseases as well as some unusual leaf symptoms such as leaves that are twisted or puckered. Plants may not show obvious hail damage, but plants that were more protected from the hail such as near grass along the edge of the field, will be taller and healthier. The yield of the first cutting will be reduced on these fields, but plants should be fine later in the season unless we have another weather event that leads to increased diseases.
Some alfalfa fields showed frost damage after the frost 2 weeks ago. Leaves on the upper half of the canopy may be almost white or translucent. Less damage was evident on clover and grasses in the field.
There have been few reports so far of problems with the alfalfa weevil this spring. For information on scouting for this pest see the April 17, 2006 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2006/4-17/alfalfa.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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