Northwest Iowa Crop Update Newsletter by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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Volume 2, Number 18

Northwest IA Crop Update, July 22, 2002
(Word Document)

Introduction
Scattered showers last night were very welcome across the region, unfortunately not everyone received precipitation.  Drought stressed crops continue to plague many producers and insect pests are taking advantage of the situation.  WBC moth flight appears to have peaked; some fields have reached treatment threshold levels.  Corn rootworm beetles are abundant and may accentuate pollination problems in drought stressed corn fields.  Mid to late season foliar diseases may also take advantage of the conditions and attack both corn and soybean fields.

Weather update
Cool and dry conditions look to be the norm for the next several days.  The extended forecast calls for a warm-up by the weekend.

Lodged Corn Recovery
It appears the area corn has gone through a remarkable recovery following last week's storm.   Many fields that were flattened from the wind have goose-necked back to the up-right position, and in many cases the damage is no longer visible from the road.  I would say the immediate concern for pollination should not be a problem in most fields.  The next challenges for the lodged and goose-necked corn will be accessing moisture and nutrients with a reduced root system, potentially decreased photosynthesis, stalk diseases this fall and harvest challenges (the fields are still a jungle even though individual plants have goosenecked).  Look to this web page for more information and progress of the area's corn as the season progresses.  http://www.extension.iastate.edu/carroll/crops/storm-damage-02.htm

Growing Degree Day Accumulation and Crop Development
Another hot seven days last week added up to 194 degree-days for the area corn crop.  Thankfully, cooler temps are forecasted for the first part of this week with a forecasted accumulation of 172 degree-days (base 50).  Mild temperatures is just what the corn and soybean crop need as soil moisture levels remain critical in some areas and corn is pollinating and beginning to fill grain.

Corn is pollinating across most of NW Iowa by this time, fortunately most of the area received some moisture over the last couple of days and the area will experience cooler temperatures as well.  Some of the more advanced fields may be finishing pollination and will be in the R2 (blister) stage.  R2 Stage normally occurs 10-14 days after silking. 

Soybean Development has reached R2 to R3 in fields across the region.  R3 is beginning pod growth.  R4 is full pod elongation.  This stage marks the beginning of the most crucial period of plant development in terms of seed yield determination.  Much of the area has received some rain in the last week; this will help the yield potential of the soybean crop as it begins to fill seed over the next several weeks.

Pest Management
Western Bean Cutworm moth catch continues across northwest Iowa, although it appears (data from light traps) that we may be past the peak flight.  The moth catch peak in pheromone traps may lag that in light traps due to fewer competing receptive female moths (releasing pheromone); therefore more males are attracted to the pheromone traps.  Egg masses have been found throughout the region and some fields have reached treatment threshold.  Degree-day accumulation for NW Iowa is near or has surpassed the 1536 degree-day mark, indicating 75% moth emergence

You can monitor current degree-day accumulations and trap catch numbers at the following web page:  http://extension.iastate.edu/carroll/crops/wbc-2002.htm

A picture of an egg mass can be seen at this web address
http://www.ent.iastate.edu/imagegal/lepidoptera/wbcutworm/western_bean_cutworm_eggs.html

For more detailed information on the WBC, refer to the Nebraska publication G98-1359-A http://www.ianr.unl.edu/pubs/insects/g1359.htm and an ISU article at http://www.ipm.iastate.edu/ipm/icm/2002/7-8-2002/wbeancutworm.html

Corn rootworm beetle emergence continues.  Fields that have been at risk should be scouted for silk clipping once beetle emergence begins.  More information on rootworm beetle scouting and control can be obtained in a recent ISU IPM newsletter http://www.ipm.iastate.edu/ipm/icm/2002/7-15-2002/rw.html

Bean Leaf Beetle information can be accessed at the following web page:  http://extension.iastate.edu/carroll/crops/blb-2002-1st-gen.htm

Spider mite infestation may become a problem in drought stressed crops.  Spider mites typically become a problem in years with low rainfall and physiologically stressed crops.  Insecticide applications to control other pests in corn and soybeans may also flair spider mite populations.  Most spider mites are greenish white to yellow, although some can be orange or red.  Spider mite injury to soybean can resemble herbicide injury or a foliar disease; however, characteristic signs are tiny yellow spots, or stipples, on leaves. As the injury becomes more severe, leaves turn yellow then brown or bronze, and finally die and drop off. Because they are small and stay on the undersides of leaves, spider mites can be difficult to see. One way to spot them is to tap leaves against a white piece of paper and look for moving yellow dots on the paper.  Be careful not to confuse spider mites with thrips, which are noticeably elongated insects that move more rapidly than spider mites.  More information on spider mites can be found at ISU’s Crop Management newsletter http://www.ipm.iastate.edu/ipm/icm/2001/7-23-2001/twospotsm.html 

Crop disease management
For a review of mid to late season corn and soybean leaf diseases, refer to the following web pages.

Corn leaf disease management
http://www.ipm.iastate.edu/ipm/icm/1999/7-19-1999/midscorndis.html
http://www.ipm.iastate.edu/ipm/icm/2001/6-25-2001/controldis.html

Soybean disease identification and management
http://www.ipm.iastate.edu/ipm/icm/2001/7-23-2001/soyscout.html

(Word Document)