Just as soils were dry enough to get back in
the field, rain returned again to the area. Northwest Iowa received from 1
to 4 inches of rain over the last 7 days. Air temperature was cooler than
predicted last week but should be warmer over the next 7 days. The 10-day
forecast calls for moderate temperatures and another chance of rain by late
week.
Row-Crop and Forage Development
How to read Figure 1. Figure 1
shows accumulated degree days (Y-axis) by planting date (X-axis) and in turn
attempts to predict growth stage of corn based on planting date.
Three data lines are used: reading the legend; “South”
represents degree days calculated (and averaged) from the Castana and Ames
weather stations and “North” represents degree days calculated (and
averaged) from the Kanawha and Sutherland weather stations. The “South”
line should be used for fields located south of Highway 7 and the “North”
line should be used for fields north of Hwy 7. The 7-day predicted
(forecasted) line is an average of all 4 weather stations using forecasted
temperature over the next 7-days.
An example would be for corn planted on April 17; the
accumulated degree-days would be 107, 111 and 155 degree days for South,
North and 7-day Forecast respectively. In other words, corn planted on
April 27 should be emerging today (typically requires 110 degree-days to
emerge). Another example would be for corn planted on April 27 has
accumulated about 45-50 degree days and according to the predicted 7-day
accumulation should be emerging in one week. A graphical display of degree
days by planting date (average of all 4 stations) can be accessed at this
web address:
http://www.extension.iastate.edu/carroll/crops/degree-days-2003.htm
Corn degree-days (Base 50) were less than
forecasted last week; accumulating only 38 DD50’s over that last 7 days.
Fortunately the daily forecasted trend is up. The next 7-day forecast total
is favorable with an estimated accumulation of 58 DD50’s which is somewhat
less than the 12-year average of 69.
The few acres of corn planted before May 18 should be
emerging now or within the next couple of days (Figure 1). On average, corn
requires 110 degree-days to emerge. Using forecasted temperatures, look for
corn planted by April 27 to be emerging over the next 7 days (Figure 1).
Soil temperature (Figure 2) trend has been down
and most recently average temperature has been around 55 degrees. Hopefully
with increased sunshine prospects the next several days, soil temperature
will be warming again. For the most recent soil temperature information,
visit the following web addresses:
http://mesonet.agron.iastate.edu/climate/daily.php
http://www.hprcc.unl.edu/products/awdn.html
Several key plant pest articles relating to Alfalfa Weevil and
Bean Leaf Beetle management and control have been written in the most
recent edition (May 5, 2003) of the ISU Integrated Crop Management
newsletter. You can access the newsletter at this web address:
http://www.ipm.iastate.edu/ipm/icm/
Also in the newsletter are articles on timing of
soybean planting, information on soybean rust and detecting early
season soybean diseases.
Bean Leaf Beetle and Bean Pod Mottle Virus Control.
Several questions still surface as to whether over-wintered Bean Leaf
Beetles (BLB) should be controlled or not in soybean fields. In the past,
early season damage to soybean leaves by BLB feeding has been more of a
cosmetic problem rather than a yield reduction problem. But the last couple
of years there has been an increase in Bean Pod Mottle Virus (BPMV) which is
vectored (transmitted) by the bean leaf beetle. And the only current method
of controlling BPMV is to control the vector, BLB.
The result of ISU studies the last couple of years
suggests that to reduce the incidence (severity) of the virus, we need to
control the beetle (as soon as they are found in soybean fields) before they
can transmit the virus to and between soybean plants. But just because BLB
are present doesn’t mean we need to be spraying all soybean fields. Early
planted fields that have a history of BPMV (distorted leaves and green-stem)
should be under consideration for control. Fields that do not have a
historical problem or that are planted later than surrounding fields should
not have an early season control application. For more information on early
season control strategies with the BLB and BPMV, refer to last week’s ICM
newsletter at
http://www.ipm.iastate.edu/ipm/icm/2003/4-28-2003/blbresearch.html
The Iowa Bee Rule. Remember, if you are
applying a pesticide that is hazardous to bees, you need to contact
registered bee yards within a two mile radius of your intent to apply the
product. More information on the IA Bee Rule can be accessed at this web
address:
http://www.agriculture.state.ia.us/apiary.html
Weather Update