When to Terminate Corn Irrigation?
Corn continues dry weight accumulation until physiological maturity is reached that is identified by an abscission layer or “black layer” located at the base of kernels. This will occur approximately 20-24 days after denting. At black layer, the starch line has advanced to the kernel base. Black layer progresses on the ear from the tip kernels to the basal kernels. The hard starch layer progresses downward on each kernel until it reaches the kernel base. This can be monitored by checking ears to show progression to black layer. Soil moisture should be maintained through this stage to optimize yield. Yields can be reduced 15-20% if irrigation is terminated at denting. Daily Evapotranspiration (ET), the combination of the amount of water consumed by the plant and evaporation, starts slowly decreasing at dent but daily ET rates are still high (.25-.28”) with 100° heat. Late February corn is at black layer this week (week of June 25, 2012).
Timing of Fungicides for Soybean Diseases:
The foundation of a fungicide program should contain a strobilurin such as Quadris or Headline applied between R3 and R5 growth stages. Tank mix options are to add thiophanate methyl (Topsin M) for increased suppression of Cercospora blight or add a triazole (Tilt) ‘rust fungicide’ if soybean rust is present or in the local area. Soybean rust fungicides are not needed in the absence of rust. Applications during R3 are more likely to be more effective for suppressing Cercospora blight and later applications could result in less pod and stem disease incidence and severity. If soybean rust is not an issue the producer may want to split the difference and apply the fungicide during late R3 to R4. Below are reproductive stages of soybeans to help in timing of fungicide applications.
R1 Beginning flower
Open flower at any node on the main stem.
R2 Full flower
Open flower at one of the two uppermost nodes on the main stem.
R3 Beginning pod
Pod is 5 mm (3/16 inch) long at one of the four uppermost nodes on the main stem.
R4 Full pod
Pod is ¾” long at one of the four uppermost nodes on the main stem with a fully developed leaf.
R5 Beginning seed
Seed is 1/8” long in a pod at one of the four uppermost nodes on the main stem.
R6 Full seed
A pod containing a green seed that fills the pod cavity is located at one of the four uppermost main stem nodes.
R7 Beginning maturity
One normal pod on the main stem has reached its mature pod color.
R8 Full maturity
Ninety-five percent of the pods have reached their mature pod color.
Sweet Potato Research Station Field Day
August 16, 2012
8:00 a.m. – 1:30 p.m.
130 Sweet Potato Road
For additional information, call Dr. Tara Smith at 318-435-2155.