USCP Agronomy Check Planting Date And Grain Sorghum


   With the potential damage and cost associated with the sugarcane aphid (SCA) in grain sorghum, many entomologists are recommending early planting as an effective integrated pest management (IPM) practice. The idea behind early planting is to “outrun” the SCA. By planting early, the hope is to delay the occurrence of an SCA infestation to later in the growth cycle of the sorghum plant. Research has confirmed that the SCA will cause less damage to sorghum when threshold levels are reached at latergrowth stages. For example, yield loss is substantially less when SCA infestation occurs at the soft‐doughstage compared to the boot stage or during flowering.
   However, there are reasons why optimum planting dates for sorghum exist, and these dates should not be ignored. Optimum planting dates are based on soil temperature, timing of seasonal rainfall, daily maximum temperatures, risk of insect infestation and length of the growing season.
   One of the first considerations for early planting should be soil temperature. The cooler the temperature, the slower the sorghum will germinate and emerge. Most agronomists suggest waiting to plant sorghum until the minimum daily soil temperature is 60 degrees and the forecast for the next 10 days is for high temperatures. The soil temperature can probably be a little cooler than 60 degrees if the near‐term forecast is for higher temperatures.
   Planting too early does not help much in outrunning the SCA if plant maturity is delayed due to cool weather. Keep in mind that how fast a sorghum plant develops is directly related to daily temperature or heat units. Early planting can delay the time when sorghum reaches the flowering stage anywhere from seven to 25 days, depending on weather conditions and, to a lesser extent, the specific hybrid. If very early planting is a goal, check with seed companies for a hybrid that has cold tolerance. These hybrids will not experience as much of a delay due to cooler temperatures.

   Typically, one of the advantages of early planting is reducing the risk of insect damage. In most regions, headworms and midge issues are much less likely with early planting. From a SCA management standpoint, this is important because many of the insecticides used for these two pests will cause SCA populations to flare.
   In summary, early planting of sorghum for managing the SCA is an effective IPM tool and should be considered. However, do not disregard sound sorghum agronomic practices. Simply moving up the planting date by a couple of weeks can make a significant difference in managing the SCA. ∆
   BRENT BEAN: USCP Agronomist

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