This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu
West Texas
West Texas & Early Planting to Minimize Potential Sugarcane Aphid Impact
United Sorghum Checkoff Program agronomist Dr. Brent Bean notes caution about planting grain sorghum too early. Producers by now across Texas have heard from AgriLife entomologists to “plant outside the normal” window, which is primarily “plant early” to reduce your potential exposure to sugarcane aphid, especially when plants are at the vulnerable seedling stage. That stage-of-growth vulnerability should be partially covered by recommended insecticide seed treatments.
Dr. Bean notes that early planting is not without question. Yes, you can plant too early thus grain sorghum is slow to germinate, slow to emerge, and may not provide you the protection you expected.
“There are reasons why optimum planting dates for sorghum exist, and these should not be ignored. Optimum planting dates are based on soil temperature, timing of seasonal rainfall and daily maximum temperatures, risk of insect infestation, and length of growing season,” Dr. Bean notes.
In the High Plains region over the years, millions of dryland sorghum acres have been planted after May and June rainfall. The outcome is May-June rainfall charges deep soil moisture then September rains (the second wettest month of the year in most West Texas counties) carry the crop through to maturity.
Grain Sorghum Germination and Soil Temperature
Again Dr. Bean notes, “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°F (usually 2-4” depth) and the forecast for the next 10 days is for warm weather.” Slightly cooler temperatures may be sufficient provided the weather is clearly warming.
How does the above sorghum germination temperature compare to cotton? The optimum planting target for cotton is a 10-day average soil temperature (not minimum) of 65°F at the 8-inch depth. Sixty degrees for sorghum is likely a more shallow temperature, and that is a minimum. A 4” depth, there is some daily fluctuation, but this would point to an initial sorghum planting temperature that is probably 7-10 days earlier than cotton.
Another safeguard against too-early grain sorghum planting: do not plant grain sorghum any earlier—regardless of soil temperature—than the point which is two weeks after your last average 32°F temperature. So, if your county’s last 32°F is April 3 (Dawson Co.) then do not plant sorghum any sooner than April 17—BUT ONLY IF soil temperatures are adequate (the West Texas Mesonet reports the Lamesa April 13 bare soil temperature minimum at 4” is 61°F, but that could be due to April 12 rains).
Here are these last average 32°F dates for selected West Texas counties:
Tom Green, March 28 Yoakum, April 5 Gray, April 13
Taylor, March 24 Lubbock, April 6 Moore, April 18
Wilbarger, March 30 Swisher, April 14 Ochiltree, April 25
Collingsworth, April 1 Bailey, April 17 Dallam, April 23
Dawson, April 3 Deaf Smith, April 19
So, early sorghum planting to minimize potential exposure to SCA is probably not worth the risk a poor or slow growing stand. Companies may have hybrids that have tolerance of cooler soils, but then you may lose proven yield potential and/or your possible SCA tolerance in the hybrid.
Early planting may also reduce the risk of other insect damage. In most regions, headworms and midge issues are much less 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, Dr. Bean notes early planting of sorghum for managing SCA is an effective IPM tool and should be considered. “However, do not disregard sound sorghum agronomic practices. Simply moving the planting date up by a couple of weeks can make a significant difference in managing SCA.”
