Texas Upper Gulf Coast
Downy Mildew Fungus & Grain Sorghum
If you farm sorghum between Victoria and Houston, you may be at risk for sorghum downy mildew (SDM), particularly for continuous sorghum. Since about 2000, there have been sporadic outbreaks of SDM, associated with 1) strains of the fungus resistant to metalaxyl, the fungicide commonly used as a seed treatment to control this disease, and 2) planting very susceptible hybrids. Efforts to manage this disease by a monoculture of SDM-resistant hybrids has led to the development of new strains (pathotype) of the fungus that defeat the host resistance. The easiest way to identify an SDM problem in your field is to inspect plants now, while they are still small. The infection occurs while seedlings are emerging from soil. Infected plants are stunted and are difficult to find in a field later in the season because the healthy plants crowd them out. If you think you have SDM, contact your county agent or me (TI), for confirmation and pathotype testing, or to assist with selecting a resistant hybrid for future planting. For more information go to http://sickcrops.tamu.edu to view documents for symptoms and control of SDM.
Submitted by Dr. Tom Isakeit, Extension plant pathologist, College Station, firstname.lastname@example.org,
Split Pivot Irrigation Scenarios — Two Crops & Two Planting Dates
With the lack of any deep soil moisture as of mid-April, many irrigated High Plains producers are evaluating strategies to reduce and minimize the risks associated with having one crop under a full pivot. Numerous cropping strategies exist for pairing cotton, corn, and peanut with other crops like grain sorghum, whose planting date, variety/hybrid days to crop maturity, and critical irrigation needs result in primary irrigation requirements at a different time, minimizing if not eliminating overlap of peak timing. Grain sorghum fits favorably in many of these scenarios as a crop with lower production costs and the ability to use limited but timely irrigation. For a PowerPoint discussion of cropping strategies involving grain sorghum, particularly for the Texas South Plains, view the discussion at http://lubbock.tamu.edu/files/2012/04/Texas-High-Plains-Irrigation-Strategies-2012b.pdf.
- Over-the-top weed control in grain sorghum
- Excellent control of pigweed and many other broadleaf species
- Greatly reduced injury potential compared to 2,4-D and dicamba
- Atrazine suggested as a key tank mix partner to enhance weed control
Huskie was approved for use in grain sorghum in July 2011. Some producers in the Texas High Plains region used the herbicide in late planted grain sorghum, and they were very pleased with the results. Texas AgriLife staff have researched Huskie since 2009 (brief summary below).
Huskie is labeled for over the top use (POST) in grain sorghum from 3-leaf stage to 12” tall. The herbicide’s active ingredients contain two formulations of chemicals in Buctril and a second a.i. pyrasulfotole. Huskie has demonstrated good post-emerge control on Palmer ameranth and other pigweed species, kochia, species of morninggloery, marestail, henbit, etc. Partial control is noted on bindweed (possession vine) and puncturevine. Best weed control is noted for weeds at ≤ 4” tall.
Also, there are numerous tank mix options particularly atrazine, which is a key for optimum weed control in grain sorghum. In fact, the Huskie label all but encourages use of atrazine to ‘strengthen and expand weed control.’ Atrazine rates, of course, are dependent on soil texture (heavy, light), but tank mix rates range from 0.25-1.0 lbs./A. Other tank mix options include Ally, dicamba, Peak, and Starane. Use spray grade ammonium sulfate (AMS) at 0.5-1.0 lbs./A and non-ionic surfactant (NIS) if the tank mix partner requires it.
Injury Potential is Low
Texas AgriLife notes only minor to ~15% injury to 4-leaf sorghum, with little evidence of injury persisting past 3 weeks. Even less injury has been observed in 8-leaf stage grain sorghum. This is much less than the injury potential from either 2,4-D and dicamba.
Sample of Weed Control Results
Bushland – 91%+ control at 7 & 42 days after treatment of 3-4” Palmer ameranth when applied alone at 13-16 oz./A; 95%+ control when applied with 0.5 lb. atrazine at 13 oz./A; adding 4 oz./A dicamba did not improve control.
Halfway – Huskie + atrazine, 94-97% control of 2-4” Palmer ameranth at 21 to 41 days after treatment; slight sorghum injury noted with all POST treatments, but ≤ 5% 21 to 41 DAT unless 2,4-D was included.
No formal trials conducted to date, but Extension observations note that weed control appeared very good and injury potential was low.
For further information consult the label and your chemical dealer. An expanded summary from Texas AgriLife is available online here.