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Desiccation timing critical to sorghum crop success

Maximising the profitability of this season’s sorghum crops could be as simple as a well-timed desiccation.

That’s the opinion of Landmark senior agronomist Paul McIntosh who said the timing of spray-out was critical to preserving yield and grain quality and avoiding lodging issues.

typical charcoal rot symptons (sorghum)

“There are some basic rules I adhere to when it comes to desiccation timing of all sorghum varieties,” Mr McIntosh said.

“Don’t judge physiological maturity by the colour of grain; get out into the crop and look at black point percentage numbers on the sorghum seed; and look on the bottom of the sorghum head on the southern side to determine if physiological maturity has reached this last area of grain turning.

“If grain moisture is less than 25 percent with over 90-odd percent physiological maturity then spray-out results are going to be far more positive and much quicker.”

Grains Research and Development Corporation (GRDC) supported research suggests that black layer (abscission layer) formation in the field is the best tool to safely schedule spray-out timing as it can help growers determine their risk approach and modify it as needed on a paddock and variety basis.

When spraying, Mr McIntosh said growers needed to ensure that application was carried out in the prime time of day, usually early morning when stomates are open; ensure water quality was good, water volume adequate and adhere to seven days withholding period.

“It is also important to remember that healthy green leaves will always accept glyphosate into the plants’ system more effectively and that spraying post first frost is a usually a no-no for continuing the spray out programme.”

typical fusarium stalk rot symptoms (sorghum)

The current dry conditions will impact on the speed of the dry-down process according to Pacific Seeds summer grains agronomist Trevor Philp and growers should have their harvest preparations finalised before undertaking desiccation.

“Due to the dry hot growing environment, stalk rot pathogens such as charcoal rot and fusarium stalk rot may well be present and desiccation could aid in their rapid development. This type of situation will further reduce the timeframe from spray-out to harvest and may pre-depose the crop to lodging,” he said.

“In badly drought-affected crops growers may find some of the plants have already dried off. These plants won’t die from a glyphosate application prior to harvest and some regrowth will occur after the next rain.

“In severely drought-affected crops, it may pay to do an initial harvest, wait for rain and then desiccate the field. This will reduce the risk of lodging and improve the effectiveness of the spray out.”

When accessing the crop for physiological maturity, Mr Philp said the crop should also be checked for lodging potential with tell-tale signs being early matured heads and plants that are fully senesced.

“When the leaves are stripped back on these plants the stem will be discoloured and soft when squashed at the base. When the stem is split, the base of the stem will discoloured,” he said.

“If a crop is showing early symptoms of these stalk rots, earlier harvest should be considered especially at the current price.”

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