Effects of Preharvest Desiccation with Glyphosate on Grain Sorghum Seed1

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Abstract
The preharvest application of chemical desiccants to reduce moisture content of grain sorghum (Sorghum bicolor (L.) Moench) may make it possible to eliminate costly mechanical drying of harvested grain. The objective of these experiments was to evaluate the effect of glyphosate on the viability of seed from field‐treated plants. Seed from grain sorghum plants desiccated with 1.12, 2.24 and 4.48 kg/ha glyphosate [(N‐phosphonomethyl) glycine] produced a high percentage of abnormal seedlings with varying amounts of interveinal areas completely devoid of chlorophyll. Mildly affected seedlings recovered from the symptoms and produced normal plants with normally appearing, viable seed. Severely varlegated plants died. Seed damage was greatest when treatments were applied 25 days after flowering when the grain had a moisture content of 30 to 40%. Damage decreased as time of treatment after flowering (30, 35, and 40 days) increased. The number of abnormal seedlings observed in standard germination tests corresponded to the number of variegated seedlings observed in growth evaluation studies. Similar effects were noted for genotypes ‘Top Hand’, BT− 399, and RT− 2536. The last two genotypes are similar to the female and male parents of Top Hand. Rate and time of treatment had no effect on yield of Top Hand.

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