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Sorghum midge

Most damage by the sorghum midge occurs in sorghum that blooms 3 to 4 weeks later than other fields in a particular community. In the Corpus Christi area that time is usually the first or second week of June. In other words it is time to start checking sorghum on a daily basis for the presence of midge females laying eggs in blooming sorghum. Again, sorghum midge will move from the early blooming fields that show little damage to the later blooming fields where damage is often very heavy.

For all practical purposes sorghum midge can only lay eggs in the part of a sorghum head exhibiting yellow anthers (bloom) since the glumes are open enough for the female to deposit eggs with the developing seed and upon hatching the grub will destroy the seed. Each female will lay between 50 and 250 eggs in her 24 hour lifetime; some may survive for 48 hours.

It is best to scout for the midge in early morning, but if none are found it is advisable to check from about 10 a.m. until just after noon to make sure some did not arrive later. The females emerge from the pupae in the older fields about daybreak, mate, and begin to migrate to find susceptible sorghum on which to lay eggs.

Closely inspect heads in the yellow anther area for the midge. It takes about 9 days for all florets on a head to pollinate with the second through the sixth day the most important for an individual head.

The susceptible period of an entire field must be considered. In a fairly uniform blooming field it generally takes about 24 days with many taking 16 to 18 days to complete bloom. Most of the sorghum is susceptible (blooming) from the third through the fourteenth day after the first anthers are observed.

Consider control when midge numbers exceed near one per head. For more exact economic injury levels refer to Table 3 or use the formula (number of sorghum midge per flowering head=cost of control as $ per acre x 33256 divided by value of grain as $ per hundredweight x number of flowering heads) to calculate your own situation. Note that the damage level is based upon the number of flowering heads per acre, which could be estimated if you know your plant population and how the field is generally blooming. It seems to me that our local plant populations range from 50,000 to 60,000 per acre.

Labeled pyrethroid insecticides Baythroid, Karate, Warrior, Asana, and Mustang Max, among others, are effective in controlling sorghum midge. Remember that “new” female midge will be moving into the field each day, which will mean one would see midge the day after treatment but unless rainfall occurred control would continue through the first 72 hour period.

If midge are still moving into the sorghum at 72 hours after treatment in high enough numbers, additional treatment is suggested. Under heavy pressure extended control has not been achieved even with the pyrethroids insecticides. Note also that these materials will control headworms, especially the corn earworm. They will also provide some control of the rice stink bug. However, it is my experience that the pyrethroids as a group are weak on the rice stink bug.

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