Today I noticed one of the seedlings (Daring Dilemma x Barefoot Bay), that survived our Texas Zone 9 summer temps, was looking poorly. Seemed to come on rather fast as I am pretty sure a week ago it wouldn't have caught my eye.

Took the shovel and dug it up with plans to relocate it, but I was way too late.... The roots were totally gone with only this fat grub where roots should have been...!

I lost another seedling a couple months ago to exact same type of "bug", but in a different area of the backyard.

Is there any granular insecticide that I could broad cast on surface of soil to prevent this...? From the size of it, I may be too late as they are already well developed in the soil.

I am in process of setting out about 150 seedlings (that I should have had out last month) and don't like losing them to these varmints.

That's a "white grub", the larva of member of the Scarab beetle family. Sometimes you can save daylilies if there is a bit of crown left by keeping them in a pot in the shade in the house. There are insecticides that can be used but hopefully they're not that numerous that you'd need to do that. Some other suggestions from AHS here:

https://daylilies.org/daylily-...

Do you get animals digging up your lawn? That's where most of the grubs are likely to be.

I never had a problem with grubs until the last two years. Seems like I have oodles of the little tiny ones everywhere, but they soon grow larger by eating my seedlings! Like you, I didn't know there was a problem until I saw the plants starting to die, and by that time it was too late for most. A few did actually come back if the grub doesn't eat the entire crown.... but unless you get him, he will just move on to another plant if one is nearby. There are products especially for lawns to help protect against grubs, but I am still fighting mine- with no end in sight! I hate the thoughts of killing everything just to eliminate grubs though. They also attack my potatoes and sweet potatoes!

Japanese beetle and June Bug larvae are the most common scarab family grub here in East Tennessee. When the former was a problem in my veggie garden, I considered using BT, an organic biological control- the same stuff found in mosquito dunks and useful for controlling fungus gnats indoors.

@Shive1 any suggestions?

These white grubs have decimated my gardens over the years. I would recommend BT. It kills both Junebug and Japanese beetle grubs. I tried GrubEx for years, and it didn't help at all. Now when I plant seedlings, I surround each plant with both BT and Milky Spore.