Help...crabgrass invaded my new apple orchard

I just planted 10 young apple trees at the edge of a hugelkultur berm I live in the desert and built rings up around the trees to contain water, and was going to plant some beneficials in a guild below the trees. Does anyone with any experience with guild planting below apple trees know of anything that I can plant that will smother out the crabgrass that keeps springing up there?

First of all I'd suggest replacing those rings with basins - http://www.harvestingrainwater.com/2014/07/12/revised-multi-use-rain-garden-lists-for-tucson-arizona-and-a-template-for-anywhere-else/ Basins are large depressions around a tree, which allow rainwater runoff to soak into the ground. Rings tend to repel water except that supplied by irrigation. Basins help reduce the need for irrigation.

You need to first let the apple trees root system get established before you go planting other water needing plants otherwise you will end up with to much competition just at the stage the trees need no competition.

I like to use lots of cardboard around a newly planted fruit tree, by using lots of pieces, you eliminate the need to have a "free" zone right at the trunk since the trunk can move the cardboards as it grows.
Laying down a layer of compost on top of the cardboard helps since it will move down into the soil over time and be a mulch at the same time.
Worms love cardboard so you will attract them to live under the cardboard around your trees, any plant under the cardboard will not get the sunlight it needs to thrive and that means little or no growth of these competitors.
Water can infiltrate through the cardboards so the tree roots receive the water they need, the cardboard acts as a mulch so the water remains available longer, so the roots can grow and establish the root zone.

Once the cardboard has done its job (3 to 5 months), you can plant brassicas, squashes, (no tomatoes, onions or garlic) etc. through the cardboard instead of having to remove it.

Vitamin B-12 helps roots establish themselves by inducing new growth (you can simply dissolve some B-12 or B-complex tablets in a gallon of water instead of buying the commercial solution).

In a dry climate make sure the ground and the cardboard are thoroughly saturated with water before putting mulch on top, otherwise the dry cardboard can repel irrigation and rain, in my experience.