Elkhorn has thick brown sawdust like stuff on the underside of its leaves. A lot of them are also going brown

Looks like the plant has been attacked by Elkhorn Caterpillar. To control, trim off the most affected leaves and spray the whole plant with ‘Yates Nature's Way Caterpillar Killer - Dipel’. This product controls a wide range of leaf eating caterpillars and is safe to beneficial insects, birds and animals. Approved for use in organic gardening.

Hope this helps and happy gardening.

Best Regards,

Louise

Yates Horticulturist