Originally Posted by
haystack
Autumn Olives are not that difficult to kill, but impossible to eradicate in my opinion. Mechanical means such as digging or pulling out is probably best where applicable. Several chemicals will also kill it, some through foliar treatments, but the most effective is applying the chemical to the cut stump immediately after cutting. Glyphosate/Roundup, Imazapyr/Arsenal AC, Triclopyr are a few known chemical controls for Autumn Olive.
This site has those chemicals listed with prices to give an idea of their uses and cost:
http://www.keystonepestsolutions.com/
Mowing/bushhogging might keep them under control and may even kill seedlings, but it will not always kill established shrubs. I know of a field that was not mowed for 6 years and the autumn olives became abundant. The same field, for the last 4 years has been mowed 2 times every year and the autumn olives are still living, waiting for their chance to take off.
Like haystack said, the best and most effective long term control is to chemicaly treat it. A 50-50 mixture of water and glyphosate applied to the cut stump would be the cheapest control method. Garlon 4 (triclopry) can cost upwards of $100 a gallon. The cut stump method can be used basically year round. If you wanted to go with Garlon 4, you would mix it with bark oil (a penetrating oil) at a rate of 26 oz garlon per gallon. I've had great success with both methods.