Broadshot is a combination of broadleaf herbicides all in one package. In the US the most popular brand is Ortho Weed-B-Gone, but you can get it from Bayer, and many other companies. Is Broadshot supposed to work against horsetail? If so then give it a whirl. Looks like you'll need repeat apps to control it to death.

To answer your direct question, if you are going to fertilize and apply weed killer, apply the fertilizer 2 weeks prior to the weed killer. That gives the fertilizer a chance to affect the growth of the weeds. Well fed weeds die faster and better than weeds that are struggling.

It also appears that horsetail thrives in poor soil. With that in mind, the fastest way to improve your soil is with organic fertilizers like corn meal and alfalfa pellets (rabbit food). The chemical fertilizer you are planning to use will turn your grass green but won't do a thing to improve the soil itself. That can only be done with organics. You can apply a lot more organic fertilizer and apply any day of the year to improve the soil more quickly. The application rate is 20 pounds per 1,000 square feet or 10 kilos per 100 square meters. It will replace all your chemical fertilizer needs. If you want to hurry things up, apply monthly. If you want to hurry it up more, apply weekly. As your soil improves, it will develop the ability to absorb all the organic fertilizer you can throw at it. We get these feed type organic fertilizers at feed stores. This link shows how to find feed stores near you.

Thanks for your reply, dchall.

Broadshot is supposed to work against horsetail, although the product label doesn't say so, it is marketed as such with apparently good results considering it is not a kill-all product.

With regards to soil quality, it's quite poor round here, to quite a depth, with heavy clay everywhere. Considering the depth of horsetail roots and its vigour I didn't think trying to do anything to the soil to any decent depth would help very much, if at all. Besides, considering the tonnage and cost involved it wasn't realistic, with a small budget and no access for machines. It was dug over to 12inches and then a good sandy loam imported and added on top to 5inches for the turf to root into.

It is my intention to move to organic lawn care in the near future, and I've been reading your posts on the subject. My plan was to amend nutrient levels and pH with chemical fertiliser as best I could first, to give it a kick start and try and hold some in the sandy layer to combat leaching, then let organic start without as steep a hill to climb as it were. It was my impression that organics can take significantly longer to change things in the soil, but I may be wrong.

Thanks for the link, I have already found a supplier of alfalfa pellets near me. Going rate seems about ã10 per 20kg.

Before you add chemistry to the soil, I would strongly suggest you get a soil test. And I would suggest you get it from Logan Labs in Ohio. Yes, I realize that's a long drive for you, but if you mail it there, I can hook you up with people who will interpret it for you, recommend specific chemicals, tell you where to buy them online, how much to use, when to use, and more. They will not interpret soil tests from other sources because they trust the reliability and quality of the Logan Labs processes. And they will do that for ã0.00. If you add the wrong lime, for example, to a soil heavy in other salts, you can end up with worse clay effect. Rather than recommending chemical fertilizers, they will recommend chemical micronutrients. They are not expensive, but they are likely going to be things you never considered using on the lawn. We have a laundry detergent product called "20-Mule Team Borax," which they sometimes suggest if your boron levels are low. Boron is one of the chemicals required for life, but if you get just a little too much, it causes immediate death. We use it here for control of insect pests in the house.

The fastest way to improve your soil is to grow grass with deep roots and fertilize organically at the surface. In three weeks the soil will be significantly improved. If you apply monthly, you should see an amazing improvement in the grass quality and, hopefully, a reduction of horsetail. Grass is a plant which loses about 1/3 of its roots every year. Those roots remain in the soil to decompose. They are organic matter, deposited several inches deep in your soil, and you didn't have to do anything but water, mow, and fertilize. But over the years the soil will improve continually.

I have had a soil test carried out already, the results of which were given with guidelines for where each value should lie. They showed pH as 7.3, phosphorus is too high at 56mg/l, potassium a little low at 70mg/l, sulphur too low at 5mg/l. Boron is spot on at 1.1mg/l. Iron was also high but I assume this is because the sample was taken a few days after a fertiliser with chelated iron was used. Molybdenum was very low at 0.04 and sodium was just off the bottom at 16.

I understand sulphate based fertiliser will help acidify the soil and add sulphur. The Proscape has potassium as well, but no phosphorus. It's slow release to try and make sure the grass is trickle fed without it all leaching out of the sandy topsoil in short time.

If no harm can come from adding alfalfa now then why not, I'll go for it and see what happens.

If you have any advice on the test results I'd be pleased to hear them.

Thanks again!