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Re: Pre-Emergent Herbicides

I vastly prefer to use corn gluten (Amaize, WOW, Safe and Simple etc.) for pre-emergent weed control because of virtually no toxicity at all. It is best applied in early season before foliage unfurls because it will damage leaves if applied in wet conditions (but will not kill the plants). The drawback is that you must think a year ahead: 90% of the effect is in the following year. In my state it can only be sold as a fertilizer (8-0-0), but the pre-emergent effect has been documented in university studies.

----- Original Message ----- From: "Bill Meyer" <njhosta@hotmail.com>
To: <hosta-open@hort.net>
Sent: Wednesday, March 02, 2005 11:01 AM
Subject: Pre-Emergent Herbicides

Hi Everybody,
I just wanted to let everybody know that now is the time to start
thinking about pre-emergent herbicides and slug control. You should be buying
your control measures soon and applying in the next few weeks depending on
your climate. The following advice is more for larger gardens, but the same
principles apply for smaller ones.

The first decision you have to make when thinking about pre-emergents is
whether you want to use a granular or a liquid. You'll need a sprayer for a
liquid. Granulars are Treflan-based and liquids are Surflan-based. You will
have to purchase these at a nursery supply store. Be prepared to have to spend
over $200US, but this will be enough for 3-4 years or more, depending on the
size of the garden. Either works well.
I did my first application with generic Surflan (Oryzalin) last year and
the results were dramatic. There were virtually no annual weeds where it was
used, with large numbers in the grass around the beds. It's amazing stuff. I
bought an electric backpack sprayer from ShurFlo and it worked beautifully.
Going with a sprayer and liquids is a good because it can also was to be used
to spray other liquid controls. You could also use it for spraying an
ammonia/water mix for slug control.
To use it, it is vital that the application be made before any annual
weeds begin to germinate. At a guess, that leaves you no more than three weeks
in a lot of areas. Apply at the lighter recommended rates the first year, then
change your rate after that if you see the need. What you want to do is to
prevent weed seeds from sprouting through the summer. It does this by adhering
to soil particles to a depth of 1/2 inch or so. If the soil is disturbed after
application, you will need to reapply to the disturbed area. It burns all fine
roots in its zone, killing all germinating seeds. Some weeds from very large
seeds might be strong enough to withstand it, but it will kill everything that
sprouts from small to medium sized seeds. This does include any plants you
want to reseed in the garden like Lunaria (money plant) or Digitalis
(foxgloves), so don't use it where you want plants like that to spread.
Don't exceed the recommended rate unless it is unsuccessful in
controlling the weeds. It will build up in the soil if you do. Your aim is to
kill all sprouting weeds through early Fall and then have it gone from the
soil so a few could sprout then (only to be winter-killed before they set
seed). It breaks down, but slowly, and overuse may cause a buildup. Use it
only to the rate you need and don't go beyond that. The necessary rate for
this will vary by soil type, so aim for 90% of the season before it breaks
down. It will take a few seasons to get your rate adjusted perfectly, so keep
records. It did no noticeable harm to any established plants, killing only
germinating seeds which are the most vulnerable. I would avoid using it around
very small plants like little rock garden miniatures, but it may be safe with
those. We didn't spray very small plants. It is important to note that it must
be watered in.
If you have perennial weeds established in numbers in the same area, you
can tank mix Surflan with Round-up and get both in one spraying. I don't do
this because the number of perennial weeds was not high. I just went around
and hit those with a one-gallon pump bottle of Round-up. Round-up is bad for a
lot of plants and you have to be far more careful with it than you do with
Granular Treflan-based pre-emergents work just as well, and similar rules
apply. The most popular of these seems to be a product called Snap-Shot, which
many nurseries use. Preen is a Treflan product for the general public and is
OK for small areas, but too expensive for larger areas. The high price is only
because of the market - it isn't better in any way. If anything the
professional products are better, but you have to buy larger quantities.

A good idea for March is to use Suflan/Treflan, then follow with slug
pellets (recommend Deadline MP) and 10-10-10 granular fertilizer as a mix.
This will put you in great shape for the beginning of the season, and let's
you get a lot of the maintenance work out of the way before you begin seeing
plants. Try this and you won't believe how great it all works for very little
time and effort.
I don't believe either the Surflan/Treflan pre-emergents, Round-Up, or
metaldehyde slug baits like Deadline MP are restricted anywhere. As always,
read the labels carefully and don't use more than the recommended rates.
Overuse usually won't accomplish any better control and can harm the
environment. Extreme overuse will definitely harm the environment.

A note about metaldehyde - Metaldehyde is a mildly dangerous poison, so be
careful with it around pets and children. It is meant to be applied lightly,
not so heavily that an animal might ingest a large amount of it. Animal
poisoning is rare but does occur. A study in England reported 17 cases of dogs
and cats being poisoned in 1998 despite widespread use of metaldehyde baits. I
only found a report on the study, and it didn't say how many were fatal or
whether they had eaten it from the ground or gotten into bags or containers of
it. I think the rate of pet poisoning with ordinary household products like
cleaners or anti-freeze is much higher to put this in perspective, and more
may be hit by lightning than that. There are millions of cats and dogs in
England and quite a few metaldehyde users as they have a very high proportion
of gardeners. Animals are not normally attracted to the small blue pelleted
forms like Deadline MP, but some do seem to zero in on it, so watch your pets
carefully after you apply to be sure they don't find it interesting. If they
show a taste for it, keep them out of treated areas for a few weeks.

.......Bill Meyer

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