NEED HELP WITH PENDIMETHALIN {PROWL(R)} HERBICIDE IN LETTUCE

[Kurt Sepp Deifel]

Please Help me,

My name is Kurt Deifel and I am the Research and Development 
Officer for a large farming co-operative here in the Darling Downs
in Queensland, Australia.

The problem that we have at the moment is with the residual effect
of pre-emergent selective herbicides in our Lettuce and Celery 
Transplants.  The active constituent that we are having trouble 
with is Pendimethalin mixed in a Liquid Hydrocarbon Solvent.  It 
is sold under the name of Prowl(R), Accotab(R), Go-Go-San(R), 
Herbdox(R), Sipaxol(R), Wax-up(R) and sold under Stomp 330E(R) 
here in Australia.  It is manufactured by the American Cyanamid 
Company in the United States.  The chemical belongs to the 
Dinitroaniline family and is originally a orange/yellow 
crystalline solid soluble in most organic solvents hence being 
mixed with the Liquid Hydrocarbon.

The problem is that we have been using this product quite 
successfully to control certain weeds in our Lettuce and Celery 
for about 15 years and have had excellent results.  Until last 
season when we started to find some abnormalities in our Lettuce 
resulting in this seasons Lettuce having catastrophic problems.  
Lettuce transplanted into blocks sprayed have very poor 
establishment figures ranging from 10-50% of the transplants 
dying.  Once these Lettuce transplants had started to grow they 
soon became very uneven.  With the plants appearing to be about 
two weeks different in the same blocks.  Once they came to 
harvest only about 30-50% of the Lettuce could be harvested with 
the rest being either too small or not forming hearts.  At first 
we thought that it was something else such as nutrition or 
insufficient irrigation but when we sprayed different blocks with
different treatments then this soon told us the real story.  
Blocks that were not sprayed with this product had an excellent 
establishment, over 99.9% with about 60-70% of the Lettuce being 
harvested.  Although this was still a disaster this was a large 
improvement on the blocks sprayed with Stomp 330E(R) with only 
30-50% being harvested.  We also applied another herbicide, 
active constituent Propyzamide or Pronamide under the trade name 
of Kerb WP(R) manufactured and released by Rohm and Haas Company.
This appeared to have no effect on the establishment or growth, 
in fact it appeared to be better than the control where no 
herbicides were applied.  There is such a large difference in the 
stunting that the rate of growth between a treated block and an 
untreated block is quite large, if you didn't know that they were
both planted on the same day you would swear that there was 
7 to 10 days difference in the two blocks.  This results in the 
treated blocks being harvested almost two weeks later than the 
untreated block.  All of these trials were replicated and the same
results appeared pointing to the Pendimethalin being the problem.
It appears that if applied this season to blocks it will result 
in killing plants and reduce yields by over 80%.  And with the 

residual or background levels in the soil it will severely effect
the growth and still result in massive reductions in yields.  We 
have been applying the product according to the label and at the 
rate of 2.5 litres / hectare with the recommended rate being from
2 - 4 litres / hectare, and been more then generous with the 
minimum interval time and the 2-7 days required with holding 
period from spraying to transplanting.  At the moment we are 
loosing $40,000 to $50,000 dollars Australian and will go broke 
very quickly if we cannot find a solution.  

If you know anything about this product or know anybody that might
be able to help me please let me know.  At the time being I would
like to find out as much as possible but am very interested in 
knowing if;
- I can take tissue and/or soil samples and send them to a 
laboratory to be analyzed to see if there has been any significant
difference  in the levels of Pendimethalin between the treatments
and other farms or is the active constituent not translocated into
the plant or does it simply effect the root system.
- Do different varieties of Lettuce get effected differently by 
this problem.
- Is there an indicator plant that I can use such as a grass 
species or other to tell us that concentrations are still toxic 
in the soil so we will know very roughly what level is in the 
field.  I have read that some grass species are susceptible to 
this so that may work.
- Is there any crop, element, chemical or technique that we can 
use to so called soak up or reduce the effects of the product in
the ground, i.e. can I grow a certain crop species that will 
absorb the chemical in stolens or tubers or other plant part and
use these to trap and store the product so we can dig this crop up
and remove the Pendimethlin from the field.  
- Does this product have a history of having such a problem as 
remaining in the soil, does it have a long half life to break 
down or does it not break down, can I accelerate the natural 
breakdown process.
- Could it be another product or product reacting with the 
Pendimethalin.

Please help we with my quest for information and possible 
contacts, your time and knowledge will be greatly appreciated, 
and maybe I can even help you with some of your own problems.  

Please E-mail and post your reply so I can get answers as soon as
possible because we have to try and find a solution very quickly.  

I will answer all letters.
Thankyou very much in Reply,

Regards

Kurt Deifel
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Mr. Kurt Sepp Deifel
Research and Development Officer
for Story Farms Pty. Ltd.
E-mail address <kurt at tmba.design.net.au>
Snail Mail - F1/311 Bridge Street, Toowoomba,
	     Queensland, 4350, Australia.
Phone - (076) 361911  Fax - (076) 362216