A Horticultural Sciences Department Extension Publication on Vegetable Crops
Eat your Veggies!!!!!
Issue No. 541 January 2009
Proper Application of the 3-Way Fumigant System for
the Post Methyl Bromide Era
By: Andrew W. MacRae, Assistant Professor, Weed Science, Gulf Coast Research and
Education Center Balm, University of Florida/IFAS
Before I start, I need to say that the system to be mentioned below is just that, a system. There
will be certain fields with certain pest pressures that will not require an entire system for control.
However, these fields will not stay relatively clean of pests if a total systems approach is not
used. This means you may get away with using a reduced system for one year, if you're lucky
two years, but a pest or several pests will eventually escape causing significant yield loss. There
is no true alternative to methyl bromide, don't believe anyone who tells you there is. We cannot
provide the level of control we used to receive with 350-400 lbs of methyl bromide 98:2, but we
can do very well with the 3-Way system in most locations.
Almost all fumigant systems will look great following decades of methyl bromide use, but there
will be some that are not sustainable. Do not make a decision on a fumigant system based on
this first year following methyl bromide use. I would encourage all growers to try several
systems on the same piece of land, for several growing seasons, to determine which one is right
for you. Sustainability is the key to a successful methyl bromide alternative.
Economics plays a huge factor in the decision for which system a grower may choose. I will not
give costs for systems as they fluctuate regularly. What I must emphasize is that growers do not
choose a fumigant program simply because it is cheap or it is easy to apply. Instead, make your
decision based on your pest pressures and the type of crop and number of crops being placed on
the mulch. If you are growing a crop such as eggplant or pepper you need to use a system
approach, especially for weed control. We do not have postemergence weed control options on
broadleaf weeds and nutsedges for these crops, so any escapes will have to be ignored or hand
pulled. If you intend to grow two or more crops on the same mulch, a system approach is
necessary to reduce initial nematode and weed populations that can cause problems in future
cropping systems. If growing a single short season crop with postemergence herbicide options, it
may be possible to cheat on the systems approach for one year and then return to the full system
the next year.
The 3-Way system uses a combination of three fumigants to achieve control of nematodes,
diseases, and weeds. When any one of the products mentioned below is removed from the
system, the level of control on one or two of the areas of pests will be reduced. The 3-Way
system is composed of three active ingredients: 1,3 Dichloropropene (1,3-D), chloropicrin (Pic),
and either metam sodium or metam potassium (Metam). 1,3 Dichloropropene and chloropicrin
can be found alone in products (Telone II and Chloropicrin, respectively) or in combinations:
Telone C17 (83% 1,3-D, 17% Pic), Telone C35 (65% 1,3-D, 35% Pic), and PicChlor 60 (40%
1,3-D, 60% Pic) are the most common of these. Metam sodium is sold as Vapam while Metam
potassium is sold as KPam.
The 3-Way system products are put out in separate passes. The 1,3-D and Pic can be put out
together using the combination products, however there are restrictions on respirator use that
must be taken into account. If they are put out together you can use your regular fumigation rig
with the knives set at 8-9 inches below the top of the bed. If put out separately, place the 1,3-D
at 12-14 inches (usually done with a pass just prior to pulling the false bed) and the Pic at 8-9
inches below the bed top. If you place the 1,3-D at 12-14 inches, do not run your seepage
irrigation constantly from the time of fumigation until planting. You will seal in the 1,3-D which
can stunt the crop even six weeks after fumigation. Wet soil will stop the movement of 1,3-D. If
you do happen to run the seepage from the time of fumigation until planting, do not stop the
seepage immediately after planting. This will cause a flush of 1,3-D to move into the root zone
and may cause severe damage to the crop. Continue running the seepage for a few weeks to
allow only a little of the 1,3-D to escape at one time. The best plan is to have the soil moist but
not wet at the point of fumigant placement for 14 days to allow the escape of the fumigant, even
if this requires shutting off the seepage prior to planting.
Metam is best applied using coulters or knives set four inches apart and placing the fumigant
four inches deep in the bed. So if you have a 28 inch wide bed top, seven knives would work the
best. The key with Metam is to place the fumigant near the top of the bed since we are aiming
for weed control with this product. Disking or rototilling the product in will dilute the fumigant
resulting in less than expected weed control. Initial fumigation should not include an application
via drip tape, unless you are using a double tape system. A single drip tape cannot cover the
width of a 28 or 24 inch bed top.
This system will require an investment on the part of the grower. If putting the 1,3-D deep, it
will be necessary to build on your false bedder (also called a hiller) a fumigant system for putting
out the product. You could also use the Yetter-Telone rig developed by John Mirruso which
does an excellent job at placing the product at the right depth. The chloropicrin and the
combination products can be put out using your regular fumigation rig so very little adjustment is
needed. The Metam application will require the creation of a new fumigation rig to properly
place the fumigant. This is often done on the press bedder which many growers use on the
second pass after the fumigation rig.
So it seems we're done, except for one thing. In the post methyl bromide era, you must include
herbicides with your fumigant systems. There are several products labeled for different crops
that can be placed under the plastic mulch. These are necessary especially if no post emergence
herbicides are available for the crop you are growing. Take note of the restrictions on some for
replanting of a second crop. All applications under mulch should be made to a finished bed top.
This means that the soil on the top of the bed cannot be disturbed after the herbicides have been
applied. If you are moving the soil you are dragging the herbicide to the end of the rows and it
will not be where you desire it to be.
Take time to plan what system you are to use when your methyl bromide allotment runs out. If
you have not started working on a system it is never too late, but it is getting close. We will
continue to see our allotted methyl bromide for CUE crops to diminish. The most important
thing to remember is not what the cheapest system is, but rather what system will be sustainable.
Having two good crops in a row and then a disaster on the third crop due to short cuts is not a
viable option. Develop and test systems for your crop and do not rely on one single fumigant
regiment for the entire farm unless you are sure the results you see will be consistent for many
years to come. I hope you do well in the years to come and feel free to contact your local
extension agent and myself if there are any questions that you have on fumigant and herbicide