Page 18 - Griffin Gazette Fall 2015

Tank Mixing Pesticides:
Yea or Nay?
By Rick Yates, GGSPro Technical Services Manager
Tank mixing pesticides is a practice employed
by nearly all growers at one time or another
for a variety of reasons. Labor savings and
efficacy are the leading reasons to use a tank
mix. Consideration of a tank mix should lead to
questions about compatibility. When growers
consult with GGSPro about tank mixes, they
are most often seeking to confirm plant safety.
Plant safety is obviously important, but there
are other factors to consider as well, including (heat producing) reactions may result. These more obvious types of
the continuous threat of pest resistance and physical compatibility.
Tank mixes do save time and can broaden control. Combining a foliar
fungicide for Botrytis with an insecticide for thrips may be done to
combine two applications into one. Tank mixing fungicide drenches
may be done in order to create a broad-spectrum treatment for
water molds (Pythium, Phytophthora), at the same time as fungal
diseases (Fusarium, Rhizoctonia, Thielaviopsis). Growers sometimes
ask about tank mixing soil drench treatments such as a fungicide
and an insecticide, or PGR. Even if these pesticides are compatible
together, the required drench volumes may not match. For example,
Citation and Bonzi have different drench volume requirements based
on pot size. Be sure to consult with GGSPro before attempting these
types of tank mixes.
Another common use of a tank mix is to create a synergistic effect. A
synergism occurs when the combination of two pesticides produces
control that is better than these pesticides being applied separately:
1 + 1 = 3, so to speak. For example, several years ago GGSPro
stopped recommending Avid alone for thrips control due to growers
reporting a loss of efficacy. However, tank-mixing Avid with a neem-
based IGR, e.g. Azatin O, Azaguard, Molt-X, yields excellent results,
better than either product alone. While very effective in certain cases,
this type of tank mixing does require two modes of action.
Pesticide resistance is a continual threat that is balanced through
rotation. Combining two or more pesticides to control a single pest
is a common practice. Using two pesticides with the same mode
of action (MOA) adds little or nothing in terms of efficacy, and this
practice will only intensify resistance pressure on that MOA. For
these reasons, these types of tank mixes are never recommended
by GGSPro.
Combining two pesticides to control different life stages of the
same pest to enhance control or lengthen the period of control can
be very effective, but may limit options for effective rotation in the
following applications. Whitefly control provides a perfect example
of this situation: Resistance has whittled down the list of effective
MOAs significantly. If a tank mix employing two different MOAs is
made, fewer MOAs remain available for rotation purposes as the
control program continues. A complicating factor is that many of the
newer pesticides limit how many times a crop can be treated with
that product. Some go so far as to limit use to twice per crop, in an
effort to slow resistance. This makes good sense from a pesticide
stewardship perspective, but it further limits rotation options.
Pesticide labels will often make note of known tank-mix
incompatibilities. Naturally, not all possible tank mixes can be
18
Geranium bloom damaged by
a tank mix of insecticides.
evaluated, so the lack of a specific caution does not necessarily give
a green light to tank mix. Some pesticide labels contain language
such as, “can be used in conjunction with most other pesticides”.
While this provides some useful general information about overall
compatibility with other pesticides, it does not remove the need
for testing and trialing under your conditions. In some cases, the
tank mixes are physically incompatible and a reaction occurs.
Precipitates, clumping, coagulation and occasional exothermic
problems can be observed and avoided ahead of time by employing
a “jar test”. (The jar test procedure and the correct order to add
pesticides and adjuvants to a tank mix can be found in the
Bonus Material found online or by contacting GGSPro.) In some
instances the tank mixing has been done for you. There are many
examples of pesticides that contain more than one active ingredient.
A few examples include Banrot, Mural (availability expected January
2016), Pageant Intrinsic, Spectro and XXpire. In these cases, the
manufacturer has ensured that the active ingredients and inert
ingredients are compatible with each other.
Give extra consideration to generic pesticides and tank compatibility.
The so-called “inert ingredients” in pesticides can vary from one
formulation of an active ingredient to another one. If you have an
established safety record with a name brand pesticide, do not
assume that the generic pesticide will also have the same inert
ingredients and, therefore, the same tank-mix performance you have
come to expect. Better safe than sorry; test them as you would any
new pesticide.
Tank-mixing discussions often start with plant safety for good
reasons. Mixing more than one pesticide or adjuvant can cause
unexpected results. Phytotoxic reactions or antagonisms that
reduce pesticide performance may still occur even if the tank mix
tests do not reveal obvious incompatibilities. Growers should always
perform small-scale trials with all pesticides and tank mixes that they
have not used on a particular crop before. Test as many different
varieties as possible as there can be differences noted even within a
species of plants.
Tank mixes do bring benefits to production, as long as precautions
are taken and the tank mix has been proven safe for your crops.
Pesticides labels are the law, and they contain lots of valuable
information. Always read and follow the pesticide labels.