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Avoid avid aphids
From the Organic Broadcaster, vol. 12 no.3
by Reg Destree
©2004 Midwest Organic and Sustainable Education Service
The aphid populations seem to be out of control in many of our
organic farming operations at some time during the growing season.
The most recent invasion is the soybean aphid. This insect is invading
our soybeans, dry edible beans and fresh green beans. There seems
to be an aphid, with some name, for every crop we grow.
It is imperative that we understand the reason why aphids arrive
in a field. Nutritionally strong plants do not have insects. When
stress occurs for reasons of it being too wet, too dry, too hot
or too cold even the healthiest of plants will draw some insects
or aphids.
How to suppress or reduce the populations
The true key to successful insect suppression is plant health and
nutrition. To assure plant health we must look at plant nutrient
uptake. This starts with soil nutrient management. When nutrients
are short in the soil, you will eventually have a stressed plant
that will draw insects. Insects have an appetite for simple sugar,
free nitrogen, and simple amino acids. Plants with complex carbohydrates
and complex proteins will not support an insect population.
In the production stages of the plant, the plant nutrients that
I have found to be short or limited in most organic plant production
systems are plant calcium (Ca), potassium (K) and boron.. Generally,
two of the three of these plant nutrients are short in the twelve
Midwest states where I work with organic growers. Begin with a soil
test to get an idea of soil nutrient levels. I would like to stress
that the soil test include soluble or "available" levels
of Ca & K, not just the conventional "total" test.
A high soluble Ca and K will aid the plants greatly when it comes
to plant nutrient availability. To identify the plant nutrient deficiencies,
do a petiole nutrient test on the growing plants prior to or during
early flower stage
Boron is the trace mineral that allows for the nutrients to be
transported in the plant. If this micronutrient is in short supply
in the plant, everything will be in short supply.
Adequate plant calcium gives you plant health, nutrient uptake,
plant stalk strength, good bold flowering and eventually fruit set.
This all adds up to higher electric conductivity in the plant. It
is this electric conductivity (plant energy field) that reduced
insects along with balanced plant turgor pressures. (Turgor pressure
is the internal pressure exerted on a cell wall by water and solutes
pushing against it. This pressure keeps cells turgid and allows
non-woody plants and plant parts to remain upright. When turgor
pressure is lost, cells become flaccid, causing plants to wilt).
Soil calcium availability is generally a problem in the Midwest
in the soils high in magnesium. The magnesium does not allow for
the uptake of calcium into the plant.
Potassium is the fruiting mineral. It is necessary in high amounts
to bulk out the fruit and give us the yield we expect. The demands
for plant potassium even in the best of organic soils are generally
the main yield deterrent. During the bulking process in grains,
fruit and vegetables, the potential high yielding crop will have
very high demand for potassium. According to research at UC-Davis,
these high demands for potassium, if not met, will alter the plant
turgor pressure. This altered pressure will cause the plants to
emit exudates and draw in the aphids. No aphid will feed on a crop
that does not emit exudates. There is nothing to eat on a healthy
plant. Research in Europe proved that insects have a "radar
system" that draws them to plants with a yellow cast, caused
by weeping exudates.
Aphids do not suck juice; the imbalanced plant pressure feeds them.
According to Doug Murray, Murray Pest Management, the aphids have
more strength built into their pipe to attach to the leaf than to
the feeding parts. They attach to a plant and it feeds them. That
is why there is so much honeydew on the leaves after aphids invade.
Personal Field Observations
For the past summer, I personally worked with aphid suppression
in a number of crop production systems. The main aphid problems
were associated with the soybean aphids. However, I also witnessed
large populations of aphids in tomatoes, cole crops, wheat and potatoes.
In all situations, the aphids were controllable using the biologicals
and botanical programs that I have worked with for years. The oils
are absorbed into the plant and have up to sixteen day systemic
affect. The essential oils only affect the herbivores (plant-eating
insects); insects stop feeding, the adults stop ovulating and the
young stop pupating.
I have used garlic oil for years to repel insects. The mode of
action of the garlic has nothing to do with smell. It is related
to the garlic oil disrupting the light receptors of insects. The
sight system of insects is related to a radar system. It is in this
manner that insects spot a plant in stress. With garlic on a plant,
the oil disrupts the insects light sensors and the insects to not
see the damaged crop. This will generally work for 7-10 days or
until the plant produces new foliage. At this time it is necessary
to apply another foliar.
The aphid that was, by far, the most prevalent regionally was the
soybean aphid. What I found is that you can repel them from a field
that is nutritionally strong (high brix and no recognized mineral
and trace mineral deficiencies). One particular field that they
never infested was an organic green bean field. This 160 acre field
of organic green beans was planted June 12 in southwest Wisconsin.
The field was foliar-fed three times for nutrient management and
insect suppression. First application was when the beans were in
the third trifoliage. The beans were foliar fed with Drammatic "ONE",
Neem oil and Safer Soap, AER SP1 and Mycotrol O. The purpose of
the application was to reduce an infestation of corn borer. (See
green bean formula).
The second application was sixteen days later with the same goal
in mind. The third application was thirteen days later with the
purpose of nutrient management to avoid an infestation of aphids.
In an adjacent soybean field, the aphids were in numbers of over
500 per plant. I had observed a conventional soybean field within
a couple of miles, at the time of the last application, that had
a population of over 3,500 aphids/plant.
With this pressure, I only found one aphid in the entire field
(160 acres) up to the harvest in mid-August. This has proved to
me that with high value crops, we can foliar at an economical cost
that will literally keep the aphid populations down.
Suppression on excessively high populations of aphids
In DeKalb County, Illinois, I witnessed populations of soybean aphids
of over 5000 aphids/plant. Foliar application included the Neem
oil, Fulvic acid, Fish hydrolysate as a ph stabilizer plus the nutrient
package of AER SP1, a stabilized microbial extract and liquid organic
fertilizer (calcium and potassium). After five days the population
began diminishing. In this particular case the lady beetles moved
into this field and within 14 days they helped clean up the aphids.
I witnessed this aphid suppression in many fields following this
initial excessive infestation in late July. Most infestations were
lighter than this and all had very effective suppression with this
foliar program.
Aerial application of aphids and leafhoppers
In southern Minnesota, a group of organic and sustainable growers
have an airplane dedicated to organically approved inputs only.
In this particular instance, early in the season they were having
problems with insect suppression because of low water volume (5
gal/acre). Corrections were made. The volume per acre was adjusted
to 7 gallons and 4 oz garlic oil was added to the insect suppression
formula. (See Aerial Formula ).
Garden Aphids
About August 10, I was in the LaCrosse Community Garden to begin
harvesting some tomatoes. The population of aphids was absolutely
overwhelming. After harvest, I prepared my insect suppression formula
including Neem oil and garlic oil, mixed it with Safer Soap, added
Drammatic Fish (to stabilize the ph), potassium sulfate, liquid
calcium and water. I sprayed this formula on the tomatoes. Within
24 hours these aphids had flown off.
Soybean aphids in late crop green beans
On July 23, we planted our late season green beans at the La Crosse
Community Garden. When they were only six days out of the ground,
the aphid population was already so heavy that they were cupping
the leaves. I continued to observe to see to what extreme the plants
would be stressed. By the third trifoliage, I went in with the foliar
suppression spray. The population at this point was 200-250 aphids/leaf.
With one application, within 8 days, the population was reduced
by over 95%. I did a second application on half of the crop. The
second application within 7 days eliminated all aphids plus leaf
hoppers. After about two weeks the half untreated with the second
application had a build up to about 10-20 aphids/ plant. In early
Sept, they just naturally disappeared, and there was no damage or
viral infection to the mature green beans.
The real highlight of this sustainable program is that the botanicals--natural
neem oil or Karanja--only affect herbivores, but do not affect the
beneficial insects.
Reg Destree is a consultant for: organic potato and vegetable
growers in the Midwest and Canada; the Onalaska Community Garden
(Onalaska, Wisconsin); and Dramm Liquid Fish of Manitowoc, Wisconsin.
Educated with a Bachelor of Science in Agriculture at UW, Reg designs
nutrient management programs for organic crop production and does
extensive hands-on trials using soil microbes, biological insecticides
and organic fertilizers. Previously, Reg was a certified organic
vegetable grower and livestock nutrition consultant. He has foliar-fed
vegetables since 1985.
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