The Yellow Farmhouse Garden

January 5, 2017

Ways insecticides work

Filed under: Insects,Pesticides — bob @ 10:42 am

Winter is a time of planning for gardeners. I decided during the deep, dark days of the dead of winter to take inventory of my fertilizers and pesticides. That got me thinking about some of the different insecticides and how they work.

Chemical insecticides have been around a long time. Fortunately, modern chemistry has eliminated the need for most of the nastiest chemicals we used to use in food products. The lead-based and arsenic-based materials used in the nineteenth and early twentieth century  were made obsolete by more sophisticated chemicals introduced into the marketplace after world war two. Take for example the organophosphates, they were the by-product of chemical warfare research done in Germany during WWII. I remember using some of those products from time to time during heavy insect outbreaks in order to save a crop. I’ll tell you one thing, they sure did the job. Unfortunately, many gardeners used them constantly and on everything. I guess they thought if it was legal and on the market it was fine to use it like that. Sometimes they even eyeballed the amount to use instead of carefully measuring it before mixing. While a few organophosphates are still on the market, most of the harsher ones are no longer available for use in the home garden.

Different insecticides work by different means. For example, the contact insecticides kill when the insect comes in contact with it, either by being directly coated by it or walking across an area on the plant that has been treated.

Stomach poisons work when an insect consumes the material and it enters into the insect’s digestive system. The biological insecticide Bacillus thuringenses  is a stomach poison. It’s commonly use in organic gardening.

Bacillus thuringiensis  was the first bacterial insecticide approve for use in home gardens.

Bacillus thuringiensis was the first bacterial insecticide approve for use in home gardens.

Some insecticides are absorbed by plants and are moved to all parts of the plant and remain inside the plant for a relatively long time. These are the systemic insecticides. They are often used on ornamental plants that are not intended to be eaten. I used systemic insecticides many years ago when I had over two hundred roses bushes to care for. The systemics work great for controlling rose pests.

The translaminar insecticides insecticides move just a short distance into the leaves and are not carried through the entire plant. Think of a leaf being constructed of a number of different layers, like a piece of  laminated plywood. A translaminar insecticide only moves into the first or second layer of the leaf. The organic pesticide spinosad is a translaminar material.

Some insecticides work by a combination of two or more of the these modes of action. Often manufactures combine insecticides in order to gain the advantage of multiple modes.

Because an insecticide can act differently on various types of plants, it’s important to closely follow the printed label and not try to extrapolate other uses on your own. This holds true for both conventional and organic insecticides.

Of course we’re not applying insecticides to our gardens right now but it’s not too early to remind ourselves of these things well before the gardening season.

Bob

August 25, 2016

Powdery mildew on pumpkins

Filed under: Disease,Pesticides,Vegetables — bob @ 7:36 am

Growing pumpkins and squash has changed sine the early days early days of my career. Back then, pumpkins rarely had any problems whatsoever. You could just plant some seeds, keep the patch weeded and you were pretty much guaranteed a fine crop.

This year demonstrates how times have changed. In addition to the squash vine borer and squash bug that I talked about the last couple of weeks, we are now seeing powdery mildew on our pumpkins and squash.

Powdery mildew shows up as a white powdery-looking coating on the surface of the leaves. It eventually cause the leaves to turn yellow and die. Under certain conditions it will eventually kill the entire plant.

We’ve had textbook weather conditions for the development of powdery mildew. This type of mildew is a fungus that thrives when daytime temperatures are high and nighttime temperatures are low enough to form morning dew.

Some varieties of pumpkins and squash are more resistant to powdery mildew than others. Here are two different varieties growing side by side.

Some varieties of pumpkins and squash are more resistant to powdery mildew than others. Here are two different varieties growing side by side.

Unlike most other fungi, powdery mildew does not need liquid water to infect a plant and grow. High humidity within the leaf canopy provides the environment powdery mildew requires.

We do not see much powdery mildew during rainy years. As a matter of fact, one non-chemical approach to controlling powdery mildew takes advantage of this. Spraying the surface of the leaves with overhead irrigation will wash off much of the infection. It also will cause existing spores to absorb so much water that they burst, greatly reducing the source of new infection. This method only works if the area is well drained, otherwise you will end up causing other problems due to excess water.

Commercial chemical and organic formulas are available on the market to control this disease. I’ve been using a homemade concoction that has been working pretty well for me. I mix one table spoon of baking soda and two tablespoons of Murphy’s Oil Soap to a gallon of water. Spray it onto the leaves no more than every seven to ten days. It’s important to use this ratio, a stronger solution will damage leaves.

The spores from the species of powdery mildew that infects the squash family of plants does not survive Michigan winters. Spores are blown in to Michigan on southerly winds each spring to start a new cycle of disease.

Powdery mildew is very species specific, meaning each species of plant is infected a specific strain of fungus. For example, the powdery mildew that infects lilacs cannot spread over to squash and vice-versa.

This, I hope, will be the last problem we’ll have to deal with on our vine crops this year.

Bob

 

 

July 8, 2011

Some Organic Pesticides Used in the Garden

Filed under: Pesticides — bob @ 12:40 pm

Someone asked me the other day, “do you spray your garden?” and “what sprays do you use?”  I gave her a short list of materials that I found useful in my garden.  Most people agree that these materials are OK for organic gardeners.

I have been a fan of Bt (Bacillus thuringiensis) since I started gardening in the 1970’s.  It is an insecticide made of naturally occurring bacteria found in garden soil.  Only surface feeding caterpillars like cabbageworms are killed by it.  Bt must be eaten by the caterpillars in order to work.   It does not harm beneficial insects.

Spinosad is another insecticide derived from soil bacteria.  The bacterium was discovered in the soil at an abandoned rum distillery, so the story goes.  This insecticide kills a wide range of insects.  It too must be eaten in order to be effective.  This reduces the likelihood that the Spinosad would kill a beneficial insect.

Pyola is a mixture of canola oil and pyrethrins.  This effective insecticide has the potential to kill any insect good or bad so be on the lookout for honeybees or other helpful insects before you spray.

For disease control, I use a liquid copper fungicide.  The other material I’ve used with mixed results is potassium bicarbonate.  Potassium bicarbonate is chemically similar to sodium bicarbonate or baking soda.

You can make your own homemade garden fungicide by mixing one tablespoon of baking soda and one tablespoon of liquid dish soap together in one gallon of water.  Just make sure your plants have had plenty of water to drink before you spray this mixture.

Bob

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