1:Types of chemicals
Herbicides, Pesticides and how they work
There are several different types of chemicals, the two most common are herbicides and pesticides.
With herbicides, these products boil down into systemic, hormonal and contact.
Systemic (like roundup and weedol) trans-locates through the leaves and gums up the plants growth causing it to die. It is only absorbed by the plant through the leaves. When it hits the soil it is locked in the soil where it degrades over a period of six weeks. When customers request to purchase a systemic herbicide the team advise them on the best time to spray the plant to ensure minimal affect on insect life.
Roundup carrier material are more destructive, weedol while it contains the same glyphosphate the carrier materials are not as destructive which is why the team will suggest this as an alternative to Roundup.
Hormonal control of plants is often used on a larger scale like farming this is because of the way hormonal controls work. The synthetic auxin class of herbicides 2,4-dichlorophenoxyacetic acid or 2,4-D mimic plant hormones, causing the plant to grow uncontrollably, breaking down critical structures like the cell walls. Another hormonal herbicide work in a slightly different way, diflufenzopyr inhibits the movement of auxinic compounds out of cells. The killing action of synthetic auxins is not caused by any single factor, but rather the disruption of several growth processes in susceptible plants. As you can imagine this is not very marketable to the general public for use in their own gardens, as often they wish to purchase a herbicide to quickly get rid of unwanted vegetation, rather than watching its uncontrollable growth for a period of time.
Hormonal controls affect broad leaf plants but do not interact with mammals or anything else, much like testosterone doesn't affect plants the hormonal control wont affect none plant life.
Contact herbicides are none selective and none residual, these work by destroying the plant tissue that is in contact with the contact herbicide. However because it is none residual and not systemic, the treatment does not reach the root system allowing for unwanted vegetation to regrow.
As long as are kept out of water they are pretty safe they work in the same way that vinegar does, vinegar is also a contact herbicide.
PESTICIDES
Pesticides, these control products are systemic, contact, biological and avoidance.
Systemic pesticides work largely the same as systemic herbicides, they are absorbed by the plant traveling up and down the xylem and phloem within the water in the plant so when a pest bites the plant - the pest dies. The systemic pesticide on average tends only to be active in the plant for around six weeks before it degrades.
Contact killer work very differently to systemic killers, the chemicals need to directly touch the pest you are trying to irradiate. While a lot of these products are organic this does not mean they are ‘safe’ in fact they are often indeterminate killers. Contact killer often contain pyrethrins which are a class of organic compounds derived from Chrysanthemum cinerofolium that have a potent insecticidal activity by targeting the nervous system. While being none toxic to birds and mammals, it is incredibly toxic to wild bees and honey bees. Contact killers are extremely lethal to the target, in some cases leaving a residue on the plant. Meaning any insects who come in to contact with the contact killer will likely die, due to their spiracles being coated in the residual solution or being sprayed directly. While there are safer ways of using this pesticide it is one that doesn’t allow the same amount of control as other pesticides.
Biological controls work by releasing a stronger predator or parasite to kill the pest. A great example of this is ladybugs as a biological control for aphids. However this is something that seems to only be effective in a greenhouse, where the ladybugs are able to be contained. The reason the garden shop does not stock biological controls is because as they are living beings - they have a certain shelf life. It has always been the case that you have to either order biological control online or from a magazine.
Avoidance pesticides work to deter pests from coming near the plant with its strong smell and sticky quality that coats the insect spiracles. However it is not something that often works for the novice gardener as you have to have an in depth knowledge of insect life cycles in order for it to be effective. Azadirachtin is the extract from neem seed oil and is responsible for killing and repelling insects, the remaining material is called clarified hydrophobic neem oil. Azadiractin is only available in commercial products used to disrupt insect hormones that control growth and reproduction. The hydrophobic neem oil is what is sold at garden centres - containing no Azadiractin it is ineffective at controlling adult pests. Hydrophobic neem oil is only effective on juvenile pest, coating the spiracles. Even then it is not effective immediately and re application may be required. Regardless of the type of plant being treated, neem oil will damage the plant by burning the foliage. Over all in our opinion not very effective.
2: SCALE OF USE
The difference between agriculture and horticulture in its affects on the use of herbicides and pesticides
There is a large difference between commercial use (agriculture) and casual garden use (horticulture). Commercial use the farmers often treat a large monoculture on mass, often not taking account for the time of day, weather etc. This is often where studies are focused for neonicotinoids, where insect are directly being sprayed with a pesticide or a herbicide.
There is a distinct difference between acute contact affect and oral exposure when looking into the effects on insect detriment. Studies surrounding the use of neonicotinoids test for effects on oral exposure and acute contact, showing a significant increase in mortality for oral exposure while acute contact shows next to no harm. It is important to remember that spraying a bee in the face with vinegar will have the same effect as using a neonicotinoid.
It is not the chemical it self, but how it is used that matters.
It is not the practice for casual gardeners to directly spray bees and or other helpful insects to orally expose them to herbicides or pesticides - we hope!
In summary the key to safely using pesticides and herbicides, is know how to use them, and what to use them on.