Tuesday, June 7, 2016

Vineyard Health: Being a Dietitian to Plants and Soil

So if you're new to my blog, you may know know that I practiced as a clinical and long term care dietitian for many years before transitioning full time to our family farm. I still use these skills day in and day out as the science of nutrition is still the same,  I'm just applying it to a different biological system. If you haven't found me yet on Facebook, I'm known as The Foodie Farmer. I post almost daily what I'm doing on the farm and use Facebook as my mini-blog or "view from the office" and general stuff of interest in ag and random topics.

Today I walked up and down and up and down about 20+ acres of grapes in our vineyard. This is a critical time of year for grapes as the plants are in bloom. The blossoms need to be pollinated in order for fruit to developed. Cultivated grapes are hermaphroditic, meaning they have both the male and the female parts needed to self-pollinate. Pollinators like bees are not required for grapes to be pollinated. Bees seldom visit grape blossoms, probably because they are near microscopic, not very floral, not very attractive, and offer little nectar for the bee. There are much bigger blossoms around that would be less work for the bee that's for sure.

Chardonnay blooms


Chardonnay blooms



Plant and soil health tools of the trade
 My goal for today is the pull soil samples to check for nematodes and petiole samples to check the nutrient uptake of the plant at this stage of growth. I need a bucket for collecting soil cores, a soil sampler, and a paper bag for collecting petioles.

Pulling a soil core
 I need about a pint of soil per sample and I've divided my vineyard into blocks basically by variety so I know what I need to do where when the test results come back. I pull more soil than I need, mix it together in a bucket and pour about a pint of soil into a ziplock bag.


4-10" of a soil core is recommended for nematode sampling in a vineyard.
Soil cores taken at random intervals from the root zone of the grapevine.
Rapeseed cover crop to remediate for nematodes

I want to know what level of nematode pressure there is in my vineyard and what types of nematodes are present at what levels. Not all nematodes are bad, some are beneficial. So my approach to remediation has been to plant a cover crop of rapeseed which is in the brassica family. When it is rototilled into the soil and decomposes, it releases glucosinolate, a biofumigant that helps lower nematode populations. In addition, rapeseed is great for breaking up compaction and improving soil filtration. It has a really long taproot that will loosen the soil and improve the soil tilth. So for me, its doing a couple of jobs to help me improve the soil health of my vineyard. We also use it pretty widely as a cover crop before many of our crops for that reason.

Not only am I sampling for nematodes, but I am also sampling soil nutrient tests. So when I get the results back for the petioles, I know what nutrients were present in the soil at what levels and comparing that info to the nutrients in the petiole analysis, tells me what the plant is able to utilize from the soil. Many factors influence how a plant is able to utilize nutrients from the soil. Just because a nutrient is present in the soil, does not mean is is automatically available to the plant. Things like pH, moisture, temperature, the cation exchange capacity (CEC) of the soil, physiologic issues with the plant, and the nutrient must be in the chemical form that the plant can utilize. For example, plants can only utilize nitrogen in the form of ammonium or nitrate. Another nutrient, phosphorus, is only available to the plant if the soil pH is between 5.5 and 7. Outside those parameters, and the plant cannot take up phosphorus as well as other nutrients.

Sampling petioles
 Petioles are the stems of the grape leaf. At bloom, I want to sample the petiole across from the developing cluster. This will tell me what the cluster is receiving in vine nutrition by sampling the petiole across from it. The analogy I use is that this is like going to the doctor for a blood test. There's a lot of information we health care practitioners can gleen from lab results - plant or human.

My petiole samples separated in bags by variety.

Off to the Post Office with my samples!

Anxious to know my results for the petioles as it will tell me if I need to make any nutrient adjustments in the different varietal blocks. It will also give me a chance to compare the previous year's results to know what direction the different nutrients are headed in so I can see if my long term plant health and nutrition plan is working (see I can still be a dietitian, just with plants and soil instead of humans).

Tuesday, May 17, 2016

"GE Crops Are Pretty Much Just Crops"

The National Academies of Science released their consensus report on genetically engineered crops today. The completion of a 2 year process by a 20 member panel of diverse experts from a variety of backgrounds reviewing the science and perspectives on genetically engineered crops. The study was meant conduct a thorough review and to address and inform the public of the results, to help guide the public discourse which was become ever polarized. 

Their mission: "Consumers in the US and abroad get conflicting information about GE crops. Proponents tout the benefits while opponents emphasize the risks. There is a need for an independent, objective study that examines what has been learned about GE crops, assess whether initial concerns and promises were realized since their introduction, and investigates new concerns and recent claims."

They examined:
  1. The history of the development and introduction of GE crops and the experiences of developers and producers of GE crops in different countries and regions.
  2. The history of GE crops that were not commercialized.
  3. The scientific basis of purported negative effects of GE crops (e.g., poor yield growth potential, deleterious effects of GE food on human and animal health, increased use of pesticides and herbicides, the creation of “super-weeds,” reduced genetic diversity, fewer seed choices for producers, and negative impacts on farmers in developing countries and on producers of non-GE crops).
  4. The scientific basis of purported benefits of GE crops (e.g., reductions in pesticide use, reduced soil loss and better water quality through synergy with no-till cultivation practices, reduced crop loss from pests and weeds, increased flexibility and time for producers, reduced spoilage and mycotoxin contamination, and better nutritional value potential).
  5. The scientific foundation of current environmental and food safety assessments for GE crops and foods and their accompanying technologies.
  6. New developments in GE crop and food science and technology and the future opportunities and challenges those technologies may present, including research and development, regulatory, and ownership, examined through the lens of agricultural innovation and agronomic sustainability.
While the report is nearly 400 pages in length, the report brief HERE summarizes their main conclusions. Or you can jump to their 16 page findings and recommendations chapter from the full report HERE

I was fortunate to be part of the process when I spoke before the committee in March of 2015. My topic was weed control in cropping systems. I spoke about our farm's experience with biotech, conventional and certified organic cropping systems which we did simultaneously. My presentation "

Integrating weed, pest, and disease management across crops within farming can be accessed HERE


As a result of watching this webcast, I have resumed my efforts to crunch the data from 2015 comparing our GMO to NonGMO production costs and yield data. I last blogged about that in one of my most popular posts GMO versus NonGMO: The Cost of Production. Its time I did the 2015 update. Preliminary data shows in soybeans, GM out yielded NonGM by over 25 bushels per acre. I haven't gotten to the corn file yet so stay tuned.

For me, this is an important report for several reasons, one because I was a presenter but second because I spent 5 years on the Advanced Technology in Food Production workgroup reviewing the same issue and science for the Academy of Nutrition and Dietetics Evidence Analysis Library. We were grading research articles to be used as part of the Academy's library as well as for updating the position paper on biotechnology. Our workgroup however, was limited to primary research on humans, no animal studies, no human cell lines studies which limited our results. I'm impressed with the depth and breadth by which the #GECropStudy committee undertook to delve into as many aspects of this issue and come up with as many findings. I look forward to reading their full report (which I ordered because I didn't not want to print 400 pages at home nor sit at the computer reading it for days on end).

The NAS GE Crop Study report affirms what we have seen on our farm since 1998 when we first planted 10 acres of biotech corn as a test plot to see for ourselves. It has been a benefit for our farm year in and year out. We like the lower impact of the herbicide and insecticide traits it provides. We like the premium that growing high oleic oil soybeans provides as a healthier fat for consumer benefits in removing transfats from packaged foods. We like the flexibility it provides us in managing our fields when Mother Nature doesn't cooperate and the reduction in tillage with no till and conservation till biotech contributes to so we preserve our topsoil helping keep sediment out of the Chesapeake Bay. 

My title came from a quote by Dr. Wayne Parrot that  I saw in the New York Times Genetically Engineered Crops Are Safe, Analysis Finds and which I think is a good assessment: 

“The inescapable conclusion, after reading the report, is the G.E. crops are pretty much just crops. They are not the panacea that some proponents claim, nor the dreaded monsters that others claim.”


Wednesday, April 20, 2016

Do GMO's cause food allergies?

I recently was interviewed for an article in Forbes.com on GMOs and food allergies. It is an area where I have spent a lot of time reviewing the scientific literature having served for 5 years on the Academy of Nutrition and Dietetics ""Advanced Technology in Food Production" Evidence Analysis workgroup. We reviewed papers and spent time with renown food allergy expert Dr. Steve Taylor who is a Professor with the University of Nebraska Department of Food Science and Technology and the Co-Founder/Director of the Food Allergy Resource and Research Program.

My Forbes interview:
Are GMOs Causing Food Allergies? A Farmer And RD Sets The Record Straight

Tuesday, December 22, 2015

Dear High School Student

It took a letter from a high schooler to bring me back to this blog. Yes, I've been absent for about 6 months now, not because I'm not blogging, but because I have been using The Foodie Farmer Facebook page as my means of "blogging". It works well for me especially to illustrate whats going on the farm day in and day out, and frankly I didn't have anything to write about. But that has now changed. Today, this post went up on Forbes and yes, the student I am responding to did receive the original letter a couple weeks ago.


POST WRITTEN BY
Jennie Schmidt, MS, RD


Jennie is a Maryland farmer. She is also a registered dietitian who speaks about food and farming systems, sustainability and family farms.


A photograph of Jennie’s farm in Maryland during the annual wheat harvest. (Image Credit: Jennie Schmidt)
Right after Thanksgiving, I received a letter in the mail from a high school student concerned about the cost of GMO labeling and identity preservation based on some readings they had done in class. The first thought that struck me was how well written, thoughtful, and respectful the letter was. My second thought was how awesome it was that a teacher would facilitate such an undertaking with a student when they could have easily taken it to social media and had an entirely different approach. I knew right away, I would respond because civil discourse is often what is most lacking in today’s society and around the topic of GMOs specifically. The student expressed concern about the cost of identity preservation and segregation of seeds based on my Foodie Farmer blog “The Cost of GMO Labeling”. They expressed support for the idea that farmers should be growing “all natural crops without altering genes.” Responding to the letter gives me the opportunity to welcome further discussion and if I’m lucky, host them on my farm. As time consuming as it is, I have found the most effective means to communicate about agriculture and help consumers understand what farming practices mean and what their implications are, is to have people visit. I hope the student and teacher take me up on the offer.

Dear High School Student,                                                                                                           December 9, 2015
                Thank you for your letter concerning our use of biotechnology on our family farm. I appreciate that while your position differs from ours, your letter was polite and respectful. That aspect is often absent in conversations around the topic of GMOs.
                Our family farm has been practicing sustainable agriculture in the United States for 3 generations. We have simultaneously practiced “conventional”, “biotech” and “certified organic” farming systems on our 2000 acres. Each of these systems has advantages and disadvantages and what’s important for each family farm is to decide what is best for their soil. Schmidt Farms has been using “GMO” seeds since 1998, 2 years after they received government approval. We also grow NonGMO crops every year however we no longer grow any certified organic crops. If you read my Foodie Farmer blog “GMO vs NonGMO: The Cost of Production”, you saw that the benefits to our farm are important. While I haven’t finished calculating the figures for this year’s harvest, historically crops grown from “GMO” seed have higher yields than our non-GMO crops. That’s important because if we do not have enough crops to sell, then the farm cannot pay its employees or pay its bills. I don’t think anyone would want to work for a business and not bring home a paycheck. We would also not want to have to sell the farm because we couldn’t make ends meet.
                Another reason we grow GMO crops is because they are good for our soils which is good for the Chesapeake Bay. I’m sure you’ve heard that the water quality in the bay is poor and that one of the biggest pollutants is sediment. Sediment comes from exposed soil from housing developments, construction, and exposed fields. Sediment blows away in the wind and runs off in the rain. About 80% of the farm fields in Maryland are “no-till” or “conservation tillage” meaning they have little to no disturbance of the soil and no deep plowing. Biotechnology has helped facilitate the reduction of sediment into the Chesapeake because farmers are better able to control weeds without plowing or disturbing the soil. How agriculture is helping meet the Chesapeake water quality goals can be found at: stat.chesapeakebay.net/BayTAS. No-Till agriculture is a very important conservation practice for farmers in Maryland.
                One of the “GMO” crops we grow are high oleic acid soybeans. We have to protect their genetic identity through segregation just like we have to protect the genetic identity of our nonGMO soybeans which go for tofu. The high oleic acid soybeans have no transfats which is an unhealthy type of fat and is being used to eliminate transfats in cooking and packaged foods. These soybeans have to be protected from nonGMO soybeans because in order to have the benefit of high oleic acid, they cannot be contaminated by nonGMO beans which don’t have the same fat content. So this example is the opposite of what most people think. The GMO crop needs to be protected from the nonGMO crop so that the oil derived has the high oleic acid content it is supposed to have and not the oil content of other soybeans. The issue of seed segregation cuts both ways, depending on the market demand for different traits. My point in the Cost of GMO Labeling blog is that to truly segregate by trait through the entire supply chain for “commodity” crops ie: general, non-specialty corn or soybeans would be prohibitively expensive.
                There are a variety of different plant breeding techniques that are used to modify seeds for crops.  You said in your letter than you wanted to see farmers grow “all natural crops without altering genes” and unfortunately, that’s impossible. Every crop we eat has been domesticated and therefore has altered genes. All types of plant breeding techniques alter genes. That’s the mechanism by which humans domesticated wild plants over time to become food crops. Plant breeding includes: traditional cross breeding, hybridization, mutagenesis, and genetic engineering . Each of these breeding types alters the genes by changing the DNA of plants. All of them except genetic engineering are approved for use in organic agriculture so your best bet if you choose to avoid GMO is to buy organic or buy foods labeled by the NonGMO Project but regardless, all food contains altered genes.
                As a Registered Dietitian, I have studied biotechnology which was the focus of my Masters degree. In addition, I have served for 5 years on a workgroup for the Academy of Nutrition and Dietetics reviewing the science around the safety of foods produced from biotech crops. The consensus is the safety of these foods is equal to the safety of foods produced through conventional breeding practices I mentioned above. As a mom of two high school students myself, the safety of the food we grow on our farm is critical because my family also eat what we grow. I encourage you to continue to seek more information. Nothing is better than to do research on both sides of any issue so that you have the full story to make a conclusion. Two very good resources are Biofortified.org and geneticliteracy.org which publish information about agriculture as well as health and other genetic issues.
                Thank you for reaching out to me. Again, I do appreciate civil discourse on this topic and I appreciate that at your age, you took this step to have an intelligent discussion on the topic. If you, your teacher, or your class is ever interested in a tour of our farm, please contact me. We are not embarrassed or ashamed of what we do and are happy to share our experiences with farming systems and the crops we grow with folks who are truly interested in learning where their food comes from.

Sincerely,
Jennie Schmidt
The Foodie Farmer







Monday, June 15, 2015

Spraying Isn't Dousing

Earlier this week, on my Foodie Farmer Facebook page, I shared this post of me spraying in my vineyard.


I've never had a post reach this many people. With over over 9,000 people reached and nearly 50 shares,it is obviously something people are interested in and hopefully want to learn more so figured it was worth a blog post for further discussion.

First, when we spray, we don't "douse". The definition of "douse" means to drench or to pour.... which is exactly what we are NOT doing. Second, ALL pesticides (fungicides, insecticides, and herbicides) whether they are organic or synthetic have a "rate per acre" which is the concentration they should be mixed and applied to be effective against a target pest. Third, all pesticides (fungicides, insecticides, and herbicides), whether organic or synthetic have a "carrier". A carrier is the means by which a pesticide is conveyed or transported. Most typically this carrier will be water.

In this picture above, I am towing an air-blast or fan sprayer with a 500 gallon tank. My goal in getting good coverage through the entire canopy of my vineyard is to apply 50 gallons per acre. So I can cover 10 acres with a full tank. I don't have 500 gallons of pesticide in this tank, I have mostly water, almost a gallon of a liquid chemical, and about 50 pounds of 2 dry/powder organic pesticides..

So let's look at this more closely....

In this tank, I used 2 fungicides to protect my vineyard from powdery and downy mildew, amongst other things. I mixed OMRI (organic approved) Sulfur at 2 pounds per acre, OMRI listed Copper at 3 pounds per acre. I also sprayed the synthetic insecticide Intrepid at 12 ounces per acre.

I stink at math so feel free to check my calculations but here is what I mixed:

I will cover 10 acres with this tank so need the right concentration in order for the product to work:

2 lb sulfur (its what we call WDG or wettable dry granular) x 10 acres = 20 pounds

3 lb copper (also granular) x 10 acres = 30 pounds

12 ounces Intrepid (liquid) x 10 acres = 120 ounces (8 ounces shy of 1 gallon)

So the dry products will displace some water because of their density, and of course the 120 ounces displaces at least 120 ounces of water in my tank, so to estimate, I'm adding approximately 495 gallons of water to 5 gallons of product (I did not do the Archimedes calculation, this is my ballpark estimate from having 15 years as a pesticide applicator and then erred on the side of caution and rounded down).

So in dilution i have a full tank of 64,000 ounces of solution to apply across 10 acres.
1 acre is 43,560 square feet, so I have 435,600 square feet to cover with my tank.

Total tank mixture: 64,000/435,600 = 0.146 ounces of solution per square foot is applied.

Of that:

Total Intrepid: 120 ounces/435,600 = .00028 ounces per square foot applied.

Total sulfur: 20 pounds/435,600 = 0.000046 pounds per square foot applied.

Total copper: 30 pounds/435,600 = 0.000069 pounds per square foot applied.

With fungicides in fruits and vegetables, we are spraying to protect the foliage because diseases that impact the health of the leaves will result in fruits and veggies that don't ripen. The leaves function to convert sunlight into carbohydrates to give the plant energy. Without healthy leaves, the plant can't send enough carbs to its "produce" to ripen.

When I spray with the fan-sprayer in the vineyard, I'm using a higher rate per acre than we would use in our corn or soybeans.


The sprayer above is used in our tomatoes, green beans, wheat, corn and soybeans. We are spraying at the 15-20 gallons per acre rate for herbicides or if the crop including our vegetables needs a fungicide, we are spraying at the 30-35 gallon per acre rate.

Its a 750 gallon tank so using 15 gallons per acre, this sprayer can cover 50 acres per tank. This equals 2,178,000 square feet.

750 gallons x 128 ounces in a gallon = 96,000.

96,000 ounces in that spray tank /2,178,000 square feet = 0.04 ounces per square foot.

This is pretty far from "dousing".......

So let's look at these labels a little closer.

Pesticide
Class
OMRI/Synthetic
Signal Word
Re-Entry Interval
LD50 (rat oral)
Sulfur
Fungicide
Organic
Caution
24 hours
2000 mg/kg
Copper Sulfate
Fungicide
Organic
Danger
48 hours
30 mg/kg
Intrepid
Insecticide
Synthetic
Caution
4 hours
5000 mg/kg
Glyphosate
Herbicide
Synthetic
Caution
12 hours
5100 mg/kg

The signal word is indicative of acute toxicity to the person who is mixing the product.

The re-entry interval is the time between application and when someone can go into that field to work without have to wear protective equipment.

The LD50 is a specific measure of acute toxicity by some means of ingestion - oral, inhalation or dermal absorption.

Make no mistake, these all are pesticides. Whether a product is organic or synthetic is irrelevant. Both are toxic and how it is derived does not necessarily make one safer than another. Pesticides are by definition toxic to something, they have to be or they would not be pesticides. The "cide" part of the compound word "pesticide" is derived from the Latin word meaning "to kill", so fungi"cide", insecti"cide" and herbi"cide" are all by definition toxic to some class of pest. That does not mean that they are universally toxic to everything. Not all insecticides kill every bug, not all herbicides kill every weed. Some are targeted, some are broad spectrum. Don't make assumptions about what we are using without asking or you might be wrong.

And be careful what you are doing yourself. According to the U.S Fish & Wildlife Service"Homeowners use up to 10 times more chemical pesticides per acre on their lawns than farmers use on crops, and they spend more per acre, on average, to maintain their lawns than farmers spend per agricultural acre." More often than not, homeowners are not wearing the mandatory protective equipment that is specified on every pesticide label, exposing themselves and others unnecessarily. Homeowners are more likely to "douse" because you may spray until the liquid drips off the plant. Exactly what we farmers don't do....

Part II: Spraying not dousing

I posted this blog this morning. This afternoon, I was back in the vineyard with my weed sprayer. I control the weeds under the vines to reduce the competition for nutrients and moisture. My sprayer has 2 nozzles, one on each side of the row, so I am doing what we call "band" spraying, a 4 foot strip, 2 feet on each side of the row, not spraying the entire vineyard floor.

I happen to have a paper towel in the cab of my tractor so I put it on the ground.

Unsprayed paper towel


Sprayed paper towel below my nozzle.

You can see my single nozzle above the paper towel. 

Because this is spraying and not dousing, I do not need to soak the paper towel. I drove the same speed past the paper towel as i would had I been spraying weeds. If you look closely, you will see that it is orange speckled. above. Below is a closer up pic.

A closer look at what a spray pattern looks like, it is not doused.

This is it. Those orange speckles are all the 6 inch by 12 inch paper towel received as I sprayed over it. The plants do not get "doused". There is no dripping off of chemical solution. They do not need to be soaked in herbicide to achieve good weed control. There is no saturation. There is no dousing.

Friday, June 5, 2015

Farming Techniques Do Not Belong To One Farming System

The subtitle to this blog is "Synergistic Farming: Using the best practices from all farming systems".

For folks who want to put our family farm "in a box", we are a conventional farm.

For folks who are of broader minds and philosophies, or can conceptualize that conventional does not equate to "bad", then we are a "synergistic" farm.

If you have followed me for any length of time, you know I talk a lot about farming systems, sustainability, conservation, and biotechnology. The practices that we use are a melding of various techniques often credited to one type of farming system or another. Rather than holding ourselves to a certain set of "rules" or limiting the tools we are able to use, we choose to practice and maximize the synergies from taking the best of organic, conventional and biotechnology in order to make our family farm as sustainable as possible.

First, let's look at what I mean by farming systems:



The chart provides a brief illustration about the "main" concept behind each farming system. There is certainly broad overlap between  these main "concepts" within each of the 3 farming systems. All 3 systems can use precision agriculture, the latest technology to reduce inputs and be more prescriptive toward each crop. All 3 systems can use modern plant breeding to enhance desired traits in plants however "genetic engineering" or "GMO" are restricted from use in organic agriculture. Conventional and organic plant breeding takes place either by traditional crossing, hybridization, or radiation or chemical mutagenesis. All 3 systems can use techniques that address and enhance soil health.

Typically what you hear in the media is that one system has cornered the market on "soil health" or another system has cornered the market on "precision agriculture".

Today, family farms use the synergies that each farming systems offers to maximize sustainability.

Today, those "farming system" lines are far more blurred.



Today, there is significant cross over between the 3 farming systems. This is what I mean by "synergistic" farming, a melding of the best each system has to offer. The chart about shows what our family farm practices. When we had about 100 acres certified organic, we did not change the way we farmed because we have been using cover crops, green manures, crop rotation, conservation tillage, and IPM for decades. To us, these are just standard operating procedures, they aren't "organic" practices. We followed Rodale's no-till organic recommendations by rolling our cover crops with a buffalo chopper and then no till seeded corn into the residue. It was a mess. The corn yielded 47 bushels per acre as compared to 110 bushels per acre in our conventional corn that same year, both dry land or unirrigated. Other years we would rotary hoe and cultivate numerous times to control for weeds but soil disturbance is soil disturbance and not something we like to do here in our Chesapeake Bay watershed. Disturbing top soil encourages erosion. Wind and rain take sediment away from disturbed top soil. Phosphorus is adsorbed to sediment so when sediment moves, so does phosphorus. The extensive tillage and yield loss in our organic field led us to choose to be synergistic rather than purely organic for the sake of being certified. For us, it was the most sustainable choice we could make.

By doing what's best for our fields, we are focused on soil health, enhancing the soil profile without excessive tillage, practicing more conservation not less, choosing the safest most effective pest control as possible whether its "natural" or "synthetic". Just because a product is organic or natural, does not make it nontoxic. Sometimes, a synthetic product is safer than an OMRI approved product. Again, that's determining for our family farm, the synergies that work in our environment and in our soils.

There is no "one" system that is "best", There is no "one" way of doing things that should be done carte blanche by every farmer, everywhere. There is no "cookie cutter" system that should be applied to every farm. What we farmers should be doing is maximizing the synergies of all best management practices that meld together the best for our soils while preserving our inputs and natural resources.

Family farms continue to move along the sustainability continuum and are fundamentally changing "farming systems" so that the synergies of each best management practices mean we do not fit into a cookie cutter mold of a certain "type" of farm.







Thursday, March 19, 2015

Nutrients Are Pesticides: The Dose Makes The Poison

Most people find it odd that I am a Registered Dietitian who is licensed as a commercial pesticide applicator. I actually find it quite advantageous because what I studied in my nutrition degrees both undergrad and grad school, applies across multiple biological systems, not just human systems, but soil and plant systems too. Because I have a solid understanding of the science of nutrition, I therefore have a solid understanding of the science of pesticides. Many of the nutrients I studied as an RD, have applications as pesticides.

Paracelsus was correct when he coined the term "The dose makes the poison". 

First, lets start with some definitions:

Nutrient: "Chemical substances obtained from food and used in the body to provide energy, structural materials, and regulating agents to support growth, maintenance and repair of teh body's tissues. Nutrients may also reduce the risk of some diseases" Whitney & Rolfe, Understanding Nutrition, 9th edition (yes I know, my copy is dated. This is the one I used to tutor undergrads during grad school, not my copy as an undergrad!)

Pesticide: A pesticide is a chemical used to prevent, destroy, or repel pests. (EPA)

Any chemical can be toxic, whether its natural or synthetic, depending on how much you eat, drink or absorb. Nutrients are the chemicals make up of food. 

Nutrients in high doses work as pesticides to control bacteria, fungi, molds and mildews, mainly in fruit and vegetable crops. Nutrients are typically used as protectant fungicides, meaning they are used proactively before disease appears to protect the foliage of the plant. Remember from high school biology how important photosynthesis is in the growth and development of a plant? Without foliage, or if foliage is damaged from mildews, a plant cannot photosynthesize efficiently. Photosynthesis is the process that converts sunlight into energy (carbohydrates). Photosynthesis is required for fruits and vegetables to ripen. Without sufficient foliage on the plant, grapes wouldn't ripen and turn sweet, tomatoes wouldn't turn red, watermelon wouldn't get sweet and pink, strawberries wouldn't turn red and sweet. Fungicides, in the form of nutrients like sulfur, copper, zinc, and manganese protect the plant in advance of any disease. They are not "treatments" and do not work after a plant has developed a disease, they only work to protect the plant from developing the disease. 

First, let's look at the recommended dietary intake of nutrients for humans:


Nutrient
RDA
UL
Major functions:
Zinc
8-11 mg/d
40 mg/d
Cellular metabolism
Protein synthesis
Wound healing
Cell division
DNA synthesis
Manganese
1.8-2.3 mg/d
11 mg/d
Activates many enzymes that are critical to metabolism, bone development, and wound healing.
Copper
700-900 µg/d
5000-10000 µg/d
Critical in the function of enzymes that control energy production, connective tissue formation, and iron metabolism.
Sulfur
No RDA-Metabolic
breakdown of the
recommended intake for
protein and sulfur amino
acids should provide
adequate inorganic sulfate
for synthesis of required sulfur-containing
compounds.
No UL
The body does not use sulfur as a nutrient by itself. Contributes to protein structure. Acts as a bridge between amino acids in hormones like insulin.

Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people.

Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.


Next, let's look at the recommended application rates of these nutrients as pesticides as approved by EPA:

Pesticide
Rate/Acre
Oral LD50
Controls For:(grapes/tomatoes)
Zinc
3-4 lb/acre
1400 mg/kg
Phomopsis, Black Rot, Botrytis, Downy Mildew
Manganese
1-4 lb/acre
5000 mg/kg
Anthracnose, Early Blight, Late blight, Bunch rot, Downy mildew
Copper
0.75 – 1.75 lb/acre
1847 mg/kg
Downy Mildew, bacterial spot, anthracnose,
Sulfur
3-20 lb/acre
2000 mg/kg
Powdery Mildew, spotted mite, red spider mite.

For comparison purposes - Vitamin D is highly toxic with an LD50 of 10 mg/kg, whereas table salt (sodium chloride) has an LD50 of 3000 mg/kg.

What is LD50?

Oral LD50An LD50 is a standard measurement of acute toxicity that is stated in milligrams (mg) of pesticide per kilogram (kg) of body weight. An LD50 represents the individual dose required to kill 50 percent of a population of test animals (e.g., rats, fish, mice, cockroaches). Because LD50 values are standard measurements, it is possible to compare relative toxicities among pesticides. The lower the LD50 dose, the more toxic the pesticide.
A pesticide with an LD50 value of 10 mg/kg is 10 times more toxic than a pesticide with an LD50 of 100 mg/kg.
We went from milligrams per day as a recommended dietary allowance to pounds per acre to control for disease. The vastly escalated dose converted these nutrients from dietary healthfulness into effective pesticides. 
You can see, although these pesticides are "natural", as in nutrients, they are still toxic. By definition, a pesticide must kill or control something. 
There is no such thing as a nontoxic pesticide. 
Here is a good graphic that depicts the toxicity of natural versus synthetic pesticides:
Sense About Science
If this topic is of interest to you, I recommend these excellent additional readings:
As an RD, I know these nutrients are essential for health and wellness in our diets.
As a pesticide applicator, I know these pesticides are essential for the health and wellness of my fruit and vegetable crops.
The nutrients in your multi-vitamin are not toxic but these nutrients are not edible at the pesticide dose.
The dose makes the poison.