The movie “Field of Dreams” is a family favorite – we love how baseball and the supernatural are interwoven to create a great story. If you haven’t seen the movie, you should – and for those of you that have, you know why it was important for Ray to build the baseball field. Like the magic that unfolded once that physical space was provided, botanical magic emerges from garden soils that support mycorrhizal life. Garden product peddlers have taken advantage of the scientifically-established relationship between plants and mycorrhizal fungi by selling inoculants. And gardeners tend to focus on which of the many brands of inoculants to buy, rather on questioning their efficacy.
I’ve attached a link to my peer-reviewed fact sheet on mycorrhizae for a more in-depth discussion about this symbiotic relationship, but the bottom line is this: inoculants don’t work. To understand why, we need to consider a modified version of the disease triangle. Many gardeners are familiar with this concept, which depicts the three criteria needed for plant disease to manifest: the presence of the pathogen, the presence of a host plant, and environmental conditions conducive to pathogen growth. Pathogen spores are EVERYWHERE in landscape and garden soils – they just aren’t activated unless their host is present and environmental conditions allow their germination. Likewise, mycorrhizal spores are EVERYWHERE in landscape and garden soils. We can make a mycorrhizal triangle to visualize the three criteria for needed for mycorrhizae to develop.
While our understanding of mycorrhizal relationships continues
to expand, we do know some of the environmental factors needed for successful
Soil oxygen. Mycorrhizal fungi are aerobes,
meaning they are active when sufficient oxygen is present.
Woody debris on the soil surface. Mycorrhizal
species are also decomposers of woody material. There is increasing evidence
that a natural woody mulch (not sawdust, not bark) is required for mycorrhizal
establishment. Fungal hyphae colonize the debris, extract nutrients, and
transport them to their host’s roots. Arborist wood chips are an ideal mulch in
this regard as they absorb water and provide an ideal substrate for hyphal
There is a robust body of peer-reviewed research conclusively demonstrating that commercial inoculants applied to plants in landscaped soils have no substantial effect on the development of mycorrhizae. This lack of efficacy has induced some inoculant manufacturers to add fertilizer, especially nitrogen, to increase plant growth and fool consumers into thinking the inoculant was responsible.
The image on the left is the label from a mycorrhizal inoculant. Close inspection (middle image) reveals addition of a fertilizer, which is identical in NPK content to a fish fertilizer (right image).
And here is the lesson “Field of Dreams” provides: if you build it, they will come. Build a healthy soil by mulching with a thick layer of arborist wood chips. Not only do they provide nutrients and absorb water, but their presence reduces soil compaction and increases aeration. You can be assured your plants will be successfully inoculated with your soil’s native mycorrhizal species.
There’s all kinds of maladies that can strike your garden plants throughout the season- diseases, insects, negligence, and more. But one common issue we are seeing more and more here in the corn belt and other places with lots of crop production is herbicide drift. Of course, you don’t have to have a corn or soy field nearby to have issues with drift – it can happen anywhere and anytime an herbicide is applied and proper precautions aren’t taken, even when you or a neighbor are just treating a small area in the yard. There are other avenues of herbicide damage on plants as well, such as using herbicide-treated grass clippings as mulch in the garden.
A wide variety of plants can be damaged by herbicide drift from a variety of different products – trees, shrubs, roses, vegetables, and more. The damage can be slight to severe, and unless the dose is large most plants will grow out of the damage. Vegetables and fruits, though, are of particular concern due to the potential food safety risk from residues of unknown herbicides on the plants. Therefore, it is especially important to be able to identify signs of herbicide drift and take the appropriate course of action which is usually and unfortunately removal of the plant from the garden.
I have to remove the plants!?!?
Yes, you read correctly, I said removal of the plant! I, along with many of my extension colleagues, encourage gardeners who have drift or herbicide damage on their plants to remove them from their gardens. Why take such a drastic measure, especially if the plant may actually recover and “grow out” of the damage? The answer is mainly one of safety. Since it is likely impossible to know exactly which chemical or product formulation was used there’s no way of knowing if the product is safe to use on consumable crops, whether its residue is safe, or whether it is systemic and has a residual effect. A gardener cannot know if there is a pre-harvest interval where the crop will be safe after a certain passage of time or if it will never be safe. And even if you do know the product (let’s say you were the one that used it or you know what is being used by the neighbors) it is likely that there won’t be safety information for use on fruit and vegetable crops, since we don’t typically apply herbicides to plants we want to keep growing. You should also remember that application of such herbicides to fruit and vegetable crops, even if accidental, technically constitutes an off-label (and illegal) application of an herbicide to a non-target crop or pest.
What are the most likely fruit and vegetable plants to be
damaged from herbicide drift?
While just about any plant can be damaged by herbicide drift if enough herbicide gets on the plant, there are a few plants that seem to be more susceptible to herbicide drift. This means that these plants exhibit damage with smaller doses of herbicides than others and will show damage while other plants nearby remain unfazed. The plant that we get the most calls about are tomatoes. This is the vegetable garden crop that is the most susceptible to herbicide drift and just so happens to be the most widely planted crop in the garden. The other edible crop that seems to be highly susceptible to herbicide drift is grape. While grapes aren’t nearly as common as tomatoes in home gardens, wineries in regions with high herbicide use rates are struggling to keep their vineyards going due to the damage.
I live nowhere near a big farm, how do I keep getting drift
Of course, drift can come from anywhere, even a small application of herbicide on a neighborhood lawn or garden. But under the right weather conditions (high temps and wind) some herbicides like dicamba can volatilize and drift for 2-3 miles or more. Even if you think you live nowhere near a farm or other area where herbicides might be used you can get drift from miles away. This makes it hard to pinpoint where the damage is coming from in order to sleuth out what exactly was used. This is especially tricky here in our area where the city of Omaha is surrounded on all sides by farmland, and even has pockets of productions fields sandwiched between residential areas. Unfortunately, one of the prime herbicide application times in our region is shortly after most gardeners plant their tomatoes so we get lots of calls and questions that end up being drift. Thankfully there’s usually still time to replant tomatoes, but it isn’t fun telling people that started plants of their favorite or special varieties that they’ll have to rip them out and go buy new plants.
The kicker is that drift can be random. It can be one or two plants out of a bed of
twenty, or one plant on one side of the garden and another somewhere else, or
an entire field full of plants. It just
really depends on the wind patterns and concentration of herbicide.
Is it drift? Or is
it something else?
At first glance it can be hard to tell if an issue is drift or something else since the signs can look like some other problem until you get up close. There are a wide variety of herbicides on the market and therefore there can be lots of different signs. The most common types of damage you’ll see are light/white colored and necrotic spots from exposure to broad-spectrum herbicides like glyphosate, and curling, twisting, stunting, yellowing, and epinasty from broadleaf herbicides like 2,4-D and dicamba. Epinasty is an unusual, twisting growth pattern on the leaves that result when one layer of the leaf (usually the upper layer) grows faster than the other. You can get weird strappy looking leaves, weird margins, and other irregular growth patterns. The damage from broadleaf herbicides can sometimes be mistaken for heat or drought damage, viral diseases, or even excess watering, all of which cause leaf curling of some sort. I’ll share a few tomato pictures below to demonstrate herbicide damage vs other types of leaf curling. For a great pictorial guide to herbicide damage symptoms, check out this resource form the University of Tennessee.
Can you avoid drift?
Unfortunately, you can only control drift from the herbicides you apply yourself. Pesticides such as herbicides can be used safely and effectively if used appropriately. Reading and following the label instruction is important and is the law, paying special attention to wind speed, temperature, and application equipment, e.g., how fine of a mist does the nozzle create. Drift from the neighbors’ lawn treatment or a nearby farm is really outside of your control, so being watchful for signs of drift is important. Sheltering susceptible crops, like tomatoes, using something as a windbreak might be helpful. As this journal article points out, a windbreak or vegetative buffer around wetlands offers some protection and I noticed a similar effect recently in one of our Master Gardener project gardens. Our Master Gardeners grow thousands of pounds of produce a year for local food banks, and on a recent visit I noticed that about 25 percent of their tomato plants were showing signs of drift (and they were removed and replaced). The pattern was interesting – the only plants damaged were the ones on the outside edge of the garden and the ones along wide walkways in the garden. But plants in the interior were spared. So perhaps planting less susceptible crops on the exterior of the garden and along walkways to act as buffers might work.
And while it isn’t useful for home gardeners, specialty crop
producers (like those all-important wineries) and beekeepers can register for a
program called DriftWatch where they can
be informed when spraying will take place on local farms.
The word “sustainable” gained new life over the last few decades as the concepts of sustainable agriculture and now sustainable landscapes were developed. But what actually are “sustainable” landscapes? This is not something that is easily defined, so I offer my own ideas on the subject here. We can think about this and be thoughtful about landscapes and garden choices as we grow, plant, and maintain landscapes at home and in public spaces.
A sustainable landscape provides benefits
If we start with soil, and nothing growing in it, we can move forward adding landscape elements and benefits begin to emerge. Plants provide habitat for animals including arthropods. As the diversity of plants in a landscape increases, so does the diversity of visitors that use that vegetation. The sculpting of the land may create water catchment areas that help sustain soil moisture. Hardscape (walls, patios, water features and rocks) may create visual focus points. Plants provide many benefits such as sound absorption, dust collection, shade, food, and of course can also be aesthetic. The most sustainable landscape provides its benefits with a minimum input of water, fertilizer and labor to maintain.
A sustainable landscape is appealing
Why expend energy or
spend money maintaining an ugly landscape? Landscapes in order to be
sustained, must appeal in some way to those that use them. In some
cases plants in landscapes are adapted to their environment and
require little applied water, pruning or other maintenance in order
to survive and provide benefits.
of color to a landscape will help its visual appeal. Surveys of
gardeners suggest that colorful landscape are more appealing than
those that are only green in color.
Points of interest within a landscape make it appealing. Also, hiding the landscape with gates, shrubs or walls provides intrigue and beckons you forward to explore the unseen parts. While mass plantings of the same plant material can be stunning so can specimen trees or other plants that are strategically placed for high impact. Landscape art either man made or nature made (rocks and logs) can be become the focus of a landscape making it appealing.
A sustainable landscape often contains trees
Trees are the workhorse of landscapes. They provide shade and thus reduce energy costs in landscapes and they are extremely visually aesthetic. Trees are very important for birds, insects, squirrels, and other animals. Trees remove carbon from the atmosphere and feed the soil food web with the captured carbon. Trees help increase the capture of rainfall and the water infiltration rate of soils. While trees do require maintenance (which can be expensive), maintenance costs can be reduced by proper selection, pruning and placement in the landscape. Trees also have proven health both (physical and psychological) benefits for people who live or reside near them.
A sustainable landscape should not consume excessive amounts of
The traditional landscapes I grew up with included lawns in the front and rear of residences. This of course required frequent mowing, often with gasoline powered equipment. Shrubs were planted that required shearing with electric or gas powered hedge clippers. Since mulches were never much used, fertilizers (derived from petroleum) were used to push growth which was clipped and hauled (using petroleum to power the trucks) to a landfill. As you can imagine a lot of energy is utilized to maintain such landscaping. Much of the petroleum-based energy expenditure can be mitigated by using more mulch especially if it is produced on site, limiting the expanse of turfgrass to needed areas, and planting or utilizing adapted plant materials to the site and climate. Surround trees with tree chip based mulches, not turfgrass.
A sustainable landscape should be water efficient
For those of us in the west we continue to suffer multidecade droughts. Water use efficiency is necessary for our landscapes to be sustainable because water is expensive and limited. For those that have excess water landscapes need to manage the excess water well without suffering erosion or soil nutrient losses that compromise the landscaping.
Sustainable landscapes provide room for waste recycling
One problem with
landscapes that don’t use mulch is that there is no place to
recycle used plant clippings. If landscapes are fertilized and
irrigated to produce lush growth that is then disposed of with a
waste hauler, this is not sustainable. It is best if clippings can
be resused as mulch under shrubs or in other out of sight mulched
Sustainable landscapes use adapted plants
Adapted plants are not necessarily native plants but plants that can live in the soils at the site with the amount of water that is available to them with a minimum of extra care, fertilizer, requirement of pruning or other inputs (pest management) to keep them looking good.
There are likely many other tenets of sustainable landscapes, but these are some of the key factors. The landscape should be adapted to the climate, provide huge benefits and require less maintenance and then it is, by all means and metrics, sustainable.
Did it rain enough last night to water your garden? Have you started running the sprinklers and aren’t sure if they’re running enough? Perhaps you’re not sure that new drip system you installed is doing its job. Or maybe you just want to be more efficient and careful with your water use. How can you know moisture is getting deep enough into the soil to benefit your plants. Is there an easy way to find out?
Yes there is – a simple soil probe will do the trick.
A soil probe can be anything long and sturdy enough to penetrate the soil at least 12 inches (~30 cm.). Handmade soil probes, long screwdrivers, skewers, even the spit from an old rotisserie grill will all work.
A probe made of metal will work best and for safety it should have a handle of some sort. If there’s no handle you should wear sturdy gloves when using it. This set of 22″ screwdrivers was purchased at the local outlet of a national low cost tool franchise. It meets all the requirements and is inexpensive. Plus it’s a set so there’s one for you and one to share!
While you only need the probe to go 12″ into the soil it’s helpful if the probe itself is longer, if only for convenince. The probes are shown here with a yardstick for scale. (Yardstick = 36″=~91.5 cm.)
So you now have a soil probe, how do you use it to measure soil moisture depth? Easy-peasy. Insert the probe straight into the soil at the spot you want to test. You’ll need to use firm pressure but don’t force it into the soil. The probe will pass through moist soil but stop when it hits dry. And this is true for any soil type, sand, loam or clay. When the probe stops, grasp the probe right at the soil surface and pull it out. The part beyond your hand towards the probe tip shows you how deep the moisture is.
Note: if you have rocky or stony soil the probe may hit a rock and stop. Usually you can hear or feel that it hit a hard object. Just adjust the probe’s postion and try again.
For trees, large shrubs and deep rooted grasses the probe showing a 12″ moisture depth is adequate. For shallower rooted plants or annuals 4-6″ is enough. Monitoring soil moisture depth is an easy way to know if your landscape or garden is adequately watered. Water is a precious resource, let’s not waste it.
To estimate how much rain has fallen on your property, check out this site: https://water.usgs.gov/edu/activity-howmuchrain.html?fbclid=IwAR3SFjeaflrsXyCtZ_qdUUeltuK9qzYolmybq0wz5KNH2xP9KdJf1g_uckk