Watch out for weeds

Watch out for weeds

‘A weed is but an unloved flower’ – that’s according to popular author and poet, Ella Wheeler Wilcox. I guess she’s right…especially the ‘unloved’ part. They may be flowers, but as long as they are growing where they should not, they are weeds and we don’t love them. We don’t love them, and we don’t want them. They steal the water and nutrients meant for our precious crops, act as hosts to various pests and diseases, and can cause damage to machinery during harvest. That’s why farmers spend a lot of time and resources on weed control. Effective control, however, starts with proper scouting and identification of weed species.

Scouting for weeds is important because that is how to locate weed populations before they spread through the field and cause more damage. Identifying specific weeds also helps to choose appropriate herbicides and best timing for maximum weed control. At this early stage of the season, weeds are mostly harmless-looking seedlings. But make no mistake about it, they can eventually outcompete your crop and can take over your patch of land. Controlling weeds when they are young is more effective than when they are mature and are producing seeds. There are various guides that help to identify weed seedlings. These days there are also apps you can install on your phone that can identify a weed from an uploaded picture. These will be helpful as you scout your fields early in the season.

One weed that you should watch out for is Kochia (Kochia scoparia; see picture below). Kochia is indeed an unloved flower. It was first introduced into Canada as an ornamental plant probably around the mid to late 1800s but has since become one of the most problematic weeds in the Prairies. It’s an annual broadleaf weed that reproduces by seed. Seeds start germinating in early spring, helped by the weed’s tolerance to frost, and may continue to germinate throughout the growing season. It can spread quickly and establish itself as the dominant weed especially in dry and saline soil conditions. In drought, roots can extend as far as 10 feet into the soil in search of water and nutrients. Our crops could definitely learn a thing or two from Kochia especially under the present dry spell.  Yield losses can be significant. Losses of 73% have been found in wheat at a Kochia density of 195 plants per square meter.

Kochia (Photo courtesy of Ohio State University)

 

The key to effective control of Kochia is to spray early because Kochia is usually one of the first weeds to emerge in the spring and is often beyond the optimal susceptible growth stage when herbicides are normally applied in-crop. Herbicides are most effective when the weed is small. Herbicidal control generally declines as plant size increases. Group 2, 4 as well as glyphosate-resistant Kochia has been found in the Prairies so, herbicide rotation and using tank mixes with multiple modes of action are recommended. Talk to your SynergyAG rep about how to control this and other problematic weeds.

 

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

What do plants need during a dry spell?

The current dry conditions across many parts of the Prairies have farmers keeping one eye on the sky and the other on their crop. Although it is heartwarming to know that dry soils in spring are not a sure sign of crop failure, it is important to be aware of a few things that happen under dry conditions: There is slow movement of soil nutrients towards plant roots so plants are unable to take up nutrients in adequate amounts; soil microorganisms involved in nutrient cycling are inhibited; plants reduce or close stomatal opening, thereby reducing transpiration; this reduction in transpiration limits nutrient transport from the roots to the shoot and results in a low absorption power in the roots. In short, dry conditions cause reduced uptake of nutrients from the soil, and poor nutrient transport within the plant.

What do water-stressed plants look like?

Even before they show any visual signs, the leaf temperature of water-stressed plants will rise. This is because when stomata are closed, energy transfer between plant and surrounding air is limited. Depending on the type of crop, visual symptoms may include dull green colour, curled leaves, droopy appearance, yellowing or browning of leaves, and wilting. By the time visual signs of water stress appear, a reduction in final yield may already have occurred.

 

So, what can we do?

Growers may be tempted to cut back on input such as fertilizers in a dry spell so as to reduce economic risk. However, research shows that good nutrition is even more important in dry periods. Crops need an adequate supply of macro and micronutrients early in the growing season to develop a strong root system and ameliorate the effects of drought. Some elements have been found to be particularly beneficial in dry conditions. For example, in 1999, south-central Ohio suffered severe drought, and corn yields ranged from 40 to 70 bushels per acre. Certain farmers in the area, however, produced more than 150 bushels per acre. Soil test results showed that these high-yield farmers also had high soil test levels of potassium (K).1 Potassium is critical in dry conditions because the element governs the stomatal opening mechanism and can help plants tolerate water stress. The ability of plants to cope with water stress has also been shown to be enhanced by adequate phosphorus nutrition2. Furthermore, trace elements such as zinc (Zn), copper (Cu) and manganese (Mn) play a role in the structure of many antioxidant enzymes; therefore, a deficiency of these elements makes the plant more susceptible to environmental stresses3.

When the soil is dry, roots are unable to take up adequate amounts of nutrients from the soil, so foliar application of nutrients will be more effective than application of fertilizers to soil. Using a fertilizer with a low salt index becomes even more important in this situation so as to avoid damage to shoots and roots. Furthermore, water-stressed plants have a reduced defence mechanism against pests and diseases, and can easily be outcompeted by weeds. Detecting and dealing with these problems early will give crops a better chance of recovery when moisture becomes adequate.  Talk to your SynergyAG rep for product and agronomic advice.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

References

  1. Mosaic Crop Nutrition. Potassium and drought (https://www.cropnutrition.com/potassium-and-drought) Assessed May 30, 2019.
  2. da Silva, E. C., Nogueira, R. J. M. C., da Silva, M. A., & de Albuquerque, M. B. (2011). Drought stress and plant nutrition. Plant Stress5(Special Issue 1), 32-41.
  3. da Silva Folli‐Pereira, M., Ramos, A. C., Canton, G. C., da Conceição, J. M., de Souza, S. B., Cogo, A. J. D., … & Rasool, N. (2016). Foliar application of trace elements in alleviating drought stress. Water Stress and Crop Plants: A Sustainable Approach2, 669-681.

 

 

 

Early season fertility: Beware of ‘hidden hunger’

Plants need 17 essential elements for growth and reproduction. The main criterion used in designating an element as essential is that it must be required for a plant to complete its life cycle. Elements were accepted into the ‘essentiality’ clique at different times based on when somebody proved they had met the aforementioned criterion. For example, nitrogen was accepted as an essential element in 1804. The newest addition to the family is nickel, determined to be essential in 1987. Crop yield and quality are reduced when plants don’t take up these nutrients in sufficient amounts.

There are 3 ways of diagnosing nutrient deficiencies – soil testing, plant tissue analysis, and visual observation of the plant.  Soil testing and plant tissue analysis are quantitative tests that compare nutrient concentrations in soil or plant to the sufficiency range for a particular crop. Visual observation, on the other hand, is a qualitative assessment of indicators such as specific leaf symptoms or stunted growth. Plants can show visual signs when there is a nutrient deficiency. But sometimes they don’t. ‘Hidden hunger’ is a term used to describe a situation in which a crop needs more of a given nutrient but shows no obvious deficiency symptoms. Hidden hunger can only be picked up by tissue or soil testing. If and when visual symptoms do appear, crop yield and quality will already have been reduced and corrective actions may not be effective. If detected early, hidden hunger can be corrected by foliar application of the insufficient nutrient. Foliar feeding normally elicits a quick response from the plant and is particularly advantageous where soil conditions keep nutrients in inaccessible forms.

As seeds become seedlings, it is important to keep the possibility of hidden hunger in mind. One nutrient that is vital at this stage of crop growth is phosphorus (P). Seedlings rely heavily on the P taken up in the first few weeks of growth for crop establishment and yield. Early season limitations in P availability can go undiagnosed but will result in consequences from which the plant will not recover, even when P supply is increased to adequate levels later in the season.

Most soils in the Prairies are low in plant-available P because their high pH and calcareous nature favour the tie-up of P in insoluble compounds. Under this condition, P use will be most efficient when soil contact with fertilizer is minimized by placing the P in a band in or near the seed-row. This allows roots to access and utilize the nutrient soon after emergence. In addition, biologicals containing microbes such as Penicillium bilaii will increase the phytoavailability of P in this kind of soils. Your SynergyAG rep can provide you with a low salt index phosphorus source, as well as natural products that solubilize P from soils.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

Dealing with insect pests of seedlings

A termite walks into a bar and asks, “Where is the bar tender?”

This joke right here is a witty reminder that insects love tender plant parts. Seedlings fit the profile perfectly. They are tender, succulent, close to the ground and are easy pickings for a host of insect pests. If left unchecked, these insects have no problem turning our farm into their stomping ground as they feast on our precious crops while singing their version of Weevil Weevil Rock You!

Insects can cause two major kinds of damage to growing crops. First, there is direct injury when insects eat leaves or burrow into stems. Then, there is indirect damage when an insect transmits a disease-causing organism into a crop. Early damage to seedlings produces uneven plant stands, and eventual yield loss. However, the presence of insects in a crop does not mean that there will be significant crop loss. The density of the insects has to reach a threshold that causes major concern. An economic threshold is the insect’s population level or extent of crop damage at which the value of the crop destroyed exceeds the cost of controlling the insect. In other words, if controlling the insect will cost you more money than the damage they’d cause, you should…choose the lesser of two weevils. In canola, for example, treatment is recommended when there is 25% defoliation in the presence of flea beetles.

Keeping insect infestations below significant levels is the goal. Effective control starts with effective monitoring. Every field should be monitored on a regular basis to estimate the populations of specific insect pests. A good understanding of an insect’s behaviour will help to know how best to scout for it. For example, cutworms, can be found first on hilltops because they prefer drier and warmer soils. They will eventually move to low-lying areas when their population increases.

If insect populations exceed economic thresholds, then it’s a good idea to control them using the appropriate methods. Biological control involves the use of the insect’s natural enemies. The northern field cricket (Gryllus pennsylvanicus), for example, is known to prey on flea beetles. In some cases, cultural control of insect pests using good agronomic practices such as effective weed control and crop rotation will help to manage certain insect pests. Chemical control using a good seed treatment or a post-emergent foliar application will also be effective.  So, take the sting out of problems with insect pests and talk to your SynergyAg rep about scouting and suitable solutions.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

Soil temperature and its implications for seeding

In many office settings, a request to adjust the temperature of the shared office space can be met with anything from a cold shoulder, to a lukewarm acknowledgement, or a heated argument. Out in the field, however, nature holds the thermostat and we do not get to make that request. So, when late April or early May arrives, our part of the world warms up and farmers in the Prairies prepare to get out into the fields and start seeding. But we also keep an eye on soil temperature – or we should. We should because although soil temperature is affected by air temperature, it is also influenced by soil moisture, soil colour, slope of the land, and vegetative cover which can vary with different soils.

Planting at the optimal soil temperature helps to ensure the best crop emergence. As temperature increases, germination becomes faster and more uniform. Seeding into cold soils can cause seeds to remain dormant and become more vulnerable to soil pathogens, diseases, and predators. This will ultimately lead to poor or staggered emergence and less-than-ideal plant stands. Reduced plant stands favours weed and pests, and also presents staging issues when timing pesticide or herbicide applications. For most spring-seeded crops, soil temperatures warmer than 10°C are optimum for germination. Various crops, however, will germinate at lower temperatures. The minimum soil temperatures needed for seeds of some common Prairie crops to germinate is shown in Table 1.

Table 1. Minimum soil temperatures needed for germination to begin (source: Saskatchewan Ministry of Agriculture)

Crop Soil temperature (°C)
Mustard 2
Canola 2
Flax 3
Wheat 4
Barley 4
Lentils 5
Peas 5
Soybeans 10

Assessing soil temperature is quite simple. First, you have to know the seeding depth of your crop. Then, using a soil thermometer, measure the soil temperature at this depth in a few areas throughout your field. Take two readings – one in the morning, and again in the evening. Take the average of these two temperatures and repeat this process for two to three days to get a multiple day average.

But should you base your seeding decision on soil temperature alone? Certainly not. Research in Western Canada has shown that early planting leads to increased yield because early-seeded crops will utilize available soil moisture better, avoid heat stress during flowering, and can evade the peak pest and disease period. So, it is important to take other prevailing conditions into consideration and plan to seed early. If you have to seed into colder soils, a good way to lower your risk is to use a seed treatment that can improve emergence in cold soils as well as protect the seed against diseases and pests before emergence. Furthermore, because root growth is slow in cold soils, a seed-placed, low salt index phosphorus product will be ideal in boosting root growth in this kind of environment. Your local SynergyAG rep can help you choose the right products.

 

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

Minimizing Nitrogen Losses

If there was a throne meant for the king of plant nutrients, I bet nitrogen will be sitting on it, unopposed. The nutrient is by far the most important in crop production. It’s also the most studied, and the most talked about. I’ve even found several songs dedicated to it, from pop to rap…that’s quite cool. What is not cool, however, is the fact that it is difficult to get nitrogen to stay where you want it to – close to plant roots. It seems to always be on the move, change forms and find pathways to leave the soil.  Knowing these forms and pathways is important in minimizing nitrogen loss.

When nitrogen sources such as urea, anhydrous ammonia or manure are applied to the soil, they rapidly convert to the ammonium form. Ammonium (NH4+) is positively charged and can, therefore, be held tightly to the surfaces of soil or organic matter, which are mostly negatively charged (opposites attract; likes repel). But, under favourable conditions, soil bacteria convert ammonium to nitrites and finally to nitrates (NO3). Nitrate is negatively charged and is repelled by the surfaces of soil and organic matter and therefore susceptible to leaching – movement of nitrate below the plant’s root zone by percolating water. Leaching is more prevalent in coarse-textured soils such as sandy soils because these soils have a lower water holding capacity. Nitrate-containing fertilizers, such as urea ammonium nitrate (UAN) and ammonium nitrate, are susceptible to leaching loss as soon as they are applied.

When soils are very wet or waterlogged for a couple of days, soil microbes starved of oxygen will strip the nitrate molecule of its oxygen. With the oxygen stripped from the nitrate, the remaining nitrogen is ultimately lost to the atmosphere as nitrogen oxides and dinitrogen gas. The process is called denitrification. Denitrification rates can range from 5 to 20% of applied nitrogen. Denitrification can be significant when nitrogen is applied in the fall, before a wet spring. It most commonly occurs in heavy clay soils because of poor drainage.

Urea-based nitrogen fertilizer products such as UAN, or dry urea are susceptible to ammonia volatilization if surface-applied and not incorporated. Ammonia is an intermediate form of nitrogen during the process in which urea is transformed to ammonium by urease enzymes. The risk of volatilization loss is high in moist soils and increases with temperature, soil pH and windspeed. Up to 64% of applied N can be lost as ammonia.

Plants take up nitrogen from the soil solution mainly as nitrates and ammonium ions. If you can delay or prevent ammonium from converting into nitrate, you will reduce nitrogen loss by leaching or denitrification. Nitrogen stabilizers can help with that. Some stabilizers can also slow down the conversion of urea to ammonium which allows more time for the nutrient to move into the soil, thereby reducing loss through volatilization. Your SynergyAG rep can help you pick out the right products.

 

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

 

 

 

When weeds refuse to die – Herbicide resistance and how to manage it

Since the 1940s when herbicides were commercially released, their use has revolutionized agricultural productivity. Without them, weed control in large-scale farming will neither be economical nor practical, and yield losses will be massive. But the innovation was unfortunately accompanied by the increase in the dominance of resistant weeds. One of the earliest recorded cases of herbicide resistance was in wild carrot in Ontario, Canada in 1957.  Although science quickly stepped in to develop herbicides with different modes of action, there has been a steady increase in the number of resistant weeds (see global trends in the figure below).  Weeds have learned to adapt and science is struggling to keep up.

Herbicide resistance is the inherited ability of a plant to survive a herbicide application that would kill a normal population of the same species. Herbicide-resistant weeds have developed genetic resistance to certain herbicide groups, or sites of action. It is important to note that herbicides do not cause resistance in weed species, rather they inadvertently favour resistant individuals that naturally occur within the weed population. Resistance proceeds when the same herbicide, or herbicides from the same group, are applied repeatedly to an area that contains resistant weeds. The susceptible plants die while the resistant ones, favoured by the reduced competition, multiply. With time, only these resistant species will remain and any weed control efforts using that herbicide will be ineffective.

The introduction of glyphosate provided relief from herbicide resistance for 15 years until glyphosate resistance was found in 1996 from rigid ryegrass in an orchard in Australia. Subsequently, several additional glyphosate-resistant weed populations have been identified even here in the Prairies. The increasing risk of glyphosate resistance means that we are in danger of losing the efficacy of one of the most potent herbicides ever produced.  Tank mixing multiple modes of action is an important step in preventing herbicide resistance in weeds, and the spring burn-off window is a good opportunity to use a tank mix rather than glyphosate alone.

Management strategies important in preventing herbicide resistance include:

  • use herbicides only when necessary, and use them at the recommended rate
  • avoid using the same herbicide or herbicides from the same group in the same field, in consecutive years
  • use herbicide mixtures that include 2 or more herbicide groups that control the target weed
  • practice crop rotation because different crops allow for a wider range of herbicide options.

Herbicides are very important tools for efficient and cost-effective weed management but their efficacy is an exhaustible resource that can be depleted over time. The present challenge is to manage them in such a way that their usefulness is prolonged while science tries to find a way to beat the constant evolution of resistant weeds. The renowned scientist Robert Pyle once said, “…make no mistake: the weeds will win; nature bats last.” For all our sakes, I hope nature slows down a bit.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

How water quality affects herbicide efficiency

Recently, I read a chemistry quote that said, “You either have to be part of the solution, or you’re going to be part of the precipitate”. Now, I know that’s a play on Eldridge Cleaver’s famous words (You either have to be part of the solution, or you’re going to be part of the problem), but when mixing herbicides with spray water, it’s a good idea to think about it that way. As far back as the 1990s, research has demonstrated that the solubility and efficacy of some herbicides can be adversely affected by the quality of water used to dilute them.

So, what are the key parameters to watch out for?

The pH measures the level of acidity or alkalinity. A pH of 7.0 is neutral. If the pH is lower than 7.0, it is acidic, higher than 7.0, it is alkaline. Herbicides such as glyphosate, 2,4-D, dicamba, and many others become negatively charged at alkaline pH. In this condition, they are more susceptible to being tied up by positively charged ions such as those of Calcium (Ca2+), Magnesium (Mg2+), and iron (Fe2+, Fe3+), and to form complexes that are not easily absorbed by the plant, thus reducing the effectiveness of the herbicide. Extreme water pH levels can also reduce the solubility of some herbicides or cause the herbicides to break down faster, and not be as effective.

Water hardness is caused by positively charged ions of mostly calcium and magnesium, and sometimes iron and sodium. These positively charged ions can bind to negatively charged herbicides such as glyphosate and 2,4-D amine thereby reducing herbicide efficacy.

Bicarbonate is known to reduce the activity of 2,4-D amine and the “dim” group of herbicides – tralkoxydims (such as Achieve), sethoxydims (such as Poast), and clethodims (such as Centurion and Select). Bicarbonate levels as low as 500 parts per million can interfere with herbicide effectiveness.

Cleanliness/turbidity refers to how much suspended matter is in the water. Soil and organic matter particles can bind onto and reduce the effectiveness of herbicides such as glyphosate, dicamba, diquat, bromoxynil and paraquat. These particles can also block spray nozzles and affect the delivery of the product.

Cost of herbicides can be substantial, and using water of poor quality will reduce the return on investment. Besides, anything that lessens the efficiency of herbicides can lead to poor weed control and significant yield loss.  Moreover, having herbicides tied up by cations in water will result in lower-than-recommended rates of herbicides and possible herbicide resistance. So, it is important to test spray water to determine its suitability for herbicide dilution. Where laboratory services are difficult to access, a good place to start is to test the electrical conductivity (EC) of the water using a conductivity meter. The EC standardized at 25 ⁰C gives a useful approximation of the Total Dissolved Solids (TDS). If EC is less than 500 µS/cm, it is unlikely that the efficacy of herbicides will be affected. Where EC is higher than 500 µS/cm further tests are necessary to confirm the culprit ions.

If your water source is of poor quality, adding water conditioners can be helpful. Some conditioners can modify the pH of the spray water to better suit the specific herbicide. Some of these products can also bind up the problematic cations so that herbicides don’t get tied up. Be sure to talk with your local SynergyAG rep for the right options.

 

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

 

Digging up the truth about soil health

When the Soil Conservation Council of Canada challenged everybody to ‘soil your undies’, the move sparked a lot of interest as farmers and gardeners buried clean underwear in the soil and then dug them up 2 months later to assess soil health. Those whose soils were healthy dug up little else besides elastic waistbands, while those with unhealthy soils dug up dirty but intact underwear. You could say that’s the soil health story in briefs.

The soil is not a lifeless mixture of sand, silt and clay. It is a living system buzzing with billions of bacteria, fungi, and other micro and macro organisms that are critical to the soil’s functions of providing and recycling nutrients for plant growth, detoxifying pollutants, retaining water for use during drier periods, and serving as a firm structure for agricultural activities. Soil health has been concisely defined as the continued capacity of the soil to function as a vital living system that sustains plants, animals and humans. Two elements in this definition are key. First, ”the continued capacity of” reflects the soil’s resilience and ability to regenerate and function well for future generations. Second, recognition of soil “as a vital living system” highlights the importance of soil biota.

The role of soil biota in the soil system was largely neglected in the past because it was poorly understood and difficult to measure. Today, however, with advanced analytical techniques, soil biota can be better studied, and its importance in the sustenance of life is gradually taking center stage.

So, how can we improve soil health? Research has shown that reducing the level of soil disturbance, diversifying the species of plants grown, keeping the soil covered all the time, keeping living plants in the soil as often as possible, and adding organic or biological soil amendments all have beneficial effects on soil health.

Recent studies warning that we are losing topsoil a lot faster than it can be replenished through natural processes should indeed make us pay attention and stop treating soil like dirt. And by the way, if you want to ‘soil your undies’ this year, now is a great time to start.  You can find the protocol for the experiment here: http://www.soilcc.ca/soilyourundies/2017/Soil-Your-Undies-Protocol.pdf

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG

 

The rise and rise of biological seed treatment

When treating seeds with biological organisms was first suggested many years ago, the idea seemed like something out of a sci-fi comic book. But today, just like how these organisms proliferate in plant systems, the idea has proliferated in the R&D departments of top agricultural companies as research scientists join the race to find the best ways to unleash the powers of these microscopic creatures. Indeed, the future of agriculture is looking more likely to be defined not necessarily by huge machinery, massive satellites and big data, but by the tiny organisms whose potentials we are just beginning to unmask.

There are billions of microbes in the soil around plant roots. Some are friends, some are enemies. The person who said ‘Keep your friends close, and your enemies closer’ wasn’t talking about crop production… not literally anyway. In farming, you’d want to keep your friends close and your enemies far, far away. Keeping the very beneficial soil microbes close is key, and forms the core of biological seed treatment.

But how do these beneficial organisms work? Farmers all over the world are familiar with Rhizobia used to inoculate legumes such as soybean, peas and lentils. These bacteria were discovered more than a century ago. When applied on seeds of legumes, the bacteria penetrate the root, resulting in the formation of root nodules that fix nitrogen from the air and make it readily available to the plant. Another bacterium, Azospirillum brasilense, in addition to fixing nitrogen, also produces plant hormones which help important plant processes such as germination, stem elongation, flower development and leaf and fruit senescence. Penicillium bilaiae, a naturally-occurring soil fungus excretes organic acids that solubilize phosphorus tied up in the soil, making the nutrient available for uptake by plant roots.  Some biological seed treatments also contain natural compounds which encourage the colonization of roots by mycorrhizal fungi thereby increasing the surface area of roots and enabling them take up more water and nutrients. There is indeed, a wide range of biologicals and at SynergyAG we are committed to ensuring that growers use the products best suited to their needs.

Science has shown that seed treatments are advantageous. The return on investment will be more apparent when growing conditions are poor. For example, if a treatment is designed to help seeds thrive during periods of moisture stress, its efficacy cannot be assessed if the soil is sufficiently moist. However, treating seeds offers insurance against unexpected crop challenges or when the weather throws us a curve ball – which seems to happen far too often these days.

-Ikenna Mbakwe, PhD, PAg
Head of Research
SynergyAG