Are we asking the right questions?
By Craig Madsen
Two events in the past two weeks offered two visions for the future. One was the annual Soilcraft Conference, and the other was the Washington State University Extension Dryland Wheat Producer meeting. Each presented entirely different approaches to insect and disease issues.
The first presentation at the Soilcraft Conference was given by Dr. Tom Dykstra. He provided an in-depth look at why insects attack plants, using soybeans and the soybean aphid as an example. Soybean aphids can detect levels of ammonia in the plant. They use ammonia as their nitrogen source to produce lots of baby aphids.
Did Dr. Dykstra tell us what chemical to spray to kill the aphid? No. He asked: Why is ammonia accumulating in the plant? What is needed to convert ammonia to nitrites in the process of making proteins? He took a sap analysis, and the plant had low levels of copper. The focus of the conference was on how to grow healthy plants that are resistant to insects and diseases and produce nutrient-dense food.
WSU Extension’s Dryland Wheat Producer meeting had presentations on criteria for using fungicides, scouting for cutworms and flea beetles on canola, the buildup of herbicide resistance in various weeds, and calculating levels of lime to raise soil pH. I did not hear one “why” question. Why are the plants being attacked by insects or fungi? Why is the soil pH so low? Is it our current management? Only one researcher mentioned the importance of rotation in the control of herbicide-resistant weeds.
The two approaches strongly contrast with each other – a strategic offense focusing on increasing plant health or playing defense by fighting threats. Each of us has a choice to make about how we grow our food or choose which type of food to buy. A great book on this subject is “What Your Food Ate,” by David Montgomery and Anne Bikle.
It is fascinating to think about ways we can grow disease and insect-resistant plants. Another presentation by Dr. Dykstra was on the brix levels in plant tissue and their resistance to different types of insects. Brix is a measurement of dissolved solids in the leaf sap. It is an indication of how well your plant photosynthesis process is working and, thus, an indicator of plant health.
The higher the brix level, the greater the plant's ability to resist insects. His research demonstrated that once the plant’s brix level exceeds 12, it becomes resistant to most insects and diseases. You will need a refractometer to measure brix. A refractometer that measures from 0 to 30 brix costs around $20.
Refractometer
To obtain accurate readings, measure brix at the maximum level, which is typically between 10 am and noon. Sample the first fully mature leaf and take 10 samples across the field to gain a clearer understanding of the crop's condition. Stick to similar soil types and aspects as much as possible. The brix level will fluctuate throughout the day, usually low in the early morning as the plant transfers sugars from the leaves to the growing points in the shoots and roots overnight. Collect samples at different times during the day to assess the plant’s performance at various intervals.
What do you do if your brix levels are low or your plants are being attacked by insects or fungus? The first place to start is to take a tissue test to find out the nutrient status of your plants. Take the sample in the early morning and collect the sample as per the lab’s suggestions based on the type of plant. This will enable you to find out which nutrients are deficient, and which are in excess. Excess nitrogen, whether nitrate or ammonia, can lead to increased disease pressure.
Once you solve the mineral issue the next stage is to evaluate the soil microbial community. When the plant is connected to its digestive system, which is the soil biome, it is able to acquire nutrients much more efficiently. Is the soil clinging to the roots? If the roots are bare the plant does not have an association with mycorrhizal fungi. Over 90% of plants have an association with mycorrhizal fungi which can increase the effective root surface area by 700%, enabling the plant to better access water and nutrients. The relationship of the plant to mycorrhizal fungi is impacted by management. This connection with be discussed in more depth in a follow-up article.
When a plant is connected to its soil biome, it can absorb microbial metabolites such as amino acids, plant growth-promoting compounds, and even bacteria through its roots. By absorbing these larger compounds, the plant has to spend less energy to grow. John Kempf talks about how much less energy is necessary to build a house from a prefabricated kit than buying all the individual pieces necessary for construction. That is what the plant is doing when it absorbs microbial metabolites versus individual ions.
When the plant has more energy, it produces more biomass, fats, and secondary compounds. The fats are used to build a waxy leaf surface that improves water efficiency and makes the leaf less susceptible to insects and diseases. The secondary compounds enhance the plant’s immune system due to their anti-fungal and anti-bacterial characteristics, as well as making them less susceptible to being eaten. These secondary compounds also play a role in the flavor and nutritional quality of the food grown.
Keep in mind sometimes less is better. Synthetic nitrogen and phosphorous fertilizers will impact the plants’ association with soil microbes. Excesses can cause as much of a problem as deficiencies.
Listed below are a two resources as a place to start your journey. Another option is to find a fellow farmer, gardener, or coach who is knowledgeable about these techniques. A healthy ecosystem is a complex self-organizing system. Nature is always changing, so there are always new things to learn. Be curious and become a good observer through the seasons.
To learn more from Dr. Dykstra go to his website at Video Presentations – Dykstra Laboratories, Inc.
To learn more about growing plants that are insect and disease-resistant, see John Kempf’s webinar on the Four Stages of Plant Health.