Using Brix measurements for pest management in my dahlia garden.
Each summer as our flowers are growing we are dealing with pest management. It may be some grasshoppers, cucumber beetles, leafhoppers, or the tarnished plant bug to name a few. I grow around 1350 dahlias from tubers or cuttings and 1400 dahlias from seed. I am located in the northern part of North Carolina in plant hardiness zone 7b. I am just on the edge of zone 8a. I grow in long rows with drip irrigation. I also use a shade structure over some of the dahlias with a 30% shade cloth. Dahlias love full sun but when you have temperatures in the 90's and high humidity, they appreciate afternoon shade. My dahlias look healthy but why do I see these chewing insects finding my dahlias so delicious! I have heard organic farmers talking about growing high brix plants. A Brix value of 12 or higher usually indicates a healthy plant and will keep most insects from recognizing your plant as food. When you take a Brix reading, you are measuring the amount of sugar in plant juices. Brix readings are commonly used in the fruit, honey, and wine making industries. The Brix scale was named after Adolf Brix, an inventor of the hydrometer which the wine industry may use to measure the sugar content of grapes. Now instead of the hydrometer you can use a more accurate device called a refractometer. To take a Brix reading, you will need a Brix refractometer. I purchased a digital Brix refractometer on Amazon for $79.99. They have refractometers that are not digital, and they are cheaper. A refractometer registers how much light is refracted so the more sugar in the solution, the greater the refraction.
Apparently, the higher the brix reading, the less pests that bother the plant. The leaves are where plant sugars are produced through photosynthesis so I can take a few leaves off a dahlia plant to obtain a Brix reading. You need enough leaves to get a good drop of liquid from the dahlia leaves. To take a Brix reading, you will need a refractometer, garlic press, or some type of tool to press liquid from the leaves. I found it hard to get enough liquid when using a garlic press. My husband made me a leaf press tool that compressed the leaves enough to give me a good drop of liquid. There is a picture of the homemade press in the below picture. I try to remove my leaves from the dahlia around noon time as I believe that is when Brix is the highest. I compress the dahlia leaves and allow the liquid to go into a small bathroom cup. Once I have the liquid in a small cup, I use a disposable dropper to place a drop on the Brix refractometer. Since I have a digital refractometer, it gives me my Brix reading immediately.
I have included a link to the product I am using that I have purchased on Amazon. As an Amazon Associate, I earn a small commission from qualifying purchases.
I am using a Difluid digital brix refractometer that is rechargeable and portable. I found it easy to use, and I like having the results quickly. It has great reviews on Amazon. I am happy with the product. In the picture below you can see the tool my husband made for me.
I found some great information about Brix on the joegardener.com website. Joe Lamp'l is the Joe behind that website. Joe Lamp'l is the creator and producer of the national PBS show "Growing A Greener World". He also has an online gardening academy. On 12/22/22, he did a podcast (#292) called “Understanding Brix and how if affects plants and pests.” On the podcast was his guest, entomologist and Brix expert, Thomas M. Dykstra PhD. When you go to Joe’s website, you can go to the podcast tab and enter #292 and that should take you to the podcast. Thomas Dykstra talks about what Brix is and discusses how he defines the insects that bother our plants.
Thomas Dykstra defines four groups of insects. The grasshopper group which are interested in a plant with less than 10 to 12 brix levels. The chewing group such as beetles and moths which are interested in a plant with less than 9 to 11 brix levels. The sucking insects like leafhoppers and thrips which are interested in a plant with less than 7 to 9 brix levels. The last group is the aphids, and they are interested in a plant with brix levels lower than 8. Joe has a “Leaf Brix chart” in that “Understanding Brix Value” article on his website. It looks like I want at least a Brix value of at least 10 to avoid most of these pests.
After listening to this podcast with Brix expert, Thomas M. Dykstra PhD, you can tell what your Brix level is in your dahlia garden without even using a Brix refractometer. If I see aphids on a dahlia plant, I know the sugar level is less than 8. Aphids are usually not on a plant with a brix level higher than 8. I know I need to improve that dahlia’s health and increase the sugar levels. Another example would be if I see thrips and leafhoppers on a dahlia. I would know that the brix value is less than 7 as they can lose interest in a dahlia when the Brix value is between 7 and 9.
So how do I raise my Brix levels. One way is to feed the microbes. Soil microbes are living organisms like bacteria and fungi. They stimulate plant growth and help plants resist the stress of diseases and be more resilient. The microbes need sugar. Healthy plants will produce sugar through their roots. As I was reading about how to raise my Brix level, I saw where some people add rock dust to your soil. Apparently, rock dusts have a lot of nutrients like calcium, potassium, magnesium, phosphorus, iron and zinc which all help plants become stronger. The stronger your plant is the more it can resist diseases and be resilient during drought conditions.
Another way to increase beneficial soil microorganisms is to add sugar to your soil. Molasses is better as it has a higher nutrient value as it has micronutrients. You can mix 1 or 2 tablespoons of molasses to one gallon of water and add that to the soil around your plant. The microbes are going to eat most of that sugar quickly, so it is good to apply the molasses every other week. I tried unsulfured molasses. I used 1 tablespoon per gallon of water to see how my dahlias reacted to this solution. I applied it to the soil around my dahlias with a 2 gallon battery operated sprayer. You do have to dissolve the molasses in some warm water so you do not clog your sprayer. Some people apply it to the leaves of the plants and the soil; however, you will need to do that on very cloudy days or in the evenings. If you were to apply this on a sunny day, you could burn the leaves. It is mainly to increase microbial activity, so I apply it to the soil.
I have used several different fish and seaweed fertilizers in the past and they all work great for using as a foliar or to add to your soil. For the last couple of years, I have been using Vigor Plant Booster. I follow Warren Vigor on Instagram. Warren was the president of the Dahlia Society of Australia. Warren now lives in the U.S. in Michigan. Warren is a champion dahlia grower, and his dahlias really stand out at dahlia exhibition shows. He contributes his success to his plant booster. He has produced this soil conditioner that strengths plant growth. It contains NPK 9-2-6, Sulphur, calcium, magnesium, boron, copper, iron, manganese, zinc, selenium, cobalt, and carbon. It is made from cool processed whole fish, deep-water kelp, humic acid, fulvic acid, and sugar.
As I have been researching information about Brix, I found articles talking about humic and fulvic acids. Humic acid provides a beneficial carbon food source for microbes. Fulvic acid is found in humus (organic matter) of soil. Humic and fulvic acids increase the root mass which allows plants to acquire more macro and micronutrients in the soil. I was happy to see that the Vigor Plant Booster has humic and fulvic acids with the fish and kelp. I use around 1 tablespoon of Vigor per gallon of water. I use a 2-gallon battery operated sprayer and spray the surface of the soil around the dahlias. If it is going to be cloudy all day, then I will spray some of the foliage.
Recently, I asked Warren what type of sugar is in Vigor Plant Booster and he said molasses. Warren uses his Vigor Plant Booster mainly in the soil to increase microbes which will help strengthen the dahlia. Since I now know that Vigor Plant Booster has molasses in it, there is no need for me to use unsulfured molasses if I do not want to but if I want to add a tablespoon of molasses per gallon with the Vigor Plant Booster I could for extra sweetness. If you are interested in Vigor Plant Booster, you can go to this website link https://www.vigorfertilizer.com. I attended a couple American Dahlia Society shows in 2022 and 2023 and was able to meet Warren in person. He is a great guy!
Last summer in 2024, I took one Brix reading in late June and the dahlia plant had a 10.85 brix level. I took another Brix reading in July and that plant had 6.91 brix value. We had a tropical storm in August, and I got busy with my dahlias so I was not able to do some more Brix readings. I hope to take some Brix readings this summer.
You can also plant cover crops over the winter in your flower garden as that will provide food for the soil microbes. Every spring I add compost to my dahlia garden. Compost provides organic matter, nutrients to the soil, and feeds the microbes. I usually water all my dahlias seedlings and dahlia cuttings with Vigor Plant Booster before I plant them in my dahlia garden. Once your plants are growing, you can spray the dahlias with compost tea, molasses or fish and seaweed products as all these will increase the microbes in your soil. I usually use Vigor Plant Booster monthly during the summer.
Isn’t fun to learn new things. I just find this so interesting learning about Brix values. This blog is just about my experience learning about Brix. If you want to learn more about Brix, google Thomas M. Dykstra PhD, and you will find some YouTube videos and other articles. He also did a podcast with Jennie Love (The No-Till Flowers Podcast) called "The Magical Brix Number That Stops Pests."