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Change nutrition management for spider mite resistance

Plants have the capacity to kill insects and mites feeding on them when they are healthy enough. These potential pests don’t show up in fields at random, but only when the plant has a nutritional profile they can utilize as a food source. When you change the plants nutritional integrity with agronomy management practices, you also change the crops susceptibility to insects and pests of all types.

Spider mites are often associated with hot and dry conditions. Spider mites are not attracted to high temperatures specifically. They are attracted to plants with abundant levels of free ammonium in the plant sap.

Elevated levels of ammonium often occur in high temperature environments when plants shift from photosynthesis dominant to photorespiration dominant. When this shift to high photorespiration occurs, plants are no longer getting enough energy (sugars) from the photosynthesis process (which has slowed down or halted). To sustain themselves, they begin catabolizing proteins to use as an energy source.

The protein catabolism during photorespiration in high temperature environments usually results in the accumulation of ammonium in the leaf, which can result in the crop being susceptible to spider mites, only when the plant does not have the needed nutrients and enzyme cofactors to convert the ammonium back into proteins at night, or as soon as carbohydrate energy become available. The critical nutrients for this conversion process are magnesium, sulfur, boron, molybdenum, adequate carbohydrates in the plant, and occasionally nickel.

In these photos, you can observe the results of a nutritional correction applied through an overhead pivot on a corn crop in SW Kansas in 2015. Spider mites were present in large numbers, and the local crop scout recommended a miticide application immediately.

The pivot took 48 hours to treat the entire circle with nutrients. In the sections that had been treated 24 hours earlier the spider mites were noticeably sluggish and moving slowly. In the section that had been treated 48 hours earlier, the spider mites were completely dead. The local crop scout assumed a miticide had been applied, but this was not the case.

Healthy plants can be completely resistant to all diseases and all insects when supported with the correct nutrition and the correct microbiome.

Of course, applying more ammonium fertilizer than plants can convert to proteins in a few days is also a great attractant for spider mites, thrips, and other related pests that are thought to like ‘warm conditions’.

2020-06-23T07:17:16-05:00June 23rd, 2020|Tags: , , , |

How the form of nitrogen influences insect feeding

The form of nitrogen influences not only the pathogenicity of soil borne fungal diseases, but also susceptibility to insects.

From the podcast interview with Larry Phelan.

John: As you were looking at these plant-insect dynamics in the field and developing your hypothesis of biological buffering, what was something that surprised you?

Larry: The one thing that was particularly exciting to us was when we took the next step and tested this idea of mineral balance resulting from this biological buffering of organic matter. We started growing plants hydroponically so that we could vary the proportions of different nutrients. The hypothesis we were testing was actually that when the plant was in good mineral balance, you would get both good growth and resistance to insect attack. And then as the plant moved out of balance nutritionally, you would see plant growth go down and insect performance actually go up. And then, ultimately, as the plant was way out of balance nutritionally, we expected the plant to not grow very well and the insects not to do very well either because of the poor host plant.

We tested this with a number of different combinations of nutrients, and the one that was most dramatic—that actually supported this prediction—was looking at soybeans in which we varied the ratios of ammonia to nitrate in the plant. We provided it all the nutrients that it needed in constant levels for all the plants. What we were testing was different ratios between these two different forms of nitrogen. And what we found was that as we increased the amount of ammonia up to about 30 percent, we saw the best plant growth. That ratio of 30 percent ammonia and 70 percent nitrate is where we got the best plant growth.

And then, when we looked at insects, we plucked the leaves off of these plants and then fed them to insects to see how the insects grew. The particular insect we were working with was the Mexican bean beetle. When we fed these leaves to the Mexican bean beetle, we saw just the opposite response. In other words, where the plant was out of bounds nutritionally and not growing very well, that’s where the insects grew the largest and that’s where we saw the best survivorship. But as we moved towards that 30 percent ammonia level, where the plants were growing their biggest, insect survivorship dropped from about 90 percent down to about 30 or 40 percent.

It was a very dramatic effect—even more dramatic than what we were expecting. When we followed up on this and measured the levels of free amino acids in these plants, it was consistent with the prediction. In other words, those plants that were not growing as well, that were out of balance in terms of this ratio, had much higher levels of free amino acids relative to that 30 percent ammonia plant.

2020-05-05T05:16:18-05:00May 12th, 2020|Tags: , , , , , |

How the form of nitrogen influences disease suppression

Nitrate and ammonium nitrogen have dramatically different impacts on soil biology and possible pathogens. Some pathogens are enhanced by nitrate and suppressed by ammonium. Others are the exact opposite. Most (but not all) soil-borne pathogens are enhanced by the presence of nitrate. This corresponds to the impact of reduced vs oxidized environments, since ammonium is the reduced form of nitrogen, and nitrate is the oxidized form of nitrogen. In general, reduced environments are very disease suppressive, and oxidized environments are disease enhancing.

I have had many discussion about this topic with Don Huber, inlcuding this one on a podcast interview.

John: What are the impacts of nitrogen and nitrogen applications on developing disease-suppressive soils?

Don: Most of your soil organisms are hungry for two things. One of them is nitrogen. The other is carbon. When you change either of those nutrients, you see tremendous stimulation of a lot of organisms in the soil, depending on what your source of nitrogen is.

One of their primary pathogens on a lot of vegetable crops in Florida is Fusarium oxysporum. It’s a vascular Fusarium. Growers can get pretty much complete control by using nitrate nitrogen and calcium. If they can stimulate nitrification, or if they apply nitrate nitrogen, potassium nitrate, or calcium nitrate—and also use some liming (lime = an oxidizer) to get their pH up—they have fairly effective control of Fusarium wilt diseases.

With tobacco, where we use fumigation to control some of the soil-borne diseases, you should have at least 30 percent of your nitrogen as nitrate nitrogen. If you don’t—if the plant is taking up all ammonium nitrogen—you can get into a carbon deficit because the plant detoxifies the nitrate or the ammonium nitrogen by combining with photosynthate from photosynthesis; that provides the carbon base for those amino acids. Then the nitrogen is translocated as the amino acid. If you don’t have enough nitrate nitrogen present to buffer against an ammonium source—if you’re going to get fumigation, because our soil fumigants tend to knock out nitrifying organisms—or if you don’t get nitrification there, it stabilizes in the ammonium form. It can be a drain on the carbon and the energy availability until that ammonium is detoxified and utilized by the plant.

John: I’m thinking about your description of how many soil-borne pathogens—soil-borne fungi such as Fusarium and Verticillium, for example—are dependent on oxidizing manganese and limiting manganese absorption by the plant. If that were the case, what would be the impact of adding ammonium to such an ecosystem—where you have a reduced form of nitrogen? What would the impact of the ammonium be on these soil-borne pathogens?

Don: On that group of pathogens, you will see a tremendous reduction in disease—with the ammonium nutrition. I wrote a chapter in one of the annual reviews on the impact of the form of nitrogen. You’ll see a tremendous benefit in different organisms by the form of nitrogen that the plant is predominantly supplied with. If you modify the environment so that those soil microorganisms make those conversions, you’ll see that the form of nitrogen will be available for the plant.

So, it’s important that you have both the management tools as well as the form. Most of our soil’s nitrification takes place very rapidly, so you need to do something to inhibit nitrification. We can do it biologically—we can modify the speed of that reaction so that we can increase the amount of nitrogen in nitrate or ammonium. When it’s taking ammonium nitrogen, you have a reducing environment. That reducing environment is favoring manganese-reducing organisms so that there will almost always be an increase in manganese availability for the plant—when you predominantly use an ammonium form of nitrogen. The more rapid, oxidative form is the nitrate source of nitrogen.

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