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Interplanting sweet allysum for aphid control

We might ask the question, “What is the root cause that allows aphids to feed on this plant?”

When we pursue the wormhole of information needed to answer this question, we can develop a description of the carbohydrate profile within plant sap that aphids are dependent on. The carbohydrate profile changes dependent on the critical minerals plants require as enzyme co-factors to develop functional enzyme systems. The mineral profile is determined by the soil biology’s capacity to supply specific nutrients. These are layers of empowering answers which indicate the management tools needed to prevent aphids from becoming a problem. You can find my previous blog posts related to aphids here.

We might ask a similar question at a different level of thinking, “Why are aphids showing up in this ecosystem?”

When we ask questions at a different level, we arrive at very different answers. How are we managing the field ecosystem that allows the aphids to proliferate unchecked? When we have a continuous mono-crop of plants with an incomplete carbohydrate profile, it is a near-perfect environment for aphids to proliferate. We are supplying them with an abundant food source, and no habitat for their natural predators. When we spray an insecticide, we improve the environment for the aphids even more, because now we have removed all the predators, and weakened the plants even further.

A natural followup to the previous question is, “How can we manage the ecosystem differently so that aphids are no longer present?

Thanks to Klaas Martens for pointing me to Eric Brennan’s research on inter-planting sweet alyssum in lettuce and broccoli as a biological control for aphids. As I followed the wormhole of published research on biological control for aphids at an ecosystem level, I was pleased to discover that adding relatively few insectary plants per acre like sweet alyssum can attract enough hoverflies to provide complete control of aphids.

I estimate that additive intercropping with about 500 to 1000 alyssum transplants per acre, distributed throughout the field should provide sufficient pollen and nectar for hoverflies to control aphids in transplanted romaine lettuce. ~ Eric Brennan

This limited population of sweet alyssum has no negative impact on lettuce yields, and seems unlikely to have a negative impact on yields of other crops. Sweet alyssum can be direct seeded, and seed is inexpensive. This seems like an imminently practical and scalable solution for other crops with aphid pressure.

What other practices or plants  provide control of different diseases and insects? This is a topic I am would like to learn  more about.

 

1. Brennan, E. B. Agronomic aspects of strip intercropping lettuce with alyssum for biological control of aphids. Biol. Control 65, 302–311 (2013).

2. Brennan, E. B. Agronomy of strip intercropping broccoli with alyssum for biological control of aphids. Biol. Control 97, 109–119 (2016).

3. Ribeiro, A. L. & Gontijo, L. M. Alyssum flowers promote biological control of collard pests. Biocontrol 62, 185–196 (2017).

4. Harris, A. S. Integrated Organic Management of Cabbage Aphid on Brussels sprouts. (University of New Hampshire, 2019).

5. Quinn, N. F., Brainard, D. C. & Szendrei, Z. Floral Strips Attract Beneficial Insects but Do Not Enhance Yield in Cucumber Fields. J. Econ. Entomol. 110, 517–524 (2017).

6. Mollaei, M., Fathi, S. A. A. & Nouri-Ganbalani, G. Effects of strip intercropping of canola with faba bean, field pea, garlic, or wheat on control of cabbage aphid and crop yield. Zhi Wu Bao Hu (2020).

2021-02-13T12:28:21-05:00February 16th, 2021|Tags: , , , , , , , |

Managing nutrition for control of aphids and flea beetles

Tom Dykstra and I discussed the concepts of plant health, nutrition management, and insect resistance in a rapid fire, intense one hour webinar, with a specific emphasis on controlling aphids in sugar beets and flea beetles in canola.

While the conversation was fairly high level, and didn’t get into the nuts and bolts of implementation, Tom’s knowledge of insect metabolism and the type of food sources they require to survive is unparalleled.

If you want to learn how to grow insect resistant crops, this webinar is a must listen. You kind find the recording on KindHarvest.ag here.

Tom uses a refractometer as a research tool, and describes a brix index of plant susceptibility to to different groups of insects at different brix levels. There is a big difference between using using brix as a research tool and using it as a crop management tool. You can read my thoughts on using brix here.

Insect and disease attraction to plants with reducing sugars

How is it possible for a high Brix plant to be resistant to insects and not provide them with an abundant food source when insects are attracted to sugars? The key insight is that plants contain different concentrations of different carbohydrates at various levels of plant health. The goal for optimal plant health is to have all photosynthates and soluble sugars such as glucose and fructose converted to non-reducing sugars in each 24-hour photoperiod. This means a healthy plant will have a high Brix concentration and very low levels of reducing sugars.

From the podcast interview with Don Huber.

John: Are there any negative health consequences of plants having high levels of fructose and glucose?

Don: Yes and no, depending on what other stresses there are present. If you have a deficiency of manganese, for instance, it can’t store the reducing sugars―glucose and fructose―that are being produced through photosynthesis. It can’t store them as sucrose, and so they become very attractive reducing sugars, and they become very attractive to insect pests and to a number of plant pathogens.

Manganese is a critical factor for that sucrose-phosphate synthase enzyme that converts glucose and fructose into sucrose for storage. If you’re deficient in manganese, you’ll have high reducing sugars―glucose and fructose. As insects like aphids fly over these plants, they can detect that high reducing sugar, and for them, it’s a red flag saying, “Hey, come in for dinner!” But if those sugars are converted to sucrose and stored there, you don’t see that attraction.

Reducing sugars come out of the root system―they’re the root exudates that are attracting Pythium and Phytophthora and Aphanomyces and those other oomycete pathogens―root-rotting pathogens.

Later:

John: Don, you described how the carbohydrate profile can attract aphids. Are there other insects that can be attracted by the carbohydrate profile?

Don: A lot of them are. I don’t know that all of them are, but many recognize the difference between the reducing sugars, and they don’t seem to be attracted to the non-reducing sugars nearly as much. You’ll see that association. When we get the minerals balanced for the plant, you’ll see all of those problems start to disappear or be very minor.

P.S. I appeared as a guest on The Modern Acre podcast in this episode.

Aphids only on milkweed in a blueberry block

These milkweed plants are being consumed by aphids while the blueberry leaves inches away have no aphids on them at all. This is a clear indicator that the soil microbial population and mineral balance is more supportive of blueberries than it is of milkweed.

The aphids are attracted to the unhealthy plants, and are taking them out of the ecosystem. If the milkweed were healthier than the blueberries, the aphids would be on the blueberries, and leave the milkweed untouched.

Since the aphids are now consuming a plant that might be considered a ‘weed’ in this particular context, does that make the aphids a pest for attacking the plants, or a beneficial ‘biocontrol’ because they are removing the ‘weed’?

2020-06-25T13:37:14-05:00July 10th, 2020|Tags: , , , |

Insects consume unhealthy ‘weeds’ growing in healthy soil

Not all plants grow equally well in the same soil. Each plant has a preferred microbial, physical, and nutritional environment it thrives in.

When soil balance is optimized for our domesticated plants, the crop plants are healthier than the weeds. Now, the weeds have lower brix readings, and are more susceptible to disease and insects than the surrounding crop.

These lambsquarter plants were growing at the intersection of three fields, growing tomatoes, mixed salad greens, and peas. The last two crops can be very susceptible to aphids. There were no aphids to be found anywhere on the crops, while the lambsquarter was being consumed, as you can see.

2020-05-16T12:48:30-05:00May 19th, 2020|Tags: , , , |

How to Propagate Aphids

It is important to propagate aphids in our fields so the beneficial insects such as lady beetles have something to feed on. It is quite easy to produce a tremendous aphid population which can sustain a large number of beneficials and not be negatively impacted. We just need to give them the right environment.

Here are the easy steps to produce an optimal environment for aphids, which require free nitrates in the plant sap.

Step one, apply more nitrogen then the plants can utilize at the current growth stage.

Step two, do not supply magnesium for better photosynthesis.

Step three, do not apply sulfur the plants needs to produce sulfur-bearing amino acids and complete proteins.

Step four, do not supply molybdenum for the nitrate reductase enzyme.

Step five, do not apply any boron that might boost plant immunity.

If you follow these five very simple steps, you can be sure that your crop will provide the perfect food source for aphids. In addition, it will also be the optimal food source for many other larval insects such as corn rootworm, earworm, corn borer, cabbage looper, tomato hornworm, and others. Really for any larvae. Propagating these larvae provides a ready food source for songbirds and beneficial insects, a valuable ecosystem service.

Of course, if you do not desire to propagate these insects on your crops, the solution is obvious. Do the reverse of the five easy steps, and these insects will not be able to use your plants as a food source.

Insect susceptibility determined by types of plant sugars

Sugar metabolism and carbohydrate synthesis are at the very foundation of plant health, but we generally don’t learn much about them in agronomy or even entomology. The types of sugars and the relative concentration of different sugars contained within the plant seem to be foundational in determining susceptibility/resistance to many herbivorous insects.

Here are a few excerpts from Harold Willis1 I found interesting:

The role of sugar in insect attack of plants is fascinating. Based on research done on various insect and plant species, apparently insects like moderate amounts of plant sugars and are attracted to plants containing them. But high concentrations of sugars are avoided by leafhoppers, grasshoppers, and the European corn borer2


Alfalfa was found to be resistant to pea aphid when its stem tissues had a more acid ph and higher levels of sugar (pentoses) and pectic substances (larger carbohydrate molecules formed by linked sugars). Pentose sugars are formed from hexose sugars which are the original products of photosynthesis. Alfalfa plants that are normally susceptible to aphids will become resistant if the above-mentioned cellular changes occur3

A possible reason that some insects avoid high sugar plants comes from research by G Fraenkel. Some sugars and sugar alcohol combinations (glucoside and mannoside) interfere with normal utilization of other sugars, and so are toxic to insects (mealworms)4. The inhibitory sugars are found mainly combined with other molecules in plants, but if digested by insects and in the presence of the sugar glucose, their toxic effects occur5.

Our knowledge of plant immunology has progressed well beyond this research in the ’40s and ’50s, but the practical application has fallen well short. I describe how we have applied these principles in our plant health pyramid infographic and on YouTube here.

1. Willis, H. Crop pests and fertilizers – is there a connection?

2. Thorsteinson, A. J. Host Selection in Phytophagous Insects. Annu. Rev. Entomol. 5, 193–218 (1960).

3. Emery, W. T. Temporary Immunity in Alfalfa Ordinarily Susceptible to Attack by the Pea Aphid. Journal of Agricultural Research 73, 33–43 (1946).

4. Fraenkel, G. Inhibitory effects of sugars on the growth of the mealworm, Tenebrio molitor L. J. Cell. Comp. Physiol. 45, 393–408 (1955).

5. Dethier, V. G. & Rhoades, M. V. Sugar preference-aversion functions for the blowfly. J. Exp. Zool. 126, 177–203 (1954).

2020-05-22T07:17:19-05:00December 7th, 2019|Tags: , , , |

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