Growing Possibilities, A blog by XiteBio | Are Pea Aphids Limiting Your Legume Yields?
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Are Pea Aphids Limiting Your Legume Yields?

As the season progresses and legume crops start seed formation, pests become a bigger issue at the forefront of growers’ minds. Today we are going to discuss one of the most prevalent pests in North American legume crops: Pea Aphids, and answer the question: What can be done to stop them limiting your yields?

Pea Aphids (Acyrthosiphon pisum) are found throughout legume cropping regions in Canada and the northern United States, and most commonly affect field peas, although lentils and faba beans can become common targets as well. Aphids generally start to appear in early July, when spring larvae develop wings and travel between fields on wind currents, settling in susceptible legume crops. Aphids persist until late in the season, closer to harvest, when crops mature and become a less attractive food source (1).Pea Aphids feed on the phloem of developing plants, which they tap into and take from plants beginning at the podding and seed formation stages (2). Aphid feeding reduces the resources available to plants for seed formation, reducing the number and size of seeds and seed pods. Protein content and seed quality is not usually affected by aphids (1).

Scouting for aphids should begin just before flowering, and should continue throughout the season. When scouting, checking the top 8 inches of five plants or conducting ten sweeps with a sweep net is recommended, as is scouting multiple locations (at least four) in a field (3). The recommended threshold for insecticide application is at 10 aphids per plant (1), 2-3 aphids per plant tip if using the plant-tip scouting method, or 90-120 aphids per ten sweeps (9-12 per sweep) if using the sweep net method (3).

Seeding your crop early is a way of avoiding aphid infestations, as plants will mature before aphid populations reach economic thresholds (1).

Insecticides for use against aphids on legume crops are common, and many commercial insecticides exist, such as Beleaf, Movento, Matador, Silencer, and Labamba. Research has shown that application of insecticides just after pod formation gives the best results for protecting yields (1). Control of Pea Aphids can also come from their natural predators, of which there are several. These include ladybugs (adults and larvae), hoverfly larvae, minute pirate bugs, damsel bugs, and parasitic wasps, most notably those of the species Aphidius ervi (1).

The potential for microbial biocontrol methods against Pea Aphids also exists. The fungal pathogen Erynia neoaphidis is deadly to pea aphids, but does not affect crops or other insects found in pea fields, with ladybugs often acting as a vector for transferring this fungus between aphid-affected fields (4). This fungal pathogen has not proven economically effective for combatting aphid infestations, but the future may prove this a viable method yet.

Recent research has shown the possibility for another biocontrol method. Pea aphids are reliant on nutrition provided by symbiotic bacteria in their digestive tract, who provide nutrients that the aphids cannot get from plant phloem alone. Disruption of these symbiotic bacteria in aphids causes severe reduction in their growth and reproduction, and can fully inhibit their life cycle (5). Using a biocontrol agent to attack these bacteria as opposed to the aphids themselves could provide a future option for aphid control that lowers insecticide use. Rotating between insecticides and biocontrol can also limit the development of resistance by aphids to either method. Both of these microbiological control methods may be the future of combatting pea aphid infestations.

References:

1) https://saskpulse.com/files/general/160712_Aphids_in_pulse_crops.pdf

2) https://www.realagriculture.com/2020/07/pulse-school-dont-delay-scouting-for-pea-aphids/

3) https://www.manitobapulse.ca/2019/03/scouting-for-pea-aphids/

4) H. E. Roy, J. K. Pell & P. G. Alderson (2001) Targeted Dispersal of the Aphid Pathogenic Fungus Erynia neoaphidis by the Aphid Predator Coccinella septempunctata, Biocontrol Science and Technology, 11:1, 99-110, DOI: 10.1080/09583150020029781

5) Uchi, N., Fukudome, M., Nozaki, N., Suzuki, M., Osuki, K. I., Shigenobu, S., & Uchiumi, T. (2019). Antimicrobial activities of cysteine-rich peptides specific to bacteriocytes of the pea aphid acyrthosiphon pisum. Microbes and Environments, 34(2), 155–160. https://doi.org/10.1264/jsme2.ME18148

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