During the SDSU Extension Field Pea & Lentil Tours in the Harrold and Fort Thompson areas last week, small populations of pea aphids were observed in each of the fields. The aphid populations were well below the recommended thresholds and shouldn’t be much of a concern at this time. However, the cooler temperatures that were experienced over the weekend may allow for population increases to occur. We recommend scouting fields to monitor pea aphids in case they become a problem.
Scouting & Economic Thresholds
Pea aphids can be scouted by either examining individual plants and counting the aphids present, or by using a 15-inch sweep net. For scouting individual plants, walk 30 to 50 feet into the field and walk in a “Z” pattern throughout the field. While walking the pattern, stop and examine 30 plants per leg of the pattern and calculate the average pea aphids present per plant. For this scouting method, an average of 2-3 pea aphids present per 8-inch plant tip exceeds the economic threshold.
Alternatively, a sweep net may be used to scout for pea aphids. This method is considered easier as pea aphids often drop when the plant is disturbed while doing visual scouting. Using a 15-inch sweep net, again walk in “Z” pattern throughout the field. Using 180 degree or pendulum sweeps, swing the net for a total of 10 times and count the number of pea aphids present. Repeat this process for each leg of the pattern. The economic threshold for sweep netting pea aphids is 90 to 120 pea aphids per 10 sweeps. If this threshold is exceeded throughout the field and few natural enemies are present, insecticide management should be considered.
Crop Injury & Management
Pea aphids feed on plants using piercing sucking mouthparts. Like many other species of aphids, pea aphids can vector viruses that can cause further yield loss. However, pea aphid feeding alone when thresholds have been exceeded can also cause yield loss. This stress associated with feeding is especially noticeable when plants are also drought stressed.
Pea aphid populations are prevented from reaching the economic threshold by rain events, natural enemies, and temperatures that exceed 90° F. At these temperatures, pea aphid reproduction is diminished and allows natural enemies to further reduce populations.
While scouting with either a sweep net or using visual counts, it is important to determine presence and levels of natural enemy populations. Seeing large numbers of mummies may be an indication that natural enemies or aphid predators are present in the crop. Lady beetle adults, their larvae, damsel bugs, or minute pirate bugs may be capable of preventing population outbreaks of pea aphids.
The current recommendation for pea aphid management is to wait until 50% of the plants in a field have formed some young pods, and pea aphid thresholds have been exceeded. If thresholds have been exceeded during flowering, consider applying insecticides later in the evening to avoid pollinators that may be foraging on the pea flowers. Refer to Table 1 for a list of insecticides available for pea aphid management on field pea.
Source: Adam J. Varenhorst, iGrow