Now that the days are getting longer and temperatures remain unseasonably warm, aphids are likely to become more abundant. Experience has also shown that aphid population growth begins to increase significantly once the weather warms in January. Our local weather forecast for the next two weeks suggests that temperatures will be in the low 70’s with moderate nighttime lows in the mid-40’s. These conditions may be ideal for aphid population growth, which is optimal at average temperatures of 55-60 °F. However, the lack of rainfall this fall and winter so far may play to your advantage.
Previous research has shown us that aphids tend to be more abundant during warm, wet winters. Nonetheless, we’ve seen an unusual abundance of aphids earlier this fall and that could continue. So, keep an eye out for colonization.
Aphid flights are ahead of schedule compared to the past few seasons (see graph below). Trap captures of winged aphids peaked in Nov and continued to move in above average numbers in December. They have been particularly heavy in the North Gila and Yuma Valleys. There were several reports of green peach aphid colonizing lettuce and broccoli in both conventional and organic produce last month, and at the Yuma Ag center, green peach aphids are beginning to colonize small plants, and we should be starting efficacy trials soon. Be on the lookout for lettuce and foxglove aphids too (see Aphid ID Guide) as they tend to develop faster at higher temperatures than other aphid species found in the desert. Consequently, PCAs should be extra vigilant in scouting for aphid colonies. If a field has been treated with imidacloprid at planting, then chances are you are in pretty good shape on young produce. However, imidacloprid doesn’t last all season. Regardless of whether you find green peach, or lettuce aphid the key to effective aphid management with foliar insecticide is to initiate sprays at the time apterous (wingless) aphids begin to colonize. The action threshold is when you can find aphid colonizes on > 5% of plants sampled. Of course, this requires diligent scouting and sampling. On older lettuce, make sure you thoroughly examine developing heads/hearts. Fortunately, PCAs have many alternatives for aphid control (see Aphid Management on Desert Produce_2025). So, keep your eyes open for new aphid colonies and treat early to keep ahead of the populations.
For more information on aphid management visit these publications:
