Aphids have been a particularly challenging pest to get under control this spring. They quickly colonized the strawberries we had growing all winter in our high tunnels, and took off as the weather sporadically warmed up (Figure 1). In my first attempt to knock them back I introduced 2,000 lacewing larvae (22-Apr), too little too late. Four days after release I did not recover a single one. They were either hiding or did not survive. However, last week I found very large larvae (Figure 2), just one or two here and there.
Figure 1. An example of the level of aphid infestations currently experienced in the high tunnel strawberries.
Figure 2. A lacewing larvae observed on the high tunnel strawberries during a pest survey on 13-May.
In the meantime, I decided to try out a few of the OMRI approved options. I will admit that at the time of the first application, the populations were high, and it explicitly states on the label for some of these products (BotaniGard® and Grandevo®), to begin applications at the onset of pest detection. That was not the case here. I applied all products at the highest recommended rate and have made three applications within a 10-day span. Table 1 shows the products, active ingredient (A.I.), application rate and dates of applications. In entomological tradition, I surveyed the aphid population prior to treatment (1-May) and after the first two applications (13-May). The changes in aphid populations are shown in Figure 3. Data below 0 on the y-axis indicate a reduction in the population, above 0 shows an increase post- application.
Two of the tested products are biological pathogens, which we can expect to take some time to negatively impact the population. BotaniGard® typically takes 7-10 days to see control, according to the label. The Grandevo® product label recommends a knockdown is applied prior to or in a tank mix application at high populations, which was the case here. The label also suggests application of the high rate with increased volume to ensure coverage and short intervals between applications. In this study we applied the high rate for all products and used an electro-static sprayer to optimize coverage of the product. The results shown here indicate good control being achieved with the Azera® and Pyganic® products, when applied at levels of high population infestations. At the last survey, 13 days post-application from the first spray, I have yet to see any evidence of infection and/or pest suppression in the BotaniGard® and Grandevo® treated plants. Admittedly, these products should have been applied earlier in the growing season, when aphid populations were low.
Stayed tuned for updates as I continue to monitor these populations.
Figure 3. The change in aphid populations between the four insecticide treatments. Means are calculated based on number of plants sampled within each treatment (N=15-17) + standard errors.
More General Aphid Management Recommendations
In general, it is important to consider resistance management when treating pests such as aphids. They reproduce quickly which is one factor that can contribute to the development of resistance to pesticides. Resistance can develop to conventional and organic active ingredients, as well as cultural tactics. It is crucial to incorporate rotation of mode of actions when applying chemicals to control these pests. When using organic pesticides, this is equally important. We have seen documentation of resistance develop to neem products, insecticidal soaps and oils. If you are losing efficacy of a preferred product, you need to be sure to switch to another mode of action incorporating one or two new products and taking a break from the preferred favorite. Note that in the trial described above, Azera® and Pyganic® both contain pyrethrin and therefore have overlapping modes of action (and A.I.). They should be used in a rotation with a biological agent, horticultural oil or soap.