The time has arrived to start implementing our scouting programs for monitoring and early detection, an integral part of your integrated pest management plan. In high tunnels or other protected environments there are a variety of insect pests that are capable of overwintering and can move into an of the early-season crops that you are growing. Two of the common and most troublesome pests that I am referring to are aphids and mites. In our strawberry high tunnel systems we have been monitoring insect populations throughout the winter, and much like last year aphids and mites are the biggest problem. Aphids have been lingering around the perimeter of the crop, hanging onto the weed population, but we have not seen them move into the berries. The mites are more widespread, occurring on the strawberry plants themselves in addition to the weeds, in particular volunteer cowpea emerging from the previous cover crop that was in the tunnel.
Utilizing sticky cards as a tool to help with monitoring or scouting the crop/weeds directly will help you make informed decisions about when to intervene. For a review of implementing sticky cards see this article. Mites create a stippling symptom on the leaves. Familiarizing yourself and your employees to recognize this early symptom can help with timely interventions. Depending on the crop, these symptoms can be more or less apparent. In our high tunnels, scouting the weeds is easier for detection than the crop itself. Cowpea is a great indicator plant. Figure 1 shows mite damage on cowpea, Figure 2 is that same pest damage on young strawberry leaves.
Figure 1. Mite symptoms on cowpea.
Figure 2. Mite symptoms on strawberry.
Mites typcially cause a stippling symptom on the upper leaf surface, small yellow spot resulting from the mite feeding on the underside, where they are sucking out the photosynthates from individual plant cells. Figure 3 is a view of the underside of the cowpea leaf, and Figure 4 is a close-up of that stippling damage on strawberry.
Figure 3. Mites on underside of cowpea.
Figure 4. Stippling damage from mites.
To prevent crop loss, be sure that you are scouting early and often, and you have a plan in place to intervene when the pest is detected. In our high tunnels, we are continuing to monitor the aphids. At this point, they continue to pop up in the weeds around the crop but are not colonzing the strawberries themselves. In this situation, we continue to work to remove the weeds and monitor on a weekly basis. The mites are treated differently. We have not seen any natural enemies and the population continues to grow and spread throughout the tunnel. For this pest, we have decided to intervene and are evaluating a variety of biopesticides for control (stay tuned). For the most recent pesticide recommendations, see the Midwest Vegetable Production or Fruit Spray guides.