Since our last scouting report for our day-neutral organic strawberry project at the West Madison Agricultural Research Station (WMARS), more and more ripe fruits are present each week throughout the field. Scouting for insects has been conducted weekly since June 15. Each week 60 randomly selected plants are sampled by tapping flower clusters and foliage over a wide funnel into plastic bags and insect of importance identified and counted. Plants are also inspected for disease symptoms which are then identified and plants with symptoms counted. We continue to observe the usual suspects for insect pests and diseases: thrips, leaf hoppers, tarnished plant bugs (Fig. 1), and spider mites (Table 1), as well as common leaf spot and phomopsis leaf blight (Table 1).

Spider mites are commonly seen occupying sampled plants but showed a decrease in prevalence this week (Table 1). Spider mites can be identified by their leaf webbing, stippling, and scaring damage. They tend to prefer hot and dry conditions. The action threshold for two-spotted spider mites used in June-bearing strawberry is set at 25% or more of leaflets sampled harboring mites (1 or more mites on 15 out of 60 leaflets sampled). In conventional production, several products are available that provide excellent control on spider mites including Abamectin (e.g. Agri-Mek), etoxazole (e.g. Zeal), hexythiazox (e.g. Savey), bifenazate (e.g. Acramite), acequinocyl (e.g., Kanemite) and fenpyroximate (e.g. Portal). Assail also provides good control for mites. In organic production, oils such as mineral oils and sesame oil have shown good control in some studies. While our sampling exceeds the action threshold for spider mites, we have not observed noticeable damage or webbing in the plants. Thus, we are foregoing pesticide applications to promote natural enemies such as predatory mites, minute pirate bugs (Orius spp.) and lady beetles that can help control mite populations naturally.

Tarnished plant bug adults (Fig. 1) and nymphs remain present throughout the field, continuing to increase in their weekly numbers over the season. Fruits exhibiting cat-faced symptoms have been collected during harvest events, reaching around 15% of harvested fruit in the past week. The economic threshold for tarnished plant bug is one nymph per 4 flower clusters or 4 adults per 20 sweeps. Our sampling indicates that the average tarnished plant bug population is below the action threshold (Table 1). Management practices include removing weeds and the application of pesticides. Because of our research on fruit quality and yield, half the plot was sprayed with Pyganic 1.4E via backpack sprayer at a rate of 1.5 fl oz/ gallon (11.7ml/L) on 07/28/22. Other insecticides that could be used include Azadirachtin which has shown control in some studies for organic production. In conventional farming, Brigade and Danitol for pyrethroids and Actara and Assail for neonicotinoids have shown good/excellent efficacy against tarnished plant bug.

Thrips have increased slightly in numbers in the field, potentially due to the high winds and storms this past weekend. However, thrips were visibly noticeable flying in and around scouting supplies (figure 2) in addition to their presence on sticky cards. Along with their obvious presence, we’ve begun seeing early signs of thrip damage among fruits including bronze patches and wet pigment variation from feeding. The action threshold of 2-10 thrips per flower or small berry may warrant an insecticide application depending on field and grower tolerance. At this time, we did not reach the threshold and no insecticide was sprayed to control thrips.

Common Leaf Spot remains a consistent disease in day-neutral strawberry with stable numbers over the past two weeks. This disease is characterized by deep purple or red spots on the upper surface of leaves. Overtime these spots develop dry tan centers within the purple spots. The fungus thrives in warm and humid conditions. With moderate distribution this disease is mainly cosmetic but if its spread becomes more significant it can affect the function of the leaf. As of the latest field observations, leaf spots are mild with only a few spots per plant.

Phomopsis Leaf Blight (figure) seems to be declining over the season with this week’s numbers following suit (Table 1). This blight prefers long stretches of wet and humid conditions. It’s identifiable by its circular or V-shaped brown lesions among leaf veins. At its later stage it can lead to defoliation and fruit rot similar to anthracnose. Management techniques include removing infected leaves, weed removal, and fungicide applications.

Dates for Weekly Scouting	Mites (Average per plant)	Thrips (Average per plant)	Tarnished plant bug (Average per plant)	Thrips (Average per flower cluster)	Tarnished plant bug (Average per flower cluster )	Common Leaf Spot (Average per plant)	Phomopsis Leaf Blight (Average per plant)
6/15/2022	0.22 ± 0.11	0.16 ± 0.09	0	0	0	0	0
6/22/2022	0.01 ± 0.01	0.03 ± 0.03	0	0	0	0	0
6/28/2022	0.08 ± 0.04	0.05± 0.03	0	0	0	0	0
7/05/2022	0.13 ± 0.06	0.12 ± 0.05	0.03 ± 0.02	0	0	0	0
7/13/2022	1.28 ± 0.35	0.25 ± 0.07	0.08 ± 0.49	0	0	0.35 ± 0.06	0
7/19/2022	4.3 ± 0.51	0.2 ± 0.06	0.33 ± 0.08	0	0	0.57 ± 0.06	0.25 ± 0.06
07/28/2022	3.37 ± 0.38	0.27 ± 0.07	1.32 ± 0.24	0	0	0.55± 0.06	0
08/02/2022	3.62 ± 0.35	0.23 ± 0.06	1.87± 0.29	0	0	0.8 ± 0.05	0.22 ± 0.05
08/09/2022	2.27± 0.27	0.35 ± 0.09	2.48± 0.34	0.3± 0.04	0.69± 0.12	0.87 ± 0.04	0.17 ± 0.05

Pest & Disease Averages per Plant ± Standard Deviation for Day-Neutral Strawberries

Table 1. The average number of insects and disease symptoms observed per plant in day-neutral strawberries during weekly sampling.

Note from the field: Sticky traps are often preferred methods for population monitoring and ease of use for large fields. It is important to remember to monitor sticky traps not just for pests but for accidental victims such as butterflies (Fig. 5) and birds.

Thank you to the personnel at WMARS for their help with this project. This project was funded by USDA-NIFA ORG award # 2021-51106-35490.

Happy growing season!

This article was posted in Berries, Disease, Insects and tagged berry, Christelle Guédot, day-neutral strawberry, disease, DNS, DNS Organic, insects, Leslie Holland, organic, Organic Day-Neutral Strawberry Production, Organic production, organic strawberries, Rachel O’Neill Lewis, strawberry.