Since the last scouting report for our day-neutral organic strawberry project at the West Madison Agricultural Research Station (WMARS), more and more ripe fruits are presenting throughout the field. Each week, 60 plants are randomly selected and sampled by tapping flower clusters and foliage over a wide funnel into plastic bags so that pests can be counted and identified. Each plant is inspected for disease symptoms and flower clusters are counted. We continue to observe the usual suspects for insect pests and diseases: thrips (Fig. 2), leaf hoppers, tarnished plant bugs (Fig. 1), spider mites (Table 1), common leaf spot (Fig. 3), and phomopsis leaf blight (Fig. 4). Field conditions during this week’s collections were moderately sunny with intermittent clouds, humid, and with low winds.
Spider mites are common among sampled plants but showed a significant decrease this week (Table 1). Spider mites can be identified by their leaf webbing, stippling, and scaring damage and tend to prefer hot and dry conditions. The action threshold for two-spotted spider mites used in June-bearing strawberry is set at a minimum 25% of leaflets sampled harboring mites (1 or more mites on 15 out of 60 leaflets sampled). While our sampling exceeds the action threshold for spider mites, we have not observed noticeable damage or webbing in the plants and we are banking on natural enemies such as predatory mites, minute pirate bugs (Orius spp.) and lady beetles, all of whom we’ve seen in the field, to continue to control mite populations. 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.
Tarnished plant bug adults (Fig. 1) and nymphs remain prevalent throughout the field. We are seeing the first decrease of the season regarding average TPB per plant. The average TPB per flower cluster is holding below the action threshold (table 1). The economic threshold for tarnished plant bug is one nymph per 4 flower clusters or 4 adults per 20 sweeps. Management practices include removing weeds and the application of pesticides. Pyganic 1.4E has been applied 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 numbers are showing a decrease in severity (Table 1). It is important to rely on sampling methods and visual observations for thrips as flighted and mobile pests can be difficult to sample. Field averages only indicate a slight decrease due to the challenges of sampling flighted pests. The action threshold of 2-10 thrips per flower or small berry may warrant a chemical control depending on field or grower tolerance.
Common Leaf Spot (figure 3)remains a consistent disease in day-neutral strawberry with stable numbers over the past few weeks and a slight decrease this week (Table 1). 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 4) has been declining throughout the season however, the most recent scouting data shows an increase (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. Management techniques include removing infected leaves, weeding, and fungicide applications.
Pest & Disease Averages per Plant ± Standard Deviation for Day-Neutral Strawberries
|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|
|08/16/2022||0.68 ± 0.12||0.25 ± 0.06||1.55 ± 0.17||0.1 ± 0.03||0.71 ± 0.11||0.77 ± 0.06||0.38 ± 0.06|
Table 1. The average number of insects and disease symptoms observed per plant in day-neutral strawberries during weekly sampling.This article was posted in Insects and tagged Christelle Guédot, day-neutral strawberry, DNS, DNS Organic, insects, Leslie Holland, Organic Day-Neutral Strawberry Production, Rachel O’Neill Lewis, Strawberries.