This scouting session for our day-neutral organic strawberry project at the West Madison Agricultural Research Station (WMARS) was conducted Friday, July 21st in the morning. Field conditions during collections were sunny and warm.
This project aims to evaluate the effects of four different film-based mulches (black, white, and reflective plastic mulches, and paper mulch) on strawberry production in an annual, day-neutral system. This system-wide field trial is evaluating yield, fruit quality, pest pressure, and economic feasibility of this regionally novel system for strawberry production. Our field was planted on the 8th of May, and plants are still developing with flowers and runners removed as they appear, with runner removal continuing indefinitely and flower removal having ceased the week of July 3rd. Berries are beginning to develop, with harvest anticipated to begin within two weeks of publication. We are irrigating for short intervals several times a week, with fertigation occurring once weekly at the rate of 5 lbs N per acre.
Sampling Methods: 160 plants (40 plants per mulch treatment) were randomly selected and assessed for insect pest and disease presence and respective pressure using the University of Wisconsin Extension BioIPM Strawberry Workbook. At each sampling point, two leaves per plant were tapped into a white tray, and any thrips or tarnished plant bugs were counted. Since 07/07/2023, thrips and tarnished plant bugs have been sampled by tapping one flower cluster per sampled plant into a tray. Mites were assessed on an incidence-basis: plants were evaluated for mite presence on older foliage and crowns. Each plant was also inspected for foliar disease symptoms. Declining or dead plants are removed and assessed in the laboratory for biotic causal agents.
Table 1. The incidence and average number of insects observed per plant in day-neutral strawberries during weekly sampling.
|Date||Mites (Incidence)||Thrips (Average per two leaves* or one flower cluster)||Tarnished Plant Bug Adults (Average per two leaves* or one flower cluster)||Tarnished Plant Bug Nymphs (Average per two leaves* or one flower cluster)||Spotted- wing Drosophila (Incidence)||Flea Beetle (Average per plant)|
|6/9/2023||0.21 ± 0.06||0.07 ± 0.07 *||0.03 ± 0.03 *||0||0||0|
|6/15/2023||0.21 ± 0.06||0.13 ± 0.1 *||0.01 ± 0.01 *||0||0||0|
|6/26/2023||0.51 ± 0.08||0.09 ± 0.07 *||0.20 ± 0.07 *||0||0||0|
|6/30/2023||0.52 ± 0.08||0.17 ± 0.10 *||0.06 ± 0.04 *||0||0||0|
|7/07/2023||0.52 ± 0.08||0.05 ± 0.05 *||0.03 ± 0.03 *||0||0||0.09 ± 0.05|
|7/14/2023||0.35 ± 0.08||0.04 ± 0.05||0.21 ± 0.09||1.09 ± 0.15||0||0.09 ± 0.04|
|7/21/2023||0.14 ± 0.08||0||0.10 ± 0.05||0.29 ± 0.09||0||0.04 ± 0.03|
Tarnished plant bugs: During last week’s scouting on 7/14, the number of tarnished plant bug adults and nymphs (Fig 1) jumped well beyond the recommended spray threshold of 1 TPB per 4 flower clusters.. We sprayed Pyganic 1.4 EC at a rate of 50 fl. oz/acre by backpack sprayer to cover the entire patch on the evening of 7/17/23 to avoid pollinators. As a result, this week, the number of TPB adults and nymphs fell sharply by 50% and nearly 75%, respectively. Adults were found on 1 in 10 flower clusters, and nymphs were found on just over 1 in 4. As this number is still at threshold for chemical management, we sprayed Pyganic 1.4 EC at a rate of 50 fl. oz/acre for a second time on the evening of 7/25/23.
We spray in the evening to avoid pollinators, as well as to maximize efficiency of the spray, as the active ingredients in Pyganic are degraded by UV light. Pyganic contains a mixture extracted from the flowers of Tanacetum cinerariifolium (Chrysanthemum)which contains six naturally occurring metabolites of insecticidal quality (cumulatively called pyrethrins). Pyganic is in the IRAC group 3A, which contains pyrethrins and the non-OMRI pyrethroids which are synthetic compounds that are very similar in structure to the pyrethrins. Pyganic should not be used more than ten times in a season with a minimum interval between applications of 3 days except in cases of extreme pest pressure (see the label for more info). The PHI (Pre-harvest interval) is 0 day and the REI (restricted entry interval) is 12 hours. The insecticide works quickly and effectively by disrupting insect nervous system function, but is of minor toxicity to mammals due to differences in physiology and metabolism. As with many organic insecticides, Pyganic is a broad spectrum insecticide, and will kill any arthropods in the canopy at the time of application including pests, pollinators, and beneficials. As part of our IPM regimen, we must weigh the potential benefits of spraying for TPB with the potential harm of killing lady beetle, Orius and predatory mite populations as well. In organic production, Pyganic is recommended for TPB management as well as other insecticides including Azadirachtin, which has shown control in some studies. In conventional farming, Brigade and Danitol for pyrethroids and Actara and Assail for neonicotinoids have shown good/excellent efficacy against Tarnished Plant Bug.
Fruits harvested on 7/24/23 exhibited moderate to severe catfacing, the main damage caused by TPB, likely caused by feeding on flowers and developing fruits during or after the week of 7/10/23.
Two-spotted spider mites: The incidence of mites decreased significantly again this week to 14% of scouted plants. Heavy rain showers earlier in the week, the presence of predatory mites, and the application of Pyganic may have contributed to the reduction in mite incidence.
Thrips: This week, there were surprisingly no thrips observed during scouting. Their presence on sticky cards indicates their existence in the field over the past two weeks, but it’s likely that last week’s Pyganic spray and heavy rainstorms reduced their numbers.
Flea Beetles: The amount of flea beetles decreased this week. Minimal damage associated with these beetles, as well as Japanese Beetles was noted in the field.
This week, the amount of some pests and beneficial insects may have been impacted by our decision to spray Pyganic on 7/17. It is always a balancing act, especially in organic production, when weighing out the role of beneficial insects in providing biological control and the need to spray insecticides for pest insects that reach an established economic threshold. In this case, because TPB is a serious pest of day-neutral strawberry, we made the hard decision to spray Pyganic to reduce TPB populations, knowing that we would likely see a reduction in beneficial insects such as predatory mites, lady beetles, and minute pirate bugs (Orius bugs).
Predatory Mites: The amount of predatory mites, along with two-spotted spider mites, decreased sharply this week: 2 of 10 sampled plants had predatory mites. More information on these mites can be found in last week’s article.
Lady beetles: Just 1 of 10 sampled plants had lady beetle larvae and/or adults this week. Lady beetles are beneficial insects and should be conserved in agroecosystems to allow them to prey on pest insects such as aphids. For more information on lady beetles, please see this article.
Orius bugs: This week, Orius bugs were still somewhat common throughout the field, and were frequently dropping during flower cluster tap-sampling. 5 of 10 randomly sampled plants had Orius bugs, many of which were insidious flower bugs (Orius insidiosus). Orius bugs are also known as minute pirate bugs and they are biological control agents that feed as immatures (nymphs) and adults on pest insects such as aphids, leafhoppper nymphs, thrips, spider mites, insect eggs and small caterpillars. Orius will insert its beak inside the host body, while immobilizing its prey with its front legs, and suck on the insect insides until it is dried up.
Pollinator Observations: There were a wide range of pollinators visiting the flowers this week. During scouting, the field was full of syrphid flies (Fig 2). Their presence is likely positively impacted by warmer temperatures and lower wind speeds, making Friday’s field conditions perfect for their visits on strawberry flowers and leaf edges.
Table 2. The incidence of diseases observed per plant in day-neutral strawberries during weekly sampling.
|Date||Common Leaf Spot||Phomopsis Leaf Blight||Verticillium Wilt||Anthracnose||Leaf Scorch||Neopest- alotiopsis|
|6/30/2023||0||0.01 ± 0.02||0||0||0||0|
|7/07/2023||0.01 ± 0.02||0.08 ± 0.04||0||0||0||0|
|7/14/2023||0.01 ± 0.01||0.06 ± 0.04||0||0||0||0|
|7/21/2023||0.01 ± 0.01||0.07 ± 0.04||0||0||0||0|
Phomopsis leaf blight (Phomopsis obscurans): The observed incidence of Phomopsis leaf blight again remained relatively constant at 7% of sampled plants this week, with infection still in early stages. We again observed one Common leaf spot (Mycospharella fragariae) lesion on our sampled plants.
Anthracnose (Colletotrichum fragariae): During walk-throughs, we observed the first sign of anthracnose in our field this week. Symptoms appeared as a dark brown, sunken lesion on a fruit (Fig 3). Anthracnose is a fungus that can affect nearly all parts of the plant, including the leaves, fruits, and crowns. The most characteristic symptoms are the firm, tan-to-brown lesions that develop on the fruit, which will produce salmon-colored spores in humid conditions. Anthracnose often enters the field on transplants or from nearby host weeds. The development of this disease can significantly impact fruit quality and yield.
Funding for this project was provided by USDA-NIFA ORG award # 2021-51106-35490.This article was posted in Berries and tagged Ariana Abbrescia, Christelle Guédot, day-neutral strawberry, DNS, DNS Organic, Jarret Miles-Kroening, Leslie Holland, Organic Day-Neutral Strawberry Production, organic strawberries, Strawberries.