May 17, 2021

Current Issues for Pennsylvania vegetable, berry crops pinpointed

After some significant rains this past week, it has been unseasonably cold across much of the state and especially in the northwest where there have been multiple freeze events over the past few weeks.

In some cases, the colder weather has delayed planting by both growers and homeowners leading to overgrown transplants for both the field and for sale.

Onions and other Alliums

The emergence of the spring adults from overwintering pupa of Alllium leafminer (ALM) started in mid-to-late March in southeast Pennsylvania and continued into mid-April in cooler areas of the state. Adult flight occurs over about 5–7 weeks. Therefore, we expect the first flight (ALM) to be over soon – around May 20 in the warmer areas and maybe extending another week in cooler areas. Growers are being advised that they can discontinue applying row covers or insecticides targeting adults by Memorial Day. Also, onions planted towards the tail end of the adult flight will have escaped significant damage: those very young leaves will become the scale leaves surrounding the bulb at harvest, and ALM trapped in those scale leaves rarely survive or will be sloughed off during harvesting and packing. Most ALM are now in the larval stage, mining the leaves.

Scout fields for oviposition marks and use systemic or translaminar insecticides to target early larvae if necessary. The most consistent effective options include the neonic dinotefuran (Scorpion), the diamide cyantraniliprole (Exirel, Verimark), and spinetoram (Radiant); also the OCIA-labelled option spinosad (Entrust) performed well in several trials. See this publication on managing Allium leafminer for a comparison of 14 ai options relevant to IPM and certified organic production. The larval stage will occur for about 3 weeks at ~60-degrees, and a bit longer under cooler temperatures. There is a new phenology model for ALM that can be run for select weather stations through the NEWA system and selecting 32°Fahrenheit for the base temperature. We are estimating spring emergence of adults will just begin at about 350 degree-days above this base temperature.

We sometimes get asked if ALM will infest the agroforestry crop ramps. Yes, we have confirmation of ALM infestation of ramps in PA!

Figure 2. Marks on ramps made by ALM female with her ovipositor, for egg-laying, or wounding that attracts more ALM. Photo: Rebecca Kutys

High tunnels

The cooler weather and high relative humidity in high tunnels and greenhouses is making conditions perfect for Botrytis/Gray mold to develop on most crops. Botrytis is favored by cool temperatures and the high relative humidity that comes from poor air circulation due to overcrowding of plant material. This can either result from tight plant spacing or crop over fertilization leading to lush crop canopies that limit air movement and promote leaf wetness. It commonly starts on damaged plant tissue or senescing flowers and then progresses onto the fruit. Fungicides such as Decree, Botran, and Scala can limit disease spread and are registered for greenhouse/high tunnel use on certain commonly grown greenhouse vegetable crops. Improving air circulation is also beneficial.

Figure 3. Left: Zonate brown necrotic lesions typical of Botrytis on tomato in a high tunnel. Photo: Beth Gugino, Penn State. Right: Dense gray sporulation caused by Botrytis on high tunnel-grown zucchini fruit. Photo: Leah Fronk,/Penn State.

Mite and thrips damage has also been observed in greenhouse crops. Keep in mind that thrips can vector viruses such as tomato spotted wilt virus. It is especially important not to comingle vegetable transplants with ornamental transplants or hanging baskets which can often be the source of thrips entry to the farm.

Crop nutritional issues have been observed in a number of high tunnels and greenhouses especially in hydroponic production causing plants in some cases to be severely stunted. It is important to know what nutrients are being applied at what rates. Water quality in terms of pH and soluble salts is also important for optimizing nutrient availability and minimizing nutritional stress. Plant tissue testing can be an important source of information during the season to help adjust in-season fertility. For a tutorial on plant nutrition in hydroponic systems check out Hydroponic Systems and Principles of Plant Nutrition: Essential Nutrients, Function, Deficiency, and Excess . For those growing in native soils check out a series of articles was recently written by Elsa Sánchez and Tom Ford based on soil samples from the high tunnels of 27 growers. These articles will help growers navigate the topics of soil chemical properties and crop health and include:

• High Tunnel Soil Health Test Report: Soil pH 
• High Tunnel Soil Health Test Report: Soluble Salt Levels
• High Tunnel Soil Health Test Report: Soil Nutrient Levels
• High Tunnel Soil Health Test Report: Organic Matter and Cation Exchange Capacity

Special note: Pesticide applications in enclosed spaces

This note was circulated last year but now is a good time for a reminder. When it comes to making pesticide applications, the Pennsylvania Department of Agriculture has updated and broadened the term “greenhouse” to an “enclosed space” which now includes high tunnels, greenhouses, and hoop houses. Per 40 CFR Part 170 enclosed space production is the production of agricultural plants indoors or in a structure or space that is covered in whole or in part by any nonporous coverings and is large enough to permit a person to enter.

Common situations that would still be considered enclosed spaces:

• A hoop house cover with plastic film, regardless of the sides being rolled up or down.
• A greenhouse with the roof vented.
• A high tunnel with both ends open.

Common situations that would not be considered enclosed spaces:

• A hoop house with all plastic film completely removed; for example, it is common to remove plastic film for summer production.
• A hoop house with a shade cloth where the plastic film traditionally would be.
• A tunnel, such as a low tunnel, that is not tall enough for a person to enter.

When selecting pesticides to manage pest and disease outbreaks in enclosed structures, only products that are labeled for use in greenhouses/enclosed structures on that crop group can be applied. If the label specifically restricts applications in the greenhouse/enclosed spaces, you are not permitted to apply it. Also, if the label does not specifically include or exclude greenhouse/enclosed spaces (no mention at all), you are not permitted to apply it. Questions can be directed to Jessica Lenker, [email protected], 717-772-5217.

Berry crops

As with last year, frost protection of strawberry blossoms has been a challenge for many growers given the wind that accompanied our cold temperatures. While some blossoms have been lost, most growers are reporting additional bloom that is expected to result in a substantial crop, especially considering that fruit size from later blossoms will increase in size to at least partially compensate for the damage.

Blueberry growers in cooler parts of the state are reporting unusual coloration to new blueberry leaves and emerging blossoms. This is thought to be a response to the combination of especially cold temperatures this spring with the stage of plant growth. There are varietal differences, with ‘Duke’, ‘Reka’, and ‘Superior’ showing especially deep reddish or copper leaf color, though all varieties are showing odd coloration to some extent.

Mid-season varieties (like Bluecrop) are in peak bloom in central Pennsylvania. Wild bees are out and actively pollinating blueberry blossoms. The most common wild pollinators that have been observed are bumble bee queens and solitary mining bees (genus Andrena). Bumble bees are going through their solitary life stage in early spring when the queens are the only individuals in the nest. This solitary life stage poses a critical time for bumble bees because if they do not find enough floral resources or if they are exposed to lethal levels of pesticides, the queen may die and the colony will not develop.

While insecticide use for blueberries is low early in the season, fungicides are used during bloom to control botrytis and secondary infections of mummy berry, and some of these are also toxic. Category 3 fungicides (Indar, Proline, Quash, and Tilt/Orbit) are known to be highly toxic to bees, so they should be avoided during bloom. They may be used earlier for sprays targeting primary infections of mummy berry, which are made prior to bloom, and fungicides in category 11 (Abound) or 9 and 12 (Switch) may be used instead of them during bloom. Take other precautions to protect pollinators, such as mowing blooming weeds like dandelion in row middles prior to spraying, and/or applying sprays after sunset to minimize bee exposure.

Figure 4. Left: Mining bee pollinating blueberry. Photo: Nash Turley. Right: Bumble bee queen pollinating blueberry. Photo: Margarita López-Uribe/Penn State

The cool temperatures are also keeping warm-weather disease issues tamped down at this point; however, growers are cautioned to remain vigilant. Symptoms of our newest strawberry disease, Neopestalotiopsis, are manageable at this point in the few plantings where this disease is present. Growers continue to report ‘Flavorfest’ plant collapse; this is thought to be due to Phytophthora crown rot that may have been transported with the plants, as even plantings on new ground have had this issue. Windy conditions have resulted in leaf rubbing on strawberries; symptoms are a brown bruising of plant tissue which could be easily mistaken for foliar disease. This type of damage can be differentiated from foliar diseases in that symptoms are present primarily on the uppermost leaves, and any discoloration is only on the surface. Brown markings on petioles are not sunken as with anthracnose.

Figure 5. Tarnished plant bug nymph on strawberry fruit and adult on a strawberry blossom. Photos: Kathy Demchak/Penn State

Tarnished plant bug nymphs are present in strawberry plantings; however, insecticide applications should be avoided until bloom is complete. The threshold for making an insecticide application is 1 tarnished plant bug nymph per 4 blossom clusters, so it is recommended that growers scout as soon as bloom is over and be ready to make an application if needed. This may need to be done by variety to avoid misshapen fruit. Tarnished plant bug nymphs look very different from the adults and do not fly. It is easiest to find the nymphs by tapping blossom clusters over a light-colored surface such as a sheet of paper, as they quickly try to hide once they detect movement. The adults fly away very quickly, so brushing the foliage and identifying them once they land elsewhere usually works best.

Resources for staying up to date with the latest information

• 1-800-PENN-IPM hotline had expanded its menu options  starting with the 2020 production season. Dial 1-800-PENN-IPM (1-800-736-6476) and select from a range of crop groups and topics from vegetables (onion, tomato/potato, sweet corn, vine crops), small fruit, tree fruit, to greenhouse IPM and hear weekly updated 90-second voice messages with the latest information on crop, pest and disease management to help you through the growing season.
• Sign-up with Penn State Extension to receive the latest news and information on vegetable and small fruit crop production as well as pest and disease management either electronically or by calling 1-877-345-0691.
• Cucurbit downy mildew alerts can be obtained by email or text message by signing up. You can specify the distance from your farm for which you would like to receive reports.
• The 2020-2021 Mid-Atlantic Fruit and Vegetable Production Recommendations has the latest information to help commercial vegetable and strawberry growers in the mid-Atlantic region make production and pest management decisions. The hardcopy can be purchased either online or by calling 1-877-345-0691. Individual sections are also available for download . This publication will now be updated every other year so the next update will be in 2022.
• Penn State Extension Informational Kiosks are available at many of the produce auctions across the state. Throughout the season they will provide both education material as well as timely pest and disease forecasting information. Three additional locations are being added this year.
• The MyIPM app is available for free from the Apple Store and Google Play and covers strawberries, blueberries, and blackberries in addition to tree fruit crops. The App is updated with current pests and cultural and chemical controls.

– Beth K. Gugino, Kathy Demchak, Margarita Lopez-Uribe and Shelby Fleisher, Penn State University