2022 PA Vegetable and Berry Current Issues for May 16

However, delays in planting are leading to overgrown transplants for both the field and for sale, and frost damage is a common sight on sensitive crops like strawberry. The cooler weather also results in reported damping-off in some crops like melon.

Onions and Other Alliums

The emergence of the spring adults from overwintering pupa of Allium leafminer (ALM) started in mid-to-late March in southeast PA 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 extended 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 (Figure 1) 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 from the Journal of Economic Entomology for a comparison of fourteen active ingredient options relevant to IPM and certified organic production. The larval stage will occur for about three weeks at approx. 60°F, 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.

Also, be on the lookout for seed corn maggot damage on onion. They overwinter as a pupa in soils and emerge as adults (like a housefly) in early spring and lay an average of 270 eggs per female in moist soil. The larvae complete their development in two to three weeks while feeding on onion as well as many other vegetable crops.

High Tunnels

The cooler weather and high relative humidity in high tunnels and greenhouses are 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 overfertilization 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 2. Zonate brown necrotic lesions are typical of Botrytis on tomato in a high tunnel. Photo: Beth Gugino, Penn State

Mite and/or thrips damage have also been observed in greenhouse crops including cucumber, lettuce, and tomato. 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.

Management options include Conserve or Spear-T Biological Insecticide/Miticide. High aphid populations were also observed in one tomato high tunnel. One recommendation is to consider spot treating with a product such a Venerate that contains the biocontrol organism Burkholderia spp.

Other sightings in high tunnels or the field include wireworm damage on high tunnel lettuce; flea beetles on cole crops; slug damage on turnip; Fusarium basil rot on garlic; and tobacco mosaic virus on pepper and eggplant.

Berry Crops

As with the last two years, frost protection of strawberry blossoms has been challenging given the wind that accompanied our cold temperatures. Damage to blossoms has been variable depending on the growth stage that the plants were at when cold temperatures hit with the most issues being in annual plasticulture plantings.

There have been some reports of frost damage to new vegetative canes of raspberries, which can be nipped by very cold temperatures. If just the tip of the cane is damaged, the plant may grow as if it had been intentionally tipped and may form lateral branches. The dead tip could be mistaken for disease later in the season. Tissue cultured bramble plug transplants are also very tender, they are not any more cold-hardy than tomatoes transplants would be, so they should not be planted until the danger of frost is past.

Figure 3. (A) ‘Niwot’ black raspberry cane damaged by spring frost resulting in lateral formation. Photo: Kathy Demchak, Penn State. (B) Fruit rot caused by Neopestalotiopsis on ‘Chandler’ fruit. Photo: Dr. Mengjun Hu, University of Maryland. (C) ‘Flavorfest’ plant diagnosed with Phytophthora crown rot. Photo: Kathy Demchak Penn State

Wild bees are out and actively pollinating blueberry blossoms. 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.

Fruit rot caused by our newest strawberry disease, Neopestalotiopsis, has been seen in Maryland for the first time. This was on ‘Chandler’ transplants that were sourced from outside of the mid-Atlantic region in this case, but we know that Neopestalotiopsis was also in plant material grown locally. This means that any growers that planted plug plants last fall should be watching for this disease, especially if the plug plants were grown outdoors. The fruit rot caused by Neopestalotiopsis fruit rot is very black in the center compared to other fruit rots such as anthracnose, which may turn dark brown but not as black. It also causes fruit to soften which could be mistaken for any other fruit rot in the early stages.

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. More information on this disease appears in the article, Disease Management Recommendations for Fall-Planted Strawberry Plug Plants. At this time of the year, treatments are limited to products with short PHIs (Aliette, Phostrol, Prophyte, etc.).

As was the case last year, windy conditions have resulted in leaf rubbing on strawberries; symptoms are a brown bruising of plant tissue which could be easily mistaken for a 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.

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 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.

Figure 4. Tarnished plant bug nymph on strawberry fruit and adult on strawberry blossom. Photo: Kathy Demchak, Penn State

Throughout the produce season, updates are based on biweekly Penn State Vegetable and Small Fruit Extension Team crop production conference calls where team members across the state share and report on observations from the field.

Resources With the Latest Information

• The 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 USPS (1-877-345-0691).
• Cucurbit downy mildew alerts can be obtained by email or text message by signing up on the Cucurbit Downy Mildew Forecasting website. You can specify the distance from your farm for which you would like to receive reports.
• The New 2021-2022 Mid-Atlantic Fruit and Vegetable Production Recommendations contains the latest information to help commercial vegetable and strawberry growers in the mid-Atlantic regional 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 by going to Mid-Atlantic Commercial Vegetable Production Recommendations (Sections).
• 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. More info can be found on the MyIPM Smartphone App Series website.