Month: September 2022

September Insect & Disease Scouting

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September Insect & Disease Scouting

Emily Zobel, UME

Remember to rotate modes of action out every 30 days. Always read the label since not all materials are labeled for all crops, insects, or application methods. See the Mid-Atlantic Commercial Vegetable Production Recommendations Guide for more information (https://go.umd.edu/MidVegGuide).

Cole Crops/ Brassicas: Continue to scout all fields for beet armyworm, fall armyworm, diamondback moth larvae ((DBM)and cabbage looper larvae.  DBM seem to be the main species seen across the regain this fall.  For fresh-market crops treat when 20% of the plants are infested during seedling stage, then 30% infestation from early vegetative to cupping stage. From early head to harvest in cabbage and Brussels sprouts use a 5% threshold. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest. If treatment is needed make sure to adjust your spray pattern such that spray is getting sideways to the undersides of leaves, particularly when using Bacillus thuringiensis and contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for control of diamondback moths. Rutger’s is reporting that DBM is not responding to chlorantraniliprole (Coragen) in many parts of the state. It is important to return to treated fields within 2-3 days to assess the efficacy of the insecticide applications.  Effective materials should eliminate DBM larvae within 48 hours.

Check young plants for flea beetles Thresholds for flea beetles are 1 per transplant or 5 beetles per 10 plants. They will lay eggs in soil and larvae can also cause significant root injury.  Downy mildew and Alternaria can be a problem in fall brassica crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days.

Sweet Corn: Scout any whorl stage sweet corn for fall armyworm (FAW). FAW can infest plants at any growth stage. Injury from newly hatched larvae shows up as “window panes.”  As larvae gain size, they begin creating ragged holes in leaves with lots of droppings. FAW can be tough to manage because it is resistant to synthetic pyrethroid insecticides (IRAC 3A). Treat when 15% early whorl infestation, 30% mid whorl, and 15% infestation at tassel push. CEW number are currently active but low across that state, so unless temperatures rise again a 4-5 days spray schedule would be suggested for corn that’s tasseling or silking. Pyrethroid (Group 3A) resistance has been reported in populations of CEW.

Pumpkins and Late Melons: Scout for cucumber beetles and rind feeding lepidopteran worms, such as melon worms and fall armyworm. Look at the undersides of leaves that have been partially shredded and look at the rinds of pumpkins to determine if they are attacking the fruit.  Due to our recent wet warm weather  scout for Downy Mildew.

Fungicide Resistance in Botrytis from Strawberry Fields, 2021-2022 Season

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Fungicide Resistance in Botrytis from Strawberry Fields,
2021-2022 Season

Mengjun Hu, Department of Plant Science and Landscape Architecture

Strawberry Botrytis fruit rot, also called gray mold, is a common disease that typically drives fungicide sprays throughout a season. Flowers are considered the gateway for the pathogen, and some flower infections can stay latent until fruit ripening while some may show up earlier at green berry stage under wet and cool conditions. The disease is relatively easy to manage with fungicides, but resistance has been a concern for most single-site fungicides labelled for gray mold control. During the 2021-2022 season, we obtained and processed a total of 75 Botrytis isolates originated from flowers from 8 commercial farms in the region (most of them are in Maryland). We tested for resistance to thiophanate-methyl (Topsin M), pyraclostrobin (one of two components of Pristine or Merivon), cyprodinil (one of two components of Switch), fenhexamid (Elevate), iprodione (Rovral), boscalid (major botryticide component of Pristine), fludioxonil (major botryticide component of Switch), penthiopyrad (Fontelis), benzovindiflupyr (Aprovia), isofetamid (Kenja), and pydiflumetophen (one of two components of Miravis Prime). Except for Aprovia, all products (in parenthesis) are labelled for strawberry production.

Gray mold on strawberry. Photo: Kathy Demchak, Penn State Extension

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Spots on Honeycrisp Apples: What are They and How to Differentiate Them?

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Spots on Honeycrisp Apples: What are They and How to Differentiate Them?

 Zarah Ahmed, Candidate for B.S. in Physiology and Neurobiology & Macarena Farcuh, Ph.D., Assistant Professor and Extension Specialist University of Maryland, College Park

What are physiological disorders?

Physiological disorders can be defined as abnormal growth patterns that can impact the external and internal conditions of fruit. They are not caused by insects, pests, or mechanical damage, but rather by environmental factors or production practices (pre- and postharvest). The development of physiological disorders will directly impact fruit quality, thus increasing fruit losses and reducing fruit marketability and profitability.

Particularly for Honeycrisp apples, there are different types of physiological disorders that can develop both on the tree as well as during storage, but only some of them are characterized by the development of spots in the skin and sometimes flesh. Some of these include bitter pit, lenticel blotch pit and lenticel breakdown. Being able to differentiate among these will be beneficial in identifying them properly and working to prevent their future incidence.

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Bacterial Canker of Tomato

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Bacterial Canker of Tomato

Jerry Brust, UME

A disease of tomato that we usually only see occasionally has been observed more frequently this year in several fields in Maryland. The disease is bacterial canker caused by the bacteria Clavibacter michiganensis. A common symptom of the disease is leaf tips and margins that are yellow surrounded by dark brown tissue (fig. 1), although at times there can no yellow border, which is typically due to the cultivar or the environmental conditions. Veins on the leaves can become dark and sunken. Leaves can wilt starting at their tips to their branches after which they die and fall from the plant. Systemic infections of bacterial canker usually occur on more mature plants that are growing poorly with the oldest leaves curling, turning yellow and wilting. Fruit symptoms usually manifest themselves as small, round, raised white lesions with yellow margins especially near the calyx.

Bacterial canker on tomato leaves
Fig. 1 Bacterial canker typical secondary symptoms on leaves. Photo G. Brust.

Bacterial canker of tomatoes is often introduced into a field via infected seed or transplants and can be spread by splashing water or plant contact (pruning and trellising). The disease can survive in soil debris for up to three years and can also survive on stakes (especially if wooden) or tools. Several nightshade species act as hosts for the disease. There are no spray treatments that are effective for its control.

Stinkbug Damage Found in Maryland Tomato Fields

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Stinkbug Damage Found in Maryland Tomato Fields

Jerry Brust, UME

There have been reports of stinkbug damage in tomatoes in Maryland for the last couple of weeks. Stinkbug feeding damage is called cloudy spot in tomato fruit (fig. 1). It occurs when the adult or immature stinkbug puts its needle-like mouth part into the fruit and removes material from a large number of cells. On green fruit the damage appears as whitish areas with a black dot in the center and indistinct borders (fig. 2) on ripe fruit the spots are golden yellow (fig. 1). Individual spots may be 1/16 -1/2 inch in diameter; or the spots may merge and encompass a large area of the fruit surface (fig. 2). Peeling back the skin shows these areas as white shiny, spongy masses of tissue (fig. 3). This damage is usually most common from mid-July until the end of the season.

Stinkbug feeding injury to tomato fruit.
Fig.1) Stinkbug injury to tomato fruit. Photo by G. Brust UMD.

The Green and Brown as well as the Brown Marmorated stinkbugs are often difficult to see and usually go unnoticed as they spend much of the day deep inside tomato plants, any disturbance and the stinkbugs will drop to the ground and move under the plastic, which results in monitoring difficulties. Only a few are necessary to cause the appearance of cloudy spot on many tomato fruit. Although stinkbug damage has been observed in slightly greater than usual amounts in tomato fields this year, observations of stinkbugs have been much less numerous.

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Precautions Fruit and Vegetable Growers Should Take During a Boil Water Advisory

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Precautions Fruit and Vegetable Growers Should Take During a Boil Water Advisory

Neith Little, Carol Allen, Shauna Henley, UMD Extension

Current situation: The Baltimore City Department of Public Works has issued a Required Boil Water Advisory (solid line in the map below) for parts of Baltimore City, and a Precautionary Boil Water Advisory (dashed line in the map below) for a larger portion of the city  and part of Baltimore County. E. coli has been identified in municipal water in the neighborhoods of Sandtown-Winchester and Harlem Park (solid line in the map below). For updates, check the Baltimore City DPW website: https://publicworks.baltimorecity.gov/node/22547

Map of boil water advisory areas as of 9/6
Map of boil water advisory areas as of 9/6/2022. Source: Baltimore City Department of Public Works.

What steps should farms in the affected area take to protect worker and customer health?

Farms in the affected region are encouraged to take precautions to protect farmer and customer health when using municipal water for worker hygiene, crop irrigation, and post-harvest washing.

In most cases, it is probably impractical to boil all the water needed for farm operations. Instead, growers can either eliminate water contact with fruit and vegetables (and other food contact surfaces), or can treat the water with a food-safe sanitizer.

A factsheet on choosing a sanitizer is available from the Produce Safety Alliance, and a spreadsheet of sanitizer products is available for download from the UMD Produce Safety Team’s website (scroll down to week #32). If you use chlorine as a sanitizer, it is important to test the chlorine levels in the water to verify that you have achieved the correct concentration. An interactive online lab from New Mexico State University teaches growers how to do this correctly.

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