Monthly Insect & Disease Scouting Tips – Sept 2023

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September Insect & Disease Scouting Tips

By Emily Zobel, AgFS Agent, Dorchester County, UME
ezobel@umd.edu

 Cole Crops/ Brassicas: Continue to scout all fields for caterpillar pests (armyworm, diamondback moth larvae (DBM), and cabbage looper larvae). For fresh-market crops, treat when 20% of the plants are infested during the seedling stage, then 30% infestation till the cupping stage. Use a 5% threshold from early head to harvest for cabbage and Brussels sprouts. For broccoli and cauliflower, use 15% at curd initiation/cupping, then 5% from curd development to harvest.

Good identification as early as possible is important because some products may not be labeled or as effective for all brassicas caterpillar pests. If treatment is needed, adjust your spray pattern so that the spray is getting sideways to the undersides of leaves, particularly when using Bt and other contact materials. Due to resistance development, pyrethroid insecticides (Group 3A) are not recommended for controling DBM. Effective materials should eliminate DBM larvae within 48 hours. Make sure to re-scout treated fields within 3 days to assess the efficacy of the insecticide applications.

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 the soil, and larvae can cause significant root injury. Downy mildew and Alternaria can be problematic in fall brassica crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears, apply a fungicide every 7 to 10 days.

Alium crops: Scout fall leeks, garlic, or other Allium species from now until the first freeze for Allium leaf miner damage. Egg-laying damage consists of several small round white dots (made by the female’s ovipositor) that appear on the leaf blades (fig 1). Larvae will live inside the leaves before moving down to the bulbs, where they feed and eventually pupate and overwinter. The feeding damage can open up the foliage and bulb to fungal infections. Row covers can be used to exclude this pest when Alliums are first planted. For organic production, spinosad (Entrust is OMRI-labelled) works well in controlling the larvae. Two or three applications of the insecticide used 2 weeks apart from each other, with the first one coming only after oviposition marks are seen, should offer good control of this pest. The use of a penetrant adjuvant such as neem oil is recommended for better control. 

Image of a Onion leaf blade showing linear white dots made by female Allium leaf miners.
Fig 1.) Onion leaf blade showing linear white dots made by female Allium leaf miners. Photo by Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org

Lima Bean: Check any latelima bean for soybean looper and stink bugs. Looper activity should decline once nighttime temperatures drop into the low 50s.

Swiss chard, Beets & Spinach: Check for beet webworm. They fold leaves and cause window-paning feeding damage. They also feed on pigweed.

Sweet Corn: Corn earworm (CEW) numbers have been declining across the state. Cooler night temperatures and shorter day lengths have triggered mature larvae to enter diapause as overwintering pupae.

Spider mites: Now is a great time to treat weeds growing in and around greenhouses. Winter annual weeds such as chickweed, henbit, dead nettle, and speedwell serve as spider mites and thrip habitats, allowing them to overwinter. Treating now will reduce the possibility of having early-season pest activity on transplants next year.

 

Superficial Scald in Apples: Strategies and Solutions

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By Agustina Salas (Candidate for B.S. in Biology Pontificia Universidad Católica de Chile) & Macarena Farcuh, Ph.D., UMD

What is superficial scald in apple fruits and what causes it?

Physiological disorders correspond to abnormalities that can occur in any of the apple tissues, and can result in loss of quality, marketability, and profitability, leading to increased loss and wastage of apples. These disorders are caused by abiotic factors such as genotype/genetic background, maturity at harvest, orchard/preharvest factors, seasonal variations, and postharvest storage conditions. It is important to mention that pathogens or mechanical damage do not lead to physiological disorders.

In particular, the physiological disorder of superficial scald in apples is the result of a chilling injury. Chilling injuries occur during cold storage at temperatures below the optimum range. During apple cold storage fruits can accumulate a-farnesene, a volatile compound present in the fruits’ wax layer. This compound can cause superficial scald when it oxidizes with atmospheric oxygen. Therefore, superficial scald generally develops during cold storage (more than 3 months in storage) but it is increased 3-7 days after taking the fruit out of cold storage.

Granny Smith apples with superficial scald on their skin.
Fig 1. Apples (Granny Smith) affected with superficial scald on their skin. Photo: Fresh Quarterly issue 9 June 2020.

Superficial scald is only restricted to the skin of the apples and usually on the shaded side. The symptoms appear as brown patches on the skin of the apple, which are diffuse (no defined edges between affected and unaffected skin) irregular, and light brown to dark brown to black in color. Superficial scald can also be accompanied by the development of a rough texture of the fruit.

Continue reading Superficial Scald in Apples: Strategies and Solutions

Cucurbit Downy Mildew Alert! 

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Cucurbit downy mildew (CDM) has been confirmed on cucumbers in Center Maryland and on the Eastern Shore. It was recently confirmed on cantaloupe in New Castle, Delaware. It was found on butternut squash and cucumber in Lancaster County, PA, on August 18, 2023. CDM has been confirmed on pumpkin, butternut, and spaghetti squash in Northern New Jersey.

Cucurbit downy mildew is a significant disease that affects all cucurbits. Commercially important species of cucurbits include:

  • Watermelon (Citrullus lanatus).
  • Muskmelon (Cucumis melo).
  • Cucumber (Cucumis sativa).
  • Squash (Cucurbita pepo, Cucurbita moschata).
  • Pumpkin (Cucurbita maxima).

The causal agent is the fungal-like organism (oomycete) Pseudoperonospora cubensis. CDM falls into two separate clades: Clade I and Clade II. Clade I predominately infects watermelon, pumpkin, and squash, and Clade II predominately infects cucumber and cantaloupe. Research suggests that isolates in Clade II can quickly become resistant to specific fungicides.

Most fungicides labeled for the control of CDM are at risk for resistance development because of the specific modes of action. Growers should scout their cucurbit fields every week, note the efficacy, or lack thereof, seen in the field, and incorporate using as many different chemical groups as possible to help mitigate fungicide resistance development. Loss of efficacy in the control of CDM has also been documented in FRAC code 4 (mefenoxam), FRAC code 11 fungicides (azoxystrobin), FRAC code 28 (propamocarb HCL), and FRAC code 43 (fluopicolide) in the mid-Atlantic region.

For more information on the specific fungicides recommended for CDM control on cucurbit crops, please see the 2022/2023 Mid-Atlantic Commercial Vegetable Production Recommendations. Always read and follow the label, as not all fungicides are listed for all cucurbit crops, and they might have a limited number of applications.

Maryland Department of Agriculture Pivots Toward a More Options-Driven Nutrient Management Plan Writing Program

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 Maryland Department of Agriculture Pivots Toward a More Options-Driven Nutrient Management Plan Writing Program 

Annapolis, MD (June 1, 2023) – The Maryland Department of Agriculture today announced a shift in its Nutrient Management Plan Writing Program that will focus on a new approach to education, training, and farmer empowerment. The decision to move to this new options-rich model comes as a greater demand for plan writing has increased following the COVID-19 pandemic.

“The Maryland Department of Agriculture and the University of Maryland have enjoyed a long-standing partnership regarding Nutrient Management Plan writing and that will continue with this new program,” said Maryland Department of Agriculture Secretary Kevin Atticks. “In addition to new incentives for farmers, this program will align with Chesapeake Bay goals while giving Maryland farmers the tools they need to succeed as strong stewards of the environment.”

Maryland law requires all farmers grossing $2,500 a year or more or livestock producers with 8,000 pounds or more of live animal weight to follow nutrient management plans when fertilizing crops and managing animal manure. Nutrient management plans specify how much fertilizer, manure or other nutrient sources may be safely applied to crops to achieve yields and prevent excess nutrients from impacting waterways.

Because of their complexity, these plans must be prepared by a certified University of Maryland specialist, certified private consultant, or farmer who is trained and certified by the department to prepare his or her own plan. Driven by input from industry, the nutrient plan writing program will expand Maryland farmers’ access to nutrient management plan writers and plan writing services, helping farmers meet their environmental stewardship needs and grow compliance with statewide regulations.

The transition is anchored by a valued partnership and educational and training expertise provided by The University of Maryland’s College of Agriculture and Natural Resources, access to new, beneficial cost-share programs and plan-writing services offered by industry professionals.

The new program features a progressive approach that includes the following:

  • Access to beneficial cost-share programs that will provide partial funding to all eligible farmers in Maryland to access plan-writing services from industry professionals;
  • Opportunities and workshops to help nutrient management advisors become aware of plan writing employment through the private sector;
  • Assisting current University of Maryland planners obtain business licenses to write plans privately;
  • MDA funded UMD specialists providing expanded nutrient management plan writing workshops across the state for ALL Maryland farmers (underserved, small, medium, and large). Support may also be provided to write nutrient management plans for smaller operations;
  • New opportunities for Maryland-based agricultural organizations to build alliances with privatized nutrient management planning services.

“The time is right to privatize and move in the direction that the department envisioned years ago, and we are supportive of this decision,” said University of Maryland’s College of Agriculture and Natural Resources Dean Craig Beyrouty. “As is our role and duty as a land-grant institution, AGNR is highly motivated to stay involved and help plan writers and producers with nutrient management education, tools, and advice.”

“We would like to recognize the University of Maryland’s College of Agriculture and Natural Resources and its Department of Environmental Science and Technology for their success and contributions over the years,” said Atticks. “We look forward to building upon their strong foundation to take this already successful program to new heights.”

For a list of frequently asked questions related to the future of this program please visit the Maryland Department of Agriculture’s website at mda.maryland.gov.

United States Department of Agriculture (USDA) Changes to Audit Costs

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USDA has just announced that proposed audit fees for the Harmonized and GAP/GHP audits will increase to $155 per hour. The average Harmonized Audit runs anywhere from 12 to 15 hours, GAP/GHP audits average 5 to 10 hours. The current fee is $132 per hour. For anyone who needs an audit try to schedule before October 1, 2023 when the new rates take effect.  For further information or discuss the proposed increases contact:  Melissa Bailey, Associate Administrator, AMS, USDA, Room 2036–S, 1400 Independence Ave. SW, Washington, DC 20250; telephone (202) 205–9356, or email melissa.bailey@usda.gov.

Spinach Crown Mites in Spinach

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Spinach Crown Mites in Spinach
by Jerry Brust, UME

Spinach crown mites Rhizoglyphus sp. feed within the folds of new leaves in the crown of spinach plants. This feeding causes the new leaves to become deformed as they grow (figs.1 and 2). Crown mite adults are extremely small bulbous nearly transparent mites that also may have a yellow-beige body color with reddish-brown legs (fig 3). A good characteristic to look for to identify these mites is the sparse long hairs mostly found on the back end of the mite (fig. 3). Crown mite eggs are spherical and clear and laid on the creased leaf surfaces in the crown area. Some reports state that crown mites can act as vectors for plant pathogens such as Pythium and Rhizoctonia, but this is not definitive.

Feeding by spinach crown mites can cause misshapen and ragged leaves with necrotic margins as they expand and crown leaves are distorted and wrinkled in appearance.
Figs. 1 & 2.) Crown leaves fed on by spinach crown mites are misshapen and ragged with necrotic margins as they expand and in the field the crown leaves are distorted and wrinkled in appearance. Photos by G. Brust, UMD.

The spinach crown mite is most damaging in soils high in organic matter and under cool moist conditions (weather conditions we have had this past week). Because these mites can consume organic matter they can survive in soils after the crop has been removed. This is one reason they are difficult to control as they can survive for fairly long periods of time with no crop being present. The other reason they are difficult to ‘control’ is we do not realize they are causing the problem until it is too late.

Spinach crown mite adult with sparse long hairs over its body.
Fig 3.) Spinach crown mite adult with sparse long hairs over its body. Photo by G. Brust, UMD.

Most control recommendations include sanitation and crop rotations as being important as are fallow periods. Pyrethroids are a possible chemical control as is Neem; any chemical control has to get down into the crown of the plant to have any chance of working. There has been little research conducted on the most efficacious material for these mites. Mostly what is needed are warm sunny days where spinach can grow well and the environment is not so conducive to the mites.

Russet on Apples: Current Understanding and Management

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Russet on Apples: Current Understanding and Management

By John Skae, Candidate for B.S. in Physiology and Neurobiology, and  Macarena Farcuh, Ph.D. Assistant Professor and Extension Specialist,  UMD

What is russet on apples?

Russet on apples is a disorder of the skin that results in discoloration and changes to the expected smooth texture of the skin of apples. Russet appears as a spectrum from mild brown weblike patterns to severe rough changes on the surface of apples and many variations in between (Fig. 1). Russeting is only skin deep and thus will not affect the flesh of the fruit. It can occur due to naturally-occurring weather conditions, particularly humid and wet weather.

Fuji apple expressing russeting.
Fig 1.) Fuji apple expressing russeting. Source: John Skae, University of Marylan

Russeting can ultimately reduce the market value of apples, decreasing grower profitability. According to the US Department of Agriculture, the presence of russet disqualifies apples from the US Extra Fancy, US Fancy grades if smooth, solid russeting is more than 10%, while excessive russeting or smooth net-like russeting exceeding 25% excludes fruit from the US No. 1 grade categories.

Apples can begin to russet within the first 30-40 days of development, starting at petal fall. The earlier the tissues are damaged, the more dramatic the damage will be. But it is important to mention that russet can also be developed later during the growing season. Russeting occurs because cracks begin to develop underneath the cuticle of the apple. The damage in the epidermal cells underneath the cuticle turns brown. The cells are then pushed upwards towards the skin because new cork cells are growing underneath the affected epidermal cells. Once the damaged cells reach the surface of the apple, they form phellogen, a wound-sealing tissue created as a result of the russeting reaching the surface. Although russeting affects the cosmetic appearance of apples, it does not harm fruit flesh taste.

What factors cause or contribute to apple russeting?

Some cultivars produced by selective breeding are more prone to russeting than others as these can alter the genetic makeup of the apple to express russet. For example, Golden Delicious apples are highly susceptible to russet, while Red Delicious apples rarely express the russeting disorder.

Continue reading Russet on Apples: Current Understanding and Management

White Rot of Onion and Garlic

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White Rot of Onion and Garlic

By Jerry Brust, UME and Karen Rane, UMD Plant Diagnostic Lab

One very serious soil disease that affects Allium species, especially onion and garlic, is white rot, caused by the fungus Stromatinia cepivorum (syn. Sclerotium cepivorum (fig. 1)). White rot is NOT the same as white mold, which is caused by Sclerotinia sclerotiorum, which has a very large host range (tomatoes, peppers and 170 other plant species); white rot only infects Allium species.

White rot on base of a garlic plant.
Fig. 1.) White rot on garlic plant. Photo By K. Rane, UMD,

Leaves of Allium plants with white rot exhibit yellowing, dieback, and wilting. Under ideal weather conditions, white mycelial growth can develop on the bulb. As the disease progresses, the mycelium becomes more compacted with numerous small, spherical black bodies (sclerotia) forming on this white mat (fig. 2). These sclerotia are the overwintering structures of the pathogen and are approximately the size of a pin head. As the disease progresses, these sclerotia are eventually released into the soil. Infected plant roots will rot, making the plant easily pulled from the soil. Disease development is favored by cool, moist soil conditions. The soil temperature range for infection is 50°-75°F, with an optimum of 60°- 65°F. At soil temperatures above 78°F, the disease is greatly inhibited. Soil moisture conditions that are favorable for onion and garlic growth are also best for white rot development.

Spherical black bodies a of mycelial growth of the white rot fungus on garlic.
Fig. 2) Sclerotia (Spherical black bodies a of mycelial growth ) of white rot fungus on garlic. Photo By G. Brust, UMD.

An increase of white rot in a field that has had several Allium crops may go unnoticed for a time as sclerotia numbers increase and disperse. One sclerotium per 20 pounds of soil will cause disease and results in measurable crop loss. The sclerotia will lay dormant until root exudates, exclusively from an Allium species, stimulate germination. Root exudates from non-Allium species will not stimulate the germination of white rot sclerotia. Cool weather is needed for both sclerotia germination and mycelia growth. Mycelia will grow through the soil until they encounter an Allium root at which time the fungus initiates infection. Mycelia can grow from one plant to a nearby plant, allowing the pathogen to move between plants.

Management of white rot should focus on disease avoidance by not introducing the pathogen into a field. Sclerotia can spread throughout a field, or from field to field, through the movement of soil, equipment, or plant material (especially garlic cloves). Sanitation is important to prevent sclerotia from moving from an infested field to a clean field. Plant only clean stock from known origins that has no history of white rot. Always clean soil off of equipment and sanitize with quaternary ammonia before moving to another field. The Allium crops from an infested field should not be used as seed. Rotation alone will not control white rot because sclerotia can survive in the soil for 20-40 years. If the disease is found, reducing or eliminating irrigation will reduce the damage to the current crop but will not stop the spread of the disease.

Because the fungus is vulnerable to temperatures above 115°F, dipping seed garlic in hot water is a possible preventive measure that will reduce the amount of pathogen but will not completely eliminate it. Temperature control is important when using this method because temperatures above 120°F may kill the garlic. There are other cultural and organic practices (i.e., biofumigation and solarization) that a grower might try to fight this disease and these can be found at: https://rvpadmin.cce.cornell.edu/uploads/doc_479.pdf

Chemical applications can be made for white rot management and include for onion tebuconazole applied in a 4-6 inch band over or into the furrow at planting or via chemigation. For garlic an in-furrow at-planting application using iprodione or tebuconazole or fludioxonil can reduce disease incidence, however there are crop rotation restrictions with the use of these chemicals so be sure to check the Mid-Atlantic Commercial Production Recommendations guide for more details.

One other note is that the presence of bulb mites can exacerbate disease problems by opening the bulb up to infection from white rot and growers also will need to manage these mites.

Check for Allium Leaf Miner in Onions and Leeks

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Check for Allium Leaf Miner in Onions and Leeks

By Jerry Brust, IPM Vegetable Specialist UME

If you grow leeks or onions or other Allium species, you should already be checking for the tell-tale marks left by Allium leaf miner. Allium leaf miner Phytomyza gymnostoma tell-tale marks consist of many linear small white dots (made by the female’s ovipositor) that appear in the middle towards the end of leaf blades (fig. 1) of their preferred hosts of leeks, onions, garlic and other Allium species. Spring crops are usually not as hard hit as fall crops especially when looking at leeks, but this pest has been steadily increasing its geographical range each year as well as its damage potential. If you had some infestation last year you will especially want to be looking for the signs of this pest.

Image of a Onion leaf blade showing linear white dots made by female Allium leaf miners.
Fig 1.) Onion leaf blade showing linear white dots made by female Allium leaf miners. Photo by Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org

To go over recommendations for this pest: New transplants or seedings of onions, leeks or garlic should be watched closely for the tell-tale signs of the fly’s damage. When eggs hatch the larvae at first mine leaves (fig. 2) and then move down to the bulbs and leaf sheathes where they feed and eventually pupate. Pupae will undergo a summer aestivation (type of hibernation because temperatures are too warm for them to be active) and only emerge again in late September. You can cover any just-transplanted Allium planting with a row cover (but don’t wait too long after transplanting) to keep the flies off or if needed treat with insecticides. Research out of Cornell University has found using just two applications of spinosad (Entrust, which is OMRI-labelled) two weeks after oviposition marks are first found and then another application 2 weeks after this will give adequate control of the pest. But the oviposition marks must be watched for carefully and discovered very soon after first being made. If new oviposition marks are being seen each week a weekly application of insecticide may be necessary. A penetrant adjuvant also is recommended to be used when treating for the larvae.

Leaf miner damage on a Onion leaf blade caused by the larva of a Allium leaf miners fly.
Fig. 2) Allium leaf miner larva mining in onion. Photo by G. Brust, University of Maryland.

MARYLAND PESTICIDE NEWS UPDATES

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MARYLAND PESTICIDE NEWS UPDATES
(April 2023)

by Niranjana Krishnan,
UMD Pesticide Safety Education Program Coordinator

The express purpose of the newsletter is to share proposed and upcoming changes to pesticide regulations; the information provided does not supersede existing pesticide labels and regulations. If you would like to receive this newsletter or have any questions about it, please email Niranjana Krishnan nkrish@umd.edu 

  1. Forthcoming change: First pesticide tolerance established for hemp 

Summary by Niranjana Krishnan nkrish@umd.edu

In April 2023, the Environmental Protection Agency (EPA) established the first pesticide  tolerance (see glossary) for hemp. This was done for the herbicide ethalfluralin. Specifically, the maximum amount of ethalfluralin residues allowed to remain in or on  hemp seeds was established.  

  • The EPA has accepted ethalfluralin labels that now contain directions for use on  hemp. The new labels will allow farmers to use ethalfluralin to control annual  broadleaf and grassy weeds that grow in hemp fields. Prior to this, only biopesticides  were registered for use on hemp. The biopesticides are tolerance exempt because of  their low risk to humans.  
  • The 2018 Farm Bill removed hemp and hemp seeds from the list of controlled  substances and authorized its production. Consequently, over the last few years, hemp  production has increased in Maryland and other states.  
  • According to the 2020 Maryland Pesticide Use Survey, ~ 122 lbs. of ethalfluralin was used on other crops. 

Reference: https://www.epa.gov/pesticides/epa-establishes-first-pesticide-tolerance hemp   

  1. Proposed change: New health protections to reduce ethylene oxide exposure In April 2023, the EPA proposed changes to ethylene oxide use to reduce air emissions  and protect exposed workers. Ethylene oxide is a gas and, for certain uses, is registered as  an antimicrobial pesticide. It is used to sterilize spices (like dried herbs and vegetables) at  commercial sterilization facilities to control food-borne pathogens. It is also used to  sterilize certain equipment like medical devices. Long-term exposure to ethylene oxide  increases the risk of certain cancers. 
  • To protect workers involved in the sterilization process, EPA is proposing the use of  self-contained breathing apparatus or a supplied airline respirator. Additionally, EPA  is proposing real-time monitoring of ethylene oxide concentrations in the workplace.  If concentrations exceed 10 parts per billion, all workers, including office workers,  will be required to wear a breathing apparatus or respirator to reduce exposure.  
  • To reduce exposure concentrations within commercial sterilization facilities, EPA is  proposing measures such as implementing air pressure gradients to regulate ethylene  oxide flow, separating HVAC systems between office and sterilization areas, 

ventilating ethylene oxide storage areas, automating the transport of sterilized  materials, etc.  

  • To reduce exposure concentrations within healthcare settings, EPA is proposing  lowering the amount of ethylene oxide used per sterilization cycle for medical devices  (lower concentrations will also meet sterility requirements), separating sterilization  spaces from other work areas, implementing air pressure gradients, using abatement  devices to remove ethylene oxide from exhaust air, etc.  
  • Public comments are being sought until June 15, 2023. 

Reference: https://www.epa.gov/newsreleases/epa-proposes-new-standards-protect public-health-reduce-exposure-ethylene-oxide 

  • Update on pesticide testing requirements for PFAS (Maryland-specific) In April 2023, two bills (SB0158 and HB0319) were amended and passed in the  Maryland General Assembly. The bills require the Maryland Department of Agriculture ̶ in consultation with the Maryland Department of Environment, Maryland Department of  Health, and the EPA ̶to study the use of PFAS in pesticides. The bills  originally proposed prohibiting pesticide products from being registered in the state  unless it was tested for PFAS. However, several questions were raised about PFAS  testing methods which resulted in the bills being amended. The bills now require: 
    • An analysis of the health and environmental impacts of PFAS in pesticides in  Maryland 
    • An identification of testing methods capable of testing PFAS in pesticides.
    • An examination of characteristics that distinguish testing methods for PFAS that are  validated for drinking water from testing methods that are validated for pesticides.
    • A status update on federal efforts to certify a method for testing PFAS in pesticides.
    • A status update on state and federal efforts to regulate or ban use of pesticides  containing PFAS. 

The bills take effect on June 1, 2023, and the Maryland Department of Agriculture must  report its findings and recommendations by November 1, 2023.  

References:  

https://mgaleg.maryland.gov/mgawebsite/Legislation/Details/sb0158?ys=2023RS https://mgaleg.maryland.gov/mgawebsite/Legislation/Details/HB0319?ys=2023RS 

Glossary: 

1) Pesticide tolerance – The maximum amount of a specific pesticide that may remain in or  on foods marketed in the United States. The EPA is responsible for setting the tolerances and ensuring they are protective of human health.  

2) PFAS (perfluoroalkyl and polyfluoroalkyl substances) – They are a class of fluorinated  compounds that do not degrade easily and are found in many products and matrices.  Exposure to certain PFAS compounds can adversely affect human health.