The UConn Plant Diagnostic Lab is open to receiving samples Monday through Friday, but will be closed in observance of 2021 Holidays on November 25, November 26, December 23, December 24, and December 31. Please arrange to have your samples delivered outside of these dates.
We hope you and your loved ones stay safe, healthy and warm this holiday season.
During these times of quarantine I’ve become very familiar with my neighborhood sidewalks, using them as new hiking trails. These neighborhood hikes have afforded me a new way to observe a city street landscape, and as a plant pathologist I’ve used this time not only as exercise but to also track common plant disease issues by just keeping my eyes open. You’d be surprised to know how many sick plants are out there to see!
While azaleas, rhododendrons, and Japanese maples are in most neighbors’ yards (and they sure are pretty right now!), I see pachysandra patches nearly everywhere. It is certainly a beloved plant, and very successful as a groundcover. Pachysandra prefers part to full shade and is typically quite low maintenance. The plant naturally grows into a dense carpet, and while this growth pattern usually doesn’t provide any reason for concern, if environmental conditions are right and a particular pathogen is present, disease in a pachysandra patch can spread fairly readily. And that’s exactly what I’ve been seeing this spring.
Volutella blight, caused by the fungus Volutella pachysandricola, is a common destructive disease to pachysandra. The disease presents as brown lesions on the leaves, often with a concentric circle pattern. The lesions expand in size until the whole leaf turns brown-black and dies. Lesions also occur on the stems, causing plants to wither and die back. Orange-pink masses of spores can be seen within lesions during wet and humid conditions. Plants die in patches, and disease spread usually appears in a circular pattern in a bed.
The classic dense planting culture of pachysandra increases the humidity in the bed, providing ideal conditions for Volutella blight to develop and spread. Further, because the pathogen thrives in cool, wet weather, all the rain we’ve had this spring in the Northeast has contributed to disease development as well. Because pachysandra plantings are usually so low maintenance, they can be easy to forget about. As such, stressed plants are more susceptible to Volutella blight. Stress from drought, winter injury, pruning injury, or insect infestations can also contribute to the spread of the disease.
To manage Volutella blight, only work in plants when they are dry, because the fungus moves through water splash. Remove infected plants and destroy them; do not compost as home composting systems typically do not reach high enough temperatures to kill spores. Thin the planting to increase airflow, which also will encourage plants to dry out more quickly. When thinning, sanitize tools with a 10% bleach or 70% rubbing alcohol solution to not accidentally infect new plants. There are fungicide options to help manage Volutella blight, but will only be useful if these other measures are taken. They will not cure infected plants.
So, head outside today and check on your pachysandra patch. Might be time to give it a little love!
The allium leaf miner (Phytomyza gymnostoma) was first reported in the northeast in 2015, but was not found in Connecticut until January 2020. Learn more about this pest and how to prepare for it this season.
The allium leafminer is an Agromizyid, or leafmining fly, native to Poland and Germany. While leek and onion may be the most heavily damaged crops, many crops in the Allium genus are susceptible, including shallot, chives, garlic, and green onion. Some species of wild onion and ornamental alliums may be hosts as well, but the full host range is currently unknown.
Adults (Fig 1a-c) lay eggs in the top of leek leaves between late March and May, by making repeated punctures with their ovipositor in the distal end of leaves (Fig. 2). These holes are the first signs of an infestation. The larva mine the leaves, creating tunnels of damage as they eat tissue (Fig 3). Larva will move down to bulb and leaf sheaths, where they pupate either in the plant or drop into the soil. The tunnels the larva create and leaf puncture holes provide good entry point for secondary fungal and bacterial infections, which can cause further damage to the crop. The second generation will emerge in September to October, laying eggs in the leaves again, and the pupa will overwinter.
Avoidance of the adult flies is one of the best prevention strategies. Covering all alliums prior to the emergence of adults (late March-May), may help exclude the pest. Alternatively, delaying planting until after the adults have emerged and their oviposition period is over, around mid-May, may be an effective strategy. If an infestation occurs, rotate out of leeks and other alliums in that area. Utilize yellow sticky cards and/or yellow bowls containing soapy water in infested fields. Contact PlantDiagnosticLab@UConn.edu to send a sample for identification.
There are insecticides that may be effective for allium leaf miner control, including both organic and conventional options. Always check the pesticide label to confirm the crop is listed, the rates, and the days to harvest intervals. This information can be found in the references section below.
Fleischer, S. and Elkner, T. 2016. Pest alert: Allium leaf miner. Penn State University Extension. https://ento.psu.edu/extension/vegetables/pest-alert-allium-leafminer
Gilrein, D. 2016. Insecticides for leafminers in onions and related crops that may be effective against allium leafminer (Phytomyza gymnostoma). Cornell Cooperative Extension of Suffolk County. https://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Documents/Insecticides%20for%20leafminers%20in%20onions%20and%20related%20crops.pdf
Hutchinson, M. Allium leaf miner. Pennsylvania Department of Agriculture. https://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/Pages/ALLIUM-LEAFMINER.aspx
This article appeared in the April 2020 edition of Crop Talk, UConn Extension and Plant Science & Landscape Architecture's Quarterly Newsletter for commercial fruit and vegetable growers. You can find the rest of the publication here: http://ipm.uconn.edu/documents/view.php?id=1663. To sign up to receive the digital newsletter, contact: firstname.lastname@example.org.
It is a familiar trope to many of us who buy raspberries in the grocery store. They look fine when you take them off the shelf, give them a rinse at home, and put them in the refrigerator for safe storage. You are excited to put them on your oatmeal, or blend them up in a smoothie. When morning comes, you open the plastic clamshell only to find the berries covered in a gray fuzzy mold. What gives? How did it happen so quickly?
The fuzz you are seeing is Botrytis cinerea, a common fungus that can infect hundreds of species of plants, and raspberries are a particularly preferable host. Botrytis thrives in humid conditions, and can spread extremely quickly. Over 60,000 Botrytis spores can be produced on a single raspberry, and it only takes one spore to cause a new infection. So while you may have rinsed the berries to ensure they were clean and ready to snack on right out of the fridge, those moist conditions were the perfect environment for Botrytis to take hold inside your clamshell.
If you grow raspberries in your own garden, you have more than likely seen Botrytis in your berry patches too. The fungus overwinters as sclerotia, which are black blister-like structures that often protrude from white lesions on canes. During periods of wet weather, spores are produced and disbursed from plant to plant by wind and rain splash. You may see the gray mold colonizing your berries just after the first fruit has ripened. Though, the more overripe the fruit becomes, the more likely the berries will rot and become colonized by Botrytis. If the infection is not managed, serious damage and yield losses can occur on your berry patches. In fact, Botrytis fruit rot is the most common and important disease on raspberries worldwide.
To control the spread of Botrytis in your raspberry (and blackberry) plantings at home, prioritize cultural practices that limit humidity. Ensure your site has good airflow by pruning canes, thinning rows, and controlling weeds. A trellising system can also help train canes upwards, preventing them from falling onto one another. Avoiding excessive nitrogen fertilizer application can help prevent plants from putting out more foliage than necessary.
Good sanitation is also key. Remove overripe fruit, spent flowers, any plant material that appears gray or fuzzy, or canes that have large lesions or black blisters on them. Do not compost infected plant parts, as home compost systems are not able to reach adequate temperatures to kill the fungus. Planting with resistant cultivars, or at the very least, not highly susceptible cultivars, can also help provide some protection.
There are some fungicide applications that can be used for Botrytis, but they will not be effective if the above cultural and sanitation recommendations are not taken. Check with UConn’s Home & Garden Education Center (http://ladybug.uconn.edu) or Plant Diagnostic Laboratory (http://plant.lab.uconn.edu) for more recommendations.
If you still want to buy and eat raspberries from the store, not all hope is lost. You can try one of two options. The first is to buy frozen raspberries, and only take them out of the freezer in a quantity you know you’ll consume in that sitting. Frozen raspberries are great in smoothies and can replace the need for ice. The other option is to take the berries home and store them in the refrigerator with a dry paper towel to help wick away moisture. Then, you can give the fresh berries a rinse just before you’d like to enjoy them. While raspberries may feel like a bit of work to be able to eat them, they sure are tasty!
Given the coronavirus pandemic, I wanted to focus on viruses to share a little more on these infectious agents.
A virus has a very simple makeup. It is just a piece of DNA or RNA, a protein coat, and in some cases a fatty (lipid) layer. The protein coat provides protection for the piece of genetic information (DNA or RNA), and can code for different functions when the virus infects a host organism.
Viruses are considered neither alive nor dead. Viruses do not consist of cells or have any components to carry out basic functions on their own. They rely on the cell functions of their host to replicate. They hijack their host’s cells to operate in a way that allows the virus to thrive.
For this exact reason, viruses have a biological incentive to keep their hosts alive. If their hosts die, the virus can no longer replicate. Viable virus particles can exist on a surface, such as a table. But without a host, the virus can not cause disease or infection.
The first virus to be crystallized and therefore each of its parts were able to be studied, was actually a plant virus, Tobacco mosaic virus. Rosalind Franklin made this discovery in 1955. Since then, thousands of new viruses have been described.
As a plant pathologist, I work with plant viruses. Let’s take a look at Potato virus Y as an example. Potato virus Y (PVY) is one of the oldest known plant viruses, and the 5th most economically important plant virus in the world, meaning that it can cause a lot of damage. Hundreds of plants can infected by PVY including potato, tomato, pepper, eggplant, tobacco, and many species of weeds.
Historically, PVY has been easy to detect in fields because of the beautiful mosaic symptoms it causes on foliage. On potatoes, other symptoms include veinal necrosis, deformed or rotting (necrotic) potatoes, and up to 70% yield losses.
However, new strains of PVY have evolved to make it more difficult to notice an infection until it is too late to do anything about it. Viruses are capable of evolving to change the symptoms they induce in hosts in order to continue to thrive.
Just like COVID-19 disease (SARS-CoV-2 virus) is spread from person to person, plant viruses are infectious and spread from plant to plant as well. The mode of transmission varies depending on the virus.
Most plant viruses require a vector to be spread among plants. A vector is an organism that does not cause disease itself, but carries an infectious agent from one host to another. Examples can include insects, parasitic plants, nematodes, and even humans. Other means of spread include infected vegetative propagates or cuttings of plants; infected seed; and mechanical transmission through infected plant sap (like pruning an infected tree and using the same tools to cut a healthy tree).
In the case of PVY, it is vectored by over 50 species of aphids. When probing plants for a tasty morsel to eat, aphids insert their needle-like stylet mouth parts into the stems and foliage. If the plant is infected, PVY particles adhere to the aphid’s stylet, and it only takes a few seconds of feeding for the aphid to be infective to new plants. And, because hundreds of species of plants can be hosts to the PVY, weeds surrounding gardens or potato fields can be important sources of PVY.
The other way PVY is spread is through infected seed. When infected seed potatoes are planted, they result in infected plants. These infected plants then are a source of PVY inoculum for aphids.
Once plants are infected, there is no cure for the virus. PVY does not kill plants, but can cause potato defects that render them unmarketable for potato growers and in some cases inedible for home gardeners. PVY also can decrease yields significantly.
The best management recommendations for PVY include:
Scout your plants regularly and often for PVY. Symptoms can change rapidly, and early observation is crucial for limiting spread of the virus.
Remove any infected plants when you see symptoms arise. Do not compost infected plants because potatoes can easily regrow in your compost pile. If you’re not sure if your plant is infected, send a sample to us for diagnostic testing.
Control weeds around plantings to limit alternative hosts of the virus.
Our diagnostician will be out of the office to attend the Northeast National Plant Diagnostic Network Meeting and the Northeastern Division-American Phytopathological Society Meeting until 3/12. Diagnoses on samples sent during this time will be delayed, and will resume on 3/13. We appreciate your understanding.
Over the past year, we’ve heard from growers and others that a UConn-based hot water seed treatment service is among the top agricultural priorities in the state. Well, we listened! Thanks to funding support from the New England Vegetable & Berry Growers Association and UConn’s Grant for Innovative Programming in Extension, the UConn Plant Diagnostic Lab in collaboration with the UConn Extension Vegetable Program is now offering hot water seed treatment for vegetable seed!
Background on hot water seed treatment
There are several plant diseases caused by fungal, bacterial, oomycete and viral pathogens that can persist on or inside seeds. At germination, infested seeds can infect the resulting plants that grow, and cause early infection. While chlorine and other chemical seed treatments can be effective at removing pathogens that adhere to the seed surface, these treatments are not able to penetrate the seed coat and eliminate pathogens that are present inside. As a result, hot water seed treatment has emerged as one of the best known methods to manage seed-borne pathogens, because of the treatment’s ability to kill pathogens that exist both on the outside and inside of seeds.
It is important to note that while hot water seed treatment can eliminate pathogens on and in seeds, it neither protects nor guarantees that plants will remain disease free throughout the growing season. Hot water treatment will enable you to start with clean seed, and strong cultural management practices (i.e. crop rotation, field sanitation, scouting, etc.) will still be important to implement on plants that grew from hot water treated seed.
Complete list of crops eligible for UConn’s Hot Water Seed Treatment
New Zeland Spinach
How it works
The treatment process is fairly simple. We follow established and tested protocols for hot water treating each species of vegetable seed to ensure the highest quality. Seed undergoes a pre-warming process in a controlled water bath at 100°F, then is subjected to treatment in another water bath at 118-125°F for 15 to 30 minutes depending on the crop. Seed is immediately air dried, carefully packaged, and shipped back to the grower at the address they provide.
0.01-1 oz of seed per cultivar submitted: $6
0.01-13 oz of seed for shipping & handling to return treated seeds to client: $6
For example: you submit 0.6 oz of cherry tomato seed ($6), 2.3 oz of kale seed ($18), and 1.1 oz of beefsteak tomato seed ($12). Your total seed treatment cost is $36, with a shipping cost of $6 (4 oz of seed ). Total cost is $42.
We accept check, credit/debit card, or money order for payment. To learn more about the fee structure, click here.
Are you a current UConn undergrad interested in plant pathology and horticulture, and looking to get more experience? Looking for a paid internship this summer? Apply for the Plant Diagnostic & Horticulture Internship! Check out the position description below.
UConn's Vegetable Extension Program is launching a new Vegetable Production Certificate Course this spring! Our Diagnostician, Abby Beissinger, is one of the instructors for the course. Using a hybrid format, the course will integrate online and in-person components for new and beginning farmers. For 2020, the course has a special introductory fee, so take advantage of the opportunity!
The Plant Diagnostic Lab will be closed due to building renovations until January 1st, 2020. No plant samples will be accepted or analyzed beginning on December 17, 2019. We will reopen and resume regular operations on January 2nd. With any questions, please contact us at PlantDiagnosticLab@uconn.edu. Thank you for your patience.