Growing Healthy Plants, part I: Sanitation is Not a Dirty Word

With spring nearly upon us, gardeners are dreaming of yards overflowing with healthy flowers, vegetables, and greenery of all kinds. Before you dig your gardening tools out of the shed and start planting, here are some tips for growing happy, healthy plants!

Sanitation is a key to growing healthy, disease-free plants. If you are growing plants in pots, baskets, or raised containers, start with sterile potting media. Old potting media can be full of pathogens ready to attack new plants. Pathogens like Pythium or Phytophthora can survive in soil for years. Using sterile pots goes hand in hand with using sterile soil. Scrub used pots with a stiff brush to remove all soil and organic debris. After a thorough cleaning, sterilize pots by soaking for at least 30 minutes in a solution of 1 part bleach to 9 parts water (about 12 ounces of bleach per gallon).


Dirty equipment is a common means of spreading pathogens to healthy plants. Remember to scrub garden tools and soak them in a bleach solution at the start of the season and after using them to cut or dig around diseased plants. Rinse metal tools after the bleach treatment to avoid corrosion. Alcohol can be used to disinfect cutting tools and is less corrosive than bleach.


Now that you have clean pots, tools, and media, it’s time to pick your plants. Always buy healthy plants from a reliable source: pathogens can enter the garden on diseased plants. A well-run nursery should be very clean, with few weeds, algae, or loose soil on the ground or benches. Nurseries with neat, well-organized displays, minimal crowding, and plants that are neither to wet nor too dry probably use good practices overall and are likely to sell only the healthiest plants. Cull piles and dumpsters should be far away from the sales and production areas. Mimic these practices if you are propagating your own plants.  

Good Practices: Notice the clean benches (Photo: B. Shew)

Poor Practice: Algae, Standing Water, Organic Debris (Photo: E. Lookabaugh)

Poor Practice: Cull pile next to healthy plants (Photo: E. Lookabaugh)

Be sure to inspect all plants before you buy or transplant them. Do not buy or move plants that are wilted, yellowed, stunted, or have any other symptoms or unusual appearance. Inspect the roots of potted plants or transplants. Look for containers or plugs thoroughly colonized (but not pot-bound) with healthy roots. Healthy roots can be brown or white, depending on the species, but they should never have obvious rot or lesions. The potting medium or soil should have a pleasant, earthy odor. Avoid plants growing in stagnant-smelling medium.

Nice White Roots (Photo: E. Lookabaugh)

Be very cautious when dividing or transplanting plants in your yard and be very, very careful with plants from neighbors or plant exchanges. Before putting these plants back into the landscape, brush or wash away excess soil, remove dried leaves, and prune away any dead stems in woody plants. Carefully inspect all parts of the plant for symptoms and do not use any plant that appears to be diseased. If at all possible, pot transplants or divisions in a location well away from your landscape. Watch transplants carefully while they are in your quarantine area and move them to their final destinations only when you are confident that they are disease-free.


In the landscape, rake up old mulch, fallen leaves and other debris before planting and LIGHTLY cover the area with a new layer of mulch after planting. Once you are done planting, be sure to monitor plants closely. Promptly remove all fallen leaves, spent flowers, unwanted produce, and dead or cankered stems. In many cases, composting cannot be counted on to kill pathogens, so promptly destroy any materials you removed from diseased plants or their surroundings.

Remove fallen, diseased flowers to prevent inoculum splashing up (Photo: B. Shew)

If you start seeing disease symptoms, contact your local county agent or the Plant Disease and Insect Clinic. Sometimes, our diagnosticians can diagnosis plant disorders from digital images. Take a photo and email it to us. We will be able to advise you as to whether you should remove the plant, or if sending a physical sample is necessary to diagnose the problem.

Sometimes gardening is best done with a buddy!

For more information on sample submission see our webpage: 
http://www.cals.ncsu.edu/plantpath/extension/clinic/submit-sample.html

Plants Pests and Pathogens 2012 Starts Next Tuesday, February 28

Next Tuesday February 28 we kick off the 2012 Season of Plants Pests and Pathogens with Dr. Larry Grand, who will speak about mushrooms and other macrofungi. Dr. Grand is part of a multidisciplinary team assessing fungal biodiversity in North Carolina state parks and the Great Smoky Mountains National Park. 

Plants, Pests and Pathogens is an in-service training program for Horticulture Extension Agents and Extension Master Gardeners. 

The Plants, Pests, and Pathogen sessions will be conducted on the fourth Tuesday of February, April, June, August, and October 2012 from 10:00 am to 12:00 pm. Every session includes a discussion of current plant disease and insect problems by the Plant Disease and Insect Clinic's Mike Munster and Dave Stephan. 

Find out about the many other exciting presentations planned for this year by checking out the Master Gardener Plants Pests and pathogens webpage. We hope to see you on-line! 

Log On To February meeting:
http://elluminate.wolfware.ncsu.edu:80/join_meeting.html?meetingId=1261509564719

General information:

http://www.ces.ncsu.edu/depts/hort/garden/PlantsPestsPathogens/index.html
 

Info for Master Gardeners

http://www.ncsugarden.com/subpages/697.html 

Info for agents

http://www.ncsugarden.com/subpages/1791.html 

Rhizoctonia Web Blight on Boston Fern

The Boston ferns that will adorn our porches and decks in a couple of months are being grown in greenhouses now. Ferns are easy to grow, but they do have a few disease problems. This week, we received a Boston fern from a greenhouse producer who was concerned about leaflets that were blackened and blighted, especially in the interior of the plant. These symptoms are typical of web blight (aerial blight) caused by the fungus Rhizoctonia. We typically think of Rhizoctonia as being a soilborne pathogen of roots, stems, and seedlings, but it causes foliar blights on several hosts, including Boston fern. The presence of Rhizoctonia on the leaves was confirmed microscopically. 

Hyphae of Rhizoctonia (Photo: M.J. Munster)

Web blight begins as irregular brown lesions on the fronds growing in the interior of the plant. 

Web blight symptoms (Photo: M.J. Munster)

Web blight symptoms (Photo: M.J. Munster)

Eventually, these lesions expand, causing the interior and lower fronds to turn black and die. The mycelium of the fungus can be seen as a web-like coating on the foliage.

Web blight is favored by high relative humidity. To control this disease, improve ventilation and make sure irrigation is timed to avoid prolonged leaf wetness. Wider plant spacing and hanging the plants will also help to improve air circulation and promote drying. Make sure to bag and discard diseased plants, and sweep up fallen leaflets to prevent inoculum from spreading to healthy plants. Greenhouse growers should always sanitize surfaces between crops, and be sure to use sterile potting media and sterile pots when planting.

Web blight is primarily a problem in a greenhouse environment. This disease is not a problem when ferns are grown indoors, as U.S. homes have notoriously low relative humidity levels. It can be a problem on outdoor ferns, especially with North Carolina's humid summers.

Sample of the Week: TSWV on Tomato

TSWV symptoms (Photo: Mike Munster)

This week's sample of the week was TSWV (Tomato Spotted Wilt Virus) on greenhouse tomato plants.  We received two tomato plants with black, necrotic spots on the foliage, a symptom associated with TSWV.  An ELISA immunostrip test confirmed this diagnosis.  We were a little surprised to see TSWV so early in the greenhouse.  Early infections usually have the most severe impact on yield because they prevent flowering and fruit set. The virus is spread by thrips and thrips populations in a greenhouse should be eliminated to prevent further spreading of the virus.  Infected plants will not recover and should be removed and destroyed.  

TSWV Symptoms (Photo: Mike Munster)

For more information on TSWV, check out our earlier blog posting here.

Sample of the Week: Sclerotinia Stem Rot of Snapdragon

Drooping snapdragons in flower bed. Jan 23, 2012.

Sclerotinia stem rot (a.k.a. Sclerotinia blight) is a disease we seldom see in ornamentals in North Carolina. The case pictured above is only the second time I've seen it from a landscape ornamental in the last three years. The cause is a cool-weather-loving fungus called Sclerotinia sclerotiorum. Although it can infect a wide range of host plants, it's best known for the damage it does on many vegetable crops. In our state the primary victim is collards, on which the disease is known as "head rot". Cabbage, lettuce, and strawberry are affected occasionally. It would be very unusual to see this disease after mid-May in North Carolina. Note that the related fungi Sclerotinia minor (the cause of Sclerotinia blight on peanuts) and Sclerotinia homeocarpa (the cause of dollar spot on turf) are comfortable with somewhat warmer temperatures.

Stem lesions and visible white mold, evidence
of the causal fungus, Sclerotinia sclerotiorum.

Diseases caused by Sclerotinia sclerotiorum are sometimes called "white mold" because of the fluffy white mycelium of the fungus that grows on affected plant parts under humid conditions.The fungus also wads itself into small, dark, hard lumps called sclerotia, which allow it to survive from season to season in the soil. It would be unwise to plant snapdragon next fall in the pictured flower bed, even if an effort is made to clean up and remove the diseased plant material. You'd also want to avoid planting flowering kale - a collard relative. There is no effective chemical control for this disease in the landscape.

Because the fungus produces airborne spores, it can sometimes even blow into greenhouses and cause stem rots on ornamentals and "collar rot" on tobacco. This is one reason it's so important to avoid leaving piles of dead plant material in and around greenhouses. Of course diseased plant material should never be composted, in this case because of the durability of the sclerotia.


Nota bene! Ojo! Vorsicht! This disease is completely different from Southern blight (Southern stem blight) caused by the unrelated fungus Sclerotiuim rolfsii. The scientific names of the fungi are confusingly similar, both cause stem rots, and both produce visible white mycelium on the plant, but there are key differences. Southern blight occurs from late spring through the heat of summer, not in the winter and early spring. Also, the mature sclerotia of Sclerotium rolfsii are tiny, round, and tan-colored (rather like radish seeds), whereas those of Sclerotinia are somewhat larger, irregular in shape, and black. Both kinds are white on the inside when cut open, and both take longer to form than the mycelium itself.

Above: Sclerotia of Sclerotinia sclerotiorum
(Photo: PP Dept. Slide Collection)

Above: Sclerotia of Sclerotium rolfsii