Thursday, May 31, 2012

Botrytis Blight in the Landscape

A couple of weeks ago, we told you that Botrytis blight was especially active in greenhouses around North Carolina. Botrytis blight is a common problem in greenhouses and can be very destructive if allowed to go unchecked. Now that the weather outdoors feels a lot like a greenhouse – warm and humid – Botrytis blight will be popping up in home landscapes everywhere. 
Botrytis blight (Photo: D. Shew)
Another name for this disease is gray mold, which perfectly describes the appearance of the pathogen, Botrytis cinerea. Most of you have probably witnessed gray fuzzy “whiskers” of Botrytis as it eats up strawberries left on the counter too long! This fungus can be particularly problematic after several days of rainy, drizzly weather or in shaded areas of dense vegetation and high humidity. Botrytis cinerea infects a wide range of ornamental hosts including petunias, pansies, geraniums, snapdragons, begonias, periwinkles, roses, and zinnia. Botrytis cinerea can also infect a variety of fruits and vegetables including beans, carrots, grapes, peppers, and tomatoes. Areas with dense plantings of bedding plants, like petunias or pansies, are good spots to find active Botrytis infections. 
Botrytis blight in bed (Photo: D. Shew)
Botrytis usually infects tender tissue like flower petals, buds, and seedlings, damaged tissue, and dying or aging tissue. Infections begin as small tan to brown spots. Over time, prolific gray spore masses are produced on dying tissue. In severe cases, Botrytis infections can cause stem cankers or even kill plants. 
Botrytis blight: Early symptoms (Photo: D. Shew)
Botrytis blight on dogwood (Photo: D. Shew)
Botrytis stem canker (Photo: D. Shew)
The best way to control Botrytis blight in the home landscape is sanitation. Inspect plants regularly and deadhead spent flowers. Be sure to carry a paper bag with you to avoid dusting spores to healthy plants. Clip or prune cankers and remove plants with severe infections. Avoid picking off infected tissue when plants are moist so you don’t spread spores around during optimal infection conditions.
Strawberry loaded with Botrytis spores (Photo: Meagan Iott)

Tuesday, May 29, 2012

2012 County Agent Training

2012 County Agent Training in Plant Disease Diagnosis

Everyone is invited to attend the upcoming on-line training in Plant Disease Diagnosis. We especially encourage Master Gardener participation. Sessions will be archived for those who cannot attend at the scheduled times.

May 31, 2012 10:00 – 11:00 a.m. (live webinar) - Introduction to Plant Disease Diagnosis - Dr. Frank Louws

June 5, 2012, 10:00 -11:00 a.m. (live webinar) - Signs and Symptoms of Plant Diseases; Collecting Samples; Submitting Samples to the PDIC - PDIC staff

June 7, 2012 8:30 AM - 4:00 PM - Hands-on Workshop for County Agents (registration required)
Detailed instructions for using Elluminate can be found at the PDIC website

Friday, May 18, 2012

Controlling Botrytis in the Greenhouse

Due to weather conditions, Botrytis epidemics are currently occurring in greenhouses across the state. A wide range of floriculture crops can be affected. Symptoms of Botrytis infection range from flecking of blossoms, blossom blight, and even leaf and stem rot. On rose canes it can cause a tan-colored canker. The characteristic gray mold may be visible under high humidity conditions. 
Botrytis sporulating on petunia stem (Photo: M.J. Munster)
The two keys to Botrytis management are keeping the relative humidity below 85% and maintaining the greenhouse free of dead or injured plant material (spent flowers, fallen leaves, pruned branches, culls, etc.) on which the fungus can produce new spores. Irrigate at times of day when foliage will dry quickly, and if possible ventilate greenhouses in the evening to bring down the humidity. Avoid wounding plants, which allows Botrytis to invade healthy tissue.  Keep fertilization at optimal levels to avoid premature leaf senescence. Plants with bloom infection or crown rot should be discarded along with the potting mix. NEVER REUSE POTTING MIX WITH THIS PATHOGEN. Clean up all plant debris from the block and discard it. Do not compost any of this material, as the sclerotia of the fungus are capable of surviving adverse conditions. Spores of this fungus can be windborne, so be sure there are no cull piles nearby on which the fungus could produce them.
Botrytis stem rot on lavender (Photo: M.J. Munster)
If re-using pots, first clean thoroughly and then sanitize with either steam (150-160F for at least an hour at the center of the pile) or one of many chemical disinfectants available.
Petal spotting by Botrytis (Photo: M.J. Munster)
Fungicides may help prevent new infections, but won't cure plants that already have symptoms like those submitted. Effective products for Botrytis control include Chipco 26019/26 GT (Iprodione), Decree, Medallion and Pageant. Chlorothalonil (e.g. Daconil) can also be used; however chlorothalonil can cause phytotoxicity on blooms so this product should not be used on flowering plants. Decree is probably the most effective product for Botrytis control; however, it is only labeled for controlling Botrytis and should be used in a rotational program. In addition, there is a new Syngenta product named Palladium that just got registered for use in greenhouses and it is very effective against Botrytis. Be sure to rotate fungicides of different modes of action (FRAC groups) so as not to pressure the fungus into becoming insensitive (resistant) to any particular chemical. Note that one of the active ingredients in Palladium (fludioxonil) is the same as that found in Medallion. Get good coverage of the stems/crowns. Test any new treatments on a small number of plants first, to ensure that there are no adverse effects.

Written by: Mike Munster and Kelly Ivors

For more information on Botrytis in the home garden, click here

Friday, May 11, 2012

Sample of the Week: Oak Leaf Blister

This week, we received two different samples of oak leaves that had the same symptoms. Chuck Hodges, our resident tree disease expert, diagnosed the pale green spots as leaf blister, caused by the fungus Taphrina caerulescens. Disease develops when leaves emerge during cool wet weather each spring. Early symptoms appear as pale yellow to white, irregular spots on the leaves. 
Early symptoms on Southern red oak (Photo: PDIC Database)
Early symptoms on water oak (Photo: PDIC Database)
As disease progresses, infected foliage puckers out, giving the leaves a “blistered” appearance. In late summer, the blistered tissue will turn brown and die. The severity of the disease will vary from year to year depending on early spring weather. Leaf blister affects only the leaves and does not damage the overall health of the tree. Chemical control is neither necessary nor practical on trees in the landscape. However, it may help to rake up and remove fallen leaves. In the nursery, a single application of chlorothalonil, maneb or mancozeb in early spring, just before the buds begin to swell, should be effective. Fungicides applied after bud break are not effective.
Late symptoms on white oak (Photo: PDIC Database)
Special thanks to Chuck Hodges for helping with this post.

Wednesday, May 2, 2012

April Showers Bring May Flowers... and DISEASES!

Last week, we told you about diseases to watch for in your home vegetable garden. In this post, we will tell you about some diseases to watch for in the home landscape. We have already seen these diseases active around campus and you can probably find them hanging out in your own back yards. 

Septoria Leaf Spot on Black Eyed Susan 
Last week we wrote about Septoria leaf spot on tomato. A different species of Septoria, Septoria rudbeckiae, attacks black eyed Susan and other members of the genera Rudbeckia and Ratibida. This species of Septoria will not cause disease on tomatoes! Symptoms on Rudbeckia begin as small, dark-brown lesions that enlarge as the disease progresses. As the lesions age, small black dots (fruiting structure of the fungus) can be seen in the lesions. Spores are released in late spring and early summer and are spread by splashing water. Lower leaves are usually infected first. To manage this disease, avoid the use of overhead watering and practice good sanitation. Remove fallen leaves at the end of the season to reduce inoculum levels for the following year. Improve air circulation in your beds by spacing plants out. Chemical control can be achieved through the use of preventative fungicides. Products containing chlorothalonil or mancozeb are recommended. 
Septoria Leaf Spot on Rudbeckia (Photo: M.J. Munster)
Hollyhock Rust 
Hollyhock rust is caused by the fungus Puccinia malvacearum. This very destructive disease often limits the use of hollyhocks in the Southern landscape. Symptoms of rust infection begin as light yellow to orange spots on the upper leaf surface. Brown pustules develop on the underside of the leaves and erupt to reveal bright orange rust spores. These spores are windblown to healthy leaves and infection begins again. Disease increases rapidly because hollyhock rust can infect over and over again. The plants become very unsightly as the infected leaves start to die and fall off. Typically, rusts are highly host-specific. This particular rust infects hollyhocks and other members of the mallow family. Control rust by limiting leaf wetness. Avoid overhead watering and space plants to improve air circulation and promote leaf drying. Rust can overwinter in plant debris so sanitation is important. Remove infected leaves in early spring and remove infected stalks and lower leaves at the end of the season. Plant debris should be buried or burned. Removing nearby susceptible plants, like rose of Sharon and mallow weeds, is important to prevent new sources of inoculum. Chemical control can be achieved through the use of products containing chlorothalonil or myclobutanil. Some seed catalogues list rust-resistant hollyhocks but we do not know of any trial results in this area. Ultimately, you may be forced to forgo planting hollyhocks. 
Hollyhock Rust (Photo: M.J. Munster)
Hollyhock Rust (Photo: M.J. Munster)
Powdery Mildews on Euonymous, Gerbera Daisy, Dogwood and Rose 
Right now, several powdery mildews are active in the landscape. Be on the look-out for powdery mildew on euonymous, gerbera daisies, dogwoods, and roses. Control of powdery mildews can be achieved through sanitation and pruning during dormancy. Take care not to over-fertilize since succulent leaves are more susceptible to infection. The best control is host resistance so try to plant resistant varieties whenever possible. Several active ingredients provide effective chemical control of powdery mildews, but control requires applications on continuous 7-14 day intervals. Repeated sprays with the same fungicide can select for fungicide-resistant strains of powdery mildew. For more detailed information about powdery mildews, click here to read our earlier blog post. 
Powdery Mildew on Euonymous (Photo: M.J. Munster)
Powdery Mildew on Gerbera Daisy (Photo: M.J. Munster)
Powdery Mildew on Rose (Photo: M.J. Munster)
Powdery Mildew on Dogwood (Photo: B.B. Shew)
Azalea and Camellia Leaf Gall 
Azalea leaf gall is caused by the fungus Exobasidium vacinii. This disease is common and widespread in the spring and often attacks new leaves and flower buds. On azalea, infected leaves become thickened, curled, fleshy and pale green to white, forming galls. Infected azalea flowers are usually pale pink. In later stages of disease, white powdery spores cover the surface of infected tissue. A different species of Exobasidium is very common on new growth of sasanqua camellia. On camellia, entire leaves are swollen and distorted and extensive swelling causes the leaf epidermis to split, revealing the white spores beneath. Spores of Exobasidium are windblown or splashed to healthy leaves or flower buds. New infections are not evident until gall-like swellings form the following year. Eventually affected leaves and flowers turn brown, become hard, and fall to the ground. This disease is favored by cool, wet weather. Although unsightly, infected plants are not usually seriously damaged. This disease can be problematic in a greenhouse setting where humid conditions promote sporulation and disease spread. The best control is sanitation. Pick or prune off diseased tissue as soon as swelling starts. Be sure to remove infected tissue before the fungus starts producing spores to prevent new infections next year. Burn or bury the swollen tissue. Often disease is not severe enough to warrant chemical control. When possible, try planting resistant varieties. Susceptible varieties of azalea include White Gumpo, Rosebud, Mother’s Day, and China Seas. Resistant varieties include Amonena, Gloria, Coral Bells, Glacier, Formosa, and Aphrodite. Exobasidium vacinii can also infect blueberries and is responsible for the “green spot” symptom on fruit and leaves. See Bill Cline’s post on Exobasidium vacinii infections of blueberry for more information.

Leaf Gall on Azalea (Photo: H.D. Shew)
Leaf Gall on Camellia (Photo: H.D. Shew)
Leaf Gall Symptoms on Camellia (Photo: H.D. Shew)
Leaf Gall Symptoms on Camellia (Photo: B.B. Shew)