HOME AT THE CCCC FARM

Throughout our research and work on this project, we maintained regular observations of what was happening in the college garden as we noted any disease issues along with taking pictures.  Below are some of our observations to include a preliminary report on 2/21/12:

Garlic: Earlier observations included the slow growth of a planted area of garlic leading us to suspect the plant pathogen "Sclerotium Cepivorum" as detailed in our posting under Alliums. A more recent observation indicated its recovery with no steps taken.  While the leaves did still seem yellow, it was determined that because the other rows were yellowing as well, the crop is merely beginning to bulb up.

Rutabaga: We also noticed some brown spots and holes in the leaves of the rutabaga and after care inspection, our diagnosis was referred to Team Insect in which they determined the pests to be the Harlequin Beetle and Non Looper Cabbage worm.

Radishes:  During harvest, it was noticed that several of the radishes in the hoop house had a condition similar to potato scab.  Details of our findings can be found in the posting for Radishes.

Iris:  Leaf spots were discovered in an overgrown area of irises.  Below is information gathered from Mary Ann Hansen, Extension Plant Pathologist, Department of Plant Pathology, Physiology and Weed Science, Virginia Tech about this disease.


Heterosporium leaf spot, or iris leaf spot, is the most common disease of iris in Virginia. It is caused by the fungus Didymellina macrospora, which is also known as Heterosporium iridis.
Although the fungus attacks bulbous iris most frequently, it can also cause severe damage to rhizomatous iris. Leaf spotting is most conspicuous on the upper half of the leaves toward the end of the season after the blooming period.

Symptoms

The first evidence of this disease is the appearance of small brown spots with water-soaked margins near the leaf tips. During the early part of the season, these spots are not conspicuous, but after blooming, the spots enlarge rapidly, coalesce, and may cause death of the leaf from the tip back.  As the spots enlarge, they become oval-shaped and tend to lose their water-soaked margin. Later the spots turn a yellow to reddish-brown color with characteristic gray centers. Although the fungus does not attack the bulbs or rhizomes, premature killing of the leaves can sufficiently weaken the underground parts so as to cause a gradual death of the entire plant.

Disease Cycle

The fungus overwinters on dead iris leaves. Spores spread from old plant debris in the spring and initiate new infections. Fungal spores (Fig. 2) produced in leaf spots during the growing season are spread by splashing rain.

Fig. 2. Microscopic spores of Heterosporium iridis. (Photo by M. A. Hansen)

Control

Cultural Control

Removing and burning or burying all diseased leaves in the fall will greatly reduce the amount of fungal inoculum available for infection the following spring and frequently will provide sufficient disease control.

Report Prepared by Team Disease: Donna, Emma, Zach, Arima, and Amber

Disease Discussions

February 21, 2012

Several observations were made at the CCCC student farm during the month of February in an attempt to record and identify any diseases found. Our findings primarily focused on the family of Brassicas with the following results documented and researched.

We noticed several cases of browned leaves, almost leaf scorched in nature, along with some stems splitting on a small scale of broccoli and kohlrabi both in the greenhouse and outside in the field along with similar symptoms with the Swiss chard (more widely infected).  The dinosaur kale grown close to the latter showed no indications of a disease condition.  The symptom of browned leaves is indicative of a biotic fungal disease (possibly downy mildew) due to the cool, moist weather.  The symptoms were reviewed by a neighboring county extension agent and his advice concluded that it appeared to be some type of fungal disease but may also be a physiological problem.  He advised the best way to know what is happening is to take a symptomatic leaf and culture it in a warm moist environment and see what grows. Once you have some distinctive fungal growth, diagnosis becomes much easier. 

A cultural control for downy mildew would be to promote dryer conditions (difficult in winter!) through pruning and site selection and growing resistant cultivar.  Physical controls would be to remove and destroy badly infected leaves.   Biological and reactive controls could be used if necessary by spraying potassium bicarbonate which may or may not reduce the spread of the disease.  A Bordeaux mix or other copper-based fungicide can be used as a last resort. (2)

Another possible condition could be an environmental abiotic condition of a potassium deficiency due to the browning appearance of the leaf margins with dead areas on the edges dropping giving the leaf a ragged appearance, along with the fact that the browning had crossed over in to a different family (the beet family of the Swiss Chard).  Cultural controls would be to determine the levels of potassium through soil test and amend as needed prior to planting and maintain with regular applications of compost or other organic fertilizers.  Kelp meal or green sand are suggested potassium sources.  Crop rotations will help with good soil fertility and nutrient management as well.  A physical control might include the determination of drought conditions which would inhibit good potassium uptake. (2)

One final possibility of the leaf browning could be another biotic condition of black rot which is caused by bacteria as show in a symptom photo in some cabbage in the Resource Guide for Organic Insect and Disease Management.   The pathogen often enters the plant through pores on the leaf margin and spreads systematically.  The veins can become black which was not seen in our visual of the plants affected.  Black rot is common in seedlings but plants can be affected at any age with the pathogen being spread by splashing water, insects, with transplants, and can be seed borne.  Cultural controls would include choosing resistant varieties along with using hot water treated seed.  The process involves soaking the seed for 25 minutes (for cabbage and Brussels sprouts) in 122 degree F water and 20 minutes for Chinese cabbage, broccoli, and cauliflower.  A minimum of a 3 year rotation away from other crucifer crops should be practiced.   Physical Controls would be to address potential threats when transplanting to the field and destroying crop debris after harvest along with avoiding overhead irrigation.  Biological/Reactive controls approved for organic production would be the use of copper compounds, however, they have not been effective in recent studies. (3)

An infected Swiss chard leaf we found on the student farm had a loan black spot on it. Our research led us in searching for black spot diseases in which most of the results fell in the "leaf spot" disease group. Leaf spot is a group of diseases that cause round blemishes on a wide variety of plants. The damage usually only affects the appearance of the plant and not the health.  It is highly possible that our sample was specifically Alternaria Leafspot which is a result of the fungus "Alternaria brassicae ".  While most leaf spots only cause cosmetic damage, Alternaria can cause damping-off in smaller leaves by taking over their stems. This specific leaf spot occurs during the coolest part of the season. The fungus also usually picks on older leaves first. The leaf we found was older and it was during a cool part of the cool season, in which images online also appeared similar.

Our investigations led us to discuss other local diseases experienced by area farmers.  Late Blight is one of the diseases that are prominent in the North Carolina area as many know. After speaking to local farmer, Austin Genke, further research was pursued on this vastly damaging disease and will be shared with the farmer to help him in the future.  Last summer Austin revealed how he took a huge financial hit when blight spread and wiped out his tomato plants.  The tomatoes were growing quite healthy until he started to notice smaller leaves dying near the ground and subsequently following some spotting on the stem.  Austin reacted with physical controls by removing the dying leaves and properly disposing of them, which unfortunately never really hindered the disease from spreading.  "One day they would be beautiful and green, the next day they look dead" said Austin's wife.  The blight spread very quickly, allowing only a quarter of the expected harvest. The blight also spread to his cucumbers.  After research about blight, Austin decided that he will not plant tomatoes in the same fields that were affected, thus utilizing a cultural control method of prevention. Blight spreads during humid days and cold nights.  It is a fungus that loves damp conditions. Like many diseases, blight is difficult to manage after it is established.  The reactive control of spraying with copper is used to help manage blight but Austin was hesitant about that.  Many farmers have had a lot of success with the biological control of compost tea along with recently documented research proving the many benefits of the natural amendment which is also recommended in the Organic Gardeners Handbook of Natural Insect and Disease Control.  We look forward to checking back with Austin and hearing of his hopeful success in trying this compost method and see if he has any problems with blight this coming season.  

Because of the many diseases that can and do affect our ongoing crops, we as “Team Disease” have committed to construct a field guide of common diseases found in prominent cash crops within the triangle area.  We will be consulting with local farmers, county extension agents, our CCCC farm manager, instructor, and resources such as the website “Growing Small Farms” in a collaboration to provide a quick and concise guide for the prevention, identification, and control of key diseases. Organization of the content will be dependent upon which diseases we include and what plants/plant families are susceptible to those diseases, but content will be presented in such a manner that the guide can be used easily in the field – photos, signs & symptoms, and information on how to deal with the particular disease will be included. 

It WILL be good!

References:

1.   Mark Daniely, Alamance County Extension Agent.

2.   The Organic Gardener’s Handbook of Natural Pest and Disease Control. 

   Edited by Bradley, Ellis, and Martin.

 Resource Guide for Organic Insect and Disease Management