FEATURED THIS MONTH: BLIGHT

photo by Kathi bangert, Master Gardener Intern

photo by Kathi bangert, Master Gardener Intern

By Kerry Lake, Master Gardener

Early Blight

We were visited by early blight this year. Over 12 inches of rain in June (more than 4 times the normal amount) and the cool June nights, set Alternaria solani into action. By the third week of June it had infected Kathi Bangert’s tomatoes, peppers and even spread to a neighboring butterfly weed. 

What is Early Blight? Alternaria solani is a fungal pathogen that usually affects tomatoes and potatoes. It is identifiable by bulls-eye patterned spots on the leaves and also stem lesions along with fruit rot on tomatoes and on the potato tuber. The leaf spot is usually brown and will be surrounded by a larger region of yellow. The leaves can dry out and fall off prematurely. The fungus usually occurs on the older leaves of the plant first. A. solani can also be a cause of damping off of seedlings.

Late Blight

Phytophthora infestans is another fungal pathogen that attacks the Solanaceae botanical family: tomato (S. lycopersicum L.), potato (S. tuberosum), eggplant (S. melongena L.), bell and hot pepper (S. capsicum). It spreads mostly by the wind, but also through the soil. It likes the humid weather of mid to late summer with its cooler nights. Phytophthora infestans is identified by its gray-green spots on leaves. The spots can appear ‘water soaked’ then enlarge to dark brown with a firm rough surface.  

Look on the underside of the leaves for the white fungal threads. From here the spores will blow in the wind or water from rain and irrigation on the leaves that can wash this disease down into the soil. Tomato fruit can show signs of the blight up to 3 days after picking from an infected plant.  Potatoes tubers can rot even after placed in winter storage.

What to do? 

  • Avoid wetting the leaves of tomatoes and potatoes when watering your garden. Drip irrigation is the recommended method for watering your plants. 
  • Be sure to water in the morning to avoid excessive wetness in the garden especially into the evening. 
  • Mulch around your plants (we recommend straw) so that any spores on the soil cannot splash up onto your plants. 
  • Rotate your Solanaceae crops within your garden so that there is a 3 year rest between Solanaceae plantings.
  • If you spot any leaf discoloration, remove leaves immediately if you think that your tomatoes have been infected.  Remove and destroy the entire plant if the fungus has spread. Kathi removed the early blight infected plants, and has replanted with new ones, with all doing well so far. 
  • When purchasing plants and seeds, look for disease-resistant varieties to slow down the development of blight and other pathogens. Seeds of tomato, eggplant, and peppers do not carry the blight fungus, but potato seed tubers can.  Do not use any seed tubers that you saved from the previous year. Only purchase certified disease-resistant varieties.
  • Increase spacing between plants to improve air circulation between rows.
  • Remove side stems of your tomato plants for better airflow. As a plus this make it easier for pollinators to find the flowers. More pollination, more fruit.
  • Once planted, frequently check your plants’ leaves for signs of spots or yellowing leaves, especially during wet and humid weather. 
  • Don’t add infected plants to your compost bin. Dispose of them thoroughly so that the blight spores do not blow into other portions of your or your neighbor’s garden.

           For more information, contact your extension service. In Western Massachusetts it is https://www.ag.umass.edu/

 

Powdery Mildew

By Norma Owlcarver, Master Gardener

Powdery mildew is a common fungal disease of plants in our area that occurs this time of year. It’s named for the grayish white powder consisting of fungus strands on the leaves of the plant. The fungus uses the host plant for its food supply by sending root-like structures into the leaves and stems.
Powdery mildew likes the humid conditions we experience in New England on warm days and cool nights. Some particularly sensitive plants are apples, roses, grapes, peas, potatoes, phlox, squash and zinnias, though there are many more. It’s common for it to start in crowded plantings where air circulation is poor and in damp, shaded areas.

If you’ve had powdery mildew on your plants in previous years, it’s likely to return this year. There are, however, some practices you can institute that can reduce or even prevent future infestations. Additionally, many resistant varieties have been developed. For information and to learn what some of these plants are, click on the website links at the end of this article. You may also want to check for resistant varieties at your favorite garden center.

                                  
Injury due to powdery mildews is often of minor consequence to healthy plants, although it can become unsightly. If damage occurs, it may include the stunting of leaves, buds, growing tips and fruit. It can cause the death of invaded tissue on some plants, i.e., begonias. Leaves can yellow and cause the death of tissue, which can produce premature leaf drop. When plants are infected, nutrients are removed from them by the fungus. This may cause the loss of vigor in the plant and produce a general decline in growth. The taste of squashes and some other vegetables may also change.


Should you wake up to those powdery looking leaves in your garden this year, consider the following cultural practices to reduce the potential of it spreading further and, perhaps, eliminating it next year

1. As much as possible, when planting flowers or vegetables that you know are prone to powdery mildew, plant in an area with full sunlight and where the soil drains well.

2. When putting in new plants assure you are not crowding them.

3. If you have plants that are already infected, you can increase the air circulation by selectively pruning overcrowded plant material on the plant and between plants. This will help reduce relative humidity and reduce the chance of further infection.

4. Avoid overhead watering to help reduce the relative humidity, or water in the early morning to let the tissue dry as soon as possible.

5. Don’t make late-summer applications of nitrogen fertilizer. This will limit the plant’s production of succulent tissue, which is more vulnerable to infection. Powdery mildew tends to increase in high nitrogen soils so you may want to consider using an organic fertilizer or a slow release fertilizer.

6. When the growing season is over and you are closing your garden for the season, remove and destroy all infected plant parts (leaves, etc.). This will decrease the ability of the fungus to survive the winter. Do not compost the infected plant debris, as the spores (seeds) can overwinter and temperatures often are not hot enough to kill the fungus.

7. Disinfect the tools you use to prune infected plants and all your other garden tools that may have contacted the diseased plant, in a bleach and water solution.

If you decide to treat plants infected with powdery mildew, researchers at the University of Rhode Island (URI) have confirmed that a combination of 1 tablespoon baking soda plus 2.5 tablespoons of horticultural oil in 1 gallon of water is effective against powdery mildew on roses. Other New England University Extension web sites suggest this combination for other crops, but URI states this is still experimental.

Sulfur products have been used to manage powdery mildew for decades, but it is only effective when applied before disease symptoms appear. If you use this method, use wetable sulfur with a sticker, as it will work best. Read all of the directions on the product. Start applications right before the mildew normally appears. As a precaution, before starting applications to the entire plant, apply the solution to a small test area to assure leaf burn will not occur. If the test is successful, apply the product carefully after each rain until the mildew is under control. Make sure to include the bottom of leaves in your applications.

As stated above, consider disease-resistant varieties before you plant, but keep in mind that resistant does not mean immune. Cornell University’s Vegetable MD Site has numerous listings of disease resistant vegetables that are available. The site address is

http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm

If you know you are already growing plants that are prone to downy mildew, which is different from powdery mildew and occurs under different environmental conditions, but is hard on many types of roses, as well as other plants, follow the 2009 mildew forecast recommend by Cornell and developed by North Carolina State University (UNCSU). UNCSU is reportedly working to expand this forecast tool to include other mildews. The forecast and alerts can be followed for the entire U.S. or just MASS. The forecasting address is

http://www.ces.ncsu.edu/depts/pp/cucurbit/?month=5&year=09

At this site you will also find alerts of when the first signs of downy mildew are first spotted in all of the 50 states.

In summary, whether you manage the plants you have to prevent and/or eliminate powdery mildew or choose to plant with resistant varieties, your first line of defense is to follow good cultural practices in your garden and with your lawn.
 

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