The Daily Southerner, Tarboro, NC

July 20, 2012

Ask A Master Gardener

FOR THE DAILY SOUTHERNER
Bob Filbrun

TARBORO — Edgecombe County’s Extension Master Gardener Volunteers’ weekly local Q&A column, “Ask A Master Gardener” is intended to engage the county’s residents in solving common problems concerning horticulture, gardening, and pest management through its trained and supervised volunteer staff.  The Extension Master Gardener program is an educational program designed to enhance public education in consumer horticulture.

Submit your questions with your email to askemgv@gmail.com.  Or, you can call the local Extension Center at 641-7815 and tell them you have a question for a master gardener. You ask the questions and a local Master Gardener will return your call with a solution to your problem and share it with our readers.

Answers reflect research collected from land grant universities (NCSU or NCA&T) and through a national extension website, www.extension.org.  



Q. Ruby K. (in the county) asks Why are my tomatoes wilting and dying in the garden?

A. Tomatoes are susceptible to several wilt diseases caused by soil-borne organisms or environmental conditions.  Here’s a link to Clemson University’s extension service site that identifies every known tomato disease.  Your Master Gardener Volunteer has singled out three that closely match your problem. http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2217.html



Bacterial wilt or Southern bacterial blight is a serious disease caused by Ralstonia solanacearum (formerly Pseudomonas solanacearum). This bacterium survives in the soil for extended periods and enters the roots through wounds made by transplanting, cultivation or insects and through natural wounds where secondary roots emerge. Disease development is favored by high temperatures and high moisture. The bacteria multiply rapidly inside the water-conducting tissue of the plant, filling it with slime. This results in a rapid wilt of the plant, while the leaves stay green. If an infected stem is cut crosswise, it will look brown and tiny drops of yellowish ooze may be visible.

Prevention & Treatment: Control of bacterial wilt of plants grown in infested soil is difficult. Rotation with non-susceptible plants, such as corn, beans and cabbage, for at least three years provides some control. Do not use pepper, eggplant, potato, sunflower or cosmos in this rotation. Remove and destroy all infected plant material. Plant only certified disease-free plants. The cultivar Kewalo is partially resistant to bacterial wilt, but is an uncommon cultivar. Chemical control is not available for this disease.

Fusarium Wilt This is a warm-weather disease caused by the fungus Fusarium oxysporum. The first indication of disease in small plants is a drooping and wilting of lower leaves with a loss of green color followed by wilting and death of the plant. Often leaves on only one side of the stem turn golden yellow at first. The stem of wilted plants shows no soft decay, but when cut lengthwise, the lower stem will have a dark brown discoloration of the water-conducting vessels. The fungus is soil-borne and passes upward from the roots into the water-conducting system of the stem. Blocking of the water-conducting vessels is the main reason for wilting. Invasion occurs through wounds in roots growing through infested soil. Long-distance spread is through seed and transplants.

Prevention & Treatment: Control can be obtained by growing plants in pathogen-free soil, using disease-free transplants and growing only cultivars at least resistant to races 1 and 2 of Fusarium wilt (indicated by FF following the tomato cultivar name). Some newer cultivars are resistant to races 1, 2 and 3, and can be found listed in Table 4. Raising the soil pH to 6.5-7.0 and using nitrate nitrogen (such as in calcium nitrate) rather than ammoniacal nitrogen (as in 5-10-10, 10-10-10, or 34-0-0) will retard disease development. No chemical control is available.

Southern Blight - The fungus Sclerotium rolfsii causes this disease. The first symptom is drooping of leaves suggestive of other wilts. On the stems, a brown, dry rot develops near the soil line. White fungal growth with brown mustard seed-sized sclerotia may be visible. The stem lesion develops rapidly, girdling the stem and resulting in a sudden and permanent wilt of all aboveground parts. Frequently, a white fungal mat covers the lesions. The fungus can also attack fruits where they touch the soil.

The fungus can survive for years in soil and plant debris. It is favored by moist conditions and high temperatures.

Prevention & Treatment: Crop rotation with non-susceptible grass crops and removal of plant debris immediately after harvest will help to control the disease. Do not plant tomatoes after beans, pepper or eggplant. Calcium nitrate may be applied at transplanting.



Q. I have noticed that many of the trees in my yard are dropping leaves.  Is this a result of the stress of all this hot, dry weather we’re having?

A. You’re right.  The weather is to blame. This answer closely relates to one of last week’s questions about dealing with exposed tree roots and recommends mulching for moisture retention.  If there’s no rain, you should provide at least one inch of watering per week preferably with drip irrigation using soaker hoses. It is also recommended that you extend the mulched area out to the tree’s drip line. Avoid mounding excessive mulch up around the trunk of the tree to prevent the bark from rotting.



Q. How can I be sure I’m correctly maintaining my lawn, even in this hot, dry weather, with regard to irrigation and mowing?

A. How often should I water my lawn? There’s no simple answer because irrigation requirements vary with grass species, with soil type, and with environmental conditions.  On average, turf will usually require from 1 to 1.5 inches of water per week for normal maintenance conditions. This can be provided by rainfall or irrigation or a combination of the two.  The best time to irrigate is also important. Overly wet conditions in the canopy can contribute to disease development. Nighttime watering will keep the turf wet for the longest period of time and should be avoided if possible. Watering during the day will allow the turf to dry quickly, but will increase water loss due to evaporation. All things considered, the early morning hours provide the best time for turf irrigation. Water loss from evaporation will be less, and the turf will dry quickly in the morning.

How short can I mow my lawn?  Turfgrasses do not thrive on mowing; they tolerate it. It may seem that mowing is good for the grass, but mowing is always a stress. The cutting of leaf tissue may allow disease organisms to enter the plant, and it reduces the photosynthetic area, lowering the production of carbohydrates that the plant needs to grow. Turfgrasses are the best-equipped plants on earth to tolerate this type of defoliation. The mowing height that a turf will tolerate is dependent on the species that are present. The cool-season species primarily used in lawn situations are Kentucky bluegrass, tall fescue, and perennial ryegrass. These three species will do best at heights of 1.5 to 3.0 inches, with higher mowing heights used during the high-temperature stress periods. Warm-season species such as Bermudagrass and Zoysiagrass can tolerate heights of 0.5 inches or less, while Bahiagrass, carpetgrass, and centipedegrass do best at heights from 1.0 to 3.0 inches, and St. Augustinegrass should be mowed in the 3.0 to 4.0 inch range.



Q. Vaden H. (Conetoe) asks Where would I find out "weight per bushel" of common garden fruits and vegetables?

A. Here’s a website (found on Google) that’ll answer a lot of conversion questions related to volume and weight:  http://www.pickyourown.org/info.htm . . . Weight per Bushel for Common Fruits and Vegetables



(“Ask A Master Gardener” also wants to include your “tried and true” gardening tips and techniques and snapshots from your garden; please share in an email to askemgv@gmail.com or by writing to “Ask A Master Gardener”, c/o The Daily Southerner, P.O. Box 1199, Tarboro, NC 27886.)