FEBRUARY
2011

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

02-03-11

Question and Answer


Q. My tomato plants this past summer started getting black spots on the bottom leaves and then more and more. Then they started looking sparse. I am told by friends that this is a fungus. How can I get rid of it... is there anything I can do right now?

A. There are several possible diseases that could cause those symptoms on tomato plants. The most common, especially in wet weather, would be early blight and Septoria leaf spot. Both diseases are caused by fungi and are common in wet weather because they require moisture, such as dew or rain, on the surface of the plant to infect the tissue. Septoria leaf spot usually appears on the lower leaves after the early fruits begin to set. Beginning as numerous small brown lesions, the spots enlarge over time and eventually the leaves turn yellow, dry up and drop from the plant.

Early blight is caused by a different species of fungus, but it too appears on the lower leaves first after fruit begin to set. The spots are dark brown to black and are typically larger in size with concentric rings, which can help distinguish this disease from Septoria leaf spot. Early blight also infects tomato plant stems and occasionally fruit, producing large sunken black target spots on the stem end of the fruit. Infected fruits often drop before they mature. Despite the name early blight, this disease is most common late in the growing season.

Regardless of which fungus is causing your tomato plant troubles, your best strategy is to prevent disease with good gardening practices. Remove plant debris from the garden at the end of the season to remove overwintering sites for the fungus. Other tactics include

* rotating your garden to different areas

* providing adequate space around the plants to encourage good air circulation

* watering early in the day to allow foliage time to dry quickly

* using trickle or drip irrigation to minimize moisture on the foliage

* removing infected leaves from the plant as soon as they are noticeable

* mulching around the plants to conserve soil moisture, reduce weed growth, and minimize soil splashing.

Fungicides can help protect foliage from getting the fungus, but they cannot cure the disease once the foliage is already infected. Fungicides must be reapplied throughout the growing season and especially following rains. Look for products containing the active ingredient chlorothalonil, and be sure to read and follow all label directions. For more information on tomato diseases, check this Purdue Department of Botany and Plant Pathology website, http://www.ppdl.purdue.edu/PPDL/weeklypics/7-12-10.html.

Q. A few of our landscape plants were broken this winter during heavy snow and ice. Is there something we can do to prevent this from happening again in the future?

A. In typical ice storms, the trees hardest hit are weak-wooded species such as silver maples, Siberian elms, river birch and willows. Trees that have been previously topped generally respond by regrowing numerous weak branches that are even more susceptible to breakage. These are among the first of the branches that fall during an ice storm.

broken tree top heavy with ice
photo by Purdue Plant and Pest Diagnostic Lab

Evergreen trees and shrubs are also particularly vulnerable because their foliage tends to collect more snow and ice loads. Evergreen trees, such as pine and spruce, are not capable of filling in new top growth where the damage has occurred, so the natural shape of the tree will be permanently affected. Damaged shrubs often can be pruned and encouraged to regrow.

There's not much that can be practically done to protect large trees from such damage. For multi-stemmed shrubs that can be reached safely, you can help prevent or at least minimize damage from heavy snow and ice loads by bundling stems together using burlap or canvas or simply tie with cord or twine.

Once the storm subsides, carefully remove heavy snow as soon as possible by using a soft broom or rubber rake; however, don't try to remove ice. Damage to the bark is more likely in trying to remove ice than simply allowing it to melt on its own.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,