NOVEMBER
2001

 

 

 

By
Beverly Shaw
 
Advanced
Master Gardener
Purdue University

 

 

 

 

 

11-01-01

Question and Answer

Q. This year, I had problems with my tomatoes. They grew well and had lots of green and ripe tomatoes on them, when all at once the leaves turned yellow and fell off. Some plants had no leaves left. The tomatoes that were ripe didn't taste good. This happened in just a week's time. Other neighbors had the same problem. – Kathryn Gilbert Cory, Ind.

A. Tomatoes are susceptible to a number of problems. One of the culprits that causes sudden leaf drop is septoria leaf spot, but your description is missing one tell-tale sign. Were the leaves spotted with one-half—inch brown spots? Septoria causes heavily spotted leaves to turn yellow, dry and fall off the plants. If the weather is warm and moist, all the leaves may become spotted and drop.

This fungus usually attacks plants after the first tomatoes are formed. As the leaves drop, the plant loses its resources for further fruit development so the remaining fruits will lack flavor. Unfortunately, this problem can persist on plant debris for several years.

Remove all tomato plants from the garden this fall, and avoid planting tomatoes in that location, if possible. Avoid overhead watering and working around the tomatoes when they are wet to reduce the spread of fungal spores. At the first sign of spotting, spray with products that preferably contain the active ingredient "chlorothalonil." Fungicides that contain "copper," "maneb" or "mancozeb" as active ingredients also can be effective, especially if disease pressure is low.

 

Q. I have some asparagus. In spring, it does fairly well, but some people say you can gather more asparagus in the fall. If so, how does a person care for it? – Mary Horn, Kewanna, Ind.

A. Fall harvesting will reduce the overall production of the plants. Asparagus yield depends on the amount of food materials stored in the root system as a result of the previous season's foliage growth. The longer the period the fern has to grow and the more vigorous the fern, the greater the amount of food materials produced and stored in the root system. Stress from overharvesting weakens the plant and reduces the time available for fern growth and energy storage. The planting becomes less vigorous and the spears more spindly each year when asparagus is diseased, overharvested or stressed in any other manner.

Asparagus spears start to emerge when the soil temperature reaches 50 F. After this, growth of asparagus is dependent on air temperature. Early in the season, 7- to 9-inch spears might be harvested every 2 to 4 days. As air temperatures increase, begin harvesting 5- to 7-inch spears daily before the tips start to fern out and lose quality.

After harvest, new spears will emerge, fern out and provide a large canopy to cover the space between the rows. Once a dense fern canopy is formed, weed growth will be reduced.

 

Q. I read somewhere about a recipe for homemade insecticidal soap. I have had three mandevillas in three years, which have all died from a fungus. I am using purchased soap but would like to make my own. Any ideas? – Tam Vogel, Winona Lake, Ind.

A. Insecticidal soaps are effective against many insect pests of mandevilla but will have no effect on diseases or fungi. If your plants died from a fungus, you'll need a fungicide; but since mandevilla are usually fungi-free, they may have died from some other cultural cause.

Mandevilla is a tropical woody vine that must be grown as an annual or brought indoors for Indiana winters. In the spring, mandevillas can be returned outside after the last spring freeze or after the threat of freezing weather has passed.

Indoors, mandevillas need curtain-filtered or bright indirect sunlight. Provide night temperatures of 60 to 65 F and day temperatures above 70 F. Plant in a mixture of equal parts peat moss, potting mix and sand. In spring and summer, feed every two weeks with a fertilizer high in phosphorus such as 10-20-10.

Outdoors, grow mandevillas in partial shade. They need rich, well-drained, sandy soil with humus added. Provide a frame, trellis or stake for support. Pinch young plants to induce branching. Since 45 to 50 F is the minimum temperature that can be tolerated by mandevilla, plants should be moved indoors for the winter. Before bringing them indoors, examine them carefully for pests. Look under the leaves and in the leaf axils for insects and their eggs. Remove any diseased or dead leaves by hand. Insect-infested plants can be doused with a forceful spray of water to dislodge the pests, or you can use insecticidal soaps or other appropriate insecticides labeled for use on your plant. It's best to use a purchased insecticidal soap as labeled. If you choose to use 2-3 tablespoons of dishwashing soap per gallon of water, as recommended by the University of California, do so with caution. Insecticidal soaps are tested to most effectively kill insects without burning plants. Homemade concoctions will vary from year to year depending upon the brand of soap chosen, unknown formula changes to soaps, etc. Since dishwashing liquids are made to clean dishes, the manufacturers are under no obligation to tell you when they make changes to their product. This could make a difference if you're using it on plants! If you use a homemade soap mixture, make sure you test it on a small area first.

When you bring plants indoors for winter, reduce the frequency of watering to coincide with the plants' rest periods induced by the cooler temperatures and reduced light. In late winter or early spring before growth begins, prune by removing old, crowded stems and shortening others. Even if mandevilla is pruned almost to the ground, it will bloom the same summer on the new shoots, which develop from the base of the plants.

 

Contact: B. Rosie Lerner
Editor: Olivia Maddox,