Replanted Vegetables Dying

Why do vegetables continue to die no matter how many times I replant? There are soil borne plant diseases that can survive in the garden, either on plant debris or in the ground itself. Once infected, the soil can remain so year after year. Some of these diseases have a wide host range, while others attack either one particular species only or may attack members within a particular plant family. Planting the same crop year after year in the same location will allow for the pathogen to build up to high levels. 

One of the best control measures for the soil borne diseases is crop rotation. This will allow time for the plant debris to decay and the associated pathogens to die out. The time required for this to happen varies. Some diseases survive up to 10 years or more, but most recommendations suggest periods of one to four years before returning to the original crop.

Keep in mind that a fungus that attacks, for example, the roots of lettuce will usually not attack beans. If tomatoes are being grown one year, do not come back and plant tomatoes again, or potatoes, peppers and eggplant for that matter – they are all in the same family.  This is a good practice even if no diseases are detected.

Another important step in disease prevention is to take advantage of any resistant varieties that may be available. For vegetables, check with seed catalogs to see if they have varieties that are resistant to a specific disease. The same is true with fruit trees since certain varieties are more resistant to diseases.   

Note: resistant (or tolerant) does not mean immune. A resistant plant will be less affected by the disease and show fewer symptoms. A plant that is immune will not be affected by the disease. Unfortunately, some resistant varieties may lack certain desirable characteristics in the plant such as flavor or high production. If you can find resistant varieties, the battle against disease is half over.

Ask the Garden Guy, Science Based Answers to Garden Questions, is an excellent resource book for gardeners. Some popular topics include Slugs and Snails, Organic Pesticides, Why Vegetable Seeds Do Not Germinate, What’s So Hot about Manure? Mushrooms in the Lawn.  Purchase by clicking on the image of the book above. 

Citrus Skirt Pruning

Occasionally citrus trees have been pruned up off the ground. Some have asked, "What is the reason for this?"

Skirt pruning of citrus has been around for a long time in those countries surrounding the Mediterranean Sea. The skirt of the tree includes those branches which hang down and touch the ground or are near to the ground.  In Italy, the skirts are pruned as high as the goats can reach.

In the United States, California in particular, skirt pruning done with clippers or a pruning saw, not goats, is a recent development and mainly came about as a means of controlling snails in the orchard.  By skirt pruning, usually 18 – 24 inches, snails as well as ants are denied easy access into the tree. Then the trunk is the only route.  Farmers can concentrate their pest control efforts on a small area, the trunk, rather than spraying the whole tree with pesticides. In the case of snails, copper foil is often banded around the trunk; snails will not cross the copper band. For ants a sticky material is sometimes applied.

Skirt pruning will also help control brown rot disease of citrus fruit. Since low hanging fruit is eliminated, the overall fruit quality will improve. 

Yams or Sweet Potatoes?

What is the difference between yams and sweet potatoes?  Are they the same, yet by a different name?
 

Many years ago orange colored sweet potatoes were introduced to the Southern United States. In an effort to distinguish these from the traditional white-fleshed potato, producers called them yams, which is the Anglicize African word, nyami. Today, most of the starchy tubers consumed in the US and labeled as yams are in reality sweet potatoes. Yet yams and sweet potatoes are not the same; in fact, they are quite different from each other. 

As far as botanical order is concerned, they are at opposite ends. The sweet potato is a dicot, set in the morning glory family. The sweet potato, whose sweet and moist flesh varies in color from white to yellow and orange, is native to South America; the skin is typically smooth. Garnet, Jewel, and Beauregard are orange fleshed sweet potatoes that often masquerade as yams in the local supermarkets.

 Yams, on the other hand, are a monocot, closely related to grasses. In contrast, yams are dry and starchy and rather bland. While yellow or purple in color, the skin is rough and a bit shaggy. Yams are native to North Africa and Asia. They range in size from that of a small potato up to 150 lbs. Yams are a primary agricultural crop in West Africa, where 95 percent of the world's yam crop is grown.  Incidentally, both yams and sweet potatoes can be purple.