Monday, June 16, 2014

Strong flavor in Onions

Sulfur is an essential element required by onions. But high levels of sulfur in the soil can contribute to pungency, that is, a strong flavor. The compound responsible for this is called allyl propyl disulfide. The term sweet, when referring to onions, is a misnomer.  Mild is the correct description for onions with low pungency.

Growing onions in high sulfur soils causes a pungent flavor. In Central America, sweet onions for export are not grown on soils that have sulfur levels above 18 ppm (parts per million). Yet, it is not realistic, or even necessary, to treat the soil in order to lower the sulfur content.  In most soils, sulfates move well in the soil profile. Since onions are a shallow rooted crop, it is easy for the sulfate to move below the root zone of onions.

What is practical is to eliminate or limit the application of sulfur fertilizers. Definitely do not apply them after bulbs begin to form. As long as high levels of sulfur are not applied, pungency should not be an issue.

Constant applications of large amounts of organic matter (OM), especially manures, can potentially increase the sulfur content of the soil. Though with ample rainfall, excesses should be leeched beyond the onion roots.  I am not recommending ending the application of organic matter, I just mention this to note there may be a limit to the amount of OM applied when growing onions.

In addition to sulfur in the soil, pungency or the strong flavor in onions can also develop when growing at high temperatures. Twice as much pungency may be expected when the temperature at bulbing is 90°F compared to 50°F. This increase, though, may be due to a greater uptake of sulfur because of the higher temperatures.  Pungency also rises under dry growing conditions.

Monday, June 9, 2014

Not All Bugs Are Bad

 Some gardeners do not want to see bugs of any kind on their plants. Yet this condition does not always spell disaster.  Consider the following situations:

1. Some bugs found on plants may not be feeding or causing damage to the plant. They are merely there for other reasons.

2. Not only might they be benign, they may be a good guy, a parasite or predator looking for pests to consume. Two well-known good bugs are preying mantis and lady bird beetles.

3. The insects, of course, may be a pest, but one that will not cause damage. Occasionally bugs will stop and feed on plants, but no real harm is brought to bear.

4. On the other hand, some bugs may be inflicting damage, but it is only cosmetic. This means that the leaves or fruit may be scared or misshapen but there is no real loss of yield. Cosmetic damage should be tolerated. This type of damage on fruit does not affect the internal quality.

5. The last possibility is an infestation of an insect pest which will cause yields to be significantly lowered. In this case, you will have to decide whether to wait a  while and see if biological control will work, if parasite/predators can control the population, or to spray. If spraying is the choice, consider first a biorational pesticide, such as soap, oil, Bt or sulfur. These are less injurious to the environment including the predator/ parasite populations. 


Sunday, June 1, 2014

Alternate Bearing of Citrus

Many citrus fruits including sweet oranges and especially mandarins (tangerines) have a strong tendency to alternate bear. Year after year, medium to heavy yields will alternate with a light yield. The reason for this is that it takes considerable energy to bring fruit to harvest. This is especially true for those varieties whose crops overlap, that is, the ‘old’ crop is still hanging on when the tree blooms once again. In essence, a tree must rest the year following high production. Again, there is just so much energy to go around. Alternate bearing isn’t always exact, but a season of heavy production will usually be followed by a year of low production.

To explain more specifically, because a tree carries such a heavy load of young developing fruit in the ON year, the number of summer and fall vegetative shoots that the tree produces will be reduced. These shoots carry flower buds for the following year’s production. Since the number of shoots is reduced, flower bud and thus fruit production will also be down, resulting in an OFF year.

Alternate bearing can be offset by reducing the fruit load on a heavy fruit set year. This is accomplished by thinning some of the fruit before the summer flush. This will also cause the remaining fruit to grow larger. Pruning the tree will give similar results. It is also recommended to pick the fruit as early as possible.