Monday, December 31, 2012

Using Surfactants with Herbicide Applications

Surfactants are chemicals that change the physical properties of liquid surfaces. Although soap and household detergents are surfactants, they are not as effective as the commercial agricultural ones.  When added to herbicides, surfactants will:                          

  •  Enhance the spread of the spray droplets on the leaf surface. This increases the effectiveness of the herbicide.
  •  Enable the herbicide to be more rain resistant.
  •  Reduce the rate of drying of the spray solution.
  •  Aid in the suspension of insoluble pesticides like powders in water.
  • Reduce the proportion of very fine droplets, thus reducing spray drift.
Gardeners should always apply herbicides (any pesticide for that matter) at the recommended label rate. Overdosing is a common error - thinking that a higher concentration will result in a better or quicker kill.  This, however, will result in unnecessary expense, an unnecessary release of herbicide into the environment, and, ironically, poor weed control. With systemic foliar herbicides, an effective weed kill depends on the herbicide being trans-located (moved) from the leaves to the roots. Too high a rate will close down the system and the necessary amount of herbicide will not reach the root system.

Monday, December 24, 2012

What Causes Misshaped Cucumbers?

                                                                  Lack of Pollination

There are a few different reasons for misshapen fruit. 

1. A lack of pollination. When this happens, the cucumber will be bulbous at one end, tapering very narrow at the other.

2. Stress during fruit formation including nutrient deficiencies.

3. When the fruit is very young, thrips feeding on the surface will cause the mature fruit to be misshapen or severely curved.

                                                                  Thrips Damage

Monday, December 17, 2012

Monkey Pod Round-Headed Borer

What causes sap to ooze from of the limbs of monkey pod trees?                             The probable cause is a beetle called the monkey pod round-headed borer (xystrocera globosa).  Not much is written about this insect, except that it infests the sapwood of stressed trees. The sapwood is the youngest, outer part of the woody stem or trunk of a tree. In many cases, these large trees are not irrigated, consequently, under drought conditions they can become stressed allowing the borer to enter. Generally, in healthy trees, flowing sap will actually deter insects from boring as they might 'drown'; when trees are stressed, the flow of sap may be minimal, allowing the insect to bore, or enter.

 When trees are attacked, the individual infested limbs could die, but typically the tree itself will survive.  If the infected limb is showing obvious signs of decline, removal of that particular branch is the best remedy. Biological control agents, i.e., parasites (the good guys) have been identified attacking this pest. Perhaps they are the reason the round-headed borer is not a major problem. 

Friday, November 30, 2012

Problems with Acidic Soils: Lime Can Work Wonders

Note: pH is the measurement of the soils acidity/alkalinity. The pH scale is from 0 to 14 with 7 as the neutral point; below 7 is acidic, above 7 is alkaline. Here are a few common pH examples:

  • Extremely acid:  lemon-2.5; vinegar-3.0; stomach acid-2.0; soda pop-2–4

  • Strongly acid:  carrots-5.0; asparagus-5.5; cabbage-5.3

  • Slightly acid:  cow's milk-6.5

  •  Neutral:  saliva-6.6–7.3; blood-7.3

  • Slightly alkaline: eggs-7.6–7.8

  • Moderately alkaline: sea water-8.2; sodium bicarbonate-8.4

  • Very strongly alkaline: soapy water-12; household bleach-12.5

Concerning the pH of soils, there is a preferred range in which plants will grow best. Most soils in Hawaii, as in other parts of the country, are acidic. Extremely acid soils can have a toxic effect on many plants. One common problem is excessive aluminum and manganese becoming soluble in the soil adversely effecting plants.  Acidic conditions can also change the type of microorganisms living in the soil. This will affect the amounts of nitrogen, sulfur and phosphorus available to the plants since the microorganisms breakdown these nutrients into plant-available forms.

These acidic soils will benefit when lime is applied. As an amendment, lime in its various forms can raise the pH of the soil and eliminate a number of problems.
Ground limestone is almost pure calcium carbonate and comprises the largest percent of lime used in the United States. It is usually the cheapest form of lime. Limestone with significant amounts of magnesium carbonate is called dolomitic limestone (dolomite), containing approximately equal parts of magnesium and calcium carbonate. Dolomite works well especially if the soil has a magnesium deficiency.

Hydrated lime, another form, is one and a half times more effective at raising the soil pH but is also more caustic, and therefore,  hazardous to handle. (Protection for the skin and lungs is recommended.) Excessive amounts of hydrated lime can cause a pH shift towards a highly alkaline condition. Conversely, when using dolomitic lime, it is difficult to apply too much as long as it is thoroughly mixed into the soil.

When purchasing lime, a fine powdered lime, about 60-100 mesh, is the fastest acting grade available.  However, being a fine powder, it is a potential eye irritant under windy conditions. It will also cake rather easily, and when improperly mixed, it will stratify forming a layer that can burn roots and repel water.

A coarser limestone (similar to salt grains) is also available and is easier to handle, but its disadvantage is that it is slower acting.  In summary, incorporating lime as an amendment in any of its forms can make a big difference in acidic soils.