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 23, 2012

Diatomaceous Earth, An Organic Insecticide

 Diatomaceous earth (DE) is an inert dust mined from the remains of fossilized silica shells of certain algae known as diatoms. It is composed of approximately 3% magnesium, 33% silicon, 19% calcium, 5% sodium, 2% iron as well as other trace minerals such as titanium, boron, manganese, copper and zirconium.

As an organic insecticide, DE works in two ways to kill an insect. 1) It absorbs water-protecting fats and oils from the outer, waxy layer on the surface of the insect and causes desiccation or dehydration.  2) Being highly abrasive, DE scrapes and cuts the insect’s cuticle layer, contributing to more desiccation. However, it is virtually nontoxic to mammals.

Around the home, dusting the powder on the floor, carpets and crevices will kill cockroaches, silverfish, ants, and fleas.  Since the powder must stay dry in order to be effective, repeat applications may be necessary in humid areas. DE is more effective in drier climates. It is also used to control beetles where grains are stored.

The same basic principles used to kill indoor insects can be applied to insects which attack plants outdoors.  Some gardeners will dust plants with diatomaceous earth in order to kill insects such as aphids and beetles which feed on the plants. The problem with outdoor use is high humidity and rainfall.   When DE becomes wet, its effectiveness is diminished.  Dusting plants with DE is the most effective application method. DE dust can cause eye irritation so wearing goggles and a dust mask is recommended.   DE is moderately effective against slugs and snails as long as the material remains dry. 

 Insecticidal DE is not the same as the DE used in swimming pool filters. Other chemicals are added to pool grade DE, and the product is heat treated. This causes it to assume a crystalline form and is a respiratory hazard. Pool grade DE should never be used for pest control.