Organic Weed Control

Organic herbicides (OH) include products with ingredients such as acetic acid (vinegar), citric acid, d-lemonene, in addition to clove, cinnamon and lemongrass oils. These products are classified as contact herbicides, meaning they will damage any green vegetation they contact; yet they have no residual activity. OH are not absorbed into the plant system and are safe when sprayed on woody stems and trunks. The foliage of perennial weeds will burn when sprayed, but the plant will recover; repeat applications are needed.

The organic herbicides are effective in controlling weeds when they are small; weeds in the first true leaf stage are easier to control than older weeds. Environmental conditions such as temperature and sunlight may also influence the effectiveness of these herbicides. Many of the products work better when temperatures are above 75F. Furthermore, broadleaf weeds are easier to control than grasses. 

No matter what the situation, good coverage is essential. Adding an organically acceptable spray adjuvant to the herbicide mix has resulted in improved control. An adjuvant is a nonpesticide material added to the spray mixture to enhance the performance of the pesticide. As a final note, organic herbicides are expensive.

Fruitless Attempts in the Garden

Spending lots of time and money in the garden with no results?  One solution is to build raised beds, and in some instances, this may be the best approach. But before building an expensive raised bed, a little investigation and a few changes may produce the desired bountiful garden.

First, efforts need to be directed toward modifying the soil.  Here are some important considerations: 1. The pH could be too low for good growth, a common occurrence in Hawaii. In this case, an application of lime will rectify the situation.  If the pH is too high, common in many areas, sulfur or sulfur products would be advisable. 

 2. Soil nutrient levels may be deficient; common elements that may be lacking include nitrogen, potassium, phosphorous, calcium and magnesium.  These can be corrected with the addition of the proper fertilizer. Both pH imbalances and nutrient deficiencies can and should be diagnosed with a soil analysis. 

3. The soil may be contaminated by plant pathogenic fungi. In this situation, planting resistant varieties to the disease is most important. Crop rotation is another approach. See the article, "Replanted Vegetables Continue to Die" at this website.

  

Additional inquiries should include learning the proper planting dates.  Failures in the garden are occasionally caused by planting cool season vegetables such as lettuce, broccoli and cabbage in the summer, or warm season crops such as peppers and tomatoes in the winter. Moreover, the wrong varieties are often planted. Reading the publications available on the CTAHR website, http://www.ctahr.hawaii.edu/site/info.aspx, will reveal which varieties do well in Hawaii. In other areas, check the local University Cooperative Extension offices or website.

These are a handful of factors that may assist you in developing a green thumb and a lush garden.  Don’t give up! First obtain a soil analysis, then educate yourself: read about the plants you want to grow. Take gardening classes. Use the CTAHR and other Extension websites along with www.gardenguyhawaii.com 

Using Soap to Kill Insects

 Is soap good to kill insects in the garden?  

 Yes it is, in fact, gardeners have been using soaps as an insecticide since the early 1800’s.  But there are some qualifications.  An insect wears its skeleton on the outside – called an exoskeleton.  This is the hard shell we see on many insects like beetles, grasshoppers and cockroaches.  Soap will breakdown this exoskeleton, causing desiccation and thus killing the insect.  But soap has no residual affect and therefore must be sprayed directly on the pest.  Soaps will not kill insects that land on plants after they have been sprayed.

The other problem with soaps is that some plants are very sensitive to them and could exhibit some burning on the leaves - called phytotoxicity.   This is especially true if you are mixing your own concoction.  Use only a mild dishwashing soap with no additives. Purchased products are well refined and would have fewer problems with phytotoxicity.    

Here is a University of Hawai`i recipe for a good oil and soap mixture:  Make a concentrate of one tablespoon dishwashing liquid and one cup of vegetable oil.   When ready to use, shake well and mix 1 – 2 ½  teaspoons of the this mixture into one cup of water.  Spray plants thoroughly, every 5 – 7 days as needed.  Don’t spray in the heat of the day.