Monday, May 25, 2015

Avocado trees - Spots on the leaves?





Originating in Mexico, the persea mite, Oligonychus perseae, was found in California in the early 1990’s and probably came to the Big Island of Hawaii in the early 2000’s. The main host for the mites is avocado trees. Some varieties are more susceptible than others; the Lamb-Haas is considered least susceptible. Many ornamentals and weeds also host the persea mite.  The adult mites have eight legs and an oval body with two dark reddish eye spots near the head end of the body. They lack antennae and body segmentation.


                                                            

Mites feed both on the fruit and leaves, most notably on the underside of leaves. The damage appears as small, circular, yellow to brown spots. Mite colonies often reside against the protruding midrib vein of the underside of the leaves. They produce a dense, silk webbing of protection over them. The webbing resembles a silvery spot on the underside of the leaf, often seen glistening under sunlight.  


Premature leaf drop will begin once the feeding damage to the leaves reaches and exceeds 10% of the surface area. This can lead to sunburned bark and fruit; yields have been reduced up to 20 %.  Trees will recover from the defoliation by producing a new flush. But repeated dropping of the foliage will severely stress the tree.


In the home garden, some mites can be tolerated. Several species of natural enemies often reduce the population of the mites. If numbers get too high, horticultural oils will suppress the mite population. It is important that the spray solution contact the undersides of the leaves, where mites are located. Where feasible, spraying the undersides with a forceful stream of water can also reduce mite populations. By using hydrated lime or diluted white latex paint, a whitewashing on the trunk and major limbs will help protect bark and wood from sunburn after a premature leaf drop.

Photo of Mites: UC IPM Program

Monday, May 18, 2015

Poor Seed Germination - Nothing's coming up!





Planting a vegetable garden has a variety of challenges. But how disappointing when the seeds are planned and nothing comes up! Here are primary reasons for poor seed germination.

 1. Planting depth – small seeded vegetables like carrots and onions can easily be planted too deep, and if planted too close to the surface, can easily be washed away during heavy rains. Consult the seed packet for proper planting depths. 

2. Temperature – some seed need the soil temperature to warm up before they will adequately germinate, while other cool season vegetables like onions, germinate best in a cool soil. 

 3. Water, of course, is important; too little and they will not germinate or dry up after germination. With too much water, seeds and seedlings can die from lack of oxygen or be overcome by fungi. Even under normal moisture conditions, different species of fungi and bacteria can cause seeds to rot.  Seeds and seedling should always be kept moist but the soil should not remain soaking wet.  

 4. Soil pH is also important. Each vegetable seed as well as other plants will have its range in which it will germinate best. 

5. Herbicide residues may still be active in the soils causing poor germination.  A high fertilizer content in the soil could also hamper germination. 

6.  Insects will often feed on  seeds and young seedlings.

7. And finally, the seed itself! Poor seed germination can particularly be a problem in humid climates.  Relative humidity influences the moisture content of the seed. The higher the moisture content, the lower the germination rate will be, especially, after one year.


As a general rule, vegetable and flower seeds can be kept for one year without appreciable decrease in germination. Storage, however, may be extended to 10 or more years under proper conditions; seed moisture and temperature are the most important factors. The drier the seeds, the longer they will store.


In humid climates such as Hawaii, storing vegetable seeds in a dry, sealed glass container should keep most seeds viable for a year. For longer storage, place seeds in a moisture-proof container and store in the refrigerator.


Longevity of vegetable seeds will also vary depending on the species.  For example, collards, cucumber, endive, radish and water cress produce some of the hard seeds, rated as lasting 5 years. Next come beets, cabbage, cauliflower, eggplant, kale, mustard, squash, swiss chard, tomato, turnip, watermelon, rated at a 4 year longevity; asparagus, beans,  carrot,  celery,  chinese cabbage, New Zealand spinach, pea, and spinach, at 3 years; leek,  sweet corn, okra and pepper are rated at 2 years; and finally, the last group is rated at a mere 1 year longevity - lettuce, parsley, parsnip and onion.



Photo: Purdue University

Monday, May 11, 2015

Pineapples - Easily Propagated





Can the top of the pineapple fruit be cut off and planted in order to produce a new plant? The answer is YES! There are many variations on how to propagate pineapple. The drier the environment, the more precise the instructions need to be followed. In Hawaii, especially in high rainfall areas, propagating pineapple is relatively easy. 
  


The simplest method is to cut off the top of the pineapple, called the crown, as you normally would do when cutting the fruit. Let the top sit in a shaded, dry area for 2-7 days. Before planting, remove the dried fruity portion and some of the lower leaves exposing  ½ -1 inch of the stem. Letting the crown sit for several days will seal the wound and make it less susceptible to rot. When planting, keep in mind that the mature plant can grow to 3-4 feet in diameter and height. Mature plants also have a tendency to fall over, thus planting several together, they will give each other support.

Alternatively, the stem can be placed in a shallow glass of water. Be careful to place only the stem and not the leaves in the water.  After a short time, roots will form; it is then ready to be planted outside.