Friday, September 25, 2020

Pickleworm

                                                           
  
Why does pumpkin squash ( kabocha/kombucha, Japanese pumpkin) grow into a nice vine, but many of the young fruit turn yellow and drop off? 

This sounds like a case of an insect pest called the pickleworm( Diaphania nitidalis).  This moth was discovered in O`ahu in 2003, and by 2005 had spread to Kauai, Maui and the Big Island.  It attacks many cucurbits such as cucumber, squash, pumpkin, zucchini and cantaloupe.  Squash seems to be the most susceptible. The caterpillars like to feed on the blossoms and afterward will burrow into the developing fruit. The adult moths are colored with yellow and brown and have a purplish sheen. 


Some insecticides are registered on cucurbits and have been successful, with diligent spraying, in commercial crops.  One organic insecticides that may be effective on the pickleworm is known as Bt, (Bacillus thuringiensis).  It is actually a bacterium which is deadly to the moth larvae, but not to humans.  One problem is coverage; the spray adheres to the surface of the leaves and blooms, while the caterpillar is on the inside of the bloom and young fruit.

                                                              

It has been difficult for the homeowner to control the pickleworm. One method is exclusion.  Place screening material over the plants, or individual blooms.  This will keep the moth out and prevent her from laying eggs.  The problem however, is that the cover would also exclude honeybees.  Honeybees are important for pollinating many of the cucurbit crops.  A lack of pollination can be a cause of blossom drop.  Because the moth is a night flyer, you can cover the crop at dusk and uncover it during the day.  This will allow honeybees to visit the plant during the daylight hours, but keep the moths out at night.  Admittedly this is quite a tedious process.

Alternatively, since the moth is relatively large, a wingspread of about one inch,  ¾ inch bird netting can be used to build a permanent structure over the plants. This will exclude the moth while allowing bees to freely move through the netting.

There are a few squash varieties which show some resistance to the moth.  They are Butternut 23, Summer Crookneck, Early Prolific Straightneck and Early Yellow Summer Crookneck.  There have also been reports from other areas of the country, that the early crops have less damage (may not be applicable to Hawaii).

Recently a company named High Mowing Organic Seeds has released a new variety of zucchini called Partenon.  It is a parthenocarpic variety which means that fruit develops without pollination. Thus this variety can be grown in places that  exclude pollinators (honeybees) such as a greenhouse or netted structure.   Partenon is also tolerant to powdery mildew.  (www.highmowingseeds.com )

Monday, August 24, 2020

The Corn Earworm



The corn earworm is one of the most destructive insect pests of corn in the world. But here in Hawaii it is not quite as destructive thanks to CTAHR (University of Hawaii College of Tropical Agriculture and Human Resources) plant breeders. Hawaii-bred corn varieties are more resistant to the earworm due to their thicker and tighter husks, thus limiting the number of larvae that can gain entry to the ear. This allows growers to simply cut off the tips of the ears to remove any damage that may have occurred.

Most of the eggs of the corn earworm are laid on the young silks soon after the silks have emerged. Young larvae crawl down the silk to feed on the kernels, soft cobs and the silk itself.  Luckily they also eat each other, keeping populations low.

Corn planted early in the year is not as seriously affected as is late corn because population densities increase as the season progresses. Early plantings will have minimal damage; later in the year one or two worms may appear in the tops of each ear of corn.

Control
To help control the pest, between plantings destroy the crop residue or haul it off to the compost bin. This eliminates places that would harbor the pest. Several natural enemies are present in Hawaii and, in general, they keep the corn earworm at tolerable levels. In most cases, control is simply a matter of cutting off damaged ends of corn at harvest.

For those gardeners who are plagued with the corn earworm, here are some organic  pesticide recommendations from the University of California IPM program:
  • Spinosad -  must be applied on silks within 3 days after first silks appear and at 3-day intervals until silks turn brown.
  • Bacillus thuringiensis (Bt) -  may be dusted on silks every 3 days after 5 to 10% silk formation for partial control.
  • Applying a few drops of mineral oil with a medicine dropper to silks just inside each ear 3 to 5 days after silks first appear may be effective.

Friday, August 7, 2020

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.