By Russell T. Nagata By Russell T. Nagata ADVERTISING University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Komohana Research and Extension Center Gardening in Hawaii can be wonderful, in that you can grow nearly anything year
By Russell T. Nagata
University of Hawaii at Manoa
College of Tropical Agriculture and Human Resources
Komohana Research and Extension Center
Gardening in Hawaii can be wonderful, in that you can grow nearly anything year round. When we lose the ability to grow plants we love due to diseases or pest that make it impossible, some of the joy of gardening is lost, and perhaps it also reduces our personal goal of achieving a sense of food self-sustainability.
Indeed, pests and diseases are usually the number-one problem with gardening in Hawaii. While some of these fly, crawl or float into our gardens, many more are inadvertently invited into our gardens. How many of you check plants that you are about to purchase or taking home from a friend’s house for hitchhiking unwanted pests or diseases that may be hiding in the soil, on or in the plant? This is also the general way many pests and diseases have made their way to Hawaii from around the world.
Seeds are also another way diseases and pest make their way into our gardens. As the adage implies, the best way to keep unwanted guest out of your house is not to invite them in in the first place. These pests and diseases can be very sneaky and hide very well, only to show themselves after there is no hope of correcting the problems short of a lava flow. Maybe a little bit dramatic, but all too real for some of you dealing with black rot or bacterial wilt.
The best way to keep seed borne diseases out of your garden is to plant disease free seeds. Today many of the reputable commercial seed companies produce seeds in areas that are free of disease or are grown in areas not conducive to disease development. They also test their seeds for diseases and conduct seed treatments as necessary. When obtaining seeds from friends or seed exchanges it is always good to ask if the seed parent plant was free of disease. It is also a good idea to look at the seeds to see if anything looks out of place. Another good idea is to quarantine questionable plants if you have to have them
To understand seed-borne disease, it is important to understand how seeds are infected in the first place and why it is impossible to clean up some seeds. Infection normally occurs during the seed development process, anywhere from the time of flowering up to the time of seed harvest. Virus infection may result from the seed parental plant being infected and the virus settling in the developing ovary like we find in lettuce mosaic virus. Bacteria and fungi can also infect early in the seed development process and become embedded within the embryo or the seed coat. Other infections occur after the seeds are partially developed but before seed maturity and harvest. These infections are generally found in or on the seed coat. In a few cases infection occur after seed maturity normally during wet seed production periods.
The ability of whether a disease organism can be cleaned from infected seeds depends on numerous factors including the disease, seed type and infection severity. Disease organisms that adhere to the seed coat are the easiest to clean through surface sterilization, washing and physical removal. Those that are embedded within the seedcoat or the cotyledons are harder to deal with. In these cases it usually comes down to differential survival of the disease organism and the seed. For long-lived seeds like celery, the control of septoria late blight is to store the seeds for a year or two, during which the disease organism dies.
Other treatments take advantage of differences in heat tolerance. Many of the cole crops (cabbage and its close relatives) are treated for black rot, a bacterial disease by soaking in hot water for 30 minutes. To be successful with hot water treatment methods of control, precise procedures need to be followed, especially water temperature and duration of soaking. Higher-vigor seeds will also better withstand heat treatment.
If you are collecting seeds from your garden, it is good practice to follow basic rules to reduce disease incident. Eliminating diseased plants (source of the disease) is the first step. Certain seasons or locations are better for seed production due to more sunshine, less rain, and more consistent breezes that lead to less disease by making it unfavorable for disease development. Once seeds are matured, do not leave them in the garden where disease organism can grow on them. Harvest immediately and place in a dry shady location preferably with air movement to aid additional drying.
Vegetatively propagated plants like potato, taro, cassava and banana can also have the same issues as seeds in that they can be host to a number of diseases. Cuttings, corms, taro huli all can harbor viruses, bacteria and fungi that can easily spread within your garden once introduced. We should all expand the number and types of plants we grow in our gardens, but we should also be vigilant about introducing those unwanted guests.
For more information on this and other gardening topics, please visit the CTAHR electronic publication website at http://www.ctahr.hawaii.edu/Site/Info.aspx or visit any of the local Cooperative Extension Service offices around the island. I can be reached at russelln@hawaii.edu.
