Bacterial diseases are a real THREAT to vegetable production. They are seed-transmitted and can destroy your crop. T he state of Idaho in the US is the world centre of disease-free seed and is a quarantine state for bean-seed production. The climate is semi-desert and no sprinkler irrigation is used. Seed introduced in the state is planted on an isolation plot and inspected six times during active growth before being permitted to go into the system. result is that bacterial diseases are insignificant for US farmers as there is virtually no inoculum.
Neither do they breed resistance into varieties as it is not necessary. For this reason, Australia will only accept seed from Idaho or California. S eed companies and authorities in the US are regularly inspected by officials wearing waders which they spray before entering any field. If they spot any signs of bacterial diseases they quarantine the area and destroy the crop if necessary. eed produced in South Africa is quite suspect and I have seen many large plantations compromised by bacterial disease caused by infected seed.
Not only is the current crop at risk, but the disease may remain in the soil to infect the next crop. Disease is spread by infected seed f you plant in an isolated field which has been deserted for years and a disease manifests, you can be sure it was introduced by infected seed. ome years ago, it was common practice to plant the wintergreen varieties at the start of the season. They were fast-growing and the seeds were locally produced and cheap, which also meant smaller losses were suffered if seed was destroyed by late frost. This was commonly followed by better-quality, higher-yielding imported varieties. he usual result was that bacterial diseases would start in the wintergreen crop when the rains began and then carry over to the expensive varieties, causing high crop loss and incurring expensive spraying costs. Unfortunately, certified seed is not necessarily disease-free, as a certain amount of disease is tolerated in certification. Bacterial diseases are easily spread by surprising means.
A hare visiting your neighbour’s farm and then coming into your fields when they are wet can cause havoc. Birds, locusts, workers and machinery moving between fields can also spread the bacteria. As a safeguard, never work in a bean field when the foliage is wet. Even if a few plants are infected, they can provide the inoculum that spreads the disease rapidly. SA farmers take bacterial diseases far too lightly. They need to understand how much such diseases sap profits every year. – Bill Kerr ([email protected] or (016) 366 0616). |fw
