I am currently at war with the invisible invader the Psyllid. I say invisible because I never see them, yet I have three patches in my greenhouse where I have lost 40 heads, in total so far, to Liberibacter. One of these patches is right next to one of the main doors!
I have just started picking my tomatoes and have applied three sprays to this crop since planting. The Whitefly is under control so the spraying has been effective. But unless you spray every day stopping Psyllid adults entering your greenhouse is down to luck. It is a nervous time because until the weather goes cold it is not known how many plants will be lost in the next month. It is also terribly depressing to cut out otherwise perfectly healthy plants that are just starting to harvest.
In my years of growing this is one of the biggest issues I have faced because any control I have is extremely limited.
Unfortunately there are no magic answers or immediate solutions. There is currently no spray, drench or beneficial insect that can give me 100% protection. Resistance to the bacterial pathogen or a way of eradicating the Psyllid is a far away dream. So it looks like we will be at war for the foreseeable future, I just need to try and win some battles along the way.
So what do we have for reducing our Psyllid risk? I don’t have a definitive answer as each grower requires a spray program tailored to their own situation. Growers who use biological controls are limited as are growers who are exporting to countries with strict regulations.
One strong recommendation I have is as soon as you identify infected plants that you cut them out, place all vegetation inside a big plastic bag, seal this bag and remove and destroy the contents. Spraying every 7 or 14 days apart during high periods of likely infestation is also recommended. Over the past two years March and April have proven to be when we need to implement a preventative programme. It also might be of limited help but spraying known host plants around your greenhouse might help reduce the risk. Killing weeds around your greenhouse is also recommended. Sticky traps are another tool to combat these pests. However, are not as necessary if you have a spray program in place.
The upshot of all of this is that you should have good control over your Whitefly population as the recommended control methods for Psyllid are all well known for controlling Whitefly.
The Future: Growers considering building should check the feasibility of building using nets on your vents. The issue has always been the warmer climate and light reduction. With increased heights of new greenhouses and the introduction of diffused glass, possibly the counter action of new technology will mean it is possible for production units. Netted areas definitely reduce the risk of contamination from insects.The general public need to understand that netted greenhouses will not eliminate the need for spraying, but should reduce it by a large percentage. Insect netting is expensive as you preferably need a continuous venting system, so return on capital investment could be hard for accountants to justify.Possible government lobbying by the industry is a way forward.