Page 44 - Simply Vegetables Winter 2020/21

Recent Vegetable Research
This article covers some of the research that has been carried out in the U.K. during the last couple of years and although some of these are not yet available to the general public they may be in a year or to.
Using Bio-pesticides
Owing to the reduction of chemicals available to both the commercial and amateur gardener a number of researchers are looking at new bio-pesticides that could replace them. There are some insecticides and fungicides that may be available in a couple of years or could be a bit longer.
The aim is to use the bio-pesticides as part of an integrated pest management (IPM) programme; this is the future way to control pest problems and not just rely on chemicals or just one product that can result in resistance building up. Instead a programme or strategy of different controls are used, these can include physical, biological and chemical, which can both prevent or reduce the initial attack as well as give some control. They may not always give 100% control
but this is often not required for fruit and vegetables grown for the kitchen. Having said that most exhibitors may want full control as they would be down pointed for the presence of pests or diseases or any damaged caused. In most cases an 80% control will be sufficient to allow a good crop to be harvested although this will depend
on which crop is involved. IPM may use some chemicals as part of the programme but where possible these will be the safer, non-persistent type and possible organic approved.
Bio-pesticides are not chemicals but are usually a fungus or virus that is sprayed onto the plant or pest which kills the pest or prevents infection. Because these products have a more complex life cycle, unlike chemicals they can be more inconsistent than synthetic chemicals.
The advantages of using bio-pesticides are:
• Safe to people and the environment
• There is no chemical residue on the
crops or in the environment
• Crops can be harvested soon after
application as there is usually no harvest interval between spraying and eating.
The disadvantages are:
• They are often slower acting
• Many bio-pesticides work by contact
with what they control and are not
systemic in the plant
• They can be more expensive than
some chemicals
• They have a low persistence which
means they will only work for a short
time after application.
This is an advantage as well as they do
not build up in the environment causing problems like many chemicals in the past (DDT being a classic a example).
Some of the bio-pesticides can be affected by environmental conditions that reduces their effectiveness; some can be affected by low or high temperatures or wet conditions.
Research is being carried out to find both new bio-pesticides and identifying why they are sometimes inconsistent. Researchers are also looking at better ways to apply the bio- pesticide to improve the performance.
An IPM strategy uses a range of control measures which are shown in the pyramid below and where possible used in that order with chemicals being the last resort if the others have not worked or are not available to control a particular problem.
stimulated the germination of the white rot fungus sclorotia (a type of resting spore in the soil). If this is done when there are no onions in the soil the disease dies. Therefore a number of garlic applications over a three year period could reduce the level of disease inoculum in the soil and reduce the severity of the disease infection. This is something gardeners could carry out at home or
on their allotments. Further experimental work is being carried out to develop the effectiveness of this technique. If you have any garlic sprays and your soil has onion white rot you could give this a try, food grade garlic granules also seem to work.
Downy Mildews
There are a number of downy mildew diseases which affect different plants. The main vegetable ones are lettuce, onion, basil, pea and spinach downy mildews. An example of how serious a disease downy mildew is, lettuce downy mildew (Bremia) is estimated to cause £15 million of crop losses a year.
Downy mildews are caused by an
air borne fungal like pathogen called oomycetes, these cause a number different vegetable diseases. At present downy mildews are controlled by using chemical fungicides but as these become less available and the diseases are developing resistance to some of the chemicals the researchers are looking for alternatives.
There are a number of lettuce cultivars that have resistance to downy mildew (this is usually indicated in the seed catalogues) but over the years the disease has developed new pathogen races that can breakdown the resistance. Hence lettuce have numbers like 23, 24 etc. which show the strains of disease the cultivar is resistance to.
Researchers are aiming to bring together a number of techniques as shown in the pyramid above to a control strategy. This could include cultural controls (a seed treatment), resistance cultivars, physical controls like removing any infected plants promptly, possible a new bio-pesticide and if these all fail then a chemical spray.
Lettuce Fusarium Wilt
I have briefly mentioned this disease in an earlier Simply Vegetables magazine. It is a new disease that is thought to have come over from Holland and was first seen in Ireland and Lancashire, but has now been found in Cambridgeshire. So far it has only been seen on indoor lettuce crops, but tests have been carried out to see if it could spread to outdoor lettuce.
Experimental work is also being carried out to find methods of controlling the disease; one is using a bio-pesticide called T34 looks like it could give some control of this new disease and work is continuing.
Viruses
At the time of typing this article it is the start of the Coronavirus pandemic so virus are all over the news and papers. It is not just humans that suffer from virus like flu, common cold or
Chemicals Bio-pesticides Physical Cultural
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Researchers have looked at the persistence of a number of bio-pesticides, one AQ10 (A. quisqualis) is used to control powdery mildew but will only work if the powdery mildew is present. If no powdery mildew the bio-pesticide fungus will die as there is nothing for it to feed on. Although another bio-pesticide called Pre-stop can survive for up to 14 days on tomato foliage even if the disease is not present.
How well the bio-pesticides work can depend on a number of factors, these include whether the pest / disease is present when they are applied, some are affected
by temperature and humidity and also the effectiveness of the application is important. This is affected by the amount of water used is it is important to get a good and thorough coverage of the pest / disease / plants.
Recently researchers have looked at the following diseases and possible biological controls.
Integrated Control of Onion White Rot
This is an important disease of onions and other Alliums like garlic, shallots and salad onions. It can wipe out large parts of the
crop and the disease is very persistent in the soil for a number of years possible up to 15 to 20 years. It is caused by a fungus called Sclerotium cepivorum which is soil borne, this is important as the disease can be spread on boots, tools and soil around plants roots as well as compost if it is infected.
The disease enters the roots of the onion plant which die and decay, this leads to poor crop growth, chlorosis (leaves going yellow) and the whole plant dying. Researchers looked at a number of chemical fungicides and as well as some bio-pesticides; the current range of bio-pesticides did not control the disease so they are now looking at further alternatives.
What was interesting was that when garlic extracts were applied to the soil this