Page 45 - Simply Vegetables Winter 2020/21

coronavirus, plants also suffer from a number of different viruses. Many of these are only
a problem to the commercial grower where they have big effect on yield and crop quality. Virus can cause a large reduction in the yield of fruits like blackcurrants and even apples so can be a problem to gardeners as well. A vegetable that is being studied at present are carrots where researchers have found a high incidence of aphid transmitted virus infection and these have included some previously unknown virus.
Carrots infected by virus give a lower yield and quality and the roots can be split or have other deformities and also internal blemishes (dead patches of tissue inside the root). Two of the viruses are spread by the willow carrot aphid and peach potato aphid as they both spread carrot red leaf virus and carrot yellow leaved virus. At present the researchers
are looking at which other aphids may be responsible for spreading virus and how it spread over time.
Other crops they are investigating are peas where they have discovered turnip yellow virus and this is also known to affect Brassicas. The good news is that another group of scientists are looking at virus management and solutions to the problem. They are reviewing a number of methods of control that could be used.
Pests
A lot of research has been looking at what they call Day Degree Forecasts for pests, these forecast when certain pests will come out of pupation or eggs will hatch and the
pest will start to become a problem. It can be very accurately forecast when a pest will emerge by measuring the acculmative day degrees. That is the number of days the temperature is above a certain level. Once a set number of degrees has been reached the pest will start to emerge. Being able to predict this helps the grower know when to look for the pest and start to take action.
A combination of data collected from around the U.K. which gives regional
details and variations allows this to be used throughout the U.K. This will form part of the growers IPM strategy, at present it is possible to forecast for cabbage root fly, carrot fly,
flea beetle, pollen beetle bean seed fly willow carrot aphid, small and large cabbage white butterfly, turnip moth, silver Y moth, large narcissi fly and diamond back moth. They are also able to predict when invasions of pests are likely from the continent and can predict both the diamond back moth and silver Y moth so growers can be ready for them.
Other research is looking at resistance development in pests including a number of aphid types, flea beetles, asparagus beetle, onion thrips and diamond back moth. Some of these have developed resistance to certain pesticides which if used will give little or no control of the pests. It is important not to use the same active ingredient (chemical) every time you spray but to ring the changes to help stop resistance developing.
Physiological Disorders
Many members may be aware of blossom end rot on tomatoes and it has also been
known on sweet peppers and aubergines. It is a very dark brown/black spot on the flower end of the fruit which makes it unusable.
The spot can be from 5 to 10mm diameter and may spread larger, infected fruit should be removed and they can be composted. Recently research has shown blossom end rot on some cucurbits like courgettes and pumpkins. It develops on these as a wet rot from the flower scar at the end of the fruit.
Blossom end rot is caused by poor calcium intake into the plant and particular the fruit, this weakens the cell structure in the fruit which can allow the entry of fungal rots. Calcium is transported into the plant by water taken up by the roots. If the plants get dry during hot weather or are being insufficiently watered especially in growbags or containers the roots cannot take up sufficient calcium for the young expanding fruit; this results in blossom end rot.
To overcome the problem improve your watering or irrigation system to ensure there is sufficient moisture in the soil / growing media. Spraying the leaves with calcium nitrate solution will control blossom end rot, if there is some boron and magnesium in the spray this is even better. Spray on dull days with a fine mist and give an even coverage
to the leaves; spray from the first flowering until the fruits are mature in courgettes and up to two weeks from harvest for pumpkins. Tomatoes should be watered or sprayed with the solution at approx. fortnightly intervals.
I will try to update members on recent research in future magazines as I become aware of new developments of interest.
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