Vegetable News February 2007
Deficiencies in vegetable crops
A number of deficiencies can affect vegetable crops These are usually caused by lack of the nutrients due to leaching or incorrect fertiliser applications. Soil compaction, waterlogging. and variations in pH can often aggravate deficiency symptoms.
Most nutrients have the greatest availability between pH 6.0 -7.0.
Nitrogen
Nitrogen deficiency can occur for a number of reasons
- insufficient nitrogen being applied to the crop
- after heavy rain
- waterlogged fields
- in very dry conditions where nitrate movement does not occur
- where planting has been into soils with insufficiently decomposed organic matter, for example, strawy residues.
Symptoms are uniform pale colour leading to yellowing especially on the lower leaves. Often a purple flush shows on the leaves and stems particularly in brassica crops
Calcium
Calcium deficiency may occur through lack of calcium but the deficiency is often induced i.e. brought about by an excess of another nutrient, often potassium or magnesium.
- brassicas, calcium deficiency manifests itself as cupping of the young leaves often followed by tipburn.
- sprouts and stored cabbage, internal browning can result
- lettuce, leaf distortion and tipburn occur.
- celery, symptoms are blacking and death of the growing point (blackheart).
Boron
Boron deficiency tends to cause brittle stems which crack easily along with death of the growing point and distortion of new leaves, often with outgrowth of side shoots. Specific symptoms are: -
- swedes – brown heart where root tissues are brown and watersoaked
- cauliflowers, cabbage and sprouts - hollow stems
- carrot – splitting of roots and partial cause of five o’clock shadow.
- celery -cracked stems
Manganese
This deficiency causes interveinal chlorosis (yellowing) which begins on new leaves giving a ‘speckled appearance’.
The deficiency is likely on soils with a high pH and where drainage is poor.
Sulphur
In sulphur deficient plants new leaves tend to be cupped and deformed. Plants may be small and spindly. Brassicas are particularly susceptible to this deficiency which is becoming more common as levels of sulphur in the soil are reduced
Magnesium
The symptom of this deficiency is first seen on the older leaves as an interveinal chlorosis (yellowing). This gives the leaves a mottled appearance. The deficiency is more common in sandy soils and in wet weather. The deficiency can be aggravated by soil compaction and waterlogging.
Good husbandry techniques and forward planning can prevent deficiencies
- Make sure drainage is good
- If soil has become compacted, due for example to heavy machinery working in very wet conditions, have the ground sub-soiled to break up pans
- Get a soil analysis including trace elements if crops susceptible to certain trace elements deficiencies are being grown
Resistance to pesticides
A resistant population (whether insect or fungal) develops when individuals survive a spray application and then reproduce to pass their resistance on to at least some of their offspring. An organism which is not resistant dies and there are no offspring. Eventually only those organisms which have resistance to the chemical are left in the population. Continuing applications of the same chemical will be ineffective.
Strategies to prevent resistance
- where possible reduce pest and disease exposure to the same chemical group by alternating products with different modes of action.
- monitor pests and diseases to determine the best application timing
- ensure correct sprayer setup for effective targeting. Uneven or poor spray coverage can result in a sub lethal dose being applied.
- use recommended label rates – using low rates can allow individuals with some level of resistance to survive and reproduce. This increases the potential for resistance.
- Minimise applications where possible.
Pesticide update
- The MRL for aldicarb (Temik) has recently been set at limit of detection in carrot, parsnip and potato. As a result uses of this product on potatoes, carrots and parsnips will have to be revoked as the use would generate residues above the new MRLs. The revocation, which is expected to be announced in Spring will have immediate effect.
- Those chemicals which were granted essential use status under the EU review of pesticides, will cease to be approved on 31 December 2007.
These are
| Active ingredient | Trade name |
|---|---|
| cyanazine | Fortrol Barclay Canter IT Cyanazine Cleancrop Vectro Clayton Gazette Standon Cyanazine 50 |
| fenuron | Croptex Chrome |
| fomesafen | Reflex T |
| metoxuron | Dosaflo |
| pentanochlor | Atlas Brown Atlas Solan Croptex Bronze |
| prometryn | Gesagard Alpha Prometryne 50WP Pennine 50 |
The following SOLA’s have been issued since the last Vegetable news
| Product | Actvie ingredient | Use | Crop | Off label number |
|---|---|---|---|---|
| Invader | dimethomorph + mancozeb | downy mildew | parsley | 2953/06 |
| Butisan S | metazachlor | weed control | leeks | 3698/06 |
| Lyric | flusilazole¤ | phoma | Brussels sprout | 3988/06 |
| Aramo | tepraloxydim | grass control | broad bean | 4020/06 |
| Aramo | tepraloxydim | grass control | parsnip | 4023/06 |
| Aramo | tepraloxydim | grass control | scallions | 4024/06 |
| Nativo | tebuconazole + trifloxystrobin | general fungicide | parsnip | 4163/06 |
Saction 25 Genie 25 Capitan 25 |
flusilazole¤ | phoma | Brussels sprout | 0100/07 0101/07 0102/07 |
| Gazelle | acetamiprid* | aphids | Lettuce, leaf herbs | 0139/07 |
¤ flusilazole is a triazole so alternate with chemicals from a different chemical group
* No more than two applications of a neonictinoid insecticide (ametamiprid, for example, Gazelle, imidacloprid eg Gaucho or thiacloprid eg Calypso) should be used. Always alternate insecticides with different modes of action.
Joan Hamilton
Edible Crops Development Adviser
Greenmount Campus, College of Agriculture, Food and Rural Enterprise
Telephone (office) 028 9442 6683
Mobile number 077 7575 7251
