After another mixed bag this week conditions remain ideal for many diseases. Blight pressure remains high with the first outbreak of the season confirmed by AFBI earlier this week.Where potato crops are at the main canopy development it is essential the product being used is fully systemic to properly protect the new leaves being put on between applications. Later planted crops are higher risk as they produce more new growth between applications than earlier planted crops, at a time when the level of inoculum in the air is progressively increasing.
During the main canopy development phase the rate of new growth is extremely rapid. This places a huge uptake demand on the uptake of all nutrients, and in conditions of such rapid growth any nutrient that is limited in availability will suppress haulm growth, and as tuber initiation begins, tell the plant to form fewer tubers also. Manganese, sulphur and magnesium are three of the potentially most limiting trace elements, and timely application of these nutrients in an immediately available foliar formulation will offset this yield limiting effect. So that the crop is not adversely affected, it is essential to apply 2-3 maintenance applications of Mn,S & Mg along with N before symptoms are seen, the first going on at the onset of tuber initiation, which normally coincides with about 30-50% ground cover.
Aphid’s damage potato plants directly through feeding damage and indirectly by transmission of several viral diseases, of particular importance in seed crops – aphid control is necessary on seed crops to prevent the spread of potato leaf-roll, mild and severe mosaic viruses. Aphids are the vectors for these viruses i.e. it is the aphids by their feeding action which pass the virus on from one plant to the next.
A number of different species of aphids are responsible for viral spread. When checking plants for aphids, look at both sides of leaves at all levels of the canopy, and monitor the whole crop, not just the headlands. The crop is most vulnerable to virus transmission at the early growth stages, so it is vital to control once aphids are seen – the early sprays are much more important than later treatments in limiting virus spread.
BISCAYA controls all important aphids, including MACE resistant species, by both its contact and systemic modes of action. Central to its efficacy is its penetrant which greatly improves retention on the leaf. The oil forms a film after the water has evaporated, enhancing penetration of the active ingredient, thiacloprid, into the leaf, thereby speeding and prolonging activity. BISCAYA provides the same degree of efficacy in the mid-canopy leaves of the potato plant as on the upper leaves, still providing over 90% control 14 days after application. As a resistance management strategy its label allows only one application in ware crops and two in seed. In order to minimise the possibility of resistance developing, other aphicides with different modes of activity should be included. BISCAYA should be used first in the control programme to take out any aphids resistant to other approved aphicides.
Ramularia (also known as leaf spot) is widespread in spring barley with the newer barley varieties showing more sensitivity to this late developing disease. It shows itself late on in the season (usually after booting), symptoms are very similar to manganese deficiency appearing as brown necrotic speckling on the upper leaves. Symptoms appear where crops are subjected to stress from alternating periods of wet weather & sunshine, or man-made as a result of scorching. Chlorothalonil (BRAVO) is very effective when used preventatively, helping to maintain green leaf area when used along with a triazole/strob mixture.
With ripening still approx 6 weeks away, the T3 treatment has to persist for all of this duration to prevent infection from a range of diseases such as SeptoriaNodorum (glume blotch), as well as Tritici, late season ear moulds and Fusarium. The cornerstone for the head spray fungicide is a strong triazole, giving strong curative activity to control any disease already on the plant as well as good persistence to prevent re-infection right up to ripening. Prothioconazole & epoxiconazole remain the most effective products to give ongoing Septoria protection as well as controlling fusariums and microdochiums on the ear. Prothioconazole (PROSARO) is the highest rated triazole for this range of diseases. The addition of a strobilurin is also essential to extend the persistence of the triazole and improve activity on Yellow Rust. Good grain fill is totally dependent on retaining green leaf area for as long as possible, and the addition of the strobilurin extends the retention of green leaf tissue.
Aphids in cereals
Aphids are now appearing in crops and as the grains begin to fill they feed at its base, drawing off the sugars that should be filling the grain if left unchecked.
Growers need to continue checking crops for aphid’s right up to milky ripe stage (GS73), and spray if present in numbers.
Grassland herbicides use growth function to kill weeds, therefore peak growth periods should be used for herbicide application. There must be sufficient growth to allow herbicides to be effective and vegetive growth is the key time to apply, as the chemical then gets drawn down into the roots. Herbicides are less successful once plants have progressed to the reproductive stage and have thrown a stem or began to seed. Once weeds are beyond the ideal growth stage for spraying they should be mown or topped and allowed to regrow again, and a herbicide applied to the fresh young growth.
To optimise efficacy of any herbicide, recommended water volumes should be observed, even when it means more time spent spraying. It is important to note ragwort plants in their second year are now coming close to flower and should be sprayed immediately as flowering ragwort is poorly controlled. The routine herbicide treatments for this weed are full rate MCPA or 2, 4-D, and they are most active on growing rosettes with reduced activity as the stem starts to extend. They are not clover safe. You can use a mixture of both these products as Nufarm Lupo which allows an increased dose herbicide compared with either alone, with a consequent activity benefit. Stock must be kept of until the weeds have rotted away, which can take up to six weeks.
Grain Store Hygiene
Ensuring stores are clean and pest free is essential to prevent any problems after all the hard work of growing and harvesting the crop. Now is the time to make grain stores ready for the coming harvest. Pest problems in stored grain arise from within the store itself, so a good clean-out is essential to minimise the carry-over of grain beetles, weevils and mites. The store should be empty and thoroughly cleaned before any treatment is carried out, removing all traces of grain and dust that might harbor insects or mites. Apply using an applicator to spray all surfaces including underside of roof and floor, concentrating especially on areas where dust can collect – cracks, light fittings, around equipment etc. RELDAN can be applied up to one month before filling the store and has no with- holding period when applied to the fabric of the store.
Carrot willow aphid is now flying into crops and they carry several virus diseases that affect both carrots and parsnips. They may cause leaf distortion and stunting if they infest plants at the seedling stage. Crops should be checked for aphids and an aphicide such as APHOX used if present. Where couch grass is a problem in carrots ARAMO can be used and has annual meadow grass as a label weed.