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Crop Crack 27.06.09
By Wendy Fearon
The pleasant weather experienced over the last week has certainly put everyone in much better form. There were quite a few late drilled crops sprayed for weeds over the last week. All weed control should now be complete with the exception of some late drilled undersown crops. Potato crops had been under extreme blight pressure which has eased with the dry sunny conditions over the past week. It is important to ensure all fertiliser applications are now up to date on spring cereals to achieve maximum yield.
Cereals
Backward spring barleys are somewhere around mid stem extension (GS32-34) whilst the most advanced have the head fully emerged. Westminster is still fairly clean with levels of Rhyncho low but Wagon & Quench are much more heavily infected .Straw stiffening will already be missed in the most advanced crops and should be done now in those fields thought to be at risk of lodging later.
Spring wheat’s are at early stem elongation (GS31-32), with low levels of Septoria and some mildew already present.
Winter barley crops have now past the flowering stage and most are now at the milky ripe stage.
Winter wheat crops range from flag leaf sheath elongating (GS41) up to ears 50% emerged, (GS55). Yellow Rust has been a particular problem this year, and infecting more than just Robigus with Oakley & Alchemy also being infected. Mildew is also present in almost all varieties with Duxsford being the worst affected. Crops treated with proquinazid (TALIUS) as part of the T1, T2 fungicide programme appear to be very clean. Late-sown winter wheat crops are often particularly prone to attack, especially when growing rapidly in the spring.
Excessive nitrogen fertiliser also encourages the disease and mildew can be particularly severe in dense crops. The visual appearance of the disease usually outweighs its damage potential. In susceptible varieties yield losses can be up to 20% and early control can be very important. However, the disease generally causes much smaller yield losses and late attacks (after flowering) on the flag leaf and ear rarely cause significant losses. Mildew can be difficult to control as it is a vertical disease and getting the spray on can prove difficult.
T3 Wheat
With ripening still 6-8 weeks away, the T3 treatment has to persist for all of this duration to prevent infection from a range of diseases. Late developing septoria Nodorum (glume blotch), as well as Tritici, a range of late season ear moulds and Fusarium are all favoured by damp and humid weather, especially at the later grain filling stages when the glumes prevent the grain from drying out properly between periods of rain.
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 in last years’ HGCA trial results.
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. Last years’ HGCA trials show pyraclostrobin (COMET) to be the highest rated strob for use in wheat being the strongest performer on Yellow rust and the late ear diseases. Talius should also be applied where there is the risk of mildew.
YELLOW RUST
Aphids in cereals
The continued warm weather has encouraged high populations in all crops. While rain will wash them onto the soil, dry weather following sees them quickly move back up onto the ears. 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.
Potatoes
Where broad-leaved weed control has not yet been completed, a reduced rate of SENCOREX tank-mixed with TITUS will provide a wider spectrum of weed control than TITUS used alone and can be used on emerged crops up to 25cm high (10cm more than if using SENCOREX alone) it is important to note the varietal restrictions with this product.AFALON may be applied up 20% emergence of the crop when mixed with RETRO. Activator must be added to both RETRO and TITUS.
There are three ways by which the blight fungicide can move through the plant.
Contact fungicides eg. DITHANE, RANMAN, SHIRLAN, and TIZCA - these products protect only the outer surface of the leaf onto which they are deposited. They do not move into the leaf and therefore do not normally protect any new growth that emerges after application.
Translaminar fungicides eg. CURZATE M WG, INVADER, OPTION, and REVUS - these products move into the leaf onto which they are sprayed and then redistribute throughout the leaf tissue as it increases in size. They become rain-fast once they are in the leaf.
Systemic fungicides eg. CONSENTO, FUBOL GOLD, INFINITO, MERLIN, and TATTOO- these products move in through the leaf surface and upwards into the new growth that emerges between applications, protecting that new growth from infection also. Products that have zoospore activity are the most effective 1st spray, applied at the rosette stage prior to rapid haulm growth. INVADER, RANMAN or SHIRLAN will control any zoospores that may be in the soil (either from ground-keepers or infected seed) and provide good protection of the new plant.
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. POTATO MICRO COMPLEX contains16%nitrogen, 6%calcium and 6%magnesium.All essential nutrients are available in foliar form.
Horticulture
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 used if present. DOVETAIL or APHOX are extremely effective.
Both scab and mildew have severely affected orchards and whilst the current weather should improve the scab infestation it will definitely favour mildew.Topas should be applied at this time and is best mixed with CAPTAN or PENCOZEB.
Orchards should continue to receive a seaweed based foliar feed as they are showing signs of stress with many having been badly affected by the hail just a few weeks ago. It is critical to inspect orchards at this time for red spider mite as conditions are highly favourable.
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