The mix of sunshine and rain over the last couple of weeks has provided a period of good growth in all crops, but with this comes a ramping up of weed and disease activity. The heavy showers in recent days have encouraged even germination of weed populations in all spring cereal crops, and if not already sprayed for these, should be done so as a priority in coming days, as performance will fall off rapidly when the weeds become larger and the crop canopy closes, shading out the weeds underneath. As a result of a near ideal balance of heat and rain since planting, all spring crops are now well established and well into the tillering growth stage. Most are clean and canopy cover is consistent right across fields.
Chlorothalonil revocation update
Following the announcement of its revocation earlier in the year, the use up period for chlorothalonil containing products has been announced. Products may be sold up to 20th November this year, and growers will have to the 20th May 2020 to use or dispose of stock. Whilst the fact growers will have the active for much of next season is better news than might have been expected, longer term its loss will impact significantly on crop protection programmes in terms of efficacy and resistance management.
At the moment crops look pretty clean, so in most cases the lower end of the dose range will suffice, but with disease risk closely linked to heat and moisture, decisions on rates are the ultimate in-field decision and should be tailored to the disease pressure in each field.
Even where crops are considered to be clean, controlling Rhyncho early is much more effective than leaving it until it is seen. Once infection has come in, any eradicant treatment has limited efficacy, and the infection will stress the crop, increasing the risk of Ramularia infection. The T1 application should be applied at the end of tillering to the start of stem extension, GS24-31.
The T2 timing should be aimed to continue control of Rhyncho and Net Blotch, but also timed to maximise control of Ramularia. Flowering and senescence are major triggers of symptoms, but other stresses also play a part including bursts of sunshine, diurnal temperature fluctuations, and the presence of other foliar diseases. This spray needs to be on ahead of Ramularia symptoms appearing on final leaves one and two and persist for long enough to keep the crop green well in to grain fill. The best compromise timing for this is booting to very early ear emergence, GS41-49.
Options for T1 are based around core triazoles such as prothio, epoxi and cyproconazole. Prothioconazole remains the strongest performing triazole but epoxiconazole mixes are equally effective options, ensuring the various strains of disease are exposed to as many different actives throughout the programme as possible. Strobilurins improve the performance of the triazole partner, improving Rhyncho, Net Blotch and Rust activity. SDHIs will also give very good broad spectrum disease control, but factoring in cost effectiveness, are a better fit at the more responsive T2 timing.
The young spring wheat plant isn’t subjected to the same disease burden as the overwintered winter wheat plant, therefore a two-spray programme usually suffices, with the T1 applied at 1st-2nd node, GS31-31, and the T2 applied at some point during booting, GS41-49. Whilst a large proportion of these crops are harvested as whole-crop earlier than the conventional combined crop, the feed quality of the harvested crop is very dependant on maximising grain-fill, therefore product choices and rates are similar to those of the winter crop, with significant yield responses to a proper programme.
Powdery Mildew and Crown Rust are the most damaging diseases in this crop. OPUS TEAM & COMET in mixture is the strongest combination in terms of controlling both these diseases and therefore yield improvement. Fenpropimorph (an active in OPUS TEAM) is extremely effective in terms of Powdery Mildew control, and the addition of COMET (a strobilurin) gives unrivalled Crown Rust control.
A single application of fungicide should be applied at 1st – 2nd node, (GS31-32) eradicating any Mildew and Rust already present, and providing persistency right through to harvest.
Application of SELON at early tillering will have increased tiller and ear numbers and therefore yield potential, but will not have given any reliable strengthening of the straw. Stems that extend rapidly during the stem elongation phase (as is likely to happen this season because of late planting, high temperatures and soil moisture at present) are more likely to be weaker and so there is a greater risk of lodging especially where the crop is being pushed on with nitrogen. SONIS can be used but its cut-off in spring barley is 2nd node, GS32. CANOPY is a very useful alternative, safe to the crop and able to be used right up to and including full flag leaf, GS39. If this timing has past, CERONE can be applied up to before awns visible, GS45.
Because the application of SELON at mid to end of tillering (GS23-30) does give reliable later season lodging control in wheat, it is less likely than spring barley that spring wheat will need a growth regulator towards flag leaf unless the crop is particularly dense. If the crop still looks very rank and at risk of lodging as the stem elongates, apply CERONE or CANOPY, as the flag leaf is emerging.
The optimum timing for treating spring oats is with SELON at 2nd node, GS32. However if the oats remain at risk of lodging, a follow up treatment of CANOPY can be applied during flag leaf emergence